Piping trades Apprenticeship Program

Transcription

1 Piping trades Apprenticeship Program Level 1 Competency B-4: Use Measuring and Levelling Tools B-4 This learning guide has been written to the organization of the Plumber Program Outline, but the instruction also addresses the competencies of the Gasfitter, Steamfitter and Sprinkler Installer Program Outlines. For each Learning Task, it will be noted if one of these other pipe trades cover that task under a different Line or Competency number.

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3 Acknowledgements & Copyright Permission The Industry Training Authority of British Columbia would like to acknowledge the Piping Trades Articulation Committee and Open School BC, a division of the BC Ministry of Education as well as the following individuals and organizations for their contributions in updating the Piping Trades Learning Guides: The Piping Trades Articulation Committee Members and Consultants The Working Group Greg Wirachowsky (Pipe Trades Articulation Committee Chair), Okanagan College (reviewer) Rod Lidstone, Camosun College (reviewer, SME image consultation) Darren Vaux, Camosun College (writer, editor and reviewer) Mick Bryant, BCIT (writer) Bruce Slater, Okanagan College (reviewer) Ron Stewart, BCIT (consulting) Rob Hughes, North Island College (consulting) Marty Old, Thompson Rivers University School of Trades and Technology (consulting) Open School BC Shannon Mitchell, Project Manager Eleanor Liddy, Director/Advisor Christine Ramkeesoon, Graphics Media Coordinator Sharon Barker, Production Technician (print layout) Beverly Carstensen, Production Technician (print layout) Dennis Evans, Production Technician (graphics, layout & photographs) Max Licht, 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 images: Acklands-Grainger Inc. Watts Canada Milwaukee Tools Ridge Tool Company (RIDGID TOOLS) Stanley Hand Tools Victaulic Wheeler Manufacturing WorkSafeBC Cover photo pipes by Hemera: used under license from Thinkstock.com ISBN Special thanks to Rod Lidstone and John Gordon at Camosun College (Piping Trades department) for assisting us with additional photographs, and to the Construction Articulation Committee for lending funds to support the production of these learning guides. Version 1 Revised, January 2015

4 Disclaimer The materials in these Learning Guides 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 al minimum legal standards. No warranty, guarantee or representation is made by the BC Piping Trades 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 piping trades practices. Do not assume, therefore, that all necessary warnings and safety precautionary measures are contained in this Competency and that other or additional measures may not be required. SAFETY ADVISORY The current Standards and Regulation in BC can be obtained at the following website: Please note that it is always the responsibility of any person using these materials to inform him/herself about the Occupational Health and Safety Regulation pertaining to his/her area of work. Industry Training Authority January 2012

5 Competency B-4: Use Measuring and Levelling Tools Contents Learning Task 1: Describe Pressure Measuring Tools Used In the Pipe Trades Learning Task 2: Use Pressure Measuring Tools Self-Test Answer Key piping trades 5

6 Competency B-4: Use Measuring and Levelling Tools This competency provides introductory information on the measuring and levelling tools used in the piping trades. The range of tools includes manometers (types, filling and fluids), and mechanical gauges, including analog, digital, standard and compound. The Use section covers operation of measuring and levelling tools, including gas pressures and diagnostics. Learning Tasks in This Competency Learning Task 1: Describe Pressure Measuring Tools Used In the Pipe Trades Learning Task 2: Use Pressure Measuring Tools Learning Objectives After completing the learning tasks in this Competency, you will be able to: Describe pressure measuring tools. Describe the use of pressure measuring tools. Describe the inspection and maintenance of pressure measuring tools. 6 PIPIng trades

