disassembling (relief,gate)valves for water and swerage valves 2

[enas]

according to the complaints of a client of the finishing of double relief and gate valves, we had to disassemble the valves completely , the question is:

**should we test the valves again hydraulically to make sure of the testing pressures or what kind of tests we should do it again and if so should we do it for all the number of the valve or just a sample?

**I should check the quality of the valves(butterfly, nonreturn check valve, gate, relief valves) after the hydrulically testing and painting stage and before the clients check it so
is there any guidance for this checking process and what defect that affects the functional of the valves and the degrees of the defect.(ex. a small fracture in the bonnet away from the holes that is covered in the painting and sometimes we exceed the tolerance of the distance between the flanges)

what problems that I should make sure that it doesn't exist

how can I check the valves, just by opening and closing it?

thanks in advance
enas

 

[JimCasey]

If there is any question about cracks you should run a dye-penetrant check on the pressure-retaining components while the paint is off. If you machine the body to a dimension outside the tolerance you need to build the body back up with weld metal if it is weldable oo scrap the casting.

Once you assemble the valve you should run a hydro (shell) test to 150% of the MAWP ( 427 psi for a class 150 valve, 1110 psi for a class 300 valve, etc.) with the valve OPEN and correct any leaks found. See ANSI B16.34 for specific ratings for different materials. Gasket and packing leaks are easier to correct than pinholes in the casting. Repair/correct any leaks and retest the valve until no leakage hrough the pressure boundary is observed.

Then close the valve and do a seat leak test to the procedures dictated by whichever standard is applicable: API 6D, FCI70.2, MSS SP61 are a few standards.

Relief valves are a different critter, and they have to be tested for opening pressure, lift, and seat tightness. If they are steam valves they have to be set on steam. Gas valves can be set on compressed air, and liquid valves can be set on water. Refer to ASME section VIII for safety-relief valves or ASME section I for Safety valves (on fired pressure vessels)

All these standards I have referenced are USA standards. If you are not in the USA, local standards may exist that apply to the situation.

 

[khan101]

Well done Jim