Handling and Storage of Gases Learning Outcome When you complete this module you will be able to: Describe the procedures for safe storage and handling of cylinders containing gases. Learning Objectives Here is what you will be able to do when you complete each objective: 1. Describe gas cylinder markings. 2. Describe the safe procedures for handling and changing gas cylinders. 3. Describe the care, maintenance and storage of gas cylinders. 4. Describe gas cylinder safety features. 5. Describe gas cylinder inspection. 1
INTRODUCTION In many installations requiring gases for fuel or other operating procedures, many or all of the gases are sent or delivered to the locations complete with their own containers - called cylinders. Such cylinders are simply metal pressure vessels, which can be easily transported. In cylinder storage systems, the individual cylinders are connected to the pressure regulating equipment, which is left permanently attached to the user s gas system. When empty, the cylinders are completely removed, replaced by other full cylinders and taken back to the bulk plant for filling. In the interest of safety it is important that employees are thoroughly trained in safe practices for handling and storing cylinders containing gases. This module therefore, is intended to inform the student of the standards and rules of handling and storing gases contained in easily movable and readily portable cylinders. Compliance with these standards will help to reduce the number of accidents in your place of work, but compliance alone will not guarantee a safe installation. This can only come through combining the knowledge you get from a thorough study of this module with the knowledge you have gained through experience in work processes of your particular industry. GAS PROPERTIES Cylinder gases, or bottled gases, are commonly used by the industry for fuel purposes. Most of these fuel gases liquefy under moderate pressure, but upon relief of the pressure are readily converted into the gaseous phase. Advantage of this characteristic is taken by the industry and for convenience the gases are shipped and stored under pressure as liquids. When in the vapor state, these gases present a hazard comparable to any flammable natural or manufactured gas, except that, being heavier than air, ventilation requires added attention. The range of combustibility is considerably narrower and lower than that of manufactured gas. Propane, for example, is a liquid at atmospheric pressure and temperature below -40 C and normally does not present a flammable liquid hazard. However, rapid vaporization takes place at temperatures above the boiling point. Likewise, butane at atmospheric pressure and temperature below 0 C is a liquid but will vaporize quickly at temperatures above 0 C. It is advisable that employees working with gas cylinders be aware at all times of the type and density of gases contained in the cylinders, whether it is in a liquid or vapor state, the vapor pressure and other related details. The vapor pressure is a number indicating the pressure of the vapor at the top of the container at 100 F, (38 C) and therefore indicates the suitability of a container for a specific product. 2
For example, if a container is a type 100, it means it is a container designed for a product with a vapor pressure not exceeding 100 psi at 100 F. Because propane has a vapor pressure of approximately 170 psi at 100 F, it cannot be placed safely in a type 100 tank. On the other hand, butane may be placed in a Type 100 tank because its vapor pressure is about 40 psi at 100 F. GAS CYLINDER MARKINGS Employees responsible for handling and using gases contained in cylinders should be aware of the general information marked on the cylinder. Gas cylinders are commonly marked with information pertaining to their size or capacity, service pressure, metal specifications under which they were made, tare weight (TW), ownership symbol, serial number, inspector s official marking, original test date and manufacturer s symbol Most of the above information is requested by authorities such as the Canadian Transport Commission (CTC) or Department of Transport, (DOT) which are responsible for the safety of these containers. Size or capacity of the cylinder is rated by the number of pounds, litres or cubic metres it is designed to hold exclusive of the weight of the cylinder itself. For example, a one hundred pound propane cylinder can hold one hundred pounds of propane with enough space left inside to allow for safe expansion of the liquid when the temperature rises. Such cylinders vary in size and capacity, from those small enough to carry conveniently to those weighing several hundred pounds when filled. Cylinders must be manufactured to rigid specifications set by the CTC or DOT. The numbers stamped on the cylinder indicate the metal specifications under which the cylinder was made, plus the service pressure of the cylinder. For example, in DOT-4BA-240, the DOT stands for Department of Transport, the 4BA for the construction specifications involved and the 240 for the fact that the cylinder is designed for service pressure of 240 pounds per square inch, or 1655 kpa in the metric system. The service pressure tells the employee whether or not the container is safe for a specific product. Tare Weight The tare weight (TW) is a number indicating how much the cylinder weighs when empty, including all permanently attached fittings except the valve protecting cap. This marking indicates to the employee how much the cylinder should weigh when filled correctly to capacity and follows the letter TW, or Tare WT, on the cylinder head. 3
