Purpose of a hydrostatic testing- Validity 1

[srijey]

I've read serious furore over the purpose of such pressure testing, calling or guessing it as strength, full stress, proof, integrity, load test, confidence, second NDE, simulation, mock-up and so on. My question is towards a paper submitted by a Japanese company in one of the Pressure Vessels and Piping Conferences. This paper claimed that hydrotest did not support: structural adequacy of transient loading condition, local yielding helping/blending (autofrettage)stress risers, increase (deformation) weld flaws, and couple of more 'supposed' merits of a hydro. I wonder what happens to such claims/ papers in ASME. No doubt, this age-old practice is very much supported by industries. When considering the exemptions available in codes such as for golden welds (100% RT), I do think that there is room for 'thinking' to change. I know it's very difficult to prove that - 'just because we did not perform a hydro, there was a failure'. My purpose of this post is to know what could go wrong if I don't perform a hydro where I'm supposed to do? When any NDE is performed, we come out with a report saying that there is no defect of this nature present in this area. We also agree that a hydro test is not a leak test. Now, it's the question time: After a hydrostatic testing, are we supposed to feel/say that this equipment is free of..........?

 

[metengr]

No, not for final construction of boilers or pressure vessels. The problem is this, hydrostatic testing will most likely never be revoked because it does provide one useful purpose, and that is to check for defects missed during fabrication. It is relatively easy to perform, and it has been used since the early 1900's. Code committee members have developed a position that hydrostatic testing is a final backstop to ensure no gross defects in pressure retaining items. Volumetric NDE can miss flaws. I agree that hydrostatic testing will be here to stay in ASME B&PV code. In repair code space, like the NBIC, that battle has been won regarding limited usefulness of an in-service hydrostatic test.