Check Valve Leakage Acceptance

[Xianglu]

We have a few ball check valves with SW ends. The valve body and the piping are heat treated after welding. Now the check valves seem not seal. Would anyone advise the acceptance criteria for the leakage rate of the valves?

Thanks,

Henry

 

[GrimesFrank]

Henry,
Thats a subjective question.
Personally I detest backflow on a check valve, its not really serving its function is it?
I have however seen plants leave ball check valves in with contaminants in the seat causing backflow for periods and didn't seem to care.

You need to look at time, cost, application, and decide.
I've had SW ball check valves installed and not had a problem with internals.....what makes you think the heat treat casued something?

Frank "Grimey" Grimes
You can only trust statistics 90% of the time.

 

[zdas04]

It is really subjective. The big question is always "why is the check valve there at all?" If the answer is "to prevent spinning a centrifugal pump backwards" then you can possibly accept quite a bit of back flow. If it is there to protect low-pressure piping from attached high pressure piping during an equipment outage (e.g., the compressor valves on a recip compressor), then you can probably accept much less back flow. Ask the question and evaluate your backflow based on the answer.


David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

The harder I work, the luckier I seem

 

[JLSeagull]

Check valves leak.

 

[Xianglu]

The check valves are for preventing back-flow of water or hydrocarbon condensate from header to the pressure vessels.

 

[dcasto]

I had the same thing on a amine contactor where they installed the check valve at the contactor. I kinda like it there versus at the pump 100 yards away. If there was a line failure, the sour gas would not back flow to the pump area AND the gas fired heater area. The contractor didn't install a check valve on the pump. That rubbed me and my common sence, but I was over ruled. Two weeks after start up, a line failed near the pump, the SW ball check seat was warped and we sent gas back to the pump area which ignited from the heaters.

My new rule is, piston checks at the pumps, keep the check at the contactor, AND NEVER EVER use a SW check valve.

PS, I kept my objection letter and was spared a horrible death and I got all the funding I needed when I rebuilt the system.

 

[zdas04]

Xianglu,
I didn't ask because I wanted to know, I posed a question that you need to answer for your process. If you have backflow from the header to the vessels, what bad thing happens? If it is a lot of backflow is the bad thing worse?

All check valves leak some, the acceptable magnitude of "some" is something that needs to be assessed based on your facility. We just can't do it from our desks all over the world.

I'm with dcasto that SW checks are pretty dumb, but they go in all the time--company specs don't like threads or small diameter flanges.

David

 

[Xianglu]

Thank you all.

To further clarify, these valves are installed on the vessel maintenance drain lines. They are all 1-1/2" CL800.

My main concern at this moment is that if the leakage is the result of PWHT which may have damaged the valve seat. If a small amount of leakage is the nature of this type of check valve, I will accept the current condition.

 

[FACS]

First, how did the valve perform before welding and heat treating?

Did the welding cause debree, and thus lodge in the seat?

Did the welding damage the seal? I would think so.

Test a virgin valve, see how it performs before welding and heat treating. If it performs well, then you may want to test it after welding to see if it damaged the valve. Welding can melt a seal and or deform the metal so that the geometry no longer lets it seal correctly.

Charlie

http://www.facsco.com

 

[dcasto]

In support of Zdas04, you have to perform a risk assesment. What are the probabilty of small, medium, large leaks versus the consequences of small medium large. If the leak was like I described, a (relatively) medium size gas leak meant a big disaster. If its just water back feeding or draining a vessel, I'd accept the risk. You state these are on maintenance lines, the probability of leak is small if there is a hand valve nearby (an assumption or better yet a must). In this case I'd look at a carseal on the maintence valve to get close to zero leak while in operation and then a permit to open hand valve and a proceedure to assure that you do have a leak while in the maintenance mode.