Welder Training Program. Theory Competencies

Transcription

1 Welder Training Program Level C P2: Oxy-Fuel Gas Cutting (OFC) Theory Competencies

2 Acknowledgements & Copyright Permission The Industry Training Authority of British Columbia would like to acknowledge the Welding Articulation Committee and Open School BC, a division of the Queen s Printer as well as the following individuals and organizations for their contributions in updating the Welder Training modules: Welding Articulation Committee (WAC) Members and Consultants The Working Group Jim Carson (Welding Articulation Committee Chair), University of the Fraser Valley (writer and senior reviewer) Peter Haigh (Welding Curriculum Review Committee Chair), Northwest Community College (writer and senior reviewer) Sheldon Frank, University of the Fraser Valley (writer and reviewer) Greg Burkett, Okanagan College (writer and reviewer) Randy Zimmerman (writer and reviewer) John H.P. Little (reviewer) Resource Training Organization (RTO) BC Council on Admissions and Transfer (BCCAT) The Queen s Printer The Queen s Printer, through its Open School BC unit, provided project management and design expertise in updating the Welder Training Level C print materials. Open School BC Solvig Norman, Senior Project Manager Eleanor Liddy, Director/Advisor Dennis Evans, Production Technician (print layout, graphics & photographs) Christine Ramkeesoon, Graphics Media Coordinator Keith Learmonth, Editor Margaret Kernaghan, Graphic Artist Publishing Services Sherry Brown, Director of Publishing Services Intellectual Property Program Ilona Ugro, Copyright Officer, Ministry of Citizens Services, Province of British Columbia Copyright Permission The following suppliers have kindly provided copyright permission for selected product images: Acklands-Grainger Inc. The Crosby Group J. Walter Company Ltd. Lincoln Electric Company NDT Systems, Inc. Praxair, Inc. Thermadyne Canada (Victor Equipment) The Miller Electric Mfg. Co. ESAB Welding & Cutting Products Photo of welder walks the high steel at a construction site, Kenneth V. Pilon, copyright Used under license from Shutterstock.com A special thank you to Lou Bonin and Jim Stratford at Camosun College (Welding department) for assisting us with additional photographs. An additional thank you to Richard Smith from England, for allowing us to use photographs of hydrogen bubbles.

3 Foreword The Industry Training Authority (ITA) is pleased to release this major update of learning resources to support the delivery of the BC Welder Program. It was made possible by the dedicated efforts of the Welding Articulation Committee of BC (WAC). The WAC is a working group of welding instructors from institutions across the province and is one of the key stakeholder groups that support and strengthen industry training in BC. It was the driving force behind the update of the welding learning modules supplying the specialized expertise required to incorporate technological, procedural and industry-driven changes. The WAC plays an important role in the province s postsecondary public institutions as discipline specialists that share information and engage in discussions of curriculum matters, particularly those affecting student mobility. ITA would also like to acknowledge the Resource Training Organization (RTO) which provides direction for improving industry training in the resource sector and which led consultation on changes related to the BC welder training program. We are grateful to WAC and RTO for their contributions to the ongoing development of BC Welder Training Program Learning Resources (materials whose ownership and copyright are maintained by the Province of British Columbia through ITA). Disclaimer Industry Training Authority August 2010 The materials in these modules are for use by students and instructional staff and have been compiled from sources believed to be reliable and to represent best current opinions on these subjects. These manuals are intended to serve as a starting point for good practices and may not specify all minimum legal standards. No warranty, guarantee or representation is made by the British Columbia Welding Articulation Committee, the British Columbia Industry Training Authority or the Queen s Printer of British Columbia as to the accuracy or sufficiency of the information contained in these publications. These manuals are intended to provide basic guidelines for welding trade practices. Do not assume, therefore, that all necessary warnings and safety precautionary measures are contained in this module and that other or additional measures may not be required.

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5 P2: Oxy-Fuel Gas Cutting (OFC) Theory Competencies Table of Contents Theory Competency P2-1: Oxy-fuel gas cutting process and its applications P2-1 Learning Task 1: Oxy-fuel gas cutting process and its applications P2-1 Learning Task 2: Cutting characteristics of ferrous and non-ferrous metals P2-1 Learning Task 3: Thermal effects of oxy-fuel gas cutting P2-1 Learning Task 4: Safety requirements for oxy-fuel gas cutting Theory Competency P2-2: Oxy-fuel gas cutting equipment P2-2 Learning Task 1: Gases used in the oxy-fuel gas cutting process P2-2 Learning Task 2: Oxygen and fuel gas cylinders P2-2 Learning Task 3: Pressure regulators and their functions P2-2 Learning Task 4: Oxy-fuel hoses and fittings P2-2 Learning Task 5: Oxy-fuel gas cutting torches, cutting tips and heating tips P2-2 Learning Task 6: Oxy-fuel gas manifold systems P2-2 Learning Task 7: Oxy-fuel gas cutting accessories and machines Theory Competency P2-3: Correct procedures to operate and maintain oxy-fuel gas cutting equipment P2-3 Learning Task 1: Correct procedures to assemble, ignite and shut down a portable oxy-fuel gas unit P2-3 Learning Task 2: Characteristics of an acceptable oxy-fuel gas cut Answer Key Welder Training Program Level C 5

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7 Theory Competency P2-1: Oxy-fuel gas cutting process and its applications P2-1

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9 Module P2 Theory Competency P2-1 Outcomes Cutting metals by the oxy-fuel gas process is a common way to prepare metals in a variety of industries. When you have completed the Learning Tasks in this Theory Competency, you should be able to identify and describe: the oxy-fuel gas cutting process the main components of an oxy-fuel gas station applications of oxy-fuel gas cutting techniques for cutting difficult-to-cut ferrous alloys ferrous and non-ferrous alloys that cannot be cut with oxy-fuel gas the thermal effects of distortion and surface hardening safety precautions for oxy-fuel gas cutting Evaluation When you have completed all the Theory Competencies in module P2, you will take a written test. You must score at least 70% on this test. The test will include questions that are based on the following material from Theory Competency P2-1: the oxy-fuel gas cutting (OFC) process and its components applications and techniques of the OFC process alloys that cannot be cut with the OFC process thermal effects of the OFC process safety precautions for the OFC process Resources Required: All required resources are contained within this Theory Competency. Optional: The following resources are optional and are NOT required to complete P2. The optional resources provide further information on a specific topic. If you want more information on these resources, please see your instructor. Air Liquide: ESAB: Harris: Linde: Smith Equipment: PraxAir: Victor: Welder Training Program Level C 9

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11 Module P2 Theory Competency P2-1 P2-1 Learning Task 1: Oxy-fuel gas cutting process and its applications The oxy-fuel gas cutting process The oxy-fuel gas cutting (OFC) process works by combining iron with oxygen to form iron oxide. It is the same process that we call rusting. Under normal atmospheric conditions, this process occurs naturally and slowly. It is also called slow oxidation. Oxy-fuel gas cutting speeds up this process so that rapid oxidation or burning takes place. Instead of forming rust, the iron oxide forms a molten slag that is blown off the metal. The oxy-fuel process uses an oxy-fuel gas flame to preheat the carbon steel to temperatures above 870 C (1600 F). A narrow stream of oxygen then cuts the steel. This stream of oxygen causes the metal to burn: The iron combines with the oxygen to form molten iron oxide or slag. As the molten slag is blown away from the metal, a narrow opening called a kerf is created in the metal (Figure 1). Since oxy-fuel cutting is based on the reaction of iron with oxygen, its use is mainly limited to metals that are iron-based (ferrous). Examples are the lowand medium-carbon steels. Figure 1 Oxy-fuel gas cutting process The cutting tip of a conventional cutting torch contains a number of small holes through which the oxygen fuel gas mixture flows. When the torch is ignited, the fuel gas mixture coming through these holes produces preheat flames. The preheat flames burn continuously and preheat the base metal during the cutting process. A number of fuel gases can be used to preheat the metal to the ignition temperature. The most commonly used Welder Training Program Level C 11

12 Module P2 Theory CoMPeTenCy P2-1 notes fuel gas is acetylene. Others include propane, natural gas and proprietary gas mixtures (e.g. Mapp ). In the centre of the cutting tip is a larger orifice (hole) from which a stream of high-pressure cutting oxygen flows when the cutting lever on the torch is fully depressed. The first step in the cutting process is to use the preheat flames to heat a small area of the base metal to a cherry red colour. Once the metal turns cherry red, the oxygen lever is depressed to start the flow of cutting oxygen. Cutting starts as soon as the flow of oxygen begins. Cutting will continue for as long as the cutting oxygen stream is supplied. Components of a basic oxy-fuel gas cutting system The main components of a typical oxy-fuel cutting unit are the oxygen and oxy-fuel gas cylinders (Figure 2). Each cylinder has a cylinder valve on top. Attached to that is a cylinder pressure regulator with gauges. Hoses are attached to the cylinder pressure regulators and lead from the regulators to the torch assembly. Notice the special devices called flashback arrestors attached to each end of the hose. These one-way valves play a crucial role in the safe operation of the oxy-fuel gas unit. Oxygen regulator Fuel gas cylinder valve Fuel gas regulator Flashback arrestors Oxygen cylinder valve Flashback arrestor Oxygen hose Oxygen cylinder Fuel gas hose Fuel gas cylinder Cutting tip Cutting torch body Figure 2 Oxy-fuel gas cutting outfit 12 WelDer TrAInInG PrOGrAM level C

13 Module P2 Theory Competency P2-1 Applications of oxy-fuel gas cutting Oxy-fuel gas cutting is a widely used process in many industries. It is possible to accurately cut very thin to very thick sections of ferrous metal. Cuts can be made faster and smoother than with machine saw cutting or other mechanical means. In an industrial or shop setting, this speed offers some cost benefits, but the main advantage is the precision and accuracy that can be achieved with this process. Some of the many applications include: cutting plate, pipe and structural shapes washing bolts and rivets gouging and scarfing Cutting plate, pipe and structural shapes Parts must often be precut to precise sizes before welding. This is the main use of oxy-fuel gas cutting. Using the oxy-fuel gas process, you can cut very thin to very thick carbon steels quickly and accurately. Preparing pipe for welding is another common use for oxy-fuel gas cutting. It is especially useful for preparing odd-shaped weld joints in the field. Oxy-fuel gas cutting is not just for cutting plate and pipe. Steel manufacturers provide a number of structural shapes for use in industry. These shapes include angle, channel, S-beam, round tubing, square tubing, solid square bar, etc. Using a hand-held torch, you can cut and fit structural shapes. This versatility makes oxy-fuel gas cutting a widely used tool. Demolition companies use oxy-fuel gas cutting when tearing down steel buildings, auto-wrecking yards use it for dismantling cars and scrap yards use it for breaking down equipment. Farmers, millwrights, mechanics and steam fitters all make use of the oxy-fuel gas cutting process. Washing bolts and rivets Washing is a process for removing nuts, bolts or rivets with a cutting torch without damaging the bolt threads, holes or the plate. Washing is commonly used in salvage operations for dismantling equipment or fabricated structures. A special cutting tip is normally used for this process (Figure 3). Welder Training Program Level C 13

14 Module P2 Theory Competency P2-1 Figure 3 Washing a bolt Gouging and scarfing Oxy-fuel gas cutting is also used for gouging and scarfing. Flame gouging is a method of removing welds or a narrow strip of surface metal (Figure 4). Figure 4 Oxy-fuel gas gouging Gouging has a number of applications. One of the most common is to remove tack welds that hold a joint together until the welding is completed. Gouging is also used to remove weld and casting defects, and for demolition work. It is also used to prepare J-groove and U-groove joints for welding. A special gouging tip is recommended and normally used for this process. Flame scarfing is another cutting process that removes a thin layer of metal from a thicker section. It is used in steel mills to remove surface defects from ingots and billots or defects such as cracks and seams on the surface of unfinished steel shapes. Welders use scarfing to prepare the edges of a plate that is to be bevelled for butt welding. Scarfing in steel mills requires a special torch. 14 Welder Training Program Level C

15 Module P2 Theory Competency P2-1 Oxygen lance cutting Oxygen lance cutting is used for cutting or piercing very thick sections of steel, cast iron or even concrete. Manual oxy-fuel gas will generally cut material up to 610 mm (24 in.), but an oxygen lance will cut material up to 2.5 m (8 ft.) thick. The oxygen lance consists of a length of ordinary 3 mm or 6 mm ( 1 8 in. or ¼ in.) low-carbon steel pipe connected to a supply of oxygen. A regular cutting torch is one method used to preheat and start the operation, after which the oxygen lance maintains the cut. The steel lance (pipe) is actually consumed (burned) during the cutting process. The combination of the burning pipe and the large volume of oxygen creates a great deal of heat within the cut. Stack cutting In stack cutting, several layers of sheet or plate are cut at the same time. The layers are clamped together and cut by an oxy-fuel gas cutting machine that has one or more torches. Stack cutting can also be done with a manually operated oxy-fuel gas cutting torch. The layers of plates are cut as a single unit to produce a number of identical parts. Cutting machines Cutting machines are very commonly used with the oxy-fuel gas process. Cutting machines produce cuts of greater quality and speed than is possible with manual torch methods. There are different sizes of cutting machines, from small, one-torch track and wheel machines to huge, multi-torch machines used in shipyards and manufacturing. Cutting machines can be used to cut almost any shape or size of steel. Very often they have multiple torch assemblies that can cut several identical parts at the same time (Figure 5). Figure 5 Multi-torch cutting machine Now complete Self-Test 1 and check your answers. Welder Training Program Level C 15

16 Module P2 Theory Competency P2-1 Answers Self-Test 1 Choose the correct response for each question and put it in the Answers column. Cover your answers when reviewing the test for study purposes. 1. The oxy-fuel gas cutting process can best be defined as a. rapid oxidation b. metal gouging c. air cutting d. semi-automatic cutting 2. The oxy-fuel gas cutting process is mainly used for cutting a. aluminum b. carbon steels c. copper and brass d. all of the above 3. The narrow opening created by the oxidation of the metal in the cutting process is called the a. groove b. edge c. bevel d. kerf 4. The molten oxide formed during oxy-fuel gas cutting is called a. kerf b. slag c. oxy-iron d. rust 5. The fuel gas most commonly used for oxy-fuel gas cutting is a. acetylene b. natural gas c. propane d. gasoline 16 Welder Training Program Level C

17 Module P2 Theory Competency P Before a cutting process can start, the spot where you want to begin the cut must be a. cooled b. cleaned c. preheated d. filed Answers 7. Using an oxy-fuel gas torch to remove bolts and rivets is called a. cleaning b. washing c. lancing d. scarfing 8. Oxy-fuel gas gouging is commonly used to a. remove tack welds b. remove weld defects c. prepare joints for welding d. all of the above 9. Oxygen lance cutting is normally used to cut a. brass b. non-ferrous alloys c. thick sections of steel d. aluminum 10. The process in which multiple layers of steel plate are cut simultaneously is called a. multi-cuts b. scarfing c. oxygen lance cutting d. stack cutting Welder Training Program Level C 17

18 Module P2 Theory Competency P2-1 Answers 11. In oxy-fuel gas cutting, the actual cutting is done by a. the fuel gas b. a stream of oxygen c. the preheat flames d. a mixture of oxygen and fuel gas 12. Gouging is an oxy-fuel gas cutting process meant for a. removing rivets b. piercing holes c. removing layers of metal d. cutting thick sections of metal Now go to the Answer Key and check your answers. 18 Welder Training Program Level C

19 Module P2 Theory Competency P2-1 P2-1 Learning Task 2: Cutting characteristics of ferrous and nonferrous metals Oxy-fuel gas easily cuts low- and medium-carbon steels. However, alloy steels, cast iron and certain other ferrous alloys present special cutting problems. For non-ferrous metals, oxy-fuel gas cutting has very limited application and is not normally used. Ferrous alloys Ferrous alloys with a high carbon/alloy content present problems for oxyfuel gas cutting. These alloys include high-speed steel, cast iron and alloy steels such as stainless steels, chromium steels and manganese steels. When you apply cutting oxygen to high-carbon and alloy steels, the oxide that is formed has a higher melting temperature than the base metal. Instead of melting and falling away, the oxide forms a protective shield on the surface of the metal. This difficult-to-melt oxide will interrupt and deflect the cut. This makes a good cut very difficult, if not impossible. The process is no longer a true cutting procedure. Instead, it consists of melting a pool of metal and then blowing it away with the cutting oxygen stream. Techniques for cutting high-carbon and alloy steels The following special techniques can be used to cope with the difficulty of cutting high-carbon and alloy steels: preheating waster plates flux cutting Preheating Cast iron has a high carbon content. It is easier to cut if you preheat before cutting. Note that when cast iron is heated for any cutting or welding process, it must also be post-heated, then cooled slowly. If you don t, the casting will crack and fail. Always follow recommended preheat and postheat procedures. Waster plates An effective way to cut high-carbon and alloy steels is to clamp a low-carbon steel plate (waster plate) over the line of cut (Figure 6). As the waster plate is burned, it adds more iron to the kerf. This raises the temperature and dilutes the base metal s heat-resistant slag. The higher heat and dilution make the slag more fluid. You can then proceed with the cut. Welder Training Program Level C 19

20 Module P2 Theory Competency P2-1 Cutting torch Waster plate Grey cast iron Kerf Figure 6 Using a waster plate In some special situations, a stringer bead is welded over the line of cut instead of using a waster plate. Flux cutting You can get the same effect as using a waster plate by introducing a flux of high cutability into the cut or feeding a low-carbon steel rod into the kerf. Both methods are referred to as flux cutting. Introducing a powdered flux is not done often because of the overall cost and the specialized equipment and fluxes required. However, feeding a low-carbon steel rod into the cut is relatively inexpensive and easy to do. Low-carbon steel wire can also be fed into the preheat flames for a faster start. This method allows for faster starts when cutting cast iron. The wire can be fed in manually or with an attachment to the torch that feeds the wire continuously. Cutting technique When cutting high-carbon and alloy steels, move the torch forward along the line of cut with a slight semicircular motion (Figure 7). The semicircular motion will produce a slightly larger kerf, preventing the slag containing carbon or alloy particles from hanging up in the kerf. Depending on the operator s skill level, this method will produce a very rough kerf. 20 Welder Training Program Level C

