Evaluating and Reducing the Risks Of Pneumatic Pressure Testing
In applications where pressure testing with liquids is undesirable, the risks of pneumatic pressure testing of pipes and vessels must be evaluated and minimized
Victor H. Edwards, Don Sanford, Brooke Bonstead and Larry Skoda, Aker Solutions Americas, Inc.
The pressure testing of process piping and vessels is essential in the chemical process industries (CPI). In liquefied natural gas (LNG) and other cryogenic facilities, residual water left by hydraulic pressure testing could result in operational problems if not completely removed, and complete removal of residual water can be very difficult and time consuming. Pneumatic pressure testing avoids these problems, and is frequently used for piping and vessels in which moisture is undesirable.
Hydraulic pressure testing with water, however, is much more common than pneumatic pressure testing with a gas because the stored energy of compressed gas can be roughly 200 times the stored hydraulic energy for the test pressures in the range of 100 barg. Therefore, rupture of a piping test system during a pneumatic pressure test can release much more energy. In applications where pressure testing with liquids is undesirable, such as in cryogenic piping systems and vessels, pneumatic pressure testing can only be justified when care in fabrication and in non-destructive examination of vessels and piping reduces the probability of loss of containment to such a small value that risk is acceptable. This article outlines methods for evaluating the risks of pneumatic pressure testing of vessels and piping, as well as methods for risk reduction.
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