PB Leaks & Excessive Product Loss

Yesterday was interesting.

Two of twelve 4LDOT cryogenic liquid cylinders tested at a client site had a combination of issues not commonly seen.

When liquid cylinders marked “bad” are returned trouble shooting is done to determine what (if anything) is “bad.” After initial visual inspection the next step is typically to put a little liquid nitrogen or oxygen into the vessel to build pressure and then leak check all up components on the vessel. This is necessary prep for NER or Simple NER testing.

Well, today while leak testing a dozen vessels, two were found to have leaks in the line between the Pressure Builder (PB) valve and the PB Regulator. This would normally not be noteworthy except for the fact that the PB isolation valve was closed on both vessels. Hence there was no way for pressure to hit this point in the line except for the fact that the PB isolation valve was obviously leaking by.

The net effect is excessive product loss that looks just like a vacuum problem.

See…. If the PB valve does not secure the PB vaporization line then liquid is allowed to leak into the line and vaporize. This liquid normally goes back into the top of the vessel creating excessive pressure. In the case of an external PB control line leaking this excess pressure leaks off. When doing an NER this would look like excessive vaporization requiring a trip to West Cryogenics for repair.

The trickiest thing about this particular issue is that neither of the leaks was apparent until the vessel was being filled with liquid. And the leaks were so small they’d have been hard to see during testing if the vessels were in a warm area.