21 Module P2 Theory Competency P2-1 High-carbon or alloy steel base metal Torch motion Kerf Direction of travel Figure 7 Semicircular torch motion technique used when cutting high-carbon or alloy steel Special oxy-fuel gas cutting processes Special cutting processes have been developed to improve the cutting capacity of oxy-fuel gas cutting equipment on ferrous alloys that form an oxide shield. These special processes and techniques do not change the fact that oxy-fuel gas is a poor process for cutting some metals. Arc cutting processes, such as plasma arc and air carbon arc, are generally better processes for cutting both ferrous and non-ferrous alloys. These special oxy-fuel cutting processes include chemical flux cutting and metal powder cutting. Chemical flux cutting Chemical flux cutting uses a standard oxy-fuel gas cutting torch attached to a chemical flux-feeding unit. This unit injects a powdered chemical flux into the hose carrying the high-pressure cutting oxygen (Figure 8). This flux removes the oxide shield that normally forms and hampers the cutting process. This process was developed for cutting stainless steel, but it is occasionally used on other alloy steels and cast iron. Welder Training Program Level C 21

22 Module P2 Theory Competency P2-1 Preheat flame oxygen hose Preheat flame fuel gas hose Cutting oxygen and chemical flux line Cutting oxygen line Cutting Torch Chemical flux feeder Work Figure 8 Chemical flux cutting outfit Metal powder cutting The metal powder cutting process uses oxy-fuel gas cutting equipment together with a unit that feeds an iron-rich powder through a tube to the torch tip. There the powder is directed into the oxygen cutting stream. The powdered iron burns with considerable heat and helps stop the oxide shield from forming. Metal powder cutting is also useful for situations where you need an instant start. Non-ferrous alloys The oxy-fuel cutting process is not normally used on non-ferrous alloys that contain little or no iron. Iron must be present for oxidation to occur. Non-ferrous alloys (many of which have low melting temperatures) do not contain iron, and therefore they will only melt and not be cut. Some non-ferrous alloys are: aluminum bronze copper magnesium Now complete Self-Test 2 and check your answers. 22 Welder Training Program Level C

23 Module P2 Theory Competency P2-1 Welder Training Program Level C 23

24 Module P2 Theory Competency P2-1 Answers Self-Test 2 Choose the correct response for each question and put it in the Answers column. Cover your answers when reviewing the test for study purposes. 1. Non-ferrous alloys are difficult to cut because they contain a. some ferrides b. little or no iron c. a large quantity of iron d. cast iron 2. Oxy-fuel gas easily cuts a. stainless steel b. high-alloy steel c. cast iron d. low-carbon steel 3. The protective oxide shield is formed when you cut cast irons or alloy steels because the a. oxide has a lower melting temperature than the base metal b. oxide has a higher melting temperature than the base metal c. iron content in the oxide is too high d. iron content in the base metal is too high 4. Cast iron can be more easily cut with the oxy-fuel gas process if it is a. sanded b. chilled c. preheated d. sandblasted 5. To make cutting cast iron easier, you can a. use a lower oxygen setting b. use a waster plate c. grind the area to be cut d. use an oxygen-rich flame 24 Welder Training Program Level C

25 Module P2 Theory Competency P A ferrous alloy is one that contains a. iron b. chromium c. manganese d. brass Answers 7. Certain ferrous alloys are hard to cut because they produce a on the surface of the metal. a. greasy residue b. protective oxide c. waster plate d. hard scale 8. A waster plate helps when cutting certain ferrous alloys by a. protecting the kerf from excessive heat b. diluting the base metal slag with iron c. removing the slag d. decreasing the heat of the flame 9. Chemical flux cutting is especially useful for cutting a. low-carbon steel b. copper c. stainless steel d. brass 10. Metal powder cutting is a process where a powder containing is injected into the cut area. a. iron b. aluminum c. chromium d. nickel 11. Aluminum cannot be cut with oxy-fuel gas because it a. is so lightweight b. has a high melting temperature c. does not contain the iron necessary for oxidation d. is a ferrous alloy Now go to the Answer Key and check your answers. Welder Training Program Level C 25

26 Module P2 Theory Competency P Welder Training Program Level C

27 Module P2 Theory Competency P2-1 P2-1 Learning Task 3: Thermal effects of oxy-fuel gas cutting The high temperature and large quantities of heat energy produced during oxy-fuel gas cutting can cause two major problems in the base metal: distortion surface hardening Distortion Distortion can be a problem when you are using oxy-fuel gas to cut sheet metal, especially light-gauge sheet metal. The underlying cause of distortion is in the characteristic of metal to expand (become larger) when heated and to contract (become smaller) when cooled. If metals are allowed to expand and contract freely with no restraint, distortion is less likely to occur. However, if the metal is restrained in some way that prevents free expansion and contraction, distortion will develop. When the heat of a cutting torch is applied, the metal in the cut area expands, but it is restrained by the surrounding, cooler metal. In light material, the result will be considerable buckling and warping (Figure 9). Original shape Figure 9 Distortion Warpage caused by heating You can minimize distortion by preheating the workpiece. Preheating helps to distribute the expansion of the metal evenly throughout the workpiece. If you use preheating techniques, you must make sure that you distribute the heat evenly throughout the metal. Other techniques that minimize distortion while cutting thin material are intermittent cutting (stopping and starting) and stack cutting. Surface hardening When cutting medium- to high-carbon steels and cast irons, you need to take special care to prevent hardening along the surfaces of the cut. As the flame moves along the cut, the surrounding cooler metal quickly draws away the heat, causing the kerf area to cool rapidly. This rapid cooling tends to harden the cut surfaces. In low-carbon steels, the hardening effect is not significant. High-carbon and alloy steels harden at a much faster rate because of the additional carbon or other elements. Welder Training Program Level C 27

28 Module P2 Theory Competency P2-1 The best way to avoid the problem of surface hardening is to slow the rate of cooling by preheating and post-heating the base metal. A surface hardened during cutting should be ground off before welding, otherwise certain weld faults may occur. If any cracks have developed during the cutting process, remove them by grinding or gouging. Now complete Self-Test 3 and check your answers. 28 Welder Training Program Level C

29 Module P2 Theory Competency P2-1 Welder Training Program Level C 29

30 Module P2 Theory Competency P2-1 Answers Self-Test 3 Choose the correct response for each question and put it in the Answers column. Cover your answers when reviewing the test for study purposes. 1. Distortion is a particular problem when cutting a. low-carbon steel b. aluminum c. sheet metal d. very wide kerfs 2. One technique often used to control distortion is to a. make intermittent cuts b. use a large cutting tip c. use high working pressure d. use an iron powder feed 3. Distortion can occur while cutting because the hot metal a. expands and contracts unevenly b. produces an oxide shield c. hardens along the surface d. has uneven melting temperatures 4. Surface hardening is a result of a. rapid cooling b. too little carbon c. rapid heating d. using a waster plate 5. Surface hardening is a problem with a. low-carbon steels b. high-carbon steels c. wrought iron d. all of the above 6. An effective way to slow the cooling rate of the kerf area is to a. dip the metal in lukewarm water after cutting b. move the cutting torch slowly c. preheat the base metal d. clamp the metal to a waster plate Now go to the Answer Key and check your answers. 30 Welder Training Program Level C

31 Module P2 Theory Competency P2-1 P2-1 Learning Task 4: Safety requirements for oxy-fuel gas cutting The oxy-fuel gas cutting process is potentially very dangerous. Extremely flammable and explosive gases are mixed and ignited at the cutting torch tip. Temperatures can reach up to 3480 C (6300 F). The process produces sparks, molten slag and, in some cases, toxic fumes. In order to work safely with oxyfuel gas processes, you must follow some important safety requirements. Protective clothing Oxy-fuel gas cutting produces extreme heat, flying sparks and molten slag. You must wear the correct protective clothing during this process. You should remember to: protect your head and hair with a Welder s cap protect your hands with leather welding gloves protect your feet with CSA-approved high-top leather boots and cuffless pants protect your arms with a long-sleeved shirt and a leather jacket wear a flame-resistant apron, shop coat or overalls Eye protection Eye protection is the most important part of your protective clothing. The ultraviolet or infrared rays produced in oxy-fuel gas cutting are not as harmful as those produced by electric-arc processes. However, it is extremely important to protect yourself from flying sparks, hot slag and the intense heat of the cutting process. At all times while cutting, you must wear CSA-approved welding goggles fitted with shaded lenses. These lenses are available in shades from 1 to 14. The correct lens shade number depends on the application and the thickness of the base metal being cut (Figure 10). Oxy-fuel gas application Base metal thickness Recommended lens shade Light cutting Up to 25 mm (1") No. 3 or 4 Medium cutting 25 mm to 150 mm (1" to 6") No. 4 or 5 Heavy cutting Over 150 mm (6") No. 5 or 6 Light welding Up to 3 mm ( 1 8") No. 4 or 5 Medium welding 3 mm to 13 mm ( 1 8" to 1 2") No. 5 or 6 Heavy welding Over 13 mm ( 1 2") No. 6 or 8 Figure 10 Recommended lens shade numbers Welder Training Program Level C 31

32 Module P2 Theory Competency P2-1 Be sure to use the correct lens shade number. If the lenses are too dark, you can develop eyestrain as you struggle to see your work. If the lens shade is too light, your eyes will not be adequately protected from harmful rays. For most of your work with oxy-fuel gas cutting and welding, the No. 5 and occasionally the No. 6 lens shade are recommended. Fire protection Oxy-fuel gas cutting works by burning metal with pure oxygen and a highly flammable fuel gas. The very nature of this process makes fire safety very important. Torch line explosions, caused by backfires or flashbacks, are a particular fire danger when you are operating oxy-fuel gas equipment. Backfire During the cutting process, the torch flame might make a loud popping sound. The flame will either go out and might reignite itself, or it will go back into the cutting tip and make a squealing sound. This is called a backfire. It is usually the result of touching the torch tip to the workpiece, of overheating the torch tip or of not having enough gas flow. Flashback Flashback is a much more serious problem. In this case, the backfire goes beyond the tip. If unchecked, the burning mixture of fuel gas and oxygen will back up behind the torch body, burning through the hoses or entering the regulators. The result of a flashback, aside from fire damage, is explosion. Flashbacks will usually damage your equipment, which will need repair or replacement. Proper handling, use and maintenance of the oxy-fuel gas equipment eliminates most fire hazards. It is important that you learn the safe procedures for operating all oxy-fuel gas equipment before using it. If you handle and maintain the equipment correctly, you will minimize the fire hazards. But you should remember these safety considerations when working with oxy-fuel gas equipment: Keep a fire extinguisher nearby while cutting. A dry chemical extinguisher good for Type A, B or C fires is the best. Floors should be concrete or some other non-flammable material. Any flammable materials or vapours should be kept away from the cutting area. If cutting must take place close to flammable substances, a firewatcher should be designated. Protect the oxy-fuel gas hoses from sparks and slag. 32 Welder Training Program Level C

33 Module P2 Theory Competency P2-1 Ventilation For oxy-fuel gas cutting indoors, there should be adequate ventilation to disperse fumes and provide you with a safe, comfortable working environment. When very toxic fumes such as lead, zinc or Teflon are being produced, you must have a localized exhaust system or an air-line respirator. Even when you are not cutting toxic substances, your welding station booth should be arranged so as to provide proper air flow. When performing cutting procedures in confined spaces where there is not enough air flow, you will need an air-line respirator. Toxic fumes While iron fumes are generally not considered harmful, other metals or materials release toxic fumes when heated by the oxy-fuel gas cutting process. The most dangerous of these fumes are those released by: cadmium zinc lead beryllium other alloys synthetic materials Cadmium Cadmium is widely used as a rust-inhibiting coating on steel. It is a silvery coating and turns a yellow-gold when heated. It produces deadly fumes, and good ventilation is essential when you are cutting cadmium. Zinc Zinc is another common coating. Galvanized sheet metal, for example, is coated with zinc. Zinc is also used in die-cast metal parts. Zinc fumes are very irritating to the respiratory system, so there must be good ventilation. Lead Lead produces extremely toxic fumes. It is sometimes used in pipes for carrying certain liquids and gases. Lead is also present in storage batteries and in many paints. Lead poisoning can produce long-term harmful effects. Make sure there is good ventilation when lead fumes are present. Beryllium Beryllium is used as plating and in lightweight aerospace metals. It is usually alloyed with copper and is called beryllium-copper. Beryllium is a suspected carcinogen that is, it can cause cancer in humans. Other alloys Certain other metals, used as alloys, also produce potentially dangerous fumes. Whenever you cut metals that contain chromium (stainless steels), copper or nickel, always make sure that there is very good ventilation. Welder Training Program Level C 33

34 Module P2 Theory Competency P2-1 Synthetic materials Some synthetic materials, such as Teflon, fiberglass and plastics, are often used for pipe linings. When these synthetics are heated, they melt and release highly toxic gases. If ventilation levels are not adequate or when the fumes are in high concentrations, you must wear an air-line respirator (Figure 11) or Self- Contained Breathing Apparatus (SCBA). For your personal safety, you should wear a respirator as well as maintain good ventilation whenever these fumes are present. Figure 11 Air-line respirator Most of these toxic fumes are difficult to identify. Before starting a cutting operation, take time to research the metal, then take the necessary precautions. Clean the base metal thoroughly before cutting. A surface contaminant of unknown composition could present a toxic fume hazard. An example is commercial degreasing solvents. Always wash these solvents and any other substances from the metal before cutting. Oil and grease hazards Oil and grease are both marginally flammable under normal conditions, but if either is brought into contact with pure oxygen (especially if it is under pressure), a violent explosion can occur. The friction of high-pressure oxygen escaping from an oxygen cylinder can cause oily or greasy substances to burst into flames with explosive violence. Special precautions are necessary when you cut with oxy-fuel gas near oil and grease: Never store oxygen or fuel gas cylinders near grease, oil or any other combustible substance. Never use oil or grease as a lubricant on oxy-fuel gas equipment. Keep all clothing free of oil and grease. Now complete Self-Test 4 and check your answers. 34 Welder Training Program Level C

35 Module P2 Theory Competency P2-1 Welder Training Program Level C 35

36 Module P2 Theory Competency P2-1 Answers Self-Test 4 Choose the correct response for each question and put it in the Answers column. Cover your answers when reviewing the test for study purposes. 1. Which of the following types of eye protection must you wear when oxyfuel gas cutting? a. shaded glasses b. welding goggles c. flash goggles d. safety glasses 2. Which lens shade can be used for most of your oxy-fuel gas cutting or welding operations? a. No. 3 b. No. 5 c. No. 8 d. No Where might a Welder come upon Teflon? a. in degreasing solvents b. in stainless steels c. as a coating on sheet metal d. as a lining for pipe 4. Which is the correct footwear for performing oxy-fuel gas cutting? a. special asbestos shoes b. CSA-approved high-top leather safety boots c. laced leather shoes d. high-top rubber boots 5. What causes a backfire? a. not enough gas flow b. gases failing to ignite c. gases mixing in the torch tip d. using the wrong fuel gas 36 Welder Training Program Level C

37 Module P2 Theory Competency P Iron fumes are extremely toxic. a. true b. false Answers 7. Where might a Welder come upon zinc? a. in lead-based paint b. in degreasing solvents c. in chromium alloys d. as a coating on sheet metal 8. Why are oil and grease special hazards when you work with oxy-fuel gas equipment? Now go to the Answer Key and check your answers. Welder Training Program Level C 37

38 Module P2 Theory Competency P Welder Training Program Level C

39 Theory Competency P2-2: Oxy-fuel gas cutting equipment P2-2

40

41 Module P2 Theory Competency P2-2 Outcomes In order to make accurate, high-quality oxy-fuel gas cuts safely, you must thoroughly understand oxy-fuel gas cutting equipment and its safe operation. When you have completed the Learning Tasks in this Theory Competency, you should be able to describe: properties and applications of oxygen and fuel gases used in oxy-fuel gas cutting oxygen and acetylene cylinders and liquid gas containers function of oxy-fuel gas cylinder pressure regulators single-stage and two-stage oxy-fuel gas cylinder pressure regulators various types of oxy-fuel gas cutting torches and their applications types of oxy-fuel gas cutting tips and their applications maintenance of oxy-fuel gas cutting tips causes and prevention of backfires and flashbacks oxygen and acetylene manifold systems and their safe operation guided oxy-fuel gas cutting attachments a variety of oxy-fuel gas cutting machines Evaluation When you have completed all the Theory Competencies in Module P2, you will take a written test. You must score at least 70% on this test. The test will include questions that are based on the following material from Theory Competency P2-2: oxygen and fuel gases used in oxy-fuel gas cutting oxy-fuel gas cylinders and containers oxy-fuel gas cylinder pressure regulators oxy-fuel gas cutting tips and attachments oxy-fuel gas cutting machines safety considerations of oxy-fuel gas cutting Resources Required: All required resources are contained within this Theory Competency. Welder Training Program Level C 41