Ownership Symbol This is a marking identifying the purchaser of the cylinder and it is registered with the Bureau of Explosives. This symbol is also called the Purchasers Registered Mark. Serial Number This a number which further identifies the container and cannot be duplicated. This provides a control record of each cylinder which is registered and maintained by the Bureau of Explosives. Inspector s Official Marking This indicates who performed or supervised the original test of the cylinder. Original Test Date This shows the date of the first test performed on the cylinder, as well as the month and year the cylinder was manufactured. In addition, the cylinder must carry the date of each subsequent inspection so the employee would know when the next inspection date is due. Manufacturer s Symbol This indicates who made the cylinder. SAFE HANDLING OF GAS CYLINDERS Gas cylinders are not considered fragile equipment; nevertheless, they should be handled with care, for they can be damaged if dropped, and they could cause serious injury to an employee. AG_5_0_1.jpg P Cylinder valves, which provide a means of filling and discharge as well as a safety relief device, are screwed onto the top of the cylinder. The cylinder valve is provided with a connection and is kept closed except when in use or during filling. The cylinder valve is the most easily damaged part of a gas container. It is commonly made of brass, which is not as strong as the metal used in the cylinder, and is screwed into the cylinder in such a position that it could be broken off. If the cylinder falls over and the valve strikes a projection it could break off and release the product. The valve could also be damaged if an object were to fall and strike it; it can be affected by exposure to the weather, and the valve could be incorrectly used as a handle by a person moving the cylinder. In any case, serious injury could result. Therefore the valve protection cap, when supplied, should be securely screwed in position whenever the cylinder is not in use or being filled. 4
When moving cylinders always use hand trucks to avoid back strain, and take special care not to drop them when loading them onto a truck. Personnel must ensure the cylinder protection caps are kept lubricated so they can be easily and completely screwed on each time. Not all cylinders have protection caps; those, which do not have, a guard ring permanently mounted on the cylinder to protect the fittings. A guard ring or cap is necessary on all cylinders. When used in the construction industry or when used inside a structure, cylinders must always be kept in a position which will allow the safety relief valve to connect with the vapor space. This will ensure that any product which is released is in a gaseous form. If the safety relief valve were to connect with the liquid space it would vent liquid when it opened. A small amount of liquid could vaporize rapidly to become a large amount of flammable gas. Gas Pressure Regulators Gas cylinders are connected to a pressure regulator commonly located on the user s property. Such an installation may have a single cylinder, two cylinders (most common) or, in some cases, multiple cylinders. The use of more than one cylinder lets the gas buyer use one cylinder while waiting for an empty cylinder to be replaced. Gas cylinder installations consist of the cylinders, pigtails, manifold, regulator and piping. The cylinders, as mentioned earlier, are equipped with the cylinder shutoff valve and the safety relief valve. These are only the basic parts of a cylinder valve, which may have other parts including a fixed tube liquid level gage to indicate when maximum safe filling limit is reached. The cylinder valve has also a female left hand thread to receive the pressure hose, which provides a connection between the cylinder valve and the manifold. This connection is left permanently attached to the manifold when changing cylinders. The manifold is usually one of the three following types: tee block, manual, or automatic throwover. They all have the same function; that is to let the delivery person remove the empty cylinder and replace it with a full one without interrupting the gas supply from the cylinder that remains in service. Manifolds also prevent gas from escaping during the changeover of cylinders. The pressure regulator reduces the cylinder gas pressure from a relatively high pressure to one suitable for the user s equipment. 5
