NDT to piping that have been working over the MAWP determinated by ASME B31.3 3

[fernandomaggi]

thread378-415848
Hi, i m studing a piping installation designed according ASME B31.3 code. For some reason the pressure riced beyond the desing and the PSV failed to open.

The piping was working over the MAWP (+136%) for a while but without visual damages.

I need some std, code or general rules that determine the NDT or calculation necesaries in order to check the integruty of the piping.

I perform some calculation using the formula of ASME B31.3 to determine how far of the admisible tension the piping has been woriking.

The resulting working membrane tension (27.1 ksi) is grater (+37%) than the admisible tension for this pipe (20 ksi) but less than the yield strenght (35 ksi), asuming the worst esenario : the thikness reduccion due corrosion allowance and fabricaion undretolerence (12.5%).

For example:
Pipe 4" - Sch 40 - ASME SA106 -GrB
Working pressure: 995 psig
Temperarute: 90°F
Corrosion allowance: 0.125"
Resulting Tension: 27.1 ksi

Many thanks in advance,




​

 

[1503-44]

Assuming Cyclic stresses or thermal damage did not occur to the material and if pressure stress did not exceed the elastic limit, deformation is not permanent and geometry returns to previous form (perhaps minus some hysteresis effect). If you can shows some inelastic deformation remained, then recalculation of a new MAWP based on permanent remaining wall thickness may be in order.

Some practices might even treat this as simply a "pressure test during operation", possibly even providing a reason for uprating the MAWP. The pipeline rating procedure for pipelines not recently, or even never hydrorested, often have a provision for pressure rating by determining MAOP/MAWP based on the highest operating pressure experienced during the last year of operation.

Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[The Obturator]

You stated "....the PSV failed to open..." are you not more concerned about this? a device which is the last line of defence against life and property?


*** Per ISO-4126, the generic term
'Safety Valve' is used regardless of application or design ***

*** 'Pressure-relief Valve' is the equivalent ASME/API term ***

 

[r6155]

1) @ The Obturator
My star for you.

2) See Acoustic Emission Examination in ASME V to check integrity.

Regards

 

[XL83NL]

136% of MAWP? Or 36% over design pressure (or perhaps set pressure of the PSV)? They’re completely different things. MAWP is uncommon in piping but more for vessels. A pipe usually has a much larger over the design pressure before it reaches its ‘MAWP’. That margin may be of importance here.

Huub
- You never get what you expect, you only get what you inspect.

 

[1503-44]

I would imagine the high pressure problem has been solved and he is just contending with possible after effects, but we actually don't know if it was a PSV malfunction, incorrect setting, or what is often the usual case, a closed block valve in front of the PSV.

Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[Krausen]

MAWP is technically a ASME Section VIII term used for pressure vessels only. In this case, you overpressured B31.3 piping beyond it's design pressure at pretty much ambient temperature. The piping should have been hydrotested to at least 1.5x the design pressure at ambient temperature before it was ever put into service, so it's no surprise the piping held up to this. Based on your data, the pipe remained under it's minimum required yield strength (in hoop stress) during this excursion. Did your system have any flanges or other limiting components in it that were also overpressured with the A106B pipe? Typically your "weak link" in most pressure piping systems are your bolted flanges, which can be visually or LDAR checked for leaks when overpressured.

 

[r6155]

@ fernandomaggi
Your numbers are wrong. You must calculate the stress with the actual thickness of the pipe.

Regards

 

[LittleInch]

Try looking at Appendix V of ASME B 31.3. Whilst tha tis about temperature you might be able to use it for pressure.

But at this sort of overpressure (i.e. less than the hydrotest), you simply need to do an engineering assessment and physical check of the system.

It almost certainly hasn't yielded anywhere so no real NDT to do.

But you need to find out how it happened, why it happened and what is being proposed to ensure that as far as possible it doesn't happen again. Like why did the control and safety systems allow this to happen? Procedures and operator awareness are not reliable enough to be used as the means to protect piping systems.

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