42 42 Welder Training Program Level C

43 Module P2 Theory Competency P2-2 P2-2 Learning Task 1: Gases used in the oxy-fuel gas cutting process Oxy-fuel gas cutting involves the mixing of two gases to complete the cutting process. One of these gases is always oxygen. The other gas is the fuel gas. The fuel gas can be acetylene, natural gas, propane, methylacetylene-propadiene, stabilized (Mapp ) or propylene. It is useful to know something of the properties and application of these gases. Oxygen is essential to all oxy-fuel gas cutting processes. All of these gases are stored in cylinders under pressure. Although metric measurements are in use, most welding equipment is graduated in imperial measurement. Pressure can be measured in kilopascals (kpa), megapascals (MPa) and pounds per square inch (psi). A megapascal is 1000 times larger than a kilopascal. Most cylinder pressure regulators are graduated in psi, but some give pressures in both psi and kpa. Always check the units of measurement being used. Oxygen (O 2 ) Oxygen is a colourless, odourless and tasteless gas found in our atmosphere. It supports both life and combustion. Our atmosphere consists of about 21% oxygen, 78% nitrogen and 1% other gases. The large nitrogen content in our air tends to slow down combustion or burning. Materials that burn in our normal atmosphere will burn much faster and more vigorously in pure oxygen. Other substances that do not burn in air (such as iron) burn very well in pure oxygen. It is this property that makes oxygen effective in cutting iron and steel. It is also this property that makes oxygen extremely dangerous. Many substances that are not considered flammable will burn with explosive violence in pure oxygen. Oxygen will cause oil and grease to explode into flame. Keep oil and grease away from oxygen equipment. Never use oil on oxygen cylinder pressure regulators, cylinder valves or torch valves. Acetylene (C 2 H 2 ) Acetylene is a compound formed by uniting two carbon atoms and two hydrogen atoms. It is colourless, but it has a strong, pungent odour. The average person can smell as little as 1% acetylene in the air. This odour makes acetylene leaks easy to detect. Acetylene is used in oxy-fuel gas cutting because it burns at an extremely high temperature. When acetylene is mixed with oxygen, the resulting Welder Training Program Level C 43

44 Module P2 Theory Competency P2-2 flame can reach 3480 C (6300 F). This is the highest flame temperature produced from the combustion of oxygen and any fuel gas. This high flame temperature makes acetylene the most preferred of the fuel gases. Acetylene is flammable and highly explosive. Even a small proportion of acetylene in the air can explode. It is important to treat any mixture of air or oxygen and acetylene as potentially explosive. Immediately extinguish all open flames and ventilate the room before even turning on a light switch. Test the acetylene equipment for leaks and repair them immediately. Acetylene is also a very unstable compound. The term unstable means that the material is likely to break down (decompose) or undergo a physical change because of slight variations in temperature or pressure. The point at which a material breaks down is called its critical point. The critical point of acetylene is 193 kpa (28 psi) pressure at 21 C (70 F). At this point, acetylene breaks down into carbon and hydrogen and explodes. If the temperature is higher, the pressure at which acetylene breaks down will be lower. To allow for temperature fluctuations in a work area, the maximum working pressure for free acetylene is set at 103 kpa (15 psi). Cylinders used for acetylene are packed with a porous filler such as asbestos, charcoal or balsa wood. The cylinder is then filled with liquid acetone in which acetylene is dissolved. The filler absorbs the liquid acetone. Free acetylene is confined to small pockets of gas. In this way, there is a minimal amount of free acetylene in the cylinder. This means the pressure in the cylinders can be high, about 1.7 MPa (250 psi). Acetylene gas reacts with copper to form acetylide, a residue that is even more unstable than acetylene. The slightest jolt can cause an explosion and fire will most certainly result. There could be injury or loss of life. Never use copper or red brass fittings or tubing on acetylene systems. Use only fittings of yellow brass, iron or steel. Other fuel gases For several reasons, fuel gases other than acetylene are often used in oxy-fuel gas cutting. It is extremely important to remember that all of these gases are potentially explosive and you must use extreme care when working with them. The more common fuel gases are: natural gas propane methylacetylene-propadiene, stabilized (MPS) propylene 44 Welder Training Program Level C

45 Module P2 Theory Competency P2-2 These fuel gases each need a different amount of oxygen in order to produce a neutral flame (a flame that burns the fuel gas completely) (Figure 12). The question of how much oxygen you need to completely burn the fuel gas is important in terms of cost, the convenience of working with the equipment and the availability of oxygen. Specially designed cutting tips and, in some cases, mixing chambers are necessary with the liquid fuels, MPS gas and propane, as the amount of oxygen required to burn them completely is considerably higher than with acetylene. Fuel Gas Oxygen to Fuel Gas Acetylene 1 to 1 Propane 4.5 to 1 Natural gas 2 to 1 MPS 2.5 to 1 Propylene 2.6 to 1 Figure 12 Volumes of oxygen to fuel gas required for a neutral flame For some cutting operations, these fuel gases might be preferred over acetylene for reasons other than cost. Acetylene and oxygen generate the highest flame temperature, which permits fast starts when cutting. Although the other fuel gases have lower flame temperatures and slower starts, they produce cleaner cuts than acetylene, with little or no slag clinging to the bottom of the cut. Acetylene has a limited draw-off rate, so it cannot be used with large tips unless you also use a manifold system. Other fuel gases have higher draw-off rates, which means you can use large tips. This is especially critical when you are using large heating tips or cutting sections that are more than 125 mm (5 in.) thick. Natural gas (CH 4 ) Natural gas is often preferred in areas where it can be piped in because it eliminates the dangerous and time-consuming handling of fuel cylinders. Natural gas generates a flame temperature of 2540 C (4600 F), which is lower than that of acetylene or Mapp gas. Although it takes longer to preheat the metal and cutting speeds are slower, natural gas is a common alternative to acetylene because it is inexpensive and convenient. It is delivered at such low pressure that special injector-type torches are needed. Propane gas (C 3 H 8 ) Propane gas is supplied in liquid form in low-pressure cylinders. It is widely used because it produces clean cuts and is relatively inexpensive. Welder Training Program Level C 45

46 Module P2 Theory Competency P2-2 Propane has a high heat value but requires volumes of oxygen to one volume of propane to burn completely. The flame temperature is similar to natural gas, 2540 C (4600 F). Propane is stored in liquid form for convenient and safe handling. Methylacetylene-propadiene gas (C 3 H 8 ) (Mapp gas and FG [fuel gas]) Methylacetylene-propadiene, stabilized (MPS) gas is produced by rearranging the molecules in acetylene and propane to form a new compound. It is sold in different configurations under such trade names as Mapp gas and FG. This compound is much more stable and less explosive than acetylene, and it produces a flame almost as hot as acetylene, 2900 C (5300 F). Like acetylene, it has a strong odour, so leaks are easy to detect. MPS gas is stored in a liquefied form under high pressure. One cylinder contains the same volume as five acetylene cylinders. The capability of using higher working pressures makes MPS gas effective for underwater cutting where acetylene would be useless due to its limited operating pressure of 103 kpa (15 psi). Because MPS gas is so stable, the cylinders are safe and easy to handle. The slightly lower flame temperature makes for slower cuts, but with its clear advantage in safety, MPS gas is an attractive alternative to acetylene. Propylene (C 3 H 6 ) Propylene fuel gas is a byproduct of the crude oil refining process. It is sold under trade names such as Apache, B-Plus, H.P.G., T9, UCON 96 and Victorgas. It is available in its pure form or it might have other fuel gases added to it. One volume of propylene requires a minimum of 2.6 volumes of oxygen for a neutral flame. The combustion characteristics of the propylene flame are similar to those of methylacetylene-propadiene and therefore propylene uses much of the same equipment. Now complete Self-Test 1 and check your answers. 46 Welder Training Program Level C

47 Module P2 Theory Competency P2-2 Welder Training Program Level C 47

48 Module P2 Theory Competency P2-2 Answers Self-Test 1 Choose the correct response for each question and put it in the Answers column. Cover your answers when reviewing the test for study purposes. 1. Which gas is not a fuel gas? a. acetylene b. oxygen c. Mapp gas d. natural gas 2. Which combination of gases is most preferred for fuel gas cutting of lowcarbon steel? a. oxygen and natural gas b. acetylene and air c. acetylene and oxygen d. air and oxygen 3. What is the name of the liquid used to stabilize acetylene in an acetylene cylinder? a. propylene b. water c. freon d. acetone 4. Which of the following gases has no odour? a. propane b. natural gas c. oxygen d. acetylene 5. Which gas produces the highest flame temperature when mixed with oxygen? a. propane b. Mapp gas c. natural gas d. acetylene 48 Welder Training Program Level C

49 Module P2 Theory Competency P What is the maximum working pressure for acetylene gas at or below 21 C (70 F)? a. 48 kpa (7 psi) b. 103 kpa (15 psi) c. 193 kpa (28 psi) d. 345 kpa (50 psi) Answers 7. What type of fittings must never be used on an acetylene system? a. aluminum b. copper c. steel d. chromium 8. Which fuel gas is the most stable and the safest? a. Mapp gas b. acetylene c. propane d. natural gas 9. Propane gas is supplied in what form? a. jelly form b. solid form c. liquid form d. combination of liquid and solid 10. The major component of air is a. hydrogen b. nitrogen c. oxygen d. acetylene 11. What might happen if pure oxygen (especially pressurized) comes in contact with grease or oil? Welder Training Program Level C 49

50 Module P2 Theory Competency P2-2 Answers 12. Name one desirable characteristic of propane. a. easy and safe to handle b. safest to weld under water c. flame is hotter than acetylene d. excellent for cutting aluminum 13. Which fuel gas needs the least amount of oxygen to produce a neutral flame? a. Mapp b. propane c. natural gas d. acetylene 14. What is one advantage acetylene has over other fuel gases? a. stability b. lower flame temperature c. high flame temperature d. lower cost 15. Acetylene can be identified by its a. colour b. pungent odour c. lack of odour d. taste 16. Which fuel gas uses the most oxygen to produce a neutral flame? a. acetylene b. propane c. natural gas d. Mapp Now go to the Answer Key and check your answers. 50 Welder Training Program Level C

51 Module P2 Theory Competency P2-2 P2-2 Learning Task 2: Oxygen and fuel gas cylinders Most Welders use oxygen and fuel gas from cylinders. Since these cylinders are an important part of your gas cutting equipment, it is important that you know about their construction and safety precautions when using them. Cylinders are not generally sold. They are usually rented by suppliers, who regularly pick up the empty cylinders and replace them with full ones. The supplier is also responsible for maintaining the cylinder in safe working condition. Any defects should be reported to the supplier immediately. Oxygen cylinders Oxygen is available either as a gas in high-pressure cylinders or as a liquid in relatively low-pressure cryogenic cylinders. High-pressure oxygen cylinders High-pressure oxygen cylinders store oxygen under pressures up to 18 MPa (2600 psi) at 21 C (70 F). This means that the cylinders have to be extremely strong. High-pressure oxygen cylinders are forged from a single piece of strong, high-carbon steel, with walls at least 6 mm ( 1 4 in.) thick. High-pressure oxygen cylinders have a threaded collar, compression-fitted to the top of the cylinder, for the removable protective cap to screw on to. They are available in a variety of capacities, ranging from 0.5 m 3 to 9.35 m 3 (20 ft. 3 to 335 ft. 3 ) (Figure 13). The two most common large-size oxygen cylinders in use in industry are the T and the K types. The T-type cylinder holds 9.35 m 3 (335 ft. 3 ) of oxygen compressed to 18 MPa (2600 psi) at 21 C (70 F). The K-type holds 7 m 3 (244 ft. 3 ) of oxygen compressed to 15 MPa (2200 psi) at 21 C (70 F). Removable protective cap Safety device in valve Wall thickness 6 mm (¼") 1422 mm (56") 230 mm (9") Figure 13 A typical 7 m 3 (244 ft. 3 ) oxygen cylinder Welder Training Program Level C 51

52 Module P2 Theory Competency P2-2 It is important to know that temperature affects the gas within the cylinder. Gases expand when heated and contract when cooled, so the pressure within the cylinder will vary with temperature changes. Since you might be working with welding equipment in a variety of climatic conditions, you need some idea of how temperature affects the pressure in a full K-type oxygen cylinder (Figure 14). Temperature Approximate pressure C ( F) MPa (psi) 49 (120) 17.3 (2500) 38 (100) 16.4 (2380) 27 (80) 15.5 (2246) 21 (70) 15.2 (2200) 16 (60) 14.8 (2140) 10 (50) 14.3 (2080) 4 (40) 13.9 (2020) 1 (30) 13.5 (1960) 7 (20) 13.1 (1900) 12 (10) 12.7 (1840) 18 (0) 12.3 (1780) 23 ( 10) 11.9 (1720) 29 ( 20) 11.5 (1660) Figure 14 Temperature versus pressure in a K-type cylinder It is important to be aware of the amount of oxygen in the cylinder. You can find this by monitoring the flame and the working pressure. If the flame is no longer consistent or the working pressure becomes difficult to maintain, remove the cylinder from service. If you continue to cut with reduced oxygen levels, your cuts will be poor in quality. The likelihood of flashback also increases. High-pressure oxygen cylinder valve The high-pressure oxygen cylinder valve is made of forged brass. The valve is specially designed to operate at high pressure. It comes with a screw-on protective cap that must be replaced when the cylinder is not being used. The cylinder valve is a double-seal construction to prevent oxygen from leaking around the stem (Figure 15). When the valve is closed, seal #1 shuts off the flow of oxygen from the cylinder. When the valve is opened all the way, seal #2 prevents any oxygen from travelling up the stem. The valve handle or handwheel at the top of the valve opens and closes the valve. Turn the valve wheel counter-clockwise to open and clockwise to close. Always open an oxygen valve slowly. This will prevent a quick release of highpressure gas that would put too much stress on the cylinder pressure regulator and gauges. In extreme cases a pressure rush could blow up the cylinder pressure regulator. The resulting metal fragments could cause serious injury. 52 Welder Training Program Level C

53 Module P2 Theory Competency P2-2 Handwheel Stem Seal #2 Safety device Oxygen out Rupture disk Threads to attach to cylinder Seal #1 Threads to attach to regulator (right-hand thread) Oxygen in Figure 15 Seals in an oxygen cylinder valve The oxygen pressure regulator attaches to an external threaded outlet fitting on the side of the valve. This fitting has right-hand threads. A fitting thread is considered to be a right-hand thread if the fitting tightens when turned in a clockwise direction. If the fitting tightens when turned in a counterclockwise direction, it is a left-hand thread. High-pressure oxygen cylinder valve safety device High-pressure oxygen cylinder valves also have a safety device. Outside the valve is a capped hexagonal nut that has small holes around the perimeter of the cap. Inside is a safety disk, made of a special material that will burst if the pressure inside the cylinder gets too high (Figure 16). If the cylinder temperature rises, the pressure increases, causing the safety disk to rupture and release the oxygen through the small holes in the hexagonal nut. Opposing vent holes allow the pressurized gas to be evenly diffused and prevent the blast effect of a single vent. The pressure at which the disk ruptures is 27 MPa (4000 psi). Welder Training Program Level C 53

54 Module P2 Theory Competency P2-2 Vent holes Oxygen from cylinder Ruptured disk Figure 16 Safety device on an oxygen cylinder valve Never try to repair a damaged cylinder valve or ruptured safety disk. Tag the cylinder to indicate the fault, move it to an open area and notify the supplier to pick it up immediately. Liquid oxygen containers When you need large volumes of oxygen, it is more economical to have liquid oxygen supplied in cryogenic containers. The term cryogenic means low temperatures, usually at or below 130 C ( 200 F). Cryogenic containers are very much like large thermos bottles in that they have an inner and outer container arrangement. The boiling point of oxygen is 183 C ( 297 F). This means that oxygen converts to a liquid when cooled below a temperature of 183 C ( 297 F). Storing gases in their liquid state allows the container to hold much higher volumes of gas. Oxygen, for example, has a cryogenic liquid to-gas expansion ratio of 1 to 861. Cryogenic containers are available in sizes ranging from 160 L to 1500 L (35 gal. to 330 gal.). Cryogenic containers that range from 160 L to 250 L (35 gal. to 55 gal.) are classed as portable. Cryogenic containers that are over 450 L (100 gal.) are considered to be bulk and therefore not portable. A 200-L (44-gal.) cryogenic container measures 167 cm (66 in.) in height and 51 cm (20 in.) in diameter. It holds 200 L (44 gal.) of liquid oxygen. The 200 L (44 gal.) of liquid oxygen produces 140 m 3 (5100 ft. 3 ) of oxygen gas. A T-type high-pressure oxygen cylinder measures 140 cm (55 in.) in height and 24 cm (9.25 in.) in diameter. It holds 9.4 m 3 (330 ft. 3 ) of oxygen gas. This means that one 200 L container of liquid oxygen holds as much as fifteen T-type cylinders of high-pressure oxygen. 54 Welder Training Program Level C

55 Module P2 Theory Competency P2-2 Cryogenic containers are designed to insulate, much like a Thermos bottle. They have three basic components: an inner vessel of a stainless steel alloy capable of handling very low temperatures an outer shell of low-carbon or stainless steel a space between the inner vessel and the outer shell filled with insulation in a vacuum The liquid oxygen is contained in the inner vessel. Large volumes of oxygen can be drawn off as a gas at a maximum working pressure of 1724 kpa (250 psi). As the gas is used, more liquid converts to gas. This process continues until all the liquid is gone. Cryogenic oxygen container safety devices Cryogenic containers are equipped with pressure relief valves. From time to time the pressure of the oxygen gas might rise above 1724 kpa (250 psi). This causes the pressure relief valve to open, allowing excess pressure to escape (bleed off). Cryogenic containers must be stored in a location where the bleed-off of excess oxygen will not present a danger. There are specific procedures for handling and operating cryogenic oxygen containers. Only properly trained people should handle or operate this equipment. The supplier will provide detailed instruction on these procedures. Acetylene gas cylinders Acetylene gas cylinders are strong, welded-steel containers that are specially designed to store the highly unstable and explosive acetylene gas. The cylinder is completely filled with a porous material such as monolithic filler, asbestos, charcoal or balsa wood. This filler material is then saturated with acetone, which has the ability to absorb twenty times its volume in acetylene gas. The inside of the cylinder resembles a very fine honeycomb. The honeycomb arrangement localizes the gas in small pockets, reducing the possibility of explosion. The acetone stabilizes the acetylene so that it can be contained at a higher pressure. The fine honeycomb prevents the mixture of acetylene and acetone from sloshing around, which would cause it to separate and possibly explode. With this arrangement, acetylene cylinders can be charged (filled) beyond the normal critical zone of 103 kpa (15 psi). The cylinders can be charged to much higher pressures, around 1.7 MPa (250 psi), so they can hold much more acetylene. Acetylene cylinders must be kept upright when in use. If not, the liquid acetone could flow into the system. Acetone would damage the acetylene pressure regulator, hoses and fittings. If it reaches the torch, acetone will contaminate the flame, resulting in poor-quality cuts. Welder Training Program Level C 55

