Pig Trap Design 1

[RW01]

Hi all,

I'm trying to wrap my head around the requirements for pig trap design for ASME B31.4/B31.8 codes.

Firstly, I can't see any clauses in ASME B31.4/B31.8 which refer to the design of pig traps / vessels, so I'm trying to get some clarity on what it means for a pig trap to be designed to these codes.

Secondly, my company has some internal standards which allow the use of the ASME pipeline codes for pig trap design, but require the use of pressure vessel design codes (e.g. ASME VIII) where fatigue loading is an issue. Is it normal for pig traps to be designed solely to the pipeline codes (unless fatigue is an issue) or do they always need to be supplemented by the pressure vessel codes?

Thanks in advance.

 

[KevinNZ]

https://www.eng-tips.com/viewthread.cfm?qid=83660

 

[LittleInch]

I disagree with 50% of the replies in the linked post.

Pig traps are part of the pipeline design. They should never be designed to B31.3 or ASME VIII. The ID of the trapneeds to match the pipeline ID and the other codes result in sometimes much thiocker wall thickness for the same design parameters.

It is almost universal (i.e. normal) that pipeline pig traps are designed to the pipeline code and the only ones that aren't are doing it wrong.

ASME B 31.4 calls them scraper traps and has a section 434.17 also section 404.7 applies for the quick opening closure (generally designed to ASME VIII for the closure mechanism only).

ASME B 31.8 doesn't seem to have a similar clause, but has the same closure section , 831.3.7 and defines a pig trap as an ancillary item of pipeline equipment

I've never heard of fatigue issues in a pig trap. Most people now vent, drain and de-pressurise pig traps when not in use so I don't know where fatigue issues would arise.

Just think of it as what it is, i.e. a piece of pipe and deflect all attempts by those who don't know to refer to it as a pressure vessel.

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

 

[RW01]

Thanks both for your replies.

I will have a look a bit more into the codes and respond if I have more questions.