Pneumatic test of Piping with pressure vessel as a System 1

[skasliwal]

Guys, I am trying to confirm if para 345.4.3(b) of ASME B31.3 "Hydrostatic test of Piping with vessel as a system" applicable to Pneumatic testing as well.

My situation is relief valve and the associated piping is rated for a much higher pressure compared to the pressure vessel it is connecting. Our plan is to pneumatically test the valve/piping assembly separately by blinding off the open ends and then after connecting to vessel (pneumatic)test the joint at vessel test pressure. Based on Para 345.4.3 (b) of ASME B31.3 it seems this is acceptable for hydrotest but the pneumatic testing does not go over this subject. So I was wondering if anyone has any experience.

Separately, Since the piping and vessel are each tested individually, wouldn't this joint be exempt as 'closure weld' if it meets the requirements of B31.3 para 345.2.3 (c) ?

TIA

 

[moltenmetal]

You need to express your question more clearly so we can provide more accurate advice.

Pressure tests don't need to be done to the true MAWP of any piping system. They may be done to demonstrate a MAWP which is lower than the true MAWP. There is no need to demonstrate a MAWP for piping which is higher than its relief pressure, unless there is a case where relief is not expected to be fast enough or large enough to be protective.

If you have a flanged spool attached to a vessel, intended to convey fluid to the inlet of a relief valve, you can take it off and bench test it hydrostatically or pneumatically, and you may set that test pressure to demonstrate a MAWP anywhere from the setpoint of the relief valve to the full limiting MAWP of whatever would fail first- flange, pipe wall, valve body etc.

If your pipe is attached to the vessel by welding, you have a closure weld situation- you can choose to inspect that last weld either by hydrostatic or pneumatic testing or via stringent NDE and a sensitive leak test.

If this is indeed piping on the inlet to a relief valve, you don't need to demonstrate an MAWP for that piping any higher than the setpoint of the relief valve, unless the relief valve may be set to a higher pressure at some later date. Unless the relief valve setting is lower than the vessel's MAWP, how that would happen in future is a puzzle to me.

 

[skasliwal]

Thanks MM for your response.

Yes the pipe is attached to vessel by welding and as such 100% UT/RT of the closure joint per para 345.2.3(c) of ASME B31.3 to qualify/test the joint. I was trying to confirm if the joint meets the definition of "Closure Weld".

Secondly, if one were to argue that a testing of the joint is required.....

As I mentioned in my original post the line is rated for "X" psig and the vessel is rated for "Y" psig (X being >Y). Blinding off the vessel at connection weld is impractical, so the unit will need to be tested as a system (vessel + piping). Now obviously we cannot test the system at higher piping test pressure (Test pressure for "X")as the vessel will typically fail. So the has to be tested at lower vessel test pressure(Test pressure for "Y") to test the joint. The line itself can be tested for higher pressure before the weld is made to qualify the line components. This seems to be an ok solution per Para 345.4.3 (b) of ASME B31.3, under required hydrotesting for pipes with vessel as a system but the pneumatic testing section does not go over this subject. So I was wondering if same interpretation can be applied to pneumatic testing as well.

Hope this makes it clear. In any case, from your response, I think the joint meets the definition of closure weld and so 100% RT/UT should be sufficient to test the joint without having to pneumatically testing it.

 

[moltenmetal]

It's not just 100% UT/RT but also a sensitive leak test, unless I misremember which is definitely possible.

 

[DekDee]

No requirement for Sensitive Leak Test but In-Process Examination is required,
Cheers,
Shane

 

[LittleInch]

You seem to be hung up on "rated pressure"

The pressure you need to consider is either design pressure or MOP which is the pressure used for pressure testing.

If your pipe is connected without segregation or pressure control to a vessel with pressure rating Y, then there is no benefit and no purpose in having your piping design set to anything different so long as it is = Y.

B31.3 uses MOP as its reference point for test pressure.

The line list should detail all this.

I note you're trying to pneumatically test the vessel? Take care and hope you have considered the consequences of vessel failure under test. This can be catastrophic.



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.