56 Module P2 Theory Competency P2-2 Acetylene cylinders are normally shorter and larger in diameter than oxygen cylinders. They are available in a variety of capacities from 0.28 m 3 to 10.8 m 3 (10 ft. 3 to 380 ft. 3 ). Acetylene cylinders come in two basic types. The more common type has a rounded top with a protective cap that fits over and protects the cylinder valve. The other type has a recessed top that by design protects the cylinder valve (Figure 17). Valve Fusible plugs Felt filter 1075 mm (43") Porous filler material Wall thickness 3 mm (1 8") Fusible plugs 300 mm (12") Figure 17 Two types of acetylene cylinders Acetylene cylinder valves Acetylene cylinder valves are less complex in construction than the special double-seal design of the high-pressure oxygen cylinder valve. This is because the pressures are relatively low. The cylinder valve might have a handwheel for opening and closing, or it might have a square shank that you operate with a cylinder valve wrench (Figure 18). When the cylinder is in use, the cylinder valve wrench should remain in place on the cylinder valve in case you need to close the valve quickly. Figure 18 Acetylene cylinder valve wrench 56 Welder Training Program Level C

57 Module P2 Theory Competency P2-2 Acetylene cylinders with a recessed top have a cylinder valve that is operated by a T-cylinder valve wrench (Figure 19). As with a cylinder valve wrench, the T-cylinder valve wrench should remain in place on the cylinder valve when the cylinder is in use in case the acetylene must be shut off quickly. Figure 19 T-cylinder valve wrench The cylinder valve must always be opened slowly, 1 to 1½ turns. Never open the cylinder valve more than 1½ turns. This will allow you to close the cylinder valve quickly in case of an emergency. As with the oxygen cylinder, the acetylene valve is turned counter-clockwise to open and clockwise to close. The valve has a threaded fitting to accept an acetylene cylinder pressure regulator with left-hand threads. Acetylene cylinder safety devices The safety device for the acetylene cylinder is not built into the valve, but consists of fusible (easily melted) plugs (Figure 20) threaded into the top and bottom of the cylinder. Heat causes these alloy plugs to melt and release the cylinder contents. The average range of melting temperatures for these plugs is 104 C to 115 C (220 F to 240 F). Body Fusible material Threads Figure 20 Fusible plug on acetylene cylinder Welder Training Program Level C 57

58 Module P2 Theory Competency P2-2 Acetylene cylinders should never be completely emptied. It is very important to monitor the acetylene level in order to prevent acetone from being drawn into the lines. Remove the cylinder from service when the flame is inconsistent and the working pressure cannot be maintained. There is a maximum rate at which acetylene can be withdrawn from the cylinder. Above this rate (the draw limit ), liquid acetone will be drawn into the system. Acetone can damage the hoses and pressure regulators and contaminate the flame. Going past the draw limit is also dangerous because the drop in pressure could lead to flashback. You can detect acetone contamination by a purple colour in the flame. Too high a rate of withdrawal can occur when the cylinder is cold, because the cylinder pressure is reduced. It can also occur when you use a large tip, since they draw more acetylene from the cylinder. For operations that require large amounts of acetylene, you must connect two or more cylinders together with an approved manifold system. The Compressed Gas Association (CGA) has established draw limits for acetylene cylinders (CGA G ). These limits are as follows: Intermittent use: one-tenth ( 1 10) of the capacity of the cylinder per hour Continuous use: one-fifteenth ( 1 15) of the capacity of the cylinder per hour This replaces the long-established draw limit guideline of 1 7 of the remaining volume of acetylene in the cylinder. The current CGA draw limit is based on cylinder capacity rather than remaining volume. This eliminates the need to determine the remaining volume of acetylene in the cylinder by either weighing the cylinder or using a chart that calculates content based on cylinder temperature and pressure. Under the current system, for a cylinder that contains 10.8 m 3 (380 ft. 3 ) of acetylene, the draw limit would be: Intermittent use: 10.8 m 3 /10 = 1.8 m 3 (380 ft. 3 /10 = 38 ft. 3 ) per hour Continuous use: 10.8 m 3 /15 = 0.72 m 3 (380 ft. 3 /15 = 25 ft. 3 ) per hour If you were to draw the acetylene from the cylinder at a higher rate, acetone would enter the system. Liquid fuel gas cylinders Fuel gases such as propane and methylacetylene-propadiene (MPS) are liquids when stored under pressure in cylinders. 58 Welder Training Program Level C

59 Module P2 Theory Competency P2-2 When the cylinders are full, a space remains above the liquid. That space is occupied by the gas (vapour). When the cylinder valve is opened, the gas flows out, reducing the pressure on the liquid. This pressure reduction allows more liquid to vaporize (become gas) and collect above the liquid (Figure 21). Cylinder valve Protective shield Fuel gas vapour Liquid fuel gas Figure 21 Liquid fuel gas cylinder Since the cylinder contains a liquid fuel gas, it must be operated in an upright position. Cylinders filled with a liquid fuel gas contain a greater volume of gas than acetylene cylinders, which are filled with not only acetylene, but acetone and a porous filler material. Since MPS gas is not so sensitive to shock, it can be stored and shipped in lighter containers. For example, an empty acetylene cylinder weighs 100 kg (220 lb.) and a comparable empty MPS cylinder weighs only 23 kg (50 lb.). Liquid fuel gas cylinders look alike and have similar valves. The safety device on liquid fuel gas cylinders is a pressure relief valve built into the cylinder valve. Liquid fuel gas cylinders are available in various sizes and also in bulksize tanks for use with a manifold system. Liquid fuel gas containers are measured in litres (gallons) or kilograms (pounds). Customers usually purchase the small tank sizes and return them to the dealer for filling. The larger, bulk-size tanks are usually leased and can be refilled on the jobsite. Storage and handling of cylinders The flammable and explosive properties of the gases used in fuel gas cutting and welding make it essential to follow safety procedures at all times. Not Welder Training Program Level C 59

60 Module P2 Theory Competency P2-2 only must you know the correct way to store and handle full and empty gas cylinders, but you must make the practice of all safety precautions a habit. Storage 1. Oxygen and fuel gas cylinders should be stored separately in designated areas. If they are stored indoors, the area should be dry and well ventilated. If they are stored outdoors, cylinders should be protected from the weather and direct sunlight, which could cause a rise in temperature. Empty cylinders should also be stored separately or with the same type of gas cylinder. If empty and full cylinders are stored together they should be separated into designated FULL and EMPTY areas (Figure 22). Empty cylinders should also be marked "MT." Figure 22 Storage of full and empty cylinders 2. Cylinders must not be stored near radiators, stoves or any other source of heat. 3. Cylinders should be stored in an upright position. 4. All cylinders must be secured to a stationary object such as a wall or to a portable cart. Store all cylinders where they will not be knocked over or struck by falling objects or passing vehicles. Handling 1. Cylinders must always be handled very carefully. Never drop cylinders or allow them to bump together or against another object. This might generate a spark and there might be enough gas leakage to cause an explosion. 60 Welder Training Program Level C

61 Module P2 Theory Competency P Special cylinder carts must be used for moving cylinders and the cylinders must be secured to the cart. 3. Cylinders can be moved short distances by tilting and rolling them on their edge. Never drag or slide cylinders across a floor. 4. To lift a cylinder with a crane, always use a cradle or box that is certified and rigged by qualified personnel (Figure 23). Never lift a cylinder by its protective valve cap. 5. When moving cylinders, always remove the cylinder pressure regulators. Make sure that the cylinder valves are closed and the protective valve caps are in place. Figure 23 Carriage for lifting cylinders Safety precautions for using cylinders 1. Keep cylinders away from live electrical wiring. 2. Keep oxygen and fuel gas cylinders as far as possible from any area where sparks or flame from welding or cutting could contact them. Never cut or weld directly over cylinders. Welder Training Program Level C 61

62 Module P2 Theory Competency P To prevent an explosion, keep oily and greasy substances away from the oxygen cylinders, valves, hoses, fittings and attachments. Take care to keep oil, paint, and grease cans far away from your oxy-fuel gas equipment. Wipe up oil spots immediately. Keep hoses and welding equipment off the floor. Never oil or grease cylinder valves, pressure regulators, torches or other oxy-fuel gas equipment. 4. Do not use leaky fuel gas cylinders. A leaking fuel gas cylinder must be moved to an area where good ventilation exists (preferably outdoors) and warning signs must be displayed to prohibit sources of ignition. 5. Always operate oxygen cylinder valves by hand. Never strike a cylinder valve with a wrench or hammer, as this could cause a spark. If a cylinder valve is clogged with snow or ice, use warm water to thaw it. Never use a flame. 6. Never tamper with or try to repair cylinder valves. If a cylinder valve does not function properly, notify the supplier. 7. Never tamper with cylinder safety devices. 8. When not in use, cylinder valves must be closed and the protective valve caps installed. Now complete Self-Test 2 and check your answers. 62 Welder Training Program Level C

63 Module P2 Theory Competency P2-2 Welder Training Program Level C 63

64 Module P2 Theory Competency P2-2 Answers Self-Test 2 Choose the correct response for each question and put it in the Answers column. Cover your answers when reviewing the test for study purposes. 1. What should you do if you notice that a fuel gas cylinder is leaking? a. use the soap test to find the leak b. wrap fire-resistant material around the stem c. lay it on its side d. move it into an open area and notify your supervisor 2. What is the safety device on acetylene cylinders? a. a ruptured disk b. fusible plugs c. a check valve d. pressure relief valves 3. When opening an oxygen cylinder valve, you should remember to a. never open more than ½ turn b. open the valve very quickly c. tap the valve first with a cylinder wrench d. open the valve all the way 4. At what pressure is oxygen stored in T-type cylinders at 21 C (70 F)? a. 1.4 MPa (200 psi) b. 3.4 MPa (500 psi) c. 18 MPa (2600 psi) d. 28 MPa (4000 psi) 5. What happens to the pressure inside an oxy-fuel gas cylinder as the temperature increases? a. The pressure increases. b. The pressure remains the same. c. The pressure decreases. d. The pressure fluctuates. 64 Welder Training Program Level C

65 Module P2 Theory Competency P The safety device on an oxygen cylinder is located on the a. bottom of the cylinder b. top of the cylinder c. cylinder valve assembly d. side of the cylinder Answers 7. The oxygen cylinder safety device could rupture if a. the internal pressure rises above 103 kpa (15 psi) b. the cylinder valve is opened quickly c. the cylinder is cooled d. the cylinder is heated 8. Cryogenic containers of liquid oxygen are preferred over high-pressure cylinders containing oxygen gas because a. fuel gas can be premixed with the liquid oxygen in the cryogenic container b. they are more economical to use than high-pressure cylinders c. liquid oxygen produces a hotter preheat flame d. cryogenic containers are designed to withstand higher pressures 9. The safety devices on cryogenic containers are a. cryogenic safety plugs b. fusible plugs c. rupture disks d. pressure relief valves 10. How many turns should you use to open an acetylene valve? a. 1½ turns b. 2½ turns c. 3½ turns d. turned all the way open 11. Why should acetylene cylinders never be completely emptied? a. The cylinder could explode. b. The safety device would rupture. c. The cylinder would have to be discarded. d. Acetone would be drawn into the pressure regulator. Welder Training Program Level C 65

66 Module P2 Theory Competency P2-2 Answers 12. When you operate liquid fuel gas cylinders, they should be a. lying on their side b. on a lower level than the oxygen c. in an upright position d. on a raised platform 13. Acetylene cylinders are filled with a. acetone b. acetone and a porous material c. nothing but acetylene d. acetylene and argon 14. The areas used to store oxy-fuel gas cylinders should be a. well ventilated b. kept very warm c. tightly sealed d. damp and humid 15. When you store cylinders outside, what precautions are necessary? a. The pressure regulator should be removed. b. They should be laid down so they don t fall over. c. They should be protected from the weather, especially the sun. d. The valves should be open. 16. Acetylene cylinders must be used in the upright position to prevent a. acetone from entering the system b. the cylinder from rolling c. damage to the pressure regulators d. pressure fluctuations 17. When you use a cylinder valve wrench or T-valve wrench to operate an acetylene cylinder valve, you need to make sure that the wrench a. remains in place on the cylinder valve while the cylinder is in use b. is removed while the cylinder valve is open c. is made of copper d. has right-hand threads 66 Welder Training Program Level C

67 Module P2 Theory Competency P When moving cylinders from a storage area to the workplace, you must make sure that a. safety lines are properly attached b. cylinder valves are open c. cylinder valve protection caps are in place d. the cylinder pressure regulator is attached Answers 19. Oxygen and fuel gas cylinders should be stored a. together in a common storage area b. in separate storage rooms c. outside in the open d. in an air-conditioned space Now go to the Answer Key and check your answers. Welder Training Program Level C 67

68 Module P2 Theory Competency P Welder Training Program Level C

69 Module P2 Theory Competency P2-2 P2-2 Learning Task 3: Pressure regulators and their functions Oxygen and fuel gas pressure regulators Oxygen and fuel gases are stored in cylinders at pressures much greater than the pressures required to perform cutting or welding tasks. The pressure of a full K-type oxygen cylinder, for example, is 15 MPa (2200 psi), while the actual working pressure required at the cutting torch might only be 275 kpa (40 psi). Pressure regulators are installed on cylinders to control the flow of gas from the cylinder so that a lower working pressure can be maintained. Oxygen and acetylene cylinder pressure regulators have many features in common (Figure 24). They are usually made from a solid piece of brass or aluminum. Most of them have two calibrated gauges attached. The gauge with the higher numbers (calibrations) shows the pressure in the cylinder. The gauge with the lower calibrations shows the working pressure. The cylinder-pressure gauge is located on the same side as the cylinder connection. The working-pressure gauge is on the same side as the hose connection. To set working pressure, turn the working pressure adjusting screw. Turn it clockwise to increase the working pressure or turn it counterclockwise to reduce the working pressure. Both oxygen and acetylene cylinder pressure regulators have a hex nut permanently attached to the cylinder connection. The connections for oxygen pressure regulators are always right-hand thread. The connections for fuel gas pressure regulators are always left-hand thread. This arrangement makes it impossible to connect a pressure regulator to the wrong cylinder. There are several important differences between oxygen and acetylene pressure regulators. The most obvious difference is the calibrations on the pressure gauges. On oxygen pressure regulators, the cylinder pressure gauge is calibrated from 0 to 27 MPa (0 to 4000 psi). The working-pressure gauge is calibrated from 0 to 1.4 MPa (0 to 200 psi). On acetylene pressure regulators, these gauges have a much lower calibration range. The cylinder pressure gauge is calibrated from 0 to 2.7 MPa (0 to 400 psi). The working-pressure gauge is calibrated from 0 to 200 kpa (0 to 30 psi). In addition, the acetylene working-pressure gauge has a red warning area that begins at 103 kpa (15 psi). Pressures in this zone are over the maximum safe working pressure. Welder Training Program Level C 69

70 Module P2 Theory Competency P2-2 Acetylene pressure regulator Oxygen pressure regulator Figure 24 Pressure regulators Acetylene working pressure must be kept below 103 kpa (15 psi) to prevent the unstable acetylene gas from exploding. Pressure regulators are usually identified by the type of gas for which they are to be used. Oxygen pressure regulators have the word oxygen printed on the regulator body and one or both gauges. The word acetylene is printed on the body and one or both gauges of acetylene pressure regulators. 70 Welder Training Program Level C

71 Module P2 Theory Competency P2-2 The gas hose and cylinder connections are threaded differently. Oxygen pressure regulators have an internal right-hand thread connection. Acetylene pressure regulators, depending on the supplier, have either an internal or an external left-hand thread connection. In addition, the hex nut on an acetylene pressure regulator is grooved while the hex nut on an oxygen pressure regulator is plain. There are variations in the fitting connections on acetylene cylinders, but the fitting connections on the acetylene pressure regulator can be changed by the use of adapters to suit the different styles of cylinder valves. Single-stage and two-stage pressure regulators Cylinder pressure regulators lower the cylinder gas pressure in either one or two steps. If the pressure is reduced in one step, the regulator is a single-stage pressure regulator. If the pressure is reduced in two steps, the regulator is a two-stage pressure regulator. Both types of regulators can be used on high-pressure cylinders, but the two-stage regulator will maintain more stable working pressures. Single-stage pressure regulators Single-stage cylinder pressure regulators are the most widely used for everyday welding and cutting. They reduce cylinder pressure to working pressure in one step. These regulators are less expensive and simpler in construction than two-stage regulators. Two-stage pressure regulators Two-stage cylinder pressure regulators look much like single-stage cylinder pressure regulators and are operated in the same manner. They accomplish the pressure reduction in two stages. In the first stage, the pressure is taken from the cylinder and reduced to a preset intermediate pressure. In the second stage, the pressure is reduced to the desired working pressure. Two-stage cylinder pressure regulators make it possible to maintain more constant outlet pressures. When large volumes of gas are being consumed, a single-stage cylinder pressure regulator will not maintain a constant gas flow rate as the cylinder pressure drops. The working pressure would have to be adjusted periodically to maintain flow rates as the pressure in the cylinder drops. A two-stage cylinder pressure regulator makes the flow of gas more constant and eliminates the need to readjust the pressure. Two-stage pressure regulators are recommended for precision cutting jobs requiring very accurate gas regulation. Many machine cutting torches use two-stage pressure regulators. Welder Training Program Level C 71

