Hydrogen leaked through threading of equalizing valve of three valve manifold. The washer of the equalizing valve was found damaged. It is in service for last 10 years. Could not guess the reason for damage to washer of only equalizing valve. Washers of other two isolation valves were found intact. Any one has experienced such leakage. How to maintain these manifolds?

 

It would seem the issue is most likely of one of two possibilities, and may even be a combination of the two.

First, that people operating the equalizing valve have been applying too much pressure/force when closing the valve.

Second, the packing/seal was improperly installed and/or was of lesser quality to begin with (poor manufacturing; porous material; wrong dimension; etc.).

It's likely some combination of the two. I have personally seen people who were terrified of natural gas and hydrogen excessively <b>cranking</b> down on manual valves in the systems, to the point that the valve stems broke. Their "training" consisted of being told the gas was explosive and that they had to be certain to fully close the valve(s). To repair/replace the valves, the turbine-generators had to be shut down and purged, causing a lot of lost generation (and revenue). Sometimes training is very important, and if people are so distrustful of valves in such service then a double block and bleed system can be employed (in some circumstances). Most block-style three-valve manifolds in instrument service I have seen use needle valves and they don't require excessive force to close, and some require them to be fully open to back-seat to prevent leakage (in other words, they can't be left partially open in service or gas can leak out along the valve stem).

Another possible issue could be that the manifold was not designed for hydrogen service. Have you confirmed the manifold is suitable/designed for service in a system with hydrogen gas?

As far as maintenance, many times items get added to outage work orders just because of failures like this. Hopefully no one was injured and damage was contained to a small area. Does the manifold manufacturer have a recommendation for maintenance intervals?

 

I suspect that this was a small leak that developed into a bigger leak over time.

If you want to find the small leaks so that you can fix or replace the seals/equipment, you can hunt for hydrogen leaks with a portable probe on a thermal conductivity gas detector/sniffer. The technology is not gas specific (it is not specific to hydrogen) but it can be sensitivity adjusted for hydrogen.

 

Thanks for your reply. Your guess is correct. We checked other high pressure DPT installations with a soap solution and found equalizing valve having minor leaks.

Thanks once again.

 

Thanks for your reply. I did not think of "Human" factor involved. We further investigated other DPT installations with high pressure gas service. We checked for leaks by spraying soap solution at possible leakage points and found minor leaks at equalizing valve threads. As suggested by you, we need to work out maintenance strategy for manifolds.

Thanks a lot.