HYDROSTATIC TESTING OF COMPRESSED GAS CYLINDERS

HYDROSTATIC TESTING OF COMPRESSED GAS CYLINDERS

By Bruce J. Cavallari

Can an SCBA cylinder be hydrotested prior to the expiration of the last hydro date? Should fiber-reinforced composite cylinders be filled in water? Do hoop or fully wrapped SCBA cylinders have a life span? This is a sampling of the questions asked every day throughout the fire service concerning compressed gas cylinder maintenance. The answers may not depend solely on region, training, and available (reliable) information. There are finite rules and regulations concerning cylinder safety, and it is our responsibility to be familiar and in compliance with these standards. They were created for our safety.

WHAT IS HYDROSTATIC TESTING?

Hydrostatic testing is the standard method of testing cylinders in the compressed gas industry. The water jacket method of testing cylinders consists essentially of enclosing the cylinder, suspended in a jacket vessel, and measuring the volume of water forced from the jacket on application of pressure to the interior of the cylinder. The pressure applied is five-thirds the operating pressure unless otherwise specified by the manufacturer. Therefore, a 4,500-pound-per-square-inch (psi) cylinder would be tested at 7,500 pounds psi. This method is used to determine the elastic expansion, which is directly related to the cylinder`s average wall thickness.

Department of Transportation (DOT) regulations require that each cylinder be inspected periodically internally and externally, calibrated testing equipment and test gauges be used, and every cylinder used for the storage of compressed gases such as air or oxygen be retested. The exact laws are in the Code of Federal Regulations (CFR), Part 49, subpart 173.34(e). The DOT requires each testing facility to submit to regular inspections; and each facility must maintain records of all tests performed, all persons performing the tests, and regular training records of personnel.

The DOT was established in 1967 and assumed the responsibility for the safety regulations formerly administered by the Interstate Commerce Commission.

CYLINDER DESCRIPTIONS

I`m sure we all can recognize a cylinder when we see one, but exactly how many different types of cylinders are we dealing with in our stations? Fire extinguishers are cylinders. Oxygen used on rescue vehicles is in cylinders. SCBAs and SCUBAs have cylinders. Large storage cylinders are on the air trailer/compressor. The cutting torch has cylinders. Air supply for the vehicles` air horn may come from a stored pressure air cylinder. All of these and more, depending on your specific locale, are cylinders that may require hydrostatic testing at a DOT-authorized cylinder requalification facility. Consider each type carefully.

Oxygen

Oxygen systems for EMS, forcible entry, and extrication uses can be found onboard the engines, rescues, ambulances, and staff cars throughout your workplace. Within the stations, oxygen-transfilling systems are commonplace. Whatever the cylinder size or use, hydrotesting is required every five years. Even the oxygen cylinder on the cutting torch must be retested.

Air

Air cylinders are used as our SCBA bottles, SCUBA tanks, and air-horn and air-chisel supply. All composite cylinders are retested every three years, and all aluminum and steel cylinders are retested every five years.

SCBA cylinders commonly are found in 20-, 40-, 45-, and 90-cubic-foot aluminum, steel, or composite construction. Seven- and 17.5-cubic-foot packs are also available.

Extinguishers

Even fire extinguishers can need hydrotesting. Stored pressure extinguishers such as dry chemical ABCs need retesting every 12 years. CO2 cylinders and pressurized water extinguishers are retested every five years. The original manufacture date often is stamped into the cylinder or listed on the identification label.

Test Facility Responsibility

Cylinder requalification facilities must follow the DOT guidelines as specifically as described in the Code of Federal Regulations (CFR) for the cylinders being tested. They must properly inspect, record, and test each cylinder and stamp the cylinder neck or affix along the barrel a sticker indicating the facility`s permit number and the month and year in which the test was completed.

Department Responsibility

Low- and high-pressure compressed gas storage systems are used for life-support functions. Each should be inspected thoroughly at least weekly, if not daily. Your inspection should include the recording of the pressure and a comparison of that pressure with previous readings, visualizing the hydrostatic test date, and examining the overall condition of the cylinder`s exterior. This examination should include the valve body and cylinder bottom. Measure or immediately clean deep pits or gouges. Pits or gouges indicate a serious structural problem. Remove the cylinder from service, and have it tested or repaired at your hydro facility.

Prompt Maintenance

Immediately report any indications of damage. Remove the cylinder from service, and tag it with specific information that indicates the exact problem. If fiber threads have become unglued, they can be re-epoxied by qualified cylinder maintenance personnel at a hydrotesting facility. Do not overlook the quantity and depth of the loose fiber or pits.

Warnings

You should be aware of the following:

All composite cylinders–hoop or fully wrapped–have a 15-year life span from the date of original manufacture. There are absolutely no exceptions. If you own a cylinder that was originally made in January 1981, its life span would have expired on January 1, 1996. Composite cylinders were just becoming popular in 1981, so keep your eyes open. Expired cylinders should begin to surface soon.