72 Module P2 Theory Competency P2-2 Safe use of pressure regulators 1. Make sure the pressure-adjusting screw (Figure 25) has been backed out before you open the cylinder valve. If the full pressure of the cylinder gas surges into the pressure regulator, the regulator mechanism and gauges could be damaged. In an extreme case, especially if oil is present, they could burst and cause personal injury. Figure 25 Pressure-adjusting screw 2. Watch for a creeping pressure regulator. This occurs when the gas hoses and torch are attached, the working pressure is set and the torch valves are closed. The working-pressure gauge tends to creep up or increase. This is usually caused by a faulty valve seat in the pressure regulator. It should be repaired before you operate the equipment. 3. Never force connections. Tighten connections with a cylinder wrench. Never use pliers or a pipe wrench. Always check the pressure regulator before trying to connect it to the cylinder. Make sure you have the correct pressure regulator for the cylinder. 4. Never use oil or grease on the connections and never use pipe compound or Teflon tape on these connections. Pipe compounds contain oil. Teflon tape will get into the system and plug small orifices. 5. Never try to repair a pressure regulator. This should only be done by a trained technician. 72 Welder Training Program Level C

73 Module P2 Theory Competency P All pressure regulators are precision mechanisms. Treat them with care and never drop or misuse them. When regulators are removed from service or transported, turn in the working pressure adjusting screw just far enough to take the pressure off the inlet valve seats. Store them in a box or suitable container with packing material to prevent damage. Clean them with a dry, clean rag. Never use oil, grease, cleaning fluids or gasoline to clean them. Now complete Self-Test 3 and check your answers. Welder Training Program Level C 73

74 Module P2 Theory Competency P2-2 Answers Self-Test 3 Choose the correct response for each question and put it in the Answers column. Cover your answers when reviewing the test for study purposes. 1. All oxygen connections have what kind of threads? a. left-hand threads b. right-hand threads c. pipe threads d. metric threads 2. All fuel gas connections have what kind of threads? a. right-hand threads b. left-hand threads c. straight threads d. horizontal threads 3. What is the main function of a cylinder pressure regulator? a. mix gases for combustion b. increase cylinder pressure to the desired level c. reduce cylinder pressure and maintain consistent flow d. keep the gases separate 4. The gauge with the higher calibrations on a cylinder pressure regulator shows the a. working pressure b. cylinder pressure c. live pressure d. maximum safe working pressure 5. To increase the working pressure on an acetylene pressure regulator, you would a. turn the working pressure adjusting screw counter-clockwise b. turn the working pressure adjusting screw clockwise c. turn the working pressure adjusting screw out d. turn the working pressure adjusting screw in a left-hand direction 74 Welder Training Program Level C

75 Module P2 Theory Competency P The gauge with the lower calibrations on a cylinder pressure regulator shows a. working pressure b. cylinder pressure c. atmospheric pressure d. pressure regulator pressure Answers 7. Before you open a cylinder valve, the working pressure adjusting screw on the cylinder pressure regulator should be a. in the off position b. removed c. backed out until tension is relieved d. screwed all the way in 8. Oxygen and acetylene pressure regulators are interchangeable. a. true b. false 9. It is advisable to use a two-stage cylinder pressure regulator when a. you pierce holes in thin steel plate b. precise gas regulation is needed c. the temperature is below freezing d. fluctuating gas flow is desirable 10. To determine if a cylinder pressure regulator is designed to be used with oxygen or acetylene, you would a. check the threads on connections b. check cylinder pressure gauge calibrations c. check the printing on the gauge d. all of the above 11. Which type of cylinder pressure regulator is most widely used? a. single-stage b. two-stage c. oxygen/acetylene combination d. gaugeless Welder Training Program Level C 75

76 Module P2 Theory Competency P2-2 Answers 12. What happens when a pressure regulator creeps? a. The torch flame goes out. b. The cylinder pressure increases. c. The working pressure increases. d. The hose connections become loosened. Now go to the Answer Key and check your answers. 76 Welder Training Program Level C

77 Module P2 Theory Competency P2-2 P2-2 Learning Task 4: Oxy-fuel hoses and fittings Oxy-fuel gas hose The hoses that carry fuel gases and oxygen are specifically designed for those purposes. The structure of the hose consists of two or three rubber layers, each separated by a layer of strong fabric for reinforcement (Figure 26). The outside layer of rubber can be plain or ribbed. The oxygen hose is coloured green or black, and the fuel gas hose (acetylene) is red. To prevent tangling, most oxy-fuel gas hoses are joined together by an outside layer of rubber. Red fuel gas hose Rubber outer casing Fabric reinforcement Rubber inner casing Green or black oxygen hose Figure 26 Double oxy-fuel gas hose Since a single hose (Figure 27) is more prone to kinking and wear, it usually has two layers of reinforcement to make it tougher. Outer rubber layer Fabric reinforcement Rubber layer Fabric reinforcement Inner rubber layer Figure 27 Single oxy-fuel gas hose Oxy-fuel gas hose is now manufactured in two grades, Grade T and Grade R: Grade T is designed for use with liquid fuel gases but can be used with all fuel gases, including acetylene. Grade T replaces the old Grade M. Grade R can only be used for acetylene. Welder Training Program Level C 77

78 Module P2 Theory Competency P2-2 Oxy-fuel gas hoses are most commonly available in 4.8 mm ( 3 16 in.), 6.4 mm ( 1 4 in.), 7.9 mm ( 5 16 in.) and 9.5 mm ( 3 8 in.). These measurements are the inside diameter of the inner tube, not the outside diameter of the hose itself. The size of hose you use depends on the size of the tip you are using and the length of the hose. For instance, 4.8 mm ( 3 16 in.) hose is the most common size for light-duty cutting and welding, but when cutting thick material with a large-volume tip, you would need a large-diameter hose to deliver the required oxygen and fuel gas. If you are using a long length of hose, you will find that the pressure decreases as the gas flows from the pressure regulator to the torch. A larger diameter hose will deliver more volume. When determining hose sizes for different applications, you should always check the hose manufacturer s oxy-fuel gas hose pressure drop data charts (Figure 28). Delivery Pressure lb. per Sq. in. OXYGEN HOSE O 2 Flow SCFH Pressure drop lb. per sq. in. 3 16" hose 1 4" hose 5 16" hose 3 8" hose Hose length in feet * * * 2.3 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * 2.8 * * * * * * * * * * * 2.8 * * * * * * * * * * * * * * * * * * * * 2.2 * * * * * * * Welder Training Program Level C

79 Module P2 Theory Competency P2-2 Delivery Pressure lb. per Sq. in. Acetylene HOSE O 2 Flow SCFH Pressure drop lb. per sq. in. 3 16" hose 1 4" hose 5 16" hose 3 8" hose Hose length in feet ** ** ** ** ** 0.3 ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** 0.4 ** ** ** ** ** ** ** Figure 28 Typical manufacturer s hose pressure drop charts Safe handling of oxy-fuel gas hose To avoid serious explosions or fires, only use an oxy-fuel gas hose that is in good condition. A faulty or damaged hose should be repaired in an approved manner or replaced immediately. Do not try to repair the hose with tape. After working with the hose, always coil and tie it to avoid kinking. Never expose the hose to oil, grease, cleaning solvents, gasoline, paint or contaminants of any kind. Keep the hose out of direct sunlight. New oxy-fuel gas hoses often contain talcum powder. These hoses should be blown out with compressed air. When using compressed air, be sure that the compressed air system is oil-less. This can be done by using a compressed air system that has an oil separator installed or by using an oil-less compressor. All oxy-fuel gas hoses must be purged before use. Purging flushes the hose with a small amount of the applicable gas by opening the pressure regulators for a brief period of time and then closing them. This assures that there is no dirt or foreign matter that can enter the small passages of the torch. These bits could plug a hole or orifice and possibly cause a flashback. Oxy-fuel gas hose fittings All fittings and connectors used to connect the oxy-fuel gas hose to the pressure regulators and torch body are made of a brass alloy. This prevents sparks if the fittings should accidentally come in violent contact with other Welder Training Program Level C 79

80 Module P2 Theory Competency P2-2 metals or materials. Brass alloy fittings will not corrode or produce any dangerous byproducts if oxy-fuel gases come in contact with them. Oxy-fuel gas hose fittings have right-hand thread connections for oxygen and left-hand thread connections for the fuel gas (acetylene) so the hoses cannot be accidentally switched. A distinct groove is cut around the outside of the hex nuts on fuel gas fittings (Figure 29). Sleeve type ferrule Figure 29 Oxygen and fuel gas hose connectors Oxygen and fuel gas connectors are made up of two pieces: a fitting with a machined seat and barbed gland and a nut (Figure 30). When the two pieces are assembled, the barbed gland fits tightly inside the hose. A metal ring (called a ferrule ) is crimped over the end of the hose to secure the hose to the barbed gland. Band-type ferrule Figure 30 Oxy-fuel connectors A special crimping tool is used to compress the ferrule on the hose (Figure 31). The connector must be firmly secured or the gas pressure will cause it to separate from the hose. 80 Welder Training Program Level C

81 Module P2 Theory Competency P2-2 Figure 31 Ferrule-crimping tools Hose couplings (Figure 32) can be used to connect two lengths of oxy-fuel gas hose. These couplings or splicers can also be inserted in a hose where a damaged section of the hose has been removed. Figure 32 Hose splice coupling Never use copper or red brass for fittings or tubing on acetylene gas systems. Acetylene gas reacts with copper to form acetylide, a residue that is even more unstable than acetylene. The slightest jolt can cause an explosion. Fire will most certainly result, causing injury or death. Only fittings made of yellow brass, iron or steel can be used on acetylene gas systems. Now complete Self-Test 4 and check your answers. Welder Training Program Level C 81

82 Module P2 Theory Competency P2-2 Answers Self-Test 4 Choose the correct response for each question and put it in the Answers column. Cover your answers when reviewing the test for study purposes. 1. Fuel gas (acetylene) hoses are usually what colour? a. red b. yellow c. blue d. green 2. Oxygen gas hoses are usually what colour? a. red b. blue c. yellow d. green 3. Which factor is important when determining the size of oxy-fuel gas hose to use? a. length of hose b. type of cylinder pressure regulator c. ferrule size d. cylinder pressure 4. Oxygen fittings can be identified by a. their right-hand threads b. their left-hand threads c. the groove in the nut d. both b and c 5. What does a grooved nut on an oxy-fuel gas fitting show? a. high pressure b. right-hand thread c. fuel gas use only d. oxygen use only 82 Welder Training Program Level C

83 Module P2 Theory Competency P Oxy-fuel gas connectors are made of what material? a. copper b. die-cast aluminum c. brass alloy d. cast iron Answers 7. To repair severed oxy-fuel gas hoses, you should use a. electrical tape b. rubber tape c. a ferrule-crimping tool d. glue 8. New oxy-fuel gas hoses, before being used, should be a. blown out with compressed air b. soaked in acetone c. thoroughly greased d. purged with oxygen 9. While cutting thick material with a large tip, you might have to a. increase the cylinder pressure b. use a larger diameter hose c. use a small-diameter hose d. decrease the working pressure 10. Oxygen and fuel gas hose connectors are identical. a. true b. false Now go to the Answer Key and check your answers. Welder Training Program Level C 83

84 Module P2 Theory Competency P Welder Training Program Level C

85 Module P2 Theory CoMPeTenCy P2-2 P2-2 learning Task 5: Oxy-fuel gas cutting torches, cutting tips and heating tips notes Basic torch features Although there are different types of oxy-fuel gas torches, all have certain elements in common (Figure 33). The most distinctive feature of a cutting torch is the cutting oxygen control lever. Depressing this lever fully releases a flow of cutting oxygen. Cutting torches also have two hose connections to supply the oxygen and fuel gas to the torch. The oxygen hose connection has right-hand threads and the fuel gas connection has left-hand threads. Cutting torches are all equipped with two needle valves that control the flow of preheat flame oxygen and fuel gas to the tip. Cutting torches all have a mixing chamber or head. Depending on the torch type, the mixing chamber can be either in the tip or in the torch body. They all use a cutting tip to concentrate and direct the preheat flame and cutting oxygen. Preheat flame oxygen valve Cutting oxygen control lever Cutting tip Preheat flame fuel gas valve Built-in flashback arrestors Figure 33 Oxy-fuel gas cutting torch In the oxy-fuel gas cutting torch (Figure 34), oxygen and fuel gas are carried in separate tubes from the inlet control valves to the mixing chamber, where they are mixed for the preheat flame. There is a separate passageway for the flow of cutting oxygen. Cutting oxygen control lever Torch body oxygen control valve Preheat flame oxygen valve Preheat flame fuel gas valve Figure 34 Cutaway of a two-piece oxy-fuel gas cutting torch WelDer TrAInInG PrOGrAM level C 85

86 Module P2 Theory Competency P2-2 Oxy-fuel gas cutting torch types Oxy-fuel gas cutting torches are either injector or equal-pressure types. The choice of which to use depends on the fuel gas supply pressure. Injector-type oxy-fuel gas cutting torch The injector-type oxy-fuel gas cutting torch is used for fuel gases supplied at low pressure, usually natural gas or low-pressure acetylene generator systems. The fuel gas is mixed with the oxygen by means of an injector nozzle in the torch handle (Figure 35). As the high-pressure oxygen flows from the tip of the injector, it draws the low-pressure fuel gas into the mixing chamber (venturi effect). Injector High-pressure oxygen Mixing chamber Low-pressure fuel gas Figure 35 Injector torch Equal pressure type oxy-fuel gas cutting torch The equal pressure type oxy-fuel gas cutting torch is more common than the injector type. It is designed for use with fuel gases supplied at higher pressures. One-piece oxy-fuel gas cutting torch The one-piece oxy-fuel gas cutting torch is designed to be used only for oxyfuel gas cutting processes. Two-piece oxy-fuel gas combination cutting torch The two-piece oxy-fuel gas combination torch consists of a torch handle designed to be used with a cutting attachment, a heating tip or a welding tip (Figure 36). The main difference between a one-piece and a two-piece oxy-fuel gas cutting torch is that the two-piece torch has three control valves rather than two. When you cut with this torch, the oxygen control valve on the torch handle is opened all the way, so in effect the valve is bypassed. Bypassing this valve supplies oxygen directly to the preheat oxygen control valve on the cutting attachment and to the cutting lever control valve. The preheat flame is adjusted by using the fuel gas control valve on the torch handle and the oxygen control valve on the torch attachment. The combination torch is an exceptionally useful tool because it can also be used with welding and heating attachments. 86 Welder Training Program Level C

87 Module P2 Theory Competency P2-2 Cutting attachment Torch body Figure 36 Two-piece combination torch Oxy-fuel gas cutting machine torch The oxy-fuel gas cutting machine torch consists of a body equipped with preheat oxygen and fuel gas control valves, a cutting oxygen control valve, a rack (flat gear) to adjust the torch height and a head to accept the cutting tip, encased in a tube for mounting on a cutting machine. Oxy-fuel gas cutting machine torches usually have a straight configuration with a rack for lifting or lowering the torch. There are three control valves, one for the preheat oxygen, one for the fuel gas and one for the cutting oxygen. A three-hose oxy-fuel gas cutting machine torch has separate lines for fuel gas, preheat oxygen and cutting oxygen (Figure 37). Three-hose machine torches are used mainly for cutting operations in which remote control is desired, large volumes of oxygen are required or precise cutting oxygen control is needed. Figure 37 Three-hose oxy-fuel gas cutting machine torch Welder Training Program Level C 87

88 Module P2 Theory Competency P2-2 Oxy-fuel gas torchline explosions: Causes and prevention Torchline explosions and fires occur when a highly explosive mixture of fuel gas and oxygen backs up into the torch. The results can be disastrous. It is important that you use your torch correctly in order to avoid torchline explosions. There are two types of explosions: backfire and flashback. Backfire During the oxy-fuel gas cutting process, the torch flame could back up into the cutting tip and make a popping sound. Usually the flame re-establishes itself instantly. In some cases the flame might go out, but since both gases are still flowing, the flame is usually rekindled from the hot work. If the flame does not rekindle, immediately close the torch oxygen preheat flame valve, close the torch preheat flame fuel gas valve and check the equipment. There are several possible causes of backfire: 1. the obstruction of gas flow at the torch tip (carbon deposits, hot metal particles) 2. touching the torch tip to the hot metal 3. torch tip is overheating 4. a faulty connection between torch handle and cutting attachment 5. working pressures that are too low With working pressures that are too low, the flame disappears into the torch tip because the gas speed (the speed at which the mixed gases come out of the torch tip) is not great enough. The gas speed must always be greater than the speed of propagation (the speed at which the flame travels toward the torch tip). Backfire is momentary and is restricted to the torch tip. It occurs most often with beginners who touch the hot metal with the torch tip. If the backfires occur repeatedly, carefully inspect the equipment, clean the torch tip, purge the hoses and relight. Flashback A flashback occurs when the backfire goes back beyond the torch tip and through the hose to the pressure regulators (Figure 38). The torch handle becomes hot, black smoke and sparks come out of the torch tip, a squealing or hissing noise is heard and the fire burns through the hose. Aside from fire damage, a flashback could cause an explosion. 88 Welder Training Program Level C