7 Learning Task 1 Competency B-4 Learning Task 1 Describe Pressure Measuring Tools Used In the Pipe Trades Notes Mechanical Gauges Analog Gauges Gauges used for pressure testing may need to be of a type that can be calibrated- either by using a gauge tester or by comparison to a master gauge. The gauges are generally of the Bourdon tube type. The size of the dial face may be specified in the contract documents for the job. The accuracy of a manual reading increases with the size of the dial face. The materials from which the gauge is constructed must be compatible with both the test fluid and the surrounding environment. Bourdon Tube Gauges The Bourdon pressure gauge uses the principle that a flattened tube tends to change to a more circular shape when pressurized (internally). Although this change in cross-section may be hardly noticeable, the strain of the material of the tube is magnified by forming the tube into a C shape, so that the entire tube tends to straighten out or uncoil as it is pressurized. Eugene Bourdon patented his gauge in France in 1849, and it was widely adopted because of its superior sensitivity and accuracy. Figure 1 Pressure Gauge Measuring Psi and kpa Figure 2 Bourdon Tube Gauge Gauge stems (sockets) may be 6 mm or 13 mm (¼ in. or ½ in. ) NPT, depending on the pressure range. Severe vibration or rapid fluctuations in pressure may cause gauges and recorders to give inaccurate readings. Circumstances may require the use of special devices or attachments to protect the gauge. Oil-filled gauges may be used on lines where vibration is not too severe. If pipe vibration is too severe, the gauge may have to be remotely mounted on a board and connected with a tube or hose to the test point. Figure 3 Oil-Filled Pressure Gauge piping trades 7

8 Learning Task 1 Competency B-4 Notes Pulsation dampeners and snubbers (Figure 4) are devices that can be installed immediately upstream of a gauge to prevent damage due to pressure pulsation or pressure surge. Figure 4 Gauge Snubber Compound Gauges A compound gauge indicates pressures above atmospheric (in psi) and vacuum pressures (inhg). Figure 5 Compound Gauge 8 PIPIng trades

9 LEARnInG TASk 1 COMPETEnCY B-4 Digital Gauges Most digital gauges have precision within ±0.25% full scale accuracy and often measure positive, negative or differential pressures. The digital displays reduce the potential for errors in readings by eliminating errors commonly experienced with the inaccuracy of analog gages. Most units are powered by DC and often have recharging capabilities as well. Keypads allow easy access to features including backlights, peak and valley readings, auto-zero and instant conversion of pressure units. Memory functions enable storage of multiple readings and often a HOLD key freezes the current pressure for situations where readings may fluctuate. notes Figure 6 Digital Pressure Gauge Fluid Manometers Fluid manometers (also called liquid column gauges) consist of a vertical column of liquid in a tube whose ends are exposed to different pressures. The column will rise or fall until its weight is in equilibrium with the pressure differential between the two ends of the tube. A very simple version is a U-shaped tube half-full of liquid, one side of which is connected to the region of interest while the reference pressure (which may be the atmospheric pressure or a vacuum pressure) is applied to the other. The difference in liquid level represents the applied pressure. Although any fluid can be used, mercury is sometimes used for its Figure 7 Fluid-Filled U-Tube Manometer high density (13.6 times that of water) and low vapour pressure. For low pressure differences, water is commonly used (inches water column is the common pressure unit). Note that in. of water would represent 1 psi pressure, while it would take only 2.04 in. of mercury to represent the same force (exactly 13.6 times smaller of a column). Some manufacturers use fluid with a unique specific gravity. This fluid must be purchased to use with their product (proprietary). So the measurement scale on these manometers may be different than that used for a water manometer. PIPInG TRADES 9

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11 Learning Task 2 Competency B-4 Learning Task 2 Use Pressure Measuring Tools Notes Pressure and Force Units The units of measurement for pressure include: pound force per square inch Ibf/in 2 or psi pound force per square foot Ibf/ft 2 or psf ounces per square inch oz./in. 2 Pascals Pa Kilopascals kpa inches of Mercury Hg or inhg The Pascal is the metric unit of pressure, and it is defined as the pressure produced when a force of one Newton is exerted over an area of one square metre. The Newton is a unit that measures force. Unlike the imperial system, which often uses the pound to measure weight, mass, pressure and force, the metric system distinguishes between types of application by using different units. The Newton is based upon the amount of force required to accelerate one kilogram at one metre per second squared. The number of Newtons is equal to the mass of an object in kilograms Hydrostatic Pressure Hydrostatics is the study of fluids under pressure and at rest. When a hydrotest is required on a piping system, the piping is filled with water or other liquid and then pressurized. It is sometimes necessary to calculate a pressure or to calculate the height of water in order to produce a certain pressure. Before you can perform these calculations, you must memorize several constants, which will be used throughout your training. Rather than trying to remember the numbers, it often helps if you understand how these constants were derived, and how to calculate them. If you understand how to obtain the constants, you do not have to rely upon your memory. Water has a density of 62.4 lb./ft 3 ; this means that one cubic foot of water (assumed at its most dense temperature of 4 C) exerts a force of 62.4 lb. Because the base of a cubic foot is equal to one square foot, the force of 62.4 lb. is exerted over an area of one square foot. Therefore, the pressure can be expressed as 62.4 lb./ft 2 or 62.4 psf. This pressure can also be expressed as pounds per square inch (psi) by dividing the pressure by 144 in. 2 to find the pressure exerted over one square inch. This equals: 62.4 lb./ft in. 2 /ft 2 = psi piping trades 11