Delivering and Changing of Gas Cylinders Empty portable cylinders are replaced by full cylinders, and taken back to the company s refilling plant. Each employee involved in such deliveries should be constantly attentive to safe practices. Cylinders, for example, are provided with foot rings, which are strengthened metal rings on the bottom of the cylinder. These should always rest on a hard, level surface and never be placed on the bare ground. A regular routine should be followed when changing cylinders to ensure that safety rules are always complied with. The procedure for changing cylinders is as follows: 1. Full and empty cylinders must always be loaded and carried on trucks in an upright position, and securely anchored or chained to prevent shifting or falling. 2. When the delivery truck cannot closely approach the cylinder installation, a hand truck should be used to carry cylinders. 3. Cylinders should not be dropped or thrown from the truck but should be eased to the ground. 4. Before disconnecting the empty cylinder from the installation, the cylinder valve must be closed to prevent air and moisture from entering the cylinder and causing corrosion. 5. The proper hand wrenches to fit the various connecting nuts must be used when changing cylinders. This will ensure that no damage occurs on these fittings. Also, the employee must be certain that the connection is turned in the correct direction since many fittings have left hand threads. 6. Cylinder connections such as pigtails, hoses and manifolds should be disconnected slowly, allowing pressure to bleed down before entirely removing the nut. If pressure does not drop, the cause should be found. If necessary, the remaining cylinders should be shut off to prevent escape of gas. 7. The cylinder valve and connections should be examined, and those with worn or damaged threads should be replaced. If the cylinder valve is damaged, the entire cylinder should be taken back to the filling plant for repair. Any dirt around the cylinder valve or valve connections should be removed promptly. 6 It is advisable to crack the valve open briefly to blow out any accumulation of dirt.
8. Each time a new cylinder is installed, the employee should make a quick safety check of related equipment, such as, the regulator and manifold valve assembly. If accumulations of rubbish, or other hazardous conditions, exist near the installation the user should be requested to correct the situation at once. 9. Cylinders must be installed vertically on their foundations. When hoods or cabinets are used, they must be closed before leaving. 10. After the full cylinder has been installed and the connection made, the cylinder valve must be opened and the connection checked for leaks. Leak checking should be done with a soap solution or other suitable solution, never with a flame. The solution is applied to the connection, and leakage is indicated by the presence of bubbles. 11. If it is necessary to shut off the gas supply to the user s line, gas should not again be turned on until all appliance valves and pilots have been turned off. Such stoppage of gas flow to the user might be required in order to change a single cylinder installation, or when all cylinders of a multiple cylinder installation are empty, or if it is necessary to repair or replace the regulator, manifold or other fittings. 12. The valve protection cap from the filled cylinder should be placed on the empty cylinder before moving it to the truck. Care and Maintenance Gas cylinders represent a substantial investment on the part of the company and therefore, they must be handled and operated with care, and maintained in top condition. In order to maintain gas cylinders and their fittings correctly, the employee must follow recommended procedures for: 1. Cleaning and painting cylinders. 2. Checking cylinder for damages each time they come to the plant. 3. Making periodic visual inspections or pressure tests as required by regulations or standards. 4. Disposing of fire damaged cylinders and cylinder fittings. 5. Inserting or replacing valves and gages when necessary. 6. Purging cylinders of air. 7. Deodorizing cylinders. 7
Storage Procedures Locating and storing containers filled with a gas is as important as handling and moving them for refilling or maintenance work. According to the Canadian Standards Association, gas cylinders shall not be placed below ground level except by special permission of the authority. These standards also stipulate that the cylinders should be located outside of the building when connected to gas consuming equipment. However, where portability of cylinders is necessary, and outside location is impractical, cylinders may be located for use, but not for storage, inside a building. In such an installation, the gas is to be used for industrial processing or repair work only, and the building has to be of an industrial nature. When in storage, gas cylinders must be provided with solid bases and must be in an upright position while firmly secured to prevent settling or rolling over. They should be protected from the weather by a proper housing and guarded from physical damage to the regulating equipment. The discharge from safety valves on cylinders located outside shall not terminate in any building or beneath any building and should be located not less than one metre horizontally away from any building opening. Always ensure gas cylinders are stored away from any direct heat and open flame and are protected from vehicular traffic and falling debris. They should be kept away from oil and grease at all times and ventilation must be appropriate in storage areas. Empty and full cylinders should not be grouped together in storage. Never store acetylene and oxygen cylinders together. They should be stored at least 6 metres apart to prevent explosive mixtures forming in the event of leakage. Finally, before leaving the cylinders in storage make sure all hoses, piping, pressure regulators, gauges, manifold connections and fittings are free from defects, leaks, or the presence of oil and grease. 8