89 Module P2 Theory Competency P2-2 Flashback area (through to cylinder pressure regulator) Backfire area The causes of a flashback are: Incorrect working pressures. Figure 38 Areas of backfire and flashback Incorrect adjustment of the torch oxygen and fuel gas control valves. Grossly unequal oxygen and fuel gas working pressures. The higher pressure gas can back up into the lower pressure line and produce a flashback. A clogged tip, along with too high oxygen pressure. Failure to purge the hoses before igniting the torch. A torch that has been sitting idle for a while might well have an explosive mixture present in one hose. To help prevent backfires and flashbacks, make sure that the valves on the torch and pressure regulators are working properly. The tip should have clear, undamaged orifices. Flashback arrestors must be used. If you have a flashback, you must stop the flame immediately before an explosion occurs. Shut down the torch preheat flame gas control valves and the cylinder valves immediately. The torch preheat flame oxygen control valve must be shut off before the torch preheat flame fuel gas control valve. A flashback indicates that something is radically wrong with the setup. Before you reignite the torch, check all equipment to see if it is damaged. Replace any damaged equipment, purge each hose separately and adjust working pressures. If a flashback occurs again, stop using the equipment and have it serviced by qualified personnel. Flashback arrestors The best way to prevent flashbacks and explosions is to keep the oxygen and fuel gases apart. Close the torch gas control valves when you are not using the torch. Bleed gas hoses properly when you are finished using the equipment. You must regularly inspect the control valves on the torch and Welder Training Program Level C 89

90 Module P2 Theory Competency P2-2 the cylinders, as well as the gauges on the pressure regulators. Remember, inspection cannot help you detect whether oxygen or fuel gases are flowing in reverse inside the torch or hoses. A device called a flashback arrestor (Figure 39) is designed to respond to the pressure of a flashback by immediately stopping the progress of the flame burning back into the hoses and stopping the reverse flow of gas. A flashback arrestor also serves as a reverse-flow check valve, automatically stopping the reverse flow of the gas the moment it starts. Reverse-flow check valves are available without flashback capability. These reverse-flow check valves are often installed in the connections between the torch and the gas hoses, but it is strongly recommended that a proper flashback arrestor be in stalled at this location. WorkSafeBC regulations require that flashback arrestors be properly installed between the torch control valves and the cylinder pressure regulators. They may be installed at either end of the hoses. Figure 39 Flashback arrestors between torch and hose Flashback arrestors are specifically designed to be used for oxygen or fuel gas (oxygen has right-hand threads, fuel gas has left-hand threads). All flashback arrestors are marked with an arrow to indicate the direction of gas flow. This tells you whether they are designed to be installed at the torch or at the pressure regulators. Most new oxy-fuel cutting torches come equipped with built-in flashback arrestors. Those that don t might have reverse-flow check valves. If your torch does not have built-in flashback arrestors, WorkSafeBC requires you to install flashback arrestors at either end of the gas hoses between the torch and the pressure regulators. Since a torch is subjected to occasional banging or dropping, the flashback arrestor at the torch end of the hose might become faulty. The flashback arrestor at the pressure regulator end serves as a critical second line of defence. Even with a flashback arrestor at both ends of the hose, the devices should be checked weekly. Reverse-flow valves can be inspected simply by blowing in the opposite direction of the arrow: if there is no bypass, the valve is good. Flashback arrestors are a different story: you will have to follow the manufacturer-specific procedures for inspection and replacement. Using flashback arrestors is an easy way to prevent personal injury, damage and expense resulting from an explosion or fire. Oxy-fuel gas cutting tips Oxy-fuel gas cutting tips are interchangeable with the same design of torch head. However, cutting tips made to one manufacturer s design cannot be used with torches made to another manufacturer s design. 90 Welder Training Program Level C

91 Module P2 Theory Competency P2-2 Oxy-fuel gas cutting tips are precision tools that should never be subjected to abuse. The tip can become damaged by extreme temperature, by dropping the torch or even by setting it down roughly on a workbench top. When tips are not attached to the cutting torch, they should be stored in their original containers or in a special storage rack. Oxy-fuel gas cutting tips have seats designed to match those in the head of the cutting torch (Figure 40). Before installing the cutting tip, you should visually inspect the seats, checking for dirt or damage to the seat surfaces. The tip nut should always be tightened snugly with a wrench to prevent gas leakage. All cutting tips have preheat flame orifices, usually arranged in an outer circle with a cutting oxygen orifice in the centre. Torch head Cutting tip nut Cutting tip Seats Cutting jet oriface Preheat flame orifiaces Figure 40 Oxy-fuel gas cutting tip Cutting tip size Oxy-fuel gas cutting tips are available in several sizes based on the thickness of the metal to be cut. The diameters of the preheat flame and cutting oxygen orifices increase as the thickness of metal to be cut increases. As the diameters increase, so do the designated tip size numbers. The numbers and the brand name are normally stamped on the cutting tip for easy identification (Figure 41). Figure 41 Oxy-fuel gas cutting tip labelling Welder Training Program Level C 91

92 Module P2 Theory Competency P2-2 The following table shows examples of cutting tip sizes and cutting pressures as they relate to the various metal thicknesses (Figure 42). Note that the pressure settings for oxygen and acetylene are listed. Tip size designations and pressure settings can vary with each equipment manufacturer. Metal Tip size Cutting pressures thickness number Oxygen (min. max. psi) Acetylene (min. max. psi) 3 mm ( 1 8") mm ( 1 4") mm ( 3 8") mm ( 1 2") mm ( 3 4") mm (1") mm (1 1 2") mm (2") mm (2 1 2") mm (3") mm (4") mm (5") mm (6") mm (8") mm (10") mm (12") Figure 42 Typical cutting tip chart Types of oxy-fuel gas cutting tips There are many cutting tip designs available. Your choice will depend on the use of the cutting tip and the type of fuel gas. Each fuel gas, such as acetylene, methylacetylene-propadiene (Mapp ), propane, natural gas or propylene, requires a specially designed tip for cutting. A cutting torch and tip assembly must never be used with a fuel gas for which it was not intended. Methylacetylene-propadiene (Mapp ), propane and natural gas all require more oxygen than acetylene to produce a neutral flame. Therefore, the mixing chambers and preheat flame orifices must be adjusted to accommodate this increase in oxygen requirements. Cutting tips for fuel gases other than acetylene are often two-piece in construction to accommodate the large volume of oxygen and fuel gas burning characteristics. 92 Welder Training Program Level C

93 Module P2 Theory Competency P2-2 Oxy-fuel gas tips for special purposes In addition to tips for general cutting duties, there are tips designed for certain special purposes. Two of the most common are: rivet-cutting tips gouging tips When using rivet-cutting tips and gouging tips, you must make sure that your working pressures are correct and you do not exceed the acetylene draw limits. Exceeding draw limits will result in drawing acetone from the acetylene cylinder, which will affect the fuel gas flow and result in backfires and flashbacks. Rivet-cutting tips Rivet-cutting tips (Figure 43) are used for cutting or washing heads off rivets and bolts. The flat part of the tip lies on the base metal, thus preventing the base metal from being burned as the rivet or nut is washed off. Figure 43 Rivet-cutting tip Gouging tips Gouging tips (Figure 44) are used for removing tack welds, weld defects and casting defects. They are also used for demolition work and to prepare J-groove and U-groove joints for welding. Figure 44 Gouging tip Heating tips Another commonly used oxy-fuel gas tip is a heating tip attachment that is often called a rosebud (Figure 45). Figure 45 Rosebud heating tip Welder Training Program Level C 93

94 Module P2 Theory Competency P2-2 Unlike a cutting tip, which has an oxygen cutting orifice as well as preheat flame holes, a heating tip has only preheat flame holes on its face. Like cutting tips, these heating tips are available for different fuel gases and must never be used with fuel gases for which they were not intended. Also like cutting tips, they are available in different sizes for various heating jobs. Heating tips can be used for preheating and post-heating weldments, and for straightening or forming structural shapes, pipe, plate and sheet metal. They can also be used to flame-harden steel parts to resist wear. Remember, when using an oxy-acetylene rosebud, you must make sure that your working pressures are correct and you do not exceed the acetylene draw limits. Exceeding draw limits will result in drawing acetone from the acetylene cylinder. This will affect the fuel gas flow and result in a flashback. The resulting explosion will extend back to the cylinder pressure regulator, blowing your gas hoses apart. This is an expensive mistake that results in the destruction of equipment. Cutting tip maintenance Cutting tips need to be cleaned frequently because the openings become clogged with oxide and slag from the cutting process. When the holes are clogged, the gas flow is reduced and the flame becomes distorted. Always use special tip cleaning needles (Figure 46). These needles are designed with tiny file-like teeth to loosen and remove oxides and slag. Always select a cleaning needle that is one size smaller than the opening. When cleaning the preheat flame orifices, open the oxygen control valve slightly. The oxygen will blow any scrapings out of the tip. Figure 46 Tip cleaning needles Use only a straight up-and-down motion with the needle (Figure 47). If you bend or twist the needle you could flare the opening, causing flame distortion. 94 Welder Training Program Level C

95 Module P2 Theory Competency P2-2 Figure 47 Cleaning a cutting tip Most tip cleaners include a small, flat, file-like scraper that is used to remove any slag. If there are worn areas or the tip has become flared, you might have to recondition the tip using a flat file or tip dresser (tip nip). Using the flat file or tip nip, you can reshape the tip end by filing or reaming up to a point where there is no longer any flare (Figure 48, the dashed line). After filing or reaming the tip, polish it with fine emery cloth. Then, you need to clean the orifices to remove any burrs and filings lodged inside. Some tip cleaner kits include a file and tip dresser for reconditioning tip ends. Do not file past this point Figure 48 Point at which flare in the orifice ends The efficient performance of torch handles, cutting attachments and cutting tips depends on careful use and handling. Cutting torches are precision tools and can easily be damaged from misuse. Never use a cutting torch as a hammer or prying tool. When the handle and attachments are removed from service or transported, they should be placed in a box and stored in a clean, dry area. They must not be exposed to oil, grease, solvents, gasoline or other contaminants. Now complete Self-Test 5 and check your answers. Welder Training Program Level C 95

96 Module P2 Theory Competency P2-2 Answers Self-Test 5 Choose the correct response for each question and put it in the Answers column. Cover your answers when reviewing the test for study purposes. 1. The cutting tip size is determined by the a. thickness of the metal it will cut b. angle of the cut c. type of torch used d. surface condition of the metal it will cut 2. What is the purpose of a reverse-flow check valve? a. check gas pressure b. decrease gas flow c. allow gas flow in both directions d. control the direction of gas flow 3. What is the purpose of a flashback arrestor? a. stops the flame burning back in the hoses and prevents reverse flow of gases b. stops the flame burning back in the hoses and allows gas flow in both directions c. stops flashbacks by limiting the amount of gas coming out of the torch d. stops flashbacks by limiting the amount of gas the pressure regulator releases 4. When cleaning an oxy-fuel gas cutting tip, what size tip cleaner should you use? a. the same size as the orifice b. one size larger than the orifice c. one size smaller than the orifice d. two sizes smaller than the orifice 96 Welder Training Program Level C

97 Module P2 Theory Competency P When cleaning the oxygen preheat flame orifices on an oxy-fuel gas cutting tip, you should a. open the fuel gas preheat flame valve slightly b. open the oxygen preheat flame valve slightly c. open both the fuel gas and the oxygen preheat flame valves slightly d. not open either the fuel gas or the oxygen preheat flame valves Answers 6. The larger the orifices of the cutting tip, the a. less gas used b. greater the heat loss c. thinner the material that can be cut d. thicker the material that can be cut 7. The single, large centre orifice of a fuel gas cutting tip is used for what gas? a. preheat flame oxygen b. preheat flame fuel gas c. cutting oxygen d. cutting fuel gas 8. Which torch is designed to be used for either cutting or welding by changing the tip attachment? a. cutting machine torch b. injector-type torch c. one-piece torch d. two-piece torch 9. The smaller holes in a cutting tip are called a. premix flame holes b. fuel gas flame holes c. cutting oxygen holes d. preheat flame holes Welder Training Program Level C 97

98 Module P2 Theory Competency P2-2 Answers 10. During cutting, the cutting oxygen lever should be a. depressed halfway b. left closed c. depressed fully d. set at 103 kpa (15 psi) 11. Injector-type torches are designed for use with a. very thick sections of steel b. fuel gases supplied at low pressure c. manifold systems d. acetylene gas only 12. A combination cutting torch attachment can be used for a. cutting only b. cutting and welding c. welding and brazing d. cutting and brazing 13. When using a combination torch for cutting, the oxygen control valve on the torch handle should be a. kept closed b. open slightly c. open 1½ turns d. opened all the way 14. Cutting tips can be used interchangeably with torches from different manufacturers. a. true b. false 15. A backfire occurs when the flame goes back into the a. tip b. mixing chamber c. torch handle d. pressure regulator 98 Welder Training Program Level C

99 Module P2 Theory Competency P A backfire is recognizable by a. sparks from the tip b. a hissing sound c. a popping sound d. a fire in the hose line Answers 17. The first step in putting out a fire in the hoses of an oxy-fuel gas outfit is to a. close the oxygen cylinder valve b. close the fuel gas cylinder valve c. use a fire extinguisher on the hose d. close both the oxygen and fuel gas cylinder valves 18. Propane gas requires what kind of cutting tip? a. a very large tip b. a specially designed tip c. a very small tip d. a one-piece tip 19. A rosebud tip is used for a. cutting aluminum b. brazing metals c. heating metals d. welding brass Now go to the Answer Key and check your answers. Welder Training Program Level C 99

100 Module P2 Theory Competency P Welder Training Program Level C

101 Module P2 Theory Competency P2-2 P2-2 Learning Task 6: Oxy-fuel gas manifold systems Large volumes of gas are required in shops employing many Welders or using large, multi-torch cutting machines. When the maximum rate of acetylene withdrawal is exceeded, liquid acetone is drawn from the cylinder. To prevent exceeding the draw limit, it is possible to connect a series of acetylene cylinders together with a manifold. Gas manifold systems can be designed to connect a number of cylinders together so that enough gas can be provided at a constant pressure. Portable manifolds (Figure 49) are normally used to connect two to five cylinders and have special couplings to a common pressure regulator. Figure 49 Portable gas manifold system Stationary gas manifold systems are used with five, 10, 30 or more cylinders. Some stationary manifold systems are supplied by bulk containers of fuel gas (Mapp gas, propane, etc.) and bulk cryogenic containers of liquefied oxygen. With the large manifold systems, gas is piped to individual work stations. The workplace is free of gas cylinders, saving space and improving safety. These systems are common in large welding shops and trade schools. Welder Training Program Level C 101

102 Module P2 Theory Competency P2-2 Oxygen manifold systems The oxygen manifold system is usually located in a special room outside the shop work area. A duplex manifold has two separate banks of cylinders (Figure 50). Both banks of the manifold system can be operated as a single bank or independently, so there is no interruption in supply while cylinders are being changed. Each side has a manual shut-off valve that is kept closed when the system is not in use. A single cryogenic liquefied oxygen container is capable of supplying large volumes of oxygen. It can also be connected to a manifold system. The cryogenic duplex system is normally designed to automatically switch from one container or bank of containers to another when the available pressure drops below a certain level. Individual cylinders are connected to the manifold by flexible high-pressure hoses sheathed in braided stainless steel. Traditionally, coiled copper alloy tubing was used to make a flexible connection between the cylinders and the manifold. These coiled tubes resembled pigs tails, so now these connections are often called pigtails. Coiled copper alloy tubing is being phased out in favour of the high-pressure braided stainless steel hoses. Figure 50 Oxygen duplex manifold system A master pressure regulator controls the pressure of the oxygen in the system. These pressure regulators are basically the same as two-stage cylinder pressure regulators, except they can handle greater volumes of gas. At each station, an oxygen low-pressure station regulator is used to set the working pressure for the welding or cutting task (Figure 51). This lowpressure station regulator has only one gauge, a working-pressure gauge. It is also equipped with a pressure relief valve to release the gas if line pressures become too high. 102 Welder Training Program Level C

103 Module P2 Theory Competency P2-2 Figure 51 Low-pressure station regulator Acetylene manifold systems Acetylene duplex manifold systems (Figure 52) are similar to oxygen manifold systems. Note that the acetylene system has some additional safety features not needed in an oxygen system. These extra features are required to prevent this unstable gas from exploding. The manifold line is filled with stainless steel rod, steel shot or silica sand to prevent the free acetylene from reaching its critical point. Acetylene manifold systems must have a hydraulic flashback arrestor. This is a special device filled with a glycol solution that prevents any flashback or reverse flow of gas from getting into the acetylene cylinders. Each cylinder also has a reverse-flow check valve (RFCV) mounted between the cylinder and the manifold. The manifold system also has a pressure relief valve that is vented into the atmosphere to prevent the accumulation of acetylene. Welder Training Program Level C 103

104 Module P2 Theory Competency P2-2 Hydraulic flashback arrestor Figure 52 Acetylene manifold system Hydraulic flashback arrestors require annual maintenance and should be serviced accordingly. Never try to install or service manifold systems. These jobs should be done only by qualified persons. Now complete Self-Test 6 and check your answers. 104 Welder Training Program Level C

105 Module P2 Theory Competency P2-2 Welder Training Program Level C 105

106 Module P2 Theory Competency P2-2 Answers Self-Test 6 Choose the correct response for each question and put it in the Answers column. Cover your answers when reviewing the test for study purposes. 1. What is the main purpose of an oxygen or fuel gas manifold system? a. increase the cylinder pressure b. deliver large volumes of gas c. decrease the rate of withdrawal d. use several fuel gases at the same time 2. Where is an oxygen manifold system usually located? a. in a special room outside the welding shop b. inside the oxy-fuel cutting station c. always outdoors d. in a refrigerated room 3. Stationary manifold systems are commonly used a. on construction sites b. on pipeline projects c. in welding repair shops d. in large welding shops and trade training institutions 4. What does the term duplex mean when referring to a manifold system? a. Gas cylinders are stacked on top of each other. b. It has two banks that can operate independently. c. One side contains the fuel gas and the other, the oxygen gas. d. Double-size gas cylinders are used. 5. Identify the safety device found on acetylene manifold systems. a. reverse-flow check valves (RFCVs) b. station pressure regulator c. high-pressure cylinders d. master pressure regulator 106 Welder Training Program Level C