12 Learning Task 2 Competency B-4 Notes 62.4 lb. 1 ft. 1 ft. (12") 1 ft. (12") Figure 1 Pressure is Force Area A column of water that is one inch in height and that has a base of one square inch weighs lb. Therefore, the pressure on the base equals psi. A column of water 12" high exerts a pressure of on the base: psi 12 = psi lb. 1" 1" 1" Figure 2 Density of 1 in³ of Water = lb. Another unit of measurement used for low pressures is ounces per square inch. One pound is equal to 16 ounces. 12 PIPIng trades

13 Learning Task 2 Competency B-4 Therefore, a cubic inch of water weighs: lb. 16 oz./lb. = ounces or a pressure of oz. per square inch. Notes oz. 1" 1" 1" Figure 3 Density of 1 in³ of Water = oz. A unit of measurement often used for atmospheric pressure is inches of mercury. The relative density of mercury is (Relative densities of liquids and solids are compared to equal quantities of water. They are simply used as multipliers versus the known properties of water.) Therefore, a one inch high column of mercury exerts a pressure of: psi (water) 13.6 = psi lb. 1" 1" 1" Figure 4 Density of 1 in³ of Mercury (inhg) = lb. piping trades 13

14 Learning Task 2 Competency B-4 Notes In the metric system, the basis for all pressures is the Pascal, which represents the force in Newtons exerted on each square metre. A Pascal is a very small unit of pressure therefore the kilopascal is more commonly used. The pressure exerted by a column of water one metre high over a base of one square metre is equal to 9.81 kpa kg = 9810 newtons 1 m 1 m 1 m 9.81 kpa Figure 5 Pressure under 1 m³ of Water = 9.81 kpa Atmospheric Pressure The atmosphere is a layer of air that surrounds the earth. This layer of air is approximately fifty kilometres thick because of the weight of this column of air, it exerts a pressure all over the earth s surface. This pressure is referred to as atmospheric pressure. Two different standards have been established to aid in reaching some conformity on the weight of air. In the imperial system, the weight of air is based on the standard conditions (STP or Standard Temperature and Pressure) of 60 F and inhg absolute, at which air has a density of lb. per cubic foot. In the metric system, the standard conditions (STP) are based on 0 C at 101 kpa, at which air has a density of 1.29 kg/m 3. These values are approximate and will vary with changes in temperature, pressure, the percentage of different gases and the location from which the readings are taken. 14 PIPIng trades

15 Learning Task 2 Competency B-4 Atmospheric Pressure and Altitude The height above, or in some remote cases below the earth s surface, has a direct effect on atmospheric pressure. For example, an elevation 2000 feet above sea level produces a drop of 1 psi, and reduces the atmospheric pressure to 13.7 psia. Not only is the pressure less; this change in elevation affects the boiling temperature of water. Other variations in atmospheric pressure (AP) are caused by variations in the constituents of the air, relative humidity, and weather conditions. Notes Atmospheric pressure decreases approximately: 25 mm (1 in.) Hg for every 300 m (1000 ft.) above sea level 1 psi for every 2000 ft. above sea level 1 kpa for every 90 m above sea level Absolute and Gauge Pressure Because atmospheric pressure is exerted in all directions, we often ignore this pressure when taking readings. For example, if you measure the pressure on a flat tire, the tire gauge reads zero. In reality, the pressure in the flat tire is 14.7 psia. This is due to the atmospheric pressure that is exerted on the outside and the inside of the tire. To avoid confusion, pressures that include atmospheric pressure are called absolute pressures, and pressures that do not include atmospheric pressure are called gauge pressures. Vacuum Pressure Pressures below standard atmospheric pressure are called vacuum pressures or negative pressures. They are encountered whenever the absolute pressure in a system drops below atmospheric pressure. A perfect vacuum is equivalent to 0 psia. Atmospheric Pressure Measurement and Conversion of Measurement There are numerous ways to measure pressure, especially atmospheric pressure. The common units are psi and kpa, but other units of measurement are often used in technical literature. This section covers the units you are most likely to encounter in the piping trades. Absolute Pressure Absolute pressure is a pressure reading that includes atmospheric pressure. The use of absolute pressure enables us to measure pressures below standard atmospheric pressure. For example, a partial vacuum in a vessel could be measured with an absolute pressure reading. Absolute pressures cannot be negative, because you cannot have less than nothing. The use of absolute scales makes all readings, except zero, positive. Atmospheric pressure is always indicated as absolute pressure (14.7 psi above a perfect vacuum or 101 kpa above a perfect vacuum). Absolute pressure is indicated with an a after the psi reading, such as 14.7 psia. piping trades 15

