Piping Systems testing. It's not th 1

[Tuga29]

Piping Systems testing. It's not the best practice, especially with ball and gate valves, but there is any standard that doesn't allow to pressure test against valves? ASME B31.3 345.3.4 seams to allow that. Can you please give me some points of view regarding this?

 

[LittleInch]

Depends a lot on the pressure and the ability to quantify any leakage through the valve.

Most valve seats are only qualified for Max design pressure as stated on the valve data sheet plus 10%. Many piping tests are max pressure plus 50%. So your seals may not handle the pressure.

All pressure tests test against valves in the pressurisation pipework, but normally you try and rate these valves much higher than the test pressure and they are normally only small bore valves.

Standards and codes tend not to say things like "Don't do it this way". Company standards and procedures can do that, but then often allow deviations if authorized.

Your call based on your particular requirements and ability to monitor any leakage through the valve. Or try it and see if the valves hold.


Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[mk3223]

It's not the best practice, especially with ball and gate valves, but....

Where is the "best practice" as mentioned from?

The B31.3 345.3.4 is related to the "Limits of Tested Piping" which states the needed proper isolation, such as valve or blind, to separate the tested and non-tested sections.

The isolation valves are part of the piping system per B31.3, either ball of gate. They should be the same pressure rating, and tested with the piping as a whole system.

 

[DekDee]

I will stress I am not an engineer so please take that in to account.
However, I have been involved in hundreds of hydrotests so can comment on that.
Testing against a valve should be a last resort, valves should be set open and the line isolated by blind flanges.
If you must test against a valve then mk3223 has replied to that.
Regards,
Shane

 

[Tuga29]

Thank you for all your answers. It's clear for me now.

 

[Ehzin]

To elaborate on small bore valves... As mentioned briefly, small bore valves can often be overrated compared to the rest of the system. If you have a 150, 300, or 600 class system they'll still likely have their small bore valves be 800 class if they happen to be socketwelded or threaded. Meaning they're rated around 1975 psig if A105 or similar. If your large bore valves happen to be flanged then you can simply blind those and then the small bore valves are much higher in comparison and can handle these test pressures. As an example, an 800 class valve should be able to handle a differential hydro of approximately 2170 (1975 x 1.1) psig while a 600 class system would be tested to 2220 psig (1480 x 1.5). This would mean, even with the 600 class system, you would only be testing the small bore valves up to 112.5% versus 110% of their rated pressure. It'd be up to you to decide if this additional percentage could lead to seat issues for your small bore valves. Otherwise open them and plug them if they're bleeds or find another isolation point. For 150 and 300 class systems, testing across 800 class valves would be a non-issue.

Thanks,
Ehzin