I would like to know the shop procedure for hydrostatic test butt weld end valve as per API 598. This procedure should be more difficult than flange end valve. Do the manufacturer weld and cut the spool after pressure testing? Do they carry out PWHT after testing low alloy steel valve body? Anyone who has experience in valve factory please advise me.

In general a test bung with an 'O' Ring is used and the bungs on both ends of the valves are clamped together before applying pressure. This is very effective and proven methodology.

Also, for buttweld end valve, since radiography is mandatory the standard allows you to offer them as special class valves with higher working pressure. Refer ASME B16.34

This is the information I got from a hectic web search.Hope it helps!




INSPECTION AND TESTING:-
For a individual valve to be pressure tested to API 598/BS 6755 Part 1 requirements are:-

TEST PRESSURES FOR STANDARD VALVES
ASME      *    Hydrostatic test pressure            
CLASS    
           Shell     BackSeat      Closure   
    
150   psig    450     315            315        100    
      kg/cm?    32     22             22        7    
300   psig    1125     815            815        100    
      kg/cm?    79     57            57          7    
600   psig    2225     1630            1630        100    
      kg/cm?    156     115            115         7    


The last column values are for pneumatic low pressure closure test.

Low pressure test for Swing Check valves:
In addition to the high pressure closure test, Swing Check valves are subjected to low pressure hydrostatic closure test at a pressure of 25% of the high pressure closure test The duration of the test is the same as for the high pressure closure test.

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