B31.3 Stress Analisys

[CGArmesto]

Dear colleagues,

I'm new in piping matters, so i ask for your understanding if my doubts are too simple.

I'm cheking a Stress Analisys Procedure for a cryogenic application in accordance with B31.3, and i'm not sure about the load combination cases to be considered and the acceptance criteria:
- When considering Sustained loads + Occasional loads < 1.33Sh, should the Displacement Stress be added taking into account that in operation we'll have all these stress togheter?.
- In what cases should the &quot;bowing effect&quot; be considered?, during start-up activities or in operation?. Our Contractor has specified 39ºC thermal gradient in section for &quot;bowing&quot; effect, is this figure correct (our operation temp. is -160ºC)?.

Thank you for your help.

Cyrus

 

[prex]

The occasional loads are typically wind or earthquake, not thermal stresses (displacement strain); so you should only use true occasional loads to check the 1.33Sh limit.
Thermal expansion stresses should be verified coupled to sustained loads (not occasional loads) per 302.3.5.
The bowing effect is also a thermal effect and should be coupled to expansion stresses in determining the displacement stress range.
Don't know if a gradient of 39°C (from top line to bottom line of pipe I suppose) is a consistent value (though it doesn't seem unrealistic): this effect depends primarily on process conditions (two phase flow perhaps?).

prex

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[LSThill]

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