SHELL PRESSURE TESTING

SHELL PRESSURE TESTING

An aspect of pressure testing that has only become apparent in the past few years is the requirement to perform a 10-minute shell pressure test only on valves and fittings. The odd part of such a test is that the client only seeks a shell pressure test, not seat leakage testing. This would seem to imply that valves will be going into a piping system and that the client wants to meet the 10-minute pressure test requirements of ASTM B31.3 for process piping. Some clients have even requested testing forged flanges and fittings with a 10-minute hold.

A misconception of this test is that the fabricator still needs to perform a full shell pressure test on the piping system as a whole to ensure joints and connections are examined for leaks. Valves manufactured to meet ASME B16.34 will have a factory pressure test done that ensures the valve itself is leak tight. Most American Society of Mechanical Engineers (ASME), American Petroleum Institute (API) and Manufacturers Standardization Society documents that apply to valve pressure testing have much shorter test duration than process piping standard B31.3. In some cases though, depending on the test standard the valve manufacturer follows, the valve may meet or exceed the 10-minute shell pressure test duration. An example would be valves 12 inches in diameter and larger that are factory pressure tested per CSA [Canadian Standards Association] Z245.15.

The problem rests in the interpretation of the ASME B31.3 code—in particular, in the following areas:

The second paragraph within ASME B31.3, 326.3 states “The design, materials, fabrication, assembly, examination, inspection, and testing requirements of this Code are not applicable to components manufactured in accordance with the documents listed in Table 326.1, unless specifically stated in this Code, or listed document.” This poses the question: would a valve manufactured to meet the requirements of ASME B16.34 and pressure-tested at factory to API-598 criteria be exempt from a pressure test required by ASME B31.3? The answer is “yes,” in the context that the valve would have been tested to ensure no body seat leaks and no atmospheric shell leaks at the factory to meet the design criteria requirements of B16.34. However, the answer is “no,” in the context that paragraph 345.1 of B31.3 states that “each piping system shall be tested to ensure tightness.” Furthermore, Paragraph 345.2.2 (a) states “Examination for Leaks. A leak test shall be maintained for at least 10 minutes, and all joints and connections shall be examined for leaks.” The only way to satisfy this requirement would be to have the spool pressure-tested by the fabricator with the individual valves, fittings, pipe, etc. assembled as a complete unit and then pressure-tested as a whole to prove that the component joints (connection ends) are free from atmospheric leaks.

To conclude, a customer that wants to do an additional 10-minute pressure test on a valve to ensure no atmospheric leaks at an extended duration time compared to what the factory would have done is no problem. An extended duration test, however, does not relieve the fabricator from the requirements of ASME B31.3 to prove that the final joints and end connections that connect the valve to the piping system are to be examined for leaks. This growing trend towards such testing shows that users are increasing efforts to prove functional assurance of components provided through global supply, not to imply replacement of final testing required by ASME B31.3.

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