With the owner’s approval, an alternative leak test is permitted when neither a hydrostatic nor a pneumatic leak test would be possible or safe. An alternative leak test contains the following required elements:
- A detailed inspection of all weld joints, including 100% radiography of all circumferential and longitudinal seam welds and liquid-penetrant or magnetic-particle examination of all welds, including structural attachment welds, that cannot be radiographed
- A formal flexibility analysis
- A sensitive leak test
A sensitive leak test is required as part of an alternative leak test and for Category M Fluid Service piping. This test is performed at low pressures to check for leaks. Methods for performing this type of test are described in ASME BPVC, Section V, Article 10. One approach is pressuring the piping system with air and checking for leaks using a bubble test solution.
The test pressure for the sensitive leak test is required to be at least 105 kPa (15 psi) or 25% of the design pressure, whichever is less. Similar to a pneumatic test, the pressure is to be increased gradually up to an intermediate hold at the lesser of one-half of the test pressure or 170 kPa (25 psi), at which point a preliminary check for leaks must be made. The pressure is then gradually increased to the test pressure, at which point the sensitive leak test is performed.
In addition to the above Code-required circumstances, a sensitive leak test is used by some owners as a supplemental tightness check of other piping systems prior to placing them in operation and/ or to check for leaks in piping systems assembled from shop-fabricated and tested subassemblies.