I think the pressure test is still needed even if not seeming to serve any useful function other than verify that a component will hold a certain pressure at that moment in time and keep the AI happy. Two of our biggest contentions was with high pressure jacketed pipe, we could test all day and not replicate inservice thermal expansion and the procurement for Cl free water for testing large SS vessels in intricate internals. The vessels always had to be tested at the fabricators with no good water and we had 3 sources of water on site. But being a requirement by the code and standards we had to do it and do a good job while doing same. It is just a little insurance.
I agree with the your statement other than to say the pressure test is just another step in the quality assurance program. I think that the emphasis should be on the QC up front as you state instead of depending on the hydro to tell what quality component we have. This seems to be the trend as I hear all the time: “Why worry we are going to hydro”, and then can’t do the pressure test correctly. I’ve seen more time and effort getting a system or pipe spool ready to test than the actual test including hold time.
We have been fortunate over the years in having very little equipment mistreated during fabrication or operation where a pressure test would have shown anything.
By doing the work up front as you state it would seem that pressure testing is redundant. Like wise I've seen some partially completed or corroded welds, very poor castings, and so on pass a pressure test. In 50 years of being around pressure testing I personally have never seen a failure at the pressure boundary on newly fabricated equipment from a pressure test. I have seen pictures and done failure analysis on other people’s failed components, not many, but enough.
I have seen a couple of rips on in-service equipment that was known to have corrosion problems and a few on new heat exchanger tubes.
We had the case of the unwelded long seams on SS pipe by a particular manufacturer that caused us a lot of grief. None of the defective pipe has ever showed up on a pressure test at fabrication or during a leak test at 1.1x during outages prior to starting up. We actually tested several failed sections up to the point where we would should start deforming the pipe and still no failure.
We either discovered it on visual inspection, during welding, or by inservice failures. More of the latter.
The only time I”ve see a pressure test help evaluate a vessel was in the evaluation of two Horton Spheres in anhydrous NH3 service. It was only effective due to being used in conjunction with Acoustic Emission testing equipment.
With all of the above said, I still think we should carry on as prescribed by the Jurisdictional Authorities. I don’t think with the liability situation as it is today I wouldn’t deviate from the proscribed procedure unless it is chiseled in stone, 3 duplicates.
.
Pressure testing still has to be done properly with direct control of someone so that the testing procedure in itself is safe.
My main concern has been and is for personnel safety as the equipment can be repaired or replaced.