107 Module P2 Theory Competency P A low-pressure station regulator is usually easily identifiable because it a. has no pressure-adjusting screw b. is a two-stage pressure regulator c. only has a working-pressure gauge d. is red in colour Answers 7. What was traditionally used to connect oxygen cylinders to a manifold system? a. a line connector b. a rubber hose c. a stainless steel pipe d. coiled copper alloy tubing 8. Acetylene manifold systems must be equipped with a. a hydraulic flashback arrestor b. emergency fire extinguishers c. a flow meter d. emergency supply lines Now go to the Answer Key and check your answers. Welder Training Program Level C 107

108 Module P2 Theory Competency P Welder Training Program Level C

109 Module P2 Theory Competency P2-2 P2-2 Learning Task 7: Oxy-fuel gas cutting accessories and machines Sometimes you will need greater precision in oxy-fuel gas cutting than is possible with unguided manual cutting. For oxy-fuel gas cutting, there are a number of cutting accessories and machines that improve the quality and speed of the cutting process. Manual oxy-fuel gas cutting guides Cutting guides are used to help control the position of the cutting torch. They do not, however, control the speed or preheat flame-to-work distance of the cutting torch. The Welder must be skilled or rough cuts will result. Straight-line cutting guide A piece of flat bar (or angle) can be used as a straight-line cutting guide (Figure 53). The cutting tip is held against the cutting guide to produce a straight cut. Remember to offset the cutting guild to allow for the radius of the tip. Figure 53 Straight-line cutting guide Circle cutting guide Circle cutting guides are used to cut circles and arcs. A typical circle-cutter attachment consists of an adjustable rod with a centre pivoting point, an adjustable wheel to set the preheat flame-to-work distance and a rotating mechanism for attaching to the cutting tip (Figure 54). Welder Training Program Level C 109

110 Module P2 Theory Competency P2-2 Figure 54 Typical circle-cutting guide Templates Templates serve as a master pattern for cutting irregular shapes. Once you have measured and cut one accurate pattern piece allowing for the kerf, you can then use that pattern piece as your template for all the identical pieces required. The use of templates saves time measuring and ensures accuracy and consistency. Oxy-fuel gas cutting machines Oxy-fuel gas cutting machines offer some decided advantages over manual oxy-fuel gas cutting. The cutting machines are electrically driven and can cut a very precise dimension at a set speed. The result is high-quality, accurate cuts done quickly and economically. Straight-line cutting machines A common straight-line oxy-fuel gas cutting machine (Figure 55) has one cutting torch and is small and portable. It has four wheels, travels on a track and is electrically operated. The cutting torch can be set perpendicular for square cuts or angled to cut bevels. It has an adjustable speed control so the travel speed can be adjusted for cutting different thicknesses of metal. Also, a straight-line cutting machine can be removed from its track and have a radius arm attached, enabling it to be used to cut arcs and circles. 110 Welder Training Program Level C

111 Module P2 Theory Competency P2-2 Figure 55 Oxy-fuel gas straight-line cutting machine Shape-cutting machines Oxy-fuel gas shape-cutting machines, sometimes called profiling machines, can be programmed to repeatedly produce a pattern accurately and quickly. Shape-cutting machines are usually multi-torch machines using from two to a dozen oxy-fuel gas cutting torches. Portable single-torch shape-cutting machines are also available. There are three main types of tracing mechanisms: the magnetic tracer, the electronic eye tracer and the computer-controlled tracer. Tracers can be set at different speeds to allow for different thicknesses of metal. They can be designed to use a single torch or multiple torches. Magnetic tracer A magnetic tracer uses a magnetized roller that keeps in contact with the edge of a metal template. As the roller follows the edge of the template, the torch cuts out the pattern. Electronic-eye tracer These tracers use a drawing with a special tracer ink as a template. A pinpoint of light follows this special ink tracer line, reflecting the light back to a photoelectric cell. The cell converts the light to electrical energy, which controls servomotors (steering motors). The motors move the cutting torches to cut a pattern exactly like the template. Welder Training Program Level C 111

112 Module P2 Theory Competency P2-2 Computer-controlled tracer A computer-controlled tracer uses computer numerical control (CNC) to direct the shape-cutting process. The computer-controlled tracer is similar to the electronic-eye tracer, but it follows computer drawings rather than a special tracer ink. The whole cutting process and template design can be set up and controlled by the computer. The oxy-fuel gas cutting torch is attached to a carriage that is controlled by the computer and can be ignited and extinguished by the computer. Pipe-bevelling machines Oxy-fuel gas pipe-bevelling machines are extremely useful for cutting pipe to size and for bevelling the pipe before welding. These machines can be hand-driven or motor-driven. They can also be portable units (Figure 56) or stationary shop units. Figure 56 Portable hand-cranked oxy-fuel gas pipe-bevelling machine Now complete Self-Test 7 and check your answers. 112 Welder Training Program Level C

113 Module P2 Theory Competency P2-2 Welder Training Program Level C 113

114 Module P2 Theory Competency P2-2 Answers Self-Test 7 Choose the correct response for each question and put it in the Answers column. Cover your answers when reviewing the test for study purposes. 1. Manual oxy-fuel gas cutting guides are used to ensure a. accurate layout measurements b. faster cuts c. accurate cuts d. cheaper cuts 2. A circle-cutting guide is usually attached to the a. cutting torch tip b. cutting torch handle c. workpiece d. fuel gas hose 3. What kind of shapes are templates generally used to cut? a. triangles b. circles c. rectangles d. irregular shapes 4. What is one advantage of oxy-fuel gas cutting machines over manual cutting? a. speed of cut can be accurately controlled b. thickness of material is of no importance c. less oxygen is needed d. fuel gas is conserved 5. A straight-line cutting machine can be used to cut a circle. a. true b. false 114 Welder Training Program Level C

115 Module P2 Theory Competency P How many torches do shape-cutting machines usually have? a. one b. two c. three or more d. could be any number Answers 7. Oxy-fuel gas pipe-bevelling machines are used to bevel pipe and to a. clean torch tips b. cut arcs on plate c. cut pipe to size d. create templates for irregular shapes 8. On what type of oxy-fuel gas cutting machine is a magnetic tracer used? a. electronic-beam b. shape-cutting c. straight-line d. circle-cutting Now go to the Answer Key and check your answers. Welder Training Program Level C 115

116 Module P2 Theory Competency P Welder Training Program Level C

117 Theory Competency P2-3: Correct procedures to operate and maintain oxy-fuel gas cutting equipment P2-3

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119 Module P2 Theory Competency P2-3 Outcomes To protect yourself, your fellow workers and the oxyacetylene equipment, it is important that you thoroughly understand the correct procedures and safety precautions to use when assembling, testing, lighting, adjusting, shutting down and disassembling a portable oxyacetylene outfit. The procedures are not complicated, but the steps must be followed precisely, and in the correct order. You should understand the potential hazards of oxyacetylene gases and the importance of following these steps. You should also know how to perform minor maintenance of oxyacetylene equipment, in order to ensure safer and more efficient operation of the equipment. When you have completed the Learning Tasks in this Theory Competency, you will be able to: describe the assembly of an oxyacetylene outfit describe the procedure for testing an oxyacetylene outfit for leaks describe the procedure for setting working pressures describe the assembly, ignition adjustment and extinguishing of a one-piece and a two-piece combination torch decribe the disassembly of an oxyacetylene outfit describe the attributes of a high-quality cut describe the effects of various factors on cutting describe good cutting techniques choose the appropriate cutting tip for the job Evaluation When you have completed all the Theory Competencies in Module P2, you will take a written test. You must score at least 70% on this test. The test will include questions that are based on the following material from Theory Competency P2-3: assembly of the oxyacetylene equipment testing of the oxyacetylene equipment for leaks setting up of the oxyacetylene equipment disassembly of the oxyacetylene equipment characteristics of an acceptable cut Resources Required: All required resources are contained within this Theory Competency. Welder Training Program Level C 119

120 120 Welder Training Program Level C

121 Module P2 Theory Competency P2-3 P2-3 Learning Task 1: Correct procedures to assemble, ignite and shut down a portable oxy-fuel gas unit Although many shops have a manifold system, portable oxy-fuel equipment is commonly used in the welding trades. Portable units can be found in many job settings, especially on industrial maintainence and construction sites or in fabrication and repair shops, where portability is required. Portable oxy-fuel units can be used with a variety of fuel gases, as discussed in P2-2. Acetylene has some advantages over other fuel gases due to its higher flame temperature and lower consumption of oxygen. Therefore, it is the most common fuel gas used with the portable oxy-fuel units. The assembly and operating procedures for oxy-fuel and oxyacetylene equipment are basically the same. This Learning Task will only discuss portable oxyacetylene equipment. The steps to follow when assembling, igniting and shutting down oxy-fuel gas equipment must be done in the correct order, without missing any. Not following these steps precisely can result in personal injury and explosion. How to assemble a portable oxyacetylene unit When assembling a portable oxyacetylene unit, you must follow these steps: 1. Secure the cylinders 2. Remove the cylinder caps 3. Crack the cylinder valves 4. Attach the cylinder pressure regulators 5. Install the flashback arrestors 6. Connect the gas hoses 7. Open the cylinder valves 8. Purge (blow out) the cylinder pressure regulators and gas hoses 9. Connect the cutting torch 10. Set the working pressure 11. Purge the closed system 12. Check the system for leaks Welder Training Program Level C 121

122 Module P2 Theory Competency P Secure the cylinders in an upright position A light chain is commonly used to secure oxy-fuel gas cylinders to a portable cart so they do not tip over or get jarred (Figure 57). The cylinder cart is designed to roll easily when tilted back on its wheels, yet be stable and secure when stationary. Figure 57 Secure oxy-fuel gas cylinders to cart 2. Remove caps covering the cylinder valves Turn the cylinder cap counter-clockwise to remove it (Figure 58). Always replace the cylinder cap when transporting an oxy-fuel gas cylinder and when the cylinder is not in service. Cap over cylinder valve Figure 58 Remove cylinder cap 122 Welder Training Program Level C

123 Module P2 Theory Competency P Crack the oxygen and the acetylene cylinder valves Slightly open and quickly close (crack) the valves (Figure 59). This procedure cleans any dust or foreign particles from the valve outlets. Stand to the side of the valve outlets and make sure they are not pointing toward you or anyone else. Any particles inside the valves are expelled with extreme force. Figure 59 Crack cylinder valve Never crack a cylinder valve near sparks or open flames. 4. Attach the oxygen and the acetylene cylinder pressure regulators First examine the outlet connection on the cylinder valve and the inlet connection on the cylinder pressure regulator to make sure the connections are clean and the threads are in good condition. Match the pressure regulator connections to the appropriate cylinder valve connection. Remember, oxygen fittings have right-hand threads; acetylene fittings have left-hand threads. While it is impossible to install the wrong regulator on a cylinder, you can damage the threads by trying. Start and turn the cylinder pressure regulator nut by hand until it is snug (it should turn easily). Then tighten it with a cylinder wrench (Figure 60). Welder Training Program Level C 123

124 Module P2 Theory Competency P2-3 Figure 60 Attach cylinder pressure regulator Never lubricate fittings, because oil or grease and pressurized oxygen can ignite and cause an explosion. Oxy-fuel gas fittings need no lubrication. 5. Install the flashback arrestors Attach flashback arrestors to the cylinder pressure regulator outlet connections. Tighten them with a cylinder wrench. Make sure to use the flashback arrestor on the correct cylinder pressure regulator. Flashback arrestors have left- or right-hand threads to match the oxygen or acetylene fittings. Make sure the direction of flow arrow marking on the flashback arrestor is pointing in the direction of the gas flow (Figure 61). Figure 61 Attach flashback arrestors to cylinder pressure regulators, then to hoses 124 Welder Training Program Level C

125 Module P2 Theory Competency P Connect hoses to flashback arrestors Attach the oxygen hose to the flashback arrestor with the right-hand threads and the acetylene hose to the flashback arrestor with left-hand threads (Figure 60). Avoid overtightening the connections. 7. Open the cylinder valves and pressure regulators a. Turn the pressure-adjusting screws out (counter-clockwise) on the cylinder pressure regulators (Figure 62). This closes off the regulators so the working-pressure gauges are not permanently damaged when high-pressure cylinder gases are allowed to flow through the cylinder valves into the pressure regulator. Note that when you open the oxygen cylinder valve, the working-pressure gauge remains at 0. Figure 62 Turn out regulator screw b. Open the oxygen cylinder valve very slowly (to prevent damaging the pressure regulator) until maximum pressure is reached. Then open the valve completely to seal the double-sealing valve. c. Open the acetylene cylinder valve very slowly, watching the cylinder pressure gauge at the same time. When the pressure has reached its maximum (when the needle stops moving), open the valve 1 to 1½ turns to maintain that pressure. Not fully opening the acetylene cylinder valve means that you can quickly close the valve in an emergency. If you use a cylinder valve wrench, leave it on the valve. Note that when you open the acetylene cylinder valve, the workingpressure gauge remains at 0. Welder Training Program Level C 125

126 Module P2 Theory Competency P2-3 Always stand to the side of a cylinder pressure regulator when you open a cylinder valve in case the regulator fails (Figure 63). Figure 63 Keep to one side 8. Purge (blow out) the cylinder pressure regulators and gas hoses Purge the cylinder pressure regulators and gas hoses to remove any dirt or debris before attaching the torch. Any debris in the system can block small orifices and is potentially flammable. Point the gas hoses away from you and blow out any dirt by turning in (clockwise) each pressure regulator adjusting screw to allow gas to flow. Then turn it out (counter-clockwise) to shut off the gas flow (Figure 64). Figure 64 Purging hoses and regulators 9. Connect the cutting torch Install the flashback arrestors on the torch handle (if required). Follow the same procedure you used to attach flashback arrestors to the cylinder pressure regulators. Remember to match the direction of flow arrow on the flashback arrestor with the gas flow. Attach the hoses to the flashback arrestors. Connect the oxygen hose to the right-hand threaded flashback arrestors and the acetylene hose to the left-hand threaded flashback arrestors (Figure 65). 126 Welder Training Program Level C

127 Module P2 Theory Competency P2-3 Figure 65 Attach flashback arrestors to torch handle, then to hoses Using a cylinder wrench, tighten the hose connections. The oxyacetylene outfit is now completely assembled. Now you need to set the working pressures. Before setting the working pressure, make sure that the cylinder valves are open and the cylinder pressure regulator working pressure adjusting screws are turned all the way out. On a one-piece torch, make sure that the cutting torch preheat flame oxygen and fuel gas valves are closed. On a two-piece combination torch, make sure that the preheat flame oxygen valve on the cutting attachment is closed and the oxygen valve on the torch handle is fully open (Figure 66). The torch handle preheat flame fuel gas valve should remain closed. Open oxygen valve fully Close oxygen preheat valve Close acetylene valve Figure 66 Two-piece torch Welder Training Program Level C 127

128 Module P2 Theory Competency P Set working pressure Turn in the pressure-adjusting screw until the working-pressure gauge reads the selected working pressure. Repeat this process for both the oxygen and the acetylene (Figure 67). How to set working pressure Select and install the appropriate cutting tip. Be sure the cutting tip is clean. Insert the tip into the cutting torch head and tighten it. Use just enough pressure to make sure that the tip is tight. The cutting tip might already be installed, but you still need to know its size so that you can find the correct working-pressure settings on the equipment manufacturer s cutting tip chart. Remember, the working pressure depends on the tip size, and the basis for selecting a tip size is the thickness of the metal being cut. Figure 67 Set the correct working pressures 11. Purge the closed system Open the torch handle fuel gas valve until you are sure only fuel gas is coming out of the cutting tip (approximately 5 seconds). Close the fuel gas valve and follow the same procedure for the oxygen. The cutting lever valve may be used instead of the oxygen preheat flame valve. Purging the closed system will ensure that the system only has fuel gas in the fuel gas side of the system and only oxygen in the oxygen side of the system. If there is mixed gas in either side of the system it could result in a torchline explosion. The cutting torch is now ready to use, but before attempting any cutting, you must test the entire outfit for leaks. 128 Welder Training Program Level C

129 Module P2 Theory Competency P Check the system for leaks Before you start to use the cutting torch, you should always check the system for leaks, whether the equipment is being assembled for the first time or the setup is being used continuously. The system should also be tested after any new cylinders or components have been installed. To detect leaks, first set the working pressure, close the torch valves, then close the cylinder valve. After you have closed the cylinder valve, watch the cylinder pressure gauge. If the gauge shows a pressure drop, you have a leak. This is a good practice that can be done every time you take a break for coffee or lunch. Just leave the system pressurized, close the cylinder valve and go for your break. When you return, watch the cylinder pressure gauge as you open the cylinder valve. If the gauge jumps up, you have a leak in the system. The easiest and most efficient way to locate the leak is by sound and smell. You might be able to hear the leak or, in the case of the fuel gas, you can smell it. If this fails, then you should use a commercially prepared leak check solution (Figure 68). If a commercially prepared leak check solution is not available, you can use a non-detergent soap solution. Be very careful not to use a hydrocarbon-based cleaning product. Commercially prepared leak check solutions are recommended as they are safe, economical and readily available. Figure 68 Use a leak check solution to check for leaks Welder Training Program Level C 129

