JIP33 Hydrotest Stress Limit 3

[pron_to]

Hello - want to ask your opinion: JIP33 contains the statement that the primary membrane PLUS primary bending stress in any pressure containing component shall not exceed 95% of the material min. yield strength during hydrotest. Is that right? I am used to the requirement for the max. membrane stress not to exceed 90-95% of the min. yield strength (for the ferritic steels)and 100% for austenitic steels. Never came across the requirement for the combined stresses limit.

 

[BJI]

Can you be more specific about the reference, in IOGP S-619 April 2022 Version 2.0, clause 4.1.5 states the following:

During the hydrotest, the general primary membrane stress in any pressure part shall not exceed 95 % of the material minimum specified yield strength.

 

[pron_to]

JIP33 Specification S-710 (June 2020) Supplementary Requirements to API Standard 661 Air-Cooled Heat Exchangers Para. 10.2.7: "If not specified in the design code, the primary membrane PLUS primary bending stress in any pressure containing component shall not exceed 95% of the material min. yield strength during hydrostatic testing". This is first time I came across this requirement. What do you think about that?

 

[BJI]

Since box headers are often involved, designs are based on membrane plus bending stress. I guess they wanted to make it clear that all primary stresses are to remain below yield.

Not sure if it factored into the decision making, but if hydrotest pressures were only limited by membrane stresses, aside from the risk of GPD, box headers may also be susceptible to local failure at internal corners.

 

[TGS4]

This is not a reasonable requirement, considering that, in most design codes, at the design pressure the Pm+Pb is permitted to go as high as yield.

VIII-2 has a much higher limit in 4.1.6.2.

 

[BJI]

Agreed, for M+B a limit above yield would be more appropriate.

 

[SJones]

“If not specified in the design code”

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[BJI]

If not specified in the design code

Then this recommendation would apply to box headers designed to ASME VIII-1 Appendix 13. Not an issue for VIII-2. I doubt there was a specific reason behind this conservative limit.

 

[TGS4]

BJI is correct - there is no limit in VIII-1, so this would apply to air cooled heat exchangers constructed to that Code.

 

[pron_to]

JIP standards is a product of collaboration of many entities - so I assume there must be a reason for this very conservative approach. In comparison, in JIP33 S-619 Specification for Unfired, Fusion Welded Pressure Vessel (para. 4.1.5), the requirement is more aligned with what I am used to: "During the hydrotest, the general primary membrane stress in any pressure vessel part shall not exceed 95% of the material min. specified yield strength". Is potential local failure at the corners of the header box due to M + B stresses exceeding 95% of min. yield strength during hydrotest a real concern?

 

[TGS4]

I'd need to discuss with the S-710 members what exactly they thought they were trying to achieve with such a stipulation/limitation.

 

[pron_to]

TGS4 - at your earliest convenience, thank you upfront!

 

[r6155]

Can anyone tell how to check the actual stress during pressure testing?

Regards

 

[TGS4]

r6155 - It's a calculation performed prior to the actual pressure test. In VIII-2, see 4.1.6.2, or 5.2.2.5, 5.2.3.6, or 5.2.4.5.

 

[r6155]

@ TGS4
Come on, you know I know the math. But how can the inspector verify that the stress limits are not exceeded during the pressure test? Calculations are not a guarantee.
Do you have a proposal for a suitable system during pressure test?. Don't tell me a pressure gauge.

Regards

 

[TGS4]

pron_to - it appears that this is an error. Feedback is being submitted to JIP33 regarding this error. I have no idea how long it takes to fix these types of errors.

 

[TGS4]

r6155 - It is not for the inspector to verify that certain stresses are not exceeded during the pressure test itself. The goal is to not have excessive deformation. The calculation limits are intended to provide some limited assurance that such excessive deformation will not occur. Beyond that, the only control is the pressure gauge.

If the pressure test is simply the minimum value required by Code, then the design margin for normal design is usually adequate in and of itself. It’s only when you want to exceed the minimum that you, as engineer, needs to verify that excessive deformation won’t occur.

Beyond that, do you have a specific proposal to limit “stresses” (where and what type, etc?)? Certainly do you have any proposal above and beyond what currently exists in the paragraphs that I listed above in VIII-2? I’d be happy to help implement it, if reasonable.

 

[SJones]

IOGP have taken to publishing standards with explanatory text for certain requirements incorporated. Perhaps they may get around to explaining their position on the subject matter in the next revision. The feedback process is laborious because they insist on using their specific tracking software that is not user friendly. The option to email comments is offered, but, from experience, emailed comments disappear into the morass.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[r6155]

@ TGS4
The user, the manufacturer and the inspector must be sure that the pressure test is carried out without any problems.
I suggest Acoustic Emission Examination during pressure test. See ASME V

Regards

 

[pron_to]

TGS4 - oh, so it's an error. Thant explains. Thanks a lot for verifying it, I appreciate it.