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 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. 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.

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