130 Module P2 Theory Competency P2-3 You should apply leak check solution to the following areas of an oxyacetylene system: oxygen cylinder valve acetylene cylinder valve oxygen cylinder pressure regulator inlet connection acetylene cylinder pressure regulator inlet connection hose and flashback arrestor connections at the cylinder pressure regulators and cutting torch oxygen and acetylene torch valves cutting oxygen lever valve preheat flame oxygen valve (two-piece torch only) If you find a leak, repair it immediately. Retighten the connection with a cylinder wrench and test the connection again. If the connection continues to leak, shut off the gas pressure, open the connection and examine the threads and seat for dirt or damage. A leaking oxygen or acetylene cylinder valve is a very serious problem. Since they pose an extreme explosion or fire hazard, they should be removed from service and placed outside. The supplier should be notified. How to ignite and adjust the preheat flame The flint lighter, also known as a spark lighter or striker, is the only approved means of lighting an oxy-fuel gas torch. The steel cup on the flint lighter (Figure 68) traps the fuel gas, and when the flint contacts the file segment, it produces a spark that ignites the gas. The two models shown in Figure 68 are the most common type. Figure 69 Flint torch lighters or strikers 130 Welder Training Program Level C

131 Module P2 Theory Competency P2-3 Pistol-grip spark lighters are also available (Figure 70). Figure 70 Pistol-grip striker Never use matches, cigarette lighters (especially pressurized lighters), another torch or hot metal to ignite your torch. Never keep pressurized lighters or matches in your pocket while you weld, as they could ignite or explode and cause severe burns or personal injury. Wear fire-retardant coveralls, leather welding gloves, CSA-approved boots, welding cap and CSA-approved safety goggles. Be careful where you point the torch flame and where you let the sparks and slag fall once you begin to cut. Take a few minutes to familiarize yourself with the feel of the cutting torch and the striker with your gloves on. Practise using the striker, holding it about 25 mm (1 in.) from the end of the cutting tip (Figure 71). Figure 71 Using striker to light torch Igniting the torch To ignite the torch, open the preheat flame acetylene valve on the torch handle no more than one-half turn and ignite the fuel gas at the tip. The flame will look long and yellow. Continue to open the acetylene valve slowly until the flame becomes turbulent and stops giving off black smoke (Figure 72A). Welder Training Program Level C 131

132 Module P2 Theory Competency P2-3 Add oxygen to the flame Slowly open the cutting torch preheat flame oxygen valve. On a two-piece combination torch, use the cutting torch attachment preheat flame valve to adjust the amount of oxygen. As preheat flame oxygen is fed into the flame, the colour changes from yellow-red to blue and a fuzzy inner cone forms. As more oxygen is added, the inner cone becomes white, round and smooth. Each of the preheat holes has such a cone. This is called a neutral flame. A neutral flame means that the oxygen and acetylene are mixed in the right proportions to burn the acetylene completely (Figure 72B). Acetylene only Long yellow-orange flame Neutral flame Blue envelope Rounded white inner cones Oxidizing flame excessive oxygen Light blue envelope Sharp white inner cones Carburizing flame excessive acetylene Blue envelope Light blue feather Rounded white inner cones Figure 72 Types of flame If the inner cone is pointed and the flame hisses, too much oxygen has been added. This is an oxidizing flame (Figure 72C). It will cause the metal being heated to burn or oxidize. A carburizing flame has too much acetylene and results in adding carbon to the metal. The carburizing flame is blue with a dark-blue, feathered inner cone (Figure 72D). Since any one of these flames can be used in a given application, it is important that you know how to make the necessary adjustments. Now press down on the cutting oxygen control lever and adjust the oxygen to maintain a neutral flame. 132 Welder Training Program Level C

133 Module P2 Theory Competency P2-3 How to shut down an oxyacetylene outfit It is very important to know how to correctly shut down an oxyacetylene outfit once the cutting is completed or when you leave the work area. A mistake could result in personal injury to you or others, so you must make sure that you follow, in the correct order, the steps listed below: 1. Close the cutting torch preheat flame acetylene valve. The flame immediately goes out and only oxygen gas flows from the tip. 2. Close the cutting torch preheat oxygen valve. On a two-piece combination torch, first close the cutting torch attachment preheat flame oxygen valve, and then close the torch handle oxygen valve. Gas is no longer leaving the cutting tip, but the system is still pressurized. In this state, you can leave the torch unmanned for only a short time. Anytime you stop work for a longer period, though, you must bleed off the pressurized oxygen and acetylene from the torch, hose and regulators. 3. Bleed the system. Bleeding the lines means releasing the gas pressure still in the system. First close the acetylene cylinder valve, then close the oxygen cylinder valve. Next, open the torch acetylene valve. The pressure reading on both acetylene pressure regulator gauges will drop to 0 and you will hear the acetylene gas left in the system being released from the cutting tip (Figure 73). Figure 73 Open torch acetylene valve Turn the acetylene pressure regulator working pressure adjusting screw all the way out (counter-clockwise) to close the regulator. Then close the torch acetylene valve. Welder Training Program Level C 133

134 Module P2 Theory Competency P2-3 Open the torch oxygen valve. The pressure reading on both oxygen pressure regulator gauges will drop to 0 and you will hear the oxygen gas left in the system being released from the cutting tip (Figure 74). Figure 74 Open torch oxygen valve Turn the oxygen pressure regulator working pressure adjusting screw all the way out (counter-clockwise) to close the regulator. Close the torch oxygen valve. Put your equipment away. Store the hose and torch off the floor and away from objects that might damage them. Make sure the hose is free of kinks. How to disassemble the oxyacetylene outfit Before you disassemble oxyacetylene equipment, make sure the pressure regulator gauges read 0, the system has been bled and the cylinder valves are tightly closed. 1. Disconnect the hose from the flashback arrestors on the torch handle. Flashback arrestors can stay on the torch handle unless they need service or replacement. If you are disassembling a two-piece cutting torch, disconnect the cutting attachment from the torch handle and store it in a container that is free of oil and grease. 2. Disconnect the hose from the flashback arrestors on the cylinder pressure regulators. Flashback arrestors can stay on the pressure regulators. Coil the hose and store it in a well-ventilated place that is free of dust, oil, grease and direct heat. 3. Disconnect the pressure regulators from the cylinder valves. Carefully place each regulator in a separate container. 4. Place the protective cylinder caps over the cylinder valves and handtighten them. You must install the cylinder caps even if the cylinders are 134 Welder Training Program Level C

135 Module P2 Theory Competency P2-3 empty. Use soapstone or blackboard chalk to label empty cylinders with the letters MT. Store them separately from full cylinders (Figure 75). Figure 75 Store full and empty cylinders separately Although an instructor will demonstrate the procedures for assembling, testing, igniting, adjusting, shutting down and disassembling the oxy-fuel gas outfit, carefully read and understand the sequences before entering the shop. After the demonstration, be prepared to answer questions and perform the steps as outlined. Do not take shortcuts, and never take safety for granted, otherwise you and others might become victims of your negligence. Now complete Self-Test 1 and check your answers. Welder Training Program Level C 135

136 Module P2 Theory Competency P2-3 Answers Self-Test 1 Choose the correct response for each question and put it in the Answers column. Cover your answers when reviewing the test for study purposes. 1. Before you attach the pressure regulators to the cylinders, you must a. replace cylinder caps on the cylinder b. install flashback arrestors c. crack the cylinder valves d. seal the double-sealing valve 2. On oxygen cylinder valves and pressure regulator connections, the threads are a. right-hand b. left-hand 3. On acetylene cylinder valves and pressure regulator connections, the threads are a. right-hand b. left-hand 4. Cracking the cylinder valves momentarily before connecting the pressure regulators helps to a. bleed off accumulated moisture b. blow away any foreign matter c. release excess pressure d. regulate work pressure 5. The valve on an oxygen cylinder should be opened a. ¼ turn b. 1½ turns c. 3 turns d. all the way 136 Welder Training Program Level C

137 Module P2 Theory Competency P Before you open the cylinder valves, the working pressure adjusting screw on the cylinder pressure regulator should be a. removed b. screwed all the way out c. screwed all the way in d. tightened with a cylinder wrench Answers 7. A flame that has too much acetylene is called a/an flame. a. oxidizing b. acetylide c. carburizing d. neutral 8. When lighting an oxy-fuel gas torch, you should use a a. long-handled wooden match b. Ronson lighter c. flint lighter d. butane lighter 9. When cracking a cylinder valve, you should a. stand to the side of the valve outlet b. stand in front of the valve so you see clearly c. open the valve fully d. close the valve slowly 10. Why should you open cylinder valves slowly? a. to prevent torchline explosions b. to save oxygen and fuel gas c. to avoid damaging the cylinder pressure regulator d. to prevent arc blow 11. You have pressurized an oxy-fuel gas system and closed the cylinder valves. There is a leak in the system if a cylinder pressure regulator gauge a. goes up b. stays steady c. goes down d. fluctuates Welder Training Program Level C 137

138 Module P2 Theory Competency P2-3 Answers 12. The maximum safe working pressure for acetylene is a. 103 kpa (15 psi) b. 138 kpa (20 psi) c. 193 kpa (28 psi) d. 345 kpa (50 psi) 13. To extinguish an oxyacetylene flame, you should first a. close the torch acetylene valve b. close the torch oxygen valve c. turn out the acetylene pressure regulator screw d. turn out the oxygen pressure regulator screw 14. Why should you NOT fully open the acetylene cylinder valve? a. to conserve acetylene b. to prevent the regulator from being damaged c. so you can close the valve quickly in an emergency d. to purge the line 15. The gas hoses and pressure regulators are purged in order to a. remove any foreign matter b. pressurize the system c. firmly seat the pressure regulator valve d. remove any contaminated gases 16. Which flame is the ideal one for oxy-fuel gas cutting? a. reducing b. carburizing c. oxidizing d. neutral 17. All empty cylinders should be marked with a. MT b. out c. refill d. return 138 Welder Training Program Level C

139 Module P2 Theory Competency P Empty oxygen cylinders should be stored a. in a well-heated room in order to maintain pressure b. on a raised platform c. in an insulated storage rack d. separately from full cylinders Answers 19. Correct working pressures can be found a. on the equipment manufacturer s cutting tip chart b. on the back of the pressure regulator c. engraved on the cutting tip d. on the tip dresser Now go to the Answer Key and check your answers. Welder Training Program Level C 139

140 Module P2 Theory Competency P Welder Training Program Level C

141 Module P2 Theory Competency P2-3 P2-3 Learning Task 2: Characteristics of an acceptable oxy-fuel gas cut Characteristics of an acceptable cut It is important that you learn to recognize what a good-quality cut looks like. A good-quality cut (Figure 76) has a number of clearly visible features: The top edge is sharp and square. The surface of the cut is relatively smooth. The draglines (lines created by the cutting action on metal) are vertical and not too pronounced or deep. There is little slag along the bottom edge and it is easily removed. The bottom edge is sharp. Square cuts (90 ) should be consistently square, and bevel cuts should maintain the angle at which they are cut. Top edge square Vertical drag lines Bottom edge sharp Figure 76 A good oxy-fuel square cut Factors that affect cut quality The main factors affecting cut quality are: surface condition of the base metal thickness of the base metal cutting tip size oxygen and fuel gas working pressures setting of the preheat flames position of the cutting torch tip not fully depressing the cutting oxygen lever speed of travel operator comfort and position Welder Training Program Level C 141

142 Module P2 Theory Competency P2-3 These factors are described in detail below. When you make a cut, you should always examine it for defects and try to determine which of these factors needs to be changed to improve the quality of later cuts. Surface condition of the base metal Before you cut a piece of steel, make sure the surfaces are clean. Any dirt, rust, grease or slag will slow the cutting speed and result in a rough and irregular kerf. Thickness of the base metal The base metal thickness has an important bearing on the quality of the cut. It is the thickness that determines the correct cutting tip size, oxygen and fuel gas working pressures, speed of travel and the angle at which you hold the torch. When cutting steel plate, you normally would hold the cutting tip perpendicular (90 ) to the base metal (Figure 77A), especially when profile cutting. However, on material 13 mm ( 1 2 in.) and thinner, it is better to use a slight push angle (70 to 90 off the base metal) when possible (Figure 77B). Using a push angle will preheat the base metal ahead of the cut as you work. Also, the slight angle allows the heat to deflect off the base metal and away from the tip. This helps to prevent the tip from overheating. When cutting steel sheet, hold the cutting tip with an extreme push angle (10 to 20 off the base metal). This low angle makes for faster, straighter and cleaner cuts with less slag attaching itself to the base metal (Figure 77C). A B C Figure 77 Angle of cutting torch depends on thickness of metal Cutting tip size and maintenance You should always check the equipment manufacturer s cutting chart for the cutting torch that you are using. The cutting chart will tell you the recommended tip size for the thickness of metal you are cutting, along with the correct working pressures. 142 Welder Training Program Level C

143 Module P2 Theory Competency P2-3 Note that there is no standard tip size numbering system that equipment manufacturers follow. Each manufacturer develops and uses its own system. Also, gas consumption can vary from manufacturer to manufacturer. This means that tips from different manufacturers might use different volumes and pressures to cut the same thickness of metal. For safety and economic reasons, it is important to check the equipment manufacturer s cutting charts. If you use a cutting tip that is too large for the material being cut, you waste oxygen and end up with an unsatisfactory, bell-shaped kerf. If you use a cutting tip that is too small for the material being cut, the cut proceeds much too slowly, causing the same effects as a slow cutting speed. As well as selecting the correct size, you must make sure to keep your cutting tip clean and free of debris. Dirt, scale or slag on the tip or in the cutting orifice will deflect the stream of cutting oxygen and cause the cut to be of poor quality (Figure 78). There might be too much bottom-edge slag, a rough cut surface and a concave cut surface. Rough cut face Bottom edge slag Irregular drag lines Figure 78 Dirty tip used Cutting oxygen pressure Since the cutting oxygen jet actually does the cutting, you must make sure that oxygen delivery is steady. When the oxygen pressure is too low, you will get a cut like that produced by a slow travel speed, with the characteristic rounded top edge. When the oxygen pressure is too high, excessive expansion can occur directly below the cutting jet resulting in a widening at the top of the kerf (Figure 79). High pressures are also uneconomical, since more oxygen than necessary is consumed in the process. Slag Figure 79 Effects of too much cutting oxygen Welder Training Program Level C 143

144 Module P2 Theory Competency P2-3 Setting of preheat flames The adjustment of the preheat flames also affects the quality of the cut. If the preheat flames are too small, preheating is too slow. The cut will have the same problems that occur when the speed of travel is too slow. When preheat flames are too long, the cut is too fast, with too much slag and an irregular top edge. Position of cutting torch tip The inner cone of the preheat flame should be held 1.5 mm to 3 mm ( 1 16 in. to 1 8 in.) from the surface of the base metal. If the tip is allowed to touch the base metal, it could cause a backfire or the tip to overheat. Also, scale or slag from the surface of the base metal can get into the cutting orifice, which will result in poor cut quality. The position of the preheat holes is another factor to consider. Cutting tips come with different numbers of preheat holes, depending on the tip size and design. For a straight, square cut, the preheat holes should be positioned so that two preheat holes follow each other along the line of cut (Figure 80). Otherwise, preheating is slower, and the cut displays the characteristic rounded top edge and irregular kerf. Cutting oxygen orifice Line of cut Line of cut Straight cut Preheat holes Bevel cut Figure 80 Cutting tip preheat hole alignment When you are cutting a bevel, you must change the position of the preheat holes in the tip (Figure 80). Setting the preheat holes in this position gives better preheat to the metal. This care in positioning is especially important for cutting tips with two or four preheat holes. For cutting tips with more than four preheat holes, the exact positioning becomes less of a consideration. Speed of travel The speed at which you move the torch across the work is one of the most important factors affecting cut quality. The effects of cutting with a travel speed that is too fast are easy to see on the cut surface (Figure 81). The draglines angle back away from the direction of travel. Too much slag clings to the bottom edge. Heavy slag buildup is undesirable because it takes time to remove the slag afterward, which greatly adds to the cost of the cut. If the travel speed is really too fast, the cut will be lost. The cutting stream will not completely penetrate the metal, and the kerf will no longer be a clean opening or it may be lost completely. 144 Welder Training Program Level C

145 Module P2 Theory Competency P2-3 Top edge square Bottom edge slag Curved drag lines Figure 81 Cutting speed too fast Cutting with a travel speed that is too slow also produces an inferior cut (Figure 82). The draglines are very pronounced and irregular, the bottom edge is very uneven and the top edge is rounded rather than square. Top edge round Bottom edge uneven Irregular drag lines Figure 82 Cutting speed too slow Operator comfort and position When cutting, you should stand in a comfortable position so that you can clearly see the cut as you make it. The torch should move away from you, so that you have a good view into the kerf. With practice you will develop a smooth, even torch movement that will enable you to produce smooth, high-quality cuts. Make sure that you keep the oxy-fuel gas hoses well out of the way (preferably behind you). Do not use your body or arms to support them. Take any twist out of the oxy-fuel gas hoses and place the hoses out of the range of falling slag and sparks from the cutting process. Starting cuts There are several methods you can use to start a cut. The most common way is to place the tip halfway over the edge of the plate, with the ends of the preheat flame cones about 3 mm ( 1 8 in.) above the base metal surface (Figure 83). When the edge reaches a cherry red colour, slowly depress the cutting oxygen lever fully to start the cutting process. Long cuts may require you to stop cutting, reposition yourself and restart the cut.. Welder Training Program Level C 145

146 Module P2 Theory Competency P2-3 Figure 83 Starting a cut Another method is to put the entire cutting tip over the edge of the material to be cut and move the preheat flame back and forth a short distance along the line of the cut until the starting edge of the material is cherry red in colour. Then move the cutting tip back from the edge, depress the cutting lever and slowly move the tip toward the base metal to begin the cut. This method has the advantage of producing sharper corners at the beginning of the cut and reducing the amount of slag that sticks to the bottom edges. Once you have started the cut (the cut is all the way through), move the cutting torch along the lines of the cut with a smooth, steady motion. Best practice is to NOT have the torch/cut move toward youself as the slag in turn will be directed toward you. Keep a constant distance between preheat flame cones and the workpiece. You should move at a speed that produces a light ripping sound and a smooth stream of molten slag. Now complete Self-Test 2 and check your answers. 146 Welder Training Program Level C