Hydrotesting Requirements of B31.3 5

[kbob]

I have a hydrotest problem. We have a tubing spec. with a design code of ASME B31.3 designed for a maximum pressure of 15,000 psig. We have successfully hydrotested our system at 22,500 psig. (1.5 times design) for several of our systems. However, one system uses Kalrez seats in the valves. This systems consistently leaks when we exceed 20,000 psig. No permanent damage is done to the system. When we drop the pressure below 20,000 psig the system does not leak. My question is: How can we accept the system as is? I do not see that B31.3 allows us to hydrotest at any pressure other than 1.5 times design.
Other input/ assumbptions:
1. Valves are not welded in place.
2. It seems the code allows reduction in hydrotest pressure when the yield stress is to be exceeded. I assumed this does not apply to the soft goods in the valves.
3. System is a chemical injection pump discharge with a normal operating pressure of 12,500 psig (Set by recycle regulator)
3. Pump discharge PSV set at 15,000 psig.

Any help would be appreciated.
Thanks

 

[bvi]

The leak test is with respect to the pressure boundary, not the valve closure element, and valves are not necessarily suitable for carrying the full hydrotest pressure across the disk, seats, etc. It appears that you are using the valve to withstand the full hydro across the closure element. This is not necessarily a requirement of the valve design, nor the piping code. As a result, when hydrotesting piping systems, valves may not be suitable for being the end points for system hydrotest.

 

[SooCS]

Valve body are normally hydrotested and is normally not tested with the piping system and if it is, the system would be tested with the valve open.

Valve leak you refer to if it is from the valve seat and is internal, that's normal and the valve standard allows certain leakage code. Your are lucky if you can test the valve at 1.1 x Max. OP without leakage.

 

[zdas04]

If the test ends at the valve, put in a blind and test with the valve partially open (to prevent high dP across internal valve components). As has been stated above, there is no requirement for the valve to not leak through at test pressure (there may be a requirement that it not leak to atmosphere through a packing gland, but it doesn't sound like you're having that problem).

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

 

[kbob]

B31.3 Hydrotesting. 15,000 psig. Clarification. The valves were hydotested in the open position. The valves were leaking through the stems. Thanks for the responses so far.

 

[bvi]

try tightening the packing. There isn't an exemption for packing with respect to satisfying the leak test requirements.

 

[davefitz]

As I recall, B16.34 ( valves) does not permit overpressure above 10% above rated pressure. This limitation was added circa 1988.

 

[reichertc]

My understanding of the code is that "a leak test shall be maintained for at least 10 minutes, and all joints and connections shall be examined for leaks." (345.2.2.a) Where does it state that leakage may not occur through the packing of a valve?

 

[JohnGP]

Valve spec is not stated, but if it is one referenced by B31.3 then testing requirements of B31.3 are not applicable (para 326.3). Design pressure of the system seems a bit high for B16.34 valves, but using that standard as an example, during valve hydrotest "leakage through the stem packing shall not be cause for rejection" (but seals must not exhibit leakage at the 100degF rating).

I can sort of understand the logic.