GAS CYLINDER SAFETY FEATURES The features and fittings gas cylinders should be equipped with are summarized in the following sections. Filler Valves These are fittings used for product transfer into cylinders. They permit product to flow in, but a check valve arrangement prevents backflow. Vapor Valves These valves allow product flow only when a hose is connected, and are equipped with a seat disc and a spring device to prevent excessive flow of vapor in the event that a hose or pipe ruptures. When both filler valves and vapor valves are used there is a separate service valve to pass vapor out. Occasionally all of these valves are combined in a combination valve. Standard types of cylinders have a single valve only, the cylinder valve mentioned earlier, which passes liquid and gas through a single opening. AG_5_0_2.jpg P Cylinder Valve Cap The cylinder valve cap is the metal screwed type cap used when it is necessary to protect the gas outlet valve and pressure relief valve from operational or accidental damage. Pressure Relief Valve The pressure relief valve is part of the cylinder output valve and is used to release product if the pressure in the cylinder gets too high. It is commonly a spring loaded valve designed to vent horizontally away from the cylinder. Top Guard Ring The top guard ring is used with small size gas cylinders to protect the outlet valve and relief valve from damage. These cylinders usually do not have valve caps, and the guard ring is also used as a handle when moving the cylinder. AG_5_0_3.jpg P 9
Foot Ring The foot ring is a reinforced metal ring welded to the bottom of the cylinder to keep it upright and protect the lower part of the cylinder from rust and damage. GAS CYLINDER INSPECTION Gas cylinders are commonly checked by personnel each time they come in for refilling. However, the law requires that pressure vessels, and of course gas containers, be subjected to more complete and conclusive inspections and tests at regular intervals. The employee must familiarize himself with the required intervals for inspections and tests for the particular type of gas and cylinders he is working with, and watch for any cylinders requiring such an inspection. There are generally two types of inspections: the visual inspection and the pressure test. During visual inspections, the employee must follow approved methods established by his company and based on certain standards. The visual inspection is the most frequent and common method and is performed by a qualified person to establish if the cylinder is fit to remain in use. During this inspection the person must: 1. Check all seams for signs of corrosion or damage. 2. Check the areas most subject to corrosion, such as inside the foot ring and on the bottom head. All rust, scale, dirt and caked paint must be removed to reveal the full extent of corrosion. When corroded areas are badly pitted and there is danger of leaks, the cylinder must be discarded. 3. Check for dents and cylinder wall deformations. If such dents are very large or deep, or have sharp angles, the cylinder may not be safe for further service. 4. Check for cuts or gouges caused by sharp objects. 5. Inspect for broken or damaged foot or protective ring. If the ring needs welding or replacing, the work must be done by a qualified welder since it is subject to approval by the local inspection authority. 6. Check for fire damage. Cylinders deformed by fire are usually destroyed. Scorched units may be returned to the manufacturer for repair and testing. Valves and safety devices are always replaced on cylinders which have been exposed to fire. 10
7. Keep an accurate record of the inspection and work done on each cylinder. Include details such as, how the cylinder was disposed of after the inspection, whether it was sent to the manufacturer for repairs, or was finally scrapped. The cylinder pressure test may be of the water jacket type or hydrostatic. In the water jacket test the cylinder is filled with a liquid and lowered into another container full of water. The cylinder is then subjected to a pressure twice the working pressure stamped on it, causing the cylinder to expand. This expansion forces the water out of the tank which, when collected and measured, indicates the amount of expansion the cylinder was subjected to. Then the pressure is removed from the cylinder, and if an excessive amount of the initial expansion still remains in the cylinder, the metal has lost its elasticity and must be either heat treated by the manufacturer or removed from service. In the hydrostatic test, the cylinder is filled with water and the pressure increased to twice its working pressure. It is then examined visually for leaks. After a cylinder has undergone the required test or inspection, it is stamped with the date of the test near the previous test date. 11
Notes: 12