16 Learning Task 2 Competency B-4 Notes Gauge Pressure The pressure in a tank or pipe is normally stated in terms of the differences between the pressure in the tank and the existing atmospheric pressure around the tank. This is known as gauge pressure. For example, a tire gauge gives the difference between the air pressure in the tire and the atmospheric pressure. Pressure gauges are generally manufactured to read zero when subjected to normal atmospheric pressure. A gauge on a tank filled with air at 14.7 psia pressure will read 0 psi. In other words, the tank would be considered to be empty. Gauge pressures are not absolute pressures; in fact, they are less than absolute pressure by one atmosphere. Gauge pressure = Absolute pressure minus Local atmospheric Absolute pressure = Gauge pressure plus Local atmospheric Static Pressure and Working Pressure Static pressure (or standing pressure) is the pressure maintained in a fluid while that fluid is at rest. In other words, no flow is taking place when a static pressure measurement is taken. The gauge reading will be highest under static conditions because there is no energy lost to friction or elevation. Working pressure is also termed operating pressure or flow pressure. It is the amount of pressure that can be maintained within a system when there is flow taking place. (It is working or operating. ) This is always less than the static pressure of the system, due to factors such as friction of the pipe walls and even the friction of the fluid s own molecules against one another. The difference between static and working pressures of a system is known as pressure drop. Excessive pressure drop within most systems is undesirable. As the flow velocity within a piping system increases, more energy will be lost to friction and the operating pressure will drop accordingly (more pressure drop). Pressure Testing and Leak Detection Hydrostatic Testing Hydrostatic testing is by far the most popular method of testing piping systems. The term hydrostatic literally means water that is not moving: hydro (water); static (stationary). However, the term is not limited to water, and covers any liquid that is not moving. This testing method is so popular because, when compared to gases such as air, water is virtually incompressible. An air pressure test on a large pipe would require large quantities of air (thousands of cubic feet) to be compressed into the pipe for a long time to achieve a high pressure. This would require powerful machinery and the high temperatures involved with the compression of gases. It would also mean that relieving the pressure on the line would take a long time, which could be critical in a dangerous situation. As well, using highly pressurized air or gas can be explosive if the pipe joints were to fail. 16 PIPIng trades