Hydrostatic testing is designed to reflect the safety of the cylinders we use. By ensuring the integrity of the cylinder, hydrotesting allows firefighters a measure of confidence while wearing what amounts to a 2,000-pound bomb on their backs.

Question: When can cylinders be tested every 10 years instead of every five years?

Answer: When the testing facility has affixed a five-point star after the last hydrotest date, the cylinder can be retested 10 years after that date. This is applicable only to certain steel cylinders. Specific requirements must be met before a star will be applied. Consult with your supplier to consider this option.

Question: Do acetylene gas cylinders need to be hydrostatically tested?

Answer: Their construction and extremely low pressure exempt acetylene cylinders from hydrostatic testing. To be certain a cylinder needs retesting, check the DOT markings on the neck or barrel. If the cylinder had a previous test date, it will need retesting. No mark, no retest.

Question: Should composite SCBA cylinders (hooped or fully wrapped) be filled in water?

Answer: I personally and some manufacturers say no, for three reasons:

Water could seep in between the fiberglass wrapping and the aluminum and begin a degradation process that could degrade the cylinder`s aluminum or fiber, or both.

If refilled properly, heat buildup is minimal and not damaging.

Using water in a cooling vat will not prevent a cylinder from rupturing; cannot contain any of the debris; and could be introduced into the cylinder via the open valve, causing a problem with internal corrosion or air contamination.

Question: Can a cylinder be retested more frequently than at its required interval (three, five, 10, or 12 years)?

Answer: Yes. Whenever a cylinder`s integrity is in question due to impact, due to excessive heat (over 170°F), or when there is any uncertainty about the cylinder`s structural makeup, the old saying “Better safe than sorry” applies.

Question: If a cylinder fails hydrotesting, should the test facility drill a hole into the cylinder, rendering it useless, or stamp into the metal the words “Failed Hydro/VIP (Visual Inspection)”?

Answer: Without the specific permission of the cylinder owner to enact such markings, the responsibility of the test facility is only to mark the cylinder in a nondamaging way and record the disposition of the cylinder in the test log. Remember, the cylinder does not belong to the test facility; no right of ownership exists. The only markings on the cylinder should be those specifically required by the DOT/CFR standard or the owner of the cylinder.

Question: What about the cylinder valve and contents pressure gauge? At the time of the hydrotest, is it required that the valve be overhauled or the contents gauge calibrated?

Answer: No. Neither the hydrotest nor any known manufacturer requires that the valve be overhauled or the gauge recalibrated at the time of retesting. Some manufacturers do “recommend” that preventive maintenance be performed on a regular basis, but the timing of this maintenance is entirely up to the end user (that`s you, not the test facility). Valve overhauls and gauge recalibrations are necessary only when their accuracy is in question. If a valve overhaul is needed, be sure the facility making the repairs is authorized by the manufacturer to service the equipment.

Question: Cylinders that have exceeded the 15-year life span should be returned to the manufacturer for rewrapping, which will give them another 15 years of service life. True or False?

Answer: False. There is absolutely, positively, and without a doubt no way to refurbish a composite cylinder. To replace this cylinder, the only course of action would be to remove and save the valve from the expired cylinder. Purchase a new cylinder shell from the original manufacturer (be sure to specify that you wish to purchase only the cylinder, not the valve), and reinstall your old valve into the new cylinder. This could save you upward of $250 on the replacement of a cylinder with valve.

What can you do with your expired composite cylinders after the 15th year? Good question. They look like good cylinders and may even hold pressure just as before. Structural decomposition after 15 years of use can be substantial. The fiberglass reinforcement may be decaying, and the aluminum may be corroding. The problem is that none of this decomposition is visible beneath the fiberglass wrapping. Dispose of these cylinders any way you see fit, but be aware of the liability you can incur by reselling a condemned cylinder.

The second problem you should be aware of is neck leaks. Aluminum cylinders may develop cracks or pinhole leaks at the neck near the valve assembly. While filling, give special attention to this area, especially since the life span issue is beginning to develop. Immediately empty cylinders with cracked necks, and return the cylinders to the manufacturer for evaluation as soon as possible. (Don`t forget to remove your valve.) n

BRUCE J. CAVALLARI has served in career and volunteer organizations during his 18-year fire service career and is a member of the Palm Beach County (FL) Fire-Rescue, where he is a lieutenant in the operations division. He also heads the consulting and instruction company Environmental Safety Specialists, specializing in the use of compressed gas equipment (SCBA, liquid 02, gas manifolds), and is a consultant for American Hydro-Test, Inc., a cylinder requalification facility in Fort Lauderdale, Florida. Cavallari is a Florida state-certified company officer, a company officer instructor, a fire safety inspector, an inspector instructor, and a minimum standards instructor.

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