how to calculate the thickness for Vacuum condition as per ASME B 31.4

[Metma]

Hi,

I have referred ASME B 31.4 edition 2012, where it is not clearly mentioned about the code or procedure to be followed for straight pipe under external condition .
whereas in ASME B 31.3, stated according to ASME sec VIII UG28.

my queries are.
1. how to verify the pipe thickness for full vacuum condition.
2. In table 403.3.1-1, allowable stress values are given for internal and external pressure, does it mean that code has take care the external load and full vacuum by stress values.

Regards,
Vinayak Nivendkar

 

[BigInch]

See this paper.

http://mycommittees.api.org/standar...ers/rationexpressionforcriticalcollapsing.pdf

It's up to you to make sure that the stress is <= allowable stress.

 

[Metma]

hello thanks for your reply ..

as per ASME B 31.4, allowable stress considered for thickness calculation are 0.72 x yield stress.
my basic doubt is whether vacuum thickness calculation applicable for ASME B 31.4, if yes then what will the ASME code to be followed.
ASME B 31.3 states ASME Sec VIII UG 28 to be followed for straight pipe under external pressure. like similar will follow in ASME B 31.4

 

[BigInch]

Any condition is applicable, if it is a condition that may possibly be experienced by the pipeline at any time during its design lifetime.

B31.4 does not prescribe an exact method, so you may use any method that your experience dictates is appropriate.

 

[LittleInch]

B31.4 doesn't give a lot of guidance does it?

I would look at either PD 8010-2 which provides some guidance or DNV OS F101.

You often need to decide what your worst out of roundness is before applying the collapse loads.

Unless you have large diameter, really thin pipe, they should normally withstand 1 bar differential from external pressure.

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

 

[BigInch]

ASME codes are specifically meant not to give cookbook guidances, only absolute minimum requirements. The responsible engineer in charge is required to have all the knowledge and experience necessary to design the system.

 

[LittleInch]

In many cases ASME codes give specific requirements, but simply to say you need to consider something (in this case collapse) without giving a hint as to what other codes might be suitable or which method is reliable is a bit of a copout in my opinion. However, maybe that's what eng tips is here for....

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

 

[BigInch]

I'm just saying that only minimum requirements are given, specifically or otherwise. There are some interpretations that have been published, mostly clarifications, but other than that, they'd rather leave the engineer to his own devices and experience. Besides they wouldn't want to have any implied responsibility, should their guidances not work as expected.

At least Tips is usually a better alternative to asking some MBA-brandishing boss.