17 Learning Task 2 Competency B-4 If the same line was hydrostatically tested, the line would be completely filled with water, and then a relatively small amount of water would be pumped in to build up the required pressure. The pressure would be relieved by bleeding out the same small amount of water that was pumped in (normally less than a gallon). This has the advantage of lowering the chances of an explosive release of gas from the pipe. An advantage of hydrostatic testing is that leaks are much easier to find; however, water can be destructive, and care must be taken to avoid building damage from negligence due to open valves, etc. Notes Pneumatic Testing There are times when it is not convenient or even possible to test a line hydrostatically. Some piping systems require that no moisture or liquid be in them at any time, and these systems must be tested with air or other gases. However, when it is too costly, or onsite conditions dictate that a liquid cannot be used for testing (for example, if there isn t sufficient water on site for a hydrostatic test,) approval may be given to test the piping with air or other gases. Air normally has relatively high moisture content. When compressed and put into cold piping, the moisture condenses and water collects in the piping. Air must be dried (mechanically cooling it to a low dew point or using a chemical resin bed) before it is allowed to enter an assembly being pneumatically tested. If drying is not possible, gases such as nitrogen or carbon dioxide may be used. Equipment Used for Pressure Testing The equipment needed to do a pressure test includes a variety of hand tools, a pump or compressor, a drive mechanism, hoses and fittings, charts and recorders, and gauges. A standard set of hand tools is used to do a preliminary check on the connections in a system and to hook up the test equipment. A flashlight and an adjustable mirror with an extension handle may also be required. Each connection should be checked to ensure that everything is tightened. A test crew may be required to install the vents and drains needed for the test. Most hydraulic tests require vents at all the high points in the system and drains at all the low points. If the system is to be tested with fluids other than water, other attachments may have to be installed prior to pressurizing the system. For example, if an antifreeze solution is used as a test fluid, separate fill and drain connections may be necessary to prevent environmental damage. Spill pans and other collection devices may have to be installed to prevent chemicals spilling onto the ground. Pumps and Compressors A pump is a mechanism designed to discharge fluids against pressure. Compressors are also pumps, but are used to discharge gases against pressure. piping trades 17

18 Learning Task 2 Notes Competency B-4 The two basic classifications of pumps and compressors: positive displacement variable displacement The majority of pumps used for testing are of the positive displacement type (also known as a constant flow machine). Positive displacement pumps are sub-classified according to the mechanisms used to pressurize the fluid. The most common types of mechanisms used for pressure test pumps are: reciprocating piston plunger diaphragm gear design rotary vane Pump Drivers An integral component of any pump is its drive mechanism. Hand lever, pneumatic motor, pneumatic diaphragm, internal combustion and electric motor drives are available for pressure test pumps. Figure 6 Hand Test Pump Hoses and Fittings Hoses are usually of composite construction, with a small-diameter liner wrapped in multiple layers of reinforcement and bonding materials. Extremely high-pressure hoses may also be externally reinforced with a metal or fiber mesh. Carbon steel fittings or copper tubing are most commonly used for pressure testing connections, but there may be cases where the characteristics of the test fluid or conditions of the surrounding atmosphere require special materials. 18 piping trades

19 Learning Task 2 Competency B-4 Gas Cylinders Pressurized gas cylinders usually supply dry gas at very high pressure through a pressure-regulating valve assembly. All hose connections for test gases will be right-hand threaded. The regulator assembly on the tank is similar to the one used for an oxygen tank on an oxy-fuel cutting system, but the threaded tank connection is different. Notes Only oxygen tanks have a CGA-540 threaded connection. All other pressurized tanks have a different CGA thread, depending on the type of gas. Low pressure gauge High pressure gauge ( psi) Pressure regulator valve Nitrogen tank valve Protective cover Hose assembly Nitrogen tank Figure 7 Nitrogen Cylinder Test Assembly Now complete Self-Test 1 and check your answers. piping trades 19

20 Learning Task 2 Competency B-4 Self-Test 1 1. What is used to dampen severe vibration or rapid fluctuations and to aid gauges and recorders from giving inaccurate readings? a. diffuser b. snubber c. reducer d. softener 2. What is the advantage of digital gauge over an analog gauge? a. accuracy in readings b. hold reading function c. multi-reading memory d. all of the above 3. What is the density comparison between equal quantities of mercury and water? (i.e., the relative density of mercury) a. 1.0 b. 4.8 c. 9.3 d is the study of fluids under pressure and at rest. a. hydraulics b. hydrostatics c. hydrotesting d. hydropneumatics 5. What is water's density in lb./ft³? a b c d PIPIng trades

21 Learning Task 2 Competency B-4 6. A one metre high column of water over a base area of one square metre will exert how much pressure in kpa? a b c d In the imperial system, the weight of air is based on measurement at what standard temperature? a. 0 F b. 32 F c. 60 F d. 100 F 8. What is the approximate absolute pressure of a gas that has a reading of 135 psig? (Assuming an installed elevation of 4000 ft. above sea level.) a psia b psia c psia d psia piping trades 21

22 Answer Key Competency B-4 Answer Key Self-Test 1 1. B. snubber 2. D. all of the above 3. D B. hydrostatics 5. D C C. 60 F 8. D psia 22 PIPIng trades

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