Possible Violations from ASME SEC VIII by some Engineering standards

[Sawsan311]

Dear All,

I would like to enquire on the following: some Engineering standards allow considering accumulations as high as 130% as corrected hydrotest pressure for scenarios identified as ''remote contingencies''. Example of those are possble but remote scenarios such as pinhole tube rupture heat exchanger failure, or gas blowby with liquids swelling etc.

Considering PSV would be mandatory required by ASME SEC VIII UG-125 code (unless UG-140 system design has been followed for mitigating, eliminating or reducing the PSV), do you consider that if we size the PSVs for the above remote contingencies for overpressure/accumulation more than 10% for non-fire scenario and consider instead corrected hydrotest pressure for estimating the relieving pressure- This would be a VIOLATION of ASME UG-125 which specifies the code allowable accumulation for PSVs as the sole overpressure protection measures? do you think that in case tube rupture is found credible (due to low pressure side corrected hydrotest pressure < high pressure side design pressure), will we still have to consider 110% accumulation for this PSV sizing or 130% as corrected hydrotest pressure?

Thanks

Regards,

 

[The Obturator]

You seem to be mixing hydrotest pressures with pressure relief valve overpressure requirements (accumulation is pressure increase in vessel). ASME VIII Non fire, single PRV requirements are 10% overpressure above the set pressure (set pressure is normally the MAWP). Please clarify what you are asking.

Per ISO-4126, only the term Safety Valve is used regardless of application or design.

 

[georgeverghese]

Tube ruptures and gas blowby are, in my opinion, not remote scenarios. Tube ruptures can occur as a result of corrosion inside or on the outside of the tubes, which is rather common. Even more frequent are leaks at tube to tubesheet joints on shell and tube HXs'. Gas blowby can occur from poor level control and sudden loss or reduction of feed liquid phase flow.

 

[Sawsan311]

Thank you The oburator and Mr.George

I totally agree with both of you that irrespective to the overpressure scenario, compliance with the code accumulation of 10% is mandatory for non-fire cases.

You might be surprized to know that some Design standards can allow considering the accumulation as 30% instead of 10% for scenarios which are remote but possible such as heat exchanger and gas blowby with liquid displacement. This is for PSV sizing and not only for deciding on the elimination of a scenario i.e. for example the 10/13th rule which is only coming for the corrected hydrotest pressure.

Regards,

 

[The Obturator]

Interesting. Please advise on the standards you refer to.

Per ISO-4126, only the term Safety Valve is used regardless of application or design.