Compressed gas regulators, when not performing optimally, can lead to many hazardous situations, such as the leakage of toxic, pyrophoric or asphyxiant gases into the atmosphere, or even the risk of explosions or fire. As such, regulators are devices that should only be used by persons experienced and aware of the inherent dangers.
Regulators are continuously exposed to high stresses due to cylinder pressures. In addition to that, the materials of construction are attacked internally by both mildly and severely corrosive gases. External corrosive environments can cause gauges and springs to rust, fittings to discolor and can severely tarnish the appearance of an otherwise brilliantly manufactured product. How long should a regulator function properly under severe conditions? How often should regulators be tested and/or refurbished? What tests should be included on preventive maintenance charts? These are questions that manufacturers are constantly asked by consumers concerning the life expectancy of compressed gas regulators. Unfortunately, the answers are varied and somewhat complicated.
Consider customer “A”. This customer uses one cylinder of argon every six months, pressurizing the regulator once a week inside a cleanroom where temperature, humidity and other environmental factors are controlled. This regulator may last 25 years or more without refurbishing or replacing any major components. In fact, Harris frequently hears from customers who have used the same Harris regulator since the 1940’s with no problems, however, these are extreme cases. Contrast that with customer “B” who uses an oxygen regulator several hours a day on an oilrig off the Gulf Coast of Mississippi. Because of the salty air and harsh environment in and around an oilrig, this regulator may need a major overhaul or replacing in as little as three months. Because the applications for compressed gas regulators are so varied, the life expectancy is varied and proportional to the gas service and the environment in which the device is used.
Factors Which Affect Regulator Life
Gas Service. Know the properties of the gas being regulated and contact a manufacturer or gas distributor for help in correctly selecting regulators for specific gases. Argon, helium and nitrogen regulators (CGA 580) will, under a given set of conditions, have a longer service life than regulators used for hydrogen chloride and hydrogen sulfide (CGA 330) simply because the gas service is more severe (corrosive).
Some non-corrosive gases can be reactive in certain environments. For example, carbon dioxide can react with moisture or condensation inside a regulator to form carbonic acid. This is a relatively weak acid, but it can attack certain elastomeric components over time and reduce the service life of a CO2 regulator. To insure that the gas service will not adversely affect the expected life of a regulator, contact the manufacturer to discuss the application as well as the regulator’s metallic and non-metallic materials of construction.
Service Environment. Many applications require that regulators function outside; exposed to rain, snow, ice and high humidity/salinity. These are conditions that can reduce the service life of regulator components. A significant percentage of gauges have steel cases, which will rust if exposed to the rain, snow or ice. Most pressure adjusting springs are also made of steel which, even though they are inside the regulator, will corrode over time in a humid environment. Steel and copper-based alloys (brass) are commonly in contact with each other inside and outside the regulator. Even though one or both components may be painted or plated, electrochemical (galvanic) corrosion cannot be ignored. Corrosion of parts and/or failure of components can be accelerated in harsh environments. Manufacturers as well as users who operate regulators in a critical service application, should consider these issues when recommending or purchasing pressure regulators.
Elastomers. Many industrial regulators have elastomeric components such as reinforced neoprene diaphragms, viton seals or seats, nitrile o-rings, etc. Elastomers can be very sensitive to extreme temperature shifts and to the elements. Over a period of time (normally years) these materials tend to become brittle and/or crack. This degradation can result in some form of leakage from the regulator.
Typical Modes Of Failure
Failure of internal components generally results in leakage of the regulated gas to the atmosphere. There are no outward indications that failure of a major component is about to occur. In regulators, there are usually two areas of concern. The first is gas leakage to the atmosphere from the external ports or from the diaphragm. Leakage from the ports is rare unless factory fittings or gauges have been changed or torque settings are lower than recommended. Leakage can also occur if port threads have been damaged due to changing connections.
Diaphragms are flexible, dynamic components that move axially as gas flows and pressures fluctuate through the regulator. When a diaphragm is pressurized and then relaxed, that constitutes one (1) sequence or cycle. According to the Compressed Gas Association Pamphlet E-4, diaphragms must have a minimum life of 25,000 cycles if made from an elastomer and 10,000 cycles if made from a metallic material (usually stainless steel). Leakage from the diaphragm can occur if it has exceeded its normal life. This is generally a greater problem for metal diaphragms than for elastomeric diaphragms. Excessive flexing of the metal diaphragm can cause a radial crack, which allows gas to escape to the atmosphere through the vent hole in the bonnet.
The second and perhaps the most common type of regulator failure is the internal leak, sometimes called creep or crawl. This can occur when the seat becomes damaged or displaced due to a foreign particle such as a metal chip or other material. When the seat cannot close completely, delivery pressure will not be maintained and regulator pressure cannot reach a state of equilibrium. Downstream or delivery pressure will continue to climb until the safety relief mechanism on the regulator is activated (usually a relief valve or a diaphragm burst hole). Checking for this type of failure is relatively easy if the device has a gauge that reads regulated pressure. The gauge pressure will start to rise above the set point and continue upward. This creates a potentially hazardous condition where any downstream equipment would be subjected to pressures beyond the rated limit. Regulators should be visually checked for this type of failure often.
Long Regulator Life Starts With Good Maintenance
To avoid unexpected downtime and to enhance safety in the work area, nothing can be more important than a routine regulator maintenance schedule. This will insure that the performance of the device is being checked at regular intervals where problems can be easily addressed.
All compressed gas regulators should, at a minimum, be checked for external leakage and internal leakage (creep or crawl) regularly. In addition to this, the device should be removed from service at least every five years (more frequent in some cases) and returned to the manufacturer, or a competent agent of the manufacturer, to be inspected and/or refurbished as necessary. Regulators should also be tagged or labeled to identify the last date of inspection. Users should consult the manufacturer for specific procedures on how to check for external and internal leakage as well as the recommended frequency of the tests.
In summary, compressed gas regulators do not have an infinite life span. Because some regulators are in severe service and some are not, it is difficult to say how and/or when a device will reach the end of its service life. Some companies publish guidelines in their literature, which attempts to define what to expect in terms of service life. Users should closely adhere to these guidelines to protect their equipment and themselves against the hazards regulator failures can produce.
David Gailey is the manager for Specialty Products for The Harris Products Group, A Lincoln Electric Co. He has been with Harris for 27 years and served as past chairman of the CGA Industrial Gas Apparatus Committee.