As most process safety professionals know, pressure testing and leak testing piping systems is an absolutely critical function of process safety efforts. And I am happy to say, the number of facilities that have begun pressure testing and leak testing their piping has grown by leaps and bounds since the passage of OSHA’s PSM and EPA’s RMP standards. But as we progress in the number of facilities doing these tests, we also find many tests that are woefully deficient in how they were carried out and documented. For example, Refrigeration Systems (regardless of the refrigerant) has some specific requirements for the “pressure testing media” that can be used. For example, ASME B31.5 (2016) states:
(emphasis added by me)
538.5 Testing Medium for Refrigerant Piping
(a) A suitable dry gas such as nitrogen or air shall be used for pressure testing per para. 538.4.2. Toxic gases shall NOT be used unless personnel are adequately protected from harmful exposure should leaks occur during testing.
(b) Oxygen or any medium with a lower flammable limit below 13% shall NOT be used for pressure testing.
(c) The system refrigerant may be used for leak testing per para. 538.4.3.
CAUTION: Comply with environmental regulations when testing with refrigerants.
(d) Water or water solutions should NOT be used in testing refrigerant piping.
So as we can see, pneumatic pressure testing to 110% of the design pressure is the preferred means to pressure test refrigeration piping, based on (a) and (d) above. We can also see that using a “dry gas” such as N2 is preferred, but we can also use “air” as long as it is “suitably dry” and unfortunately neither ASME B31.5 or the International Mechanical Code quantify a “dew point” for which we can say “air” is a “suitable dry gas” for pressure testing purposes.
When we take a look at the International Mechanical Code’s requirements for pressure testing media, we see the following:
1108.2 Test gases.
Tests shall be performed with an inert dried gas including, but not limited to, nitrogen and carbon dioxide. Oxygen, air, combustible gases and mixtures containing such gases shall NOT be used.
Exception: The use of air is ALLOWED to test R-717, ammonia, systems provided that they are subsequently evacuated before charging with refrigerant.
So whether your process is PSM/RMP covered or not, we can clearly see that refrigeration piping systems MUST be pressure tested (as well as leak tested). But as we can also see, compressed air is allowed as long as it is “suitably dry” AND the piping system(s) are evacuated after the testing.