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Valve passing at site 1

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onrush

New member
Aug 22, 2004
58
Dear members,

Based on API 589 closure test requirements, some passing (leakage) is permitted during manufacturer shop closure test.

However what about the passing at construction site during line hydrotest?
Is there any international code or standard for that case?

You know that the test pressure during line hydrotest at site may be lower than that during shop closure test.

Thanks in advance..

 
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onrush,
I'm not aware of any International Standards dealing with line hydrotests of newly constructed plants (and I would be curious to read one...), but I believe every Engineering and End-User Company has own its own Specification.

You will not find an answer to your specific question, but you can probably read some stimulating hints about the same subject within thread408-150132.

Regards, 'NGL
 
You should not be hydrotesting against valves during line hydrotesting. This is for verifying welds and other joints, so valve performance is not addressed. Xalves are normally removed or partially opened. In general, valves are only required to pass a test in the works. Years ago, an experienced (ball) valve designer and manufacturer told me he worked in the best business in the world - his product only has to work once (during the works test) and thereafter should always be assumed to pass.
 
Thanks, BillBirch

These valves are block valves to be installed in inlet of spare-pumps. It means that these valves are normally closed. What about this case? In this case, should the blank be used instead of valve?
 
Yes, blinds should be used because the test pressure is way above the capability that valve seats are expected to achieve.
 
BillBirch is right. I am a valve designer and we test and design our valve to seat at 110% of rated pressure (MSS SP 61 section 4). The valve shell is designed to meet or exceed 150% (Same standard section 3) ANSI B16.5 also requires the "flange fittings" to pass a 150% rating test (section 8.3), but that will only be against the shell also.

Many system hydro tests are done at 150% rated and will lift (open) the seats on most of our valves (some are over designed). Likewise, other valves from other valve manufacturers if they are building to the same standards will also have their seats lift or open.
 


I will echo the previous posts for EN standards and confirm the viewpoints presented.

There is always a limit to what the valve manufacturor will allow as maximum for a valve at a line test. This is partly given by the valve standard, wich will be higher for the housing (open valve housing test 1,5 times pressure class (or more depending on pressure class, dimension and producer and valvetype)) than the seat (operating pressure equal to pressure class normally 1,1 times (again also depending on valve type - for instance will often smaller valves (ball valves for instanca) over-qualify) on allowed seat pressure.

Under line pressure tests there is always a risk of something malfunctioning and giving water hammer, which in addition to overpressure of seats can damage (permanently) the valve sealing or valves.

Generally: blinds should be used and all valves be left open under line tests.

Or (the world is not always ideal) if valves are closed under line-tests, all care should be taken, the valve manufacturor to allow in writing the given pressure.

Two buts: For some types of resilient seated gate-valves for instance, a somewhat higer seat pressure will have less impact than for other constructions.

Secondly: anything going wrong and valves not operating properly or leaking after a (too high) test the responsibillity and guarantee that everything was done properly lies on the test executing side.



 
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