Allowable strees ASME B31.3 & ASME Section II Part D

[Meck91]

Dear Members,

There is a difference between maximum allowable stresses found in ASME B31.3 and ASME Section VIII part D for the same material and garde. Any specific reasons?

Also, do i strictly need to use allowable stresses for pipe design from B31.3 ONLY.

Would appreciate your feedback.

Regards,

Meck91

 

[TGS4]

There are different design margins between the two codes.

You HAVE to use the allowable stresses from your specific design code. There's no option of cherry-picking allowable stresses.

Why would you think that this is acceptable?

 

[rneill]

B31.3 provides guidance on how the allowable stress values were obtained. When an allowable stress value is shown, the value in B31.3 must be used. When a material is not listed, you should apply the same "rules" to the material properties as is done in Table A-1 so that the same safety factors are present.

You can't use a different basis for determination of allowable stress values for piping than that provided in B31.3. Different design codes provide different design rules and may have more or less conservatism or accuracy in the design approach and therefor provided different allowable stress values.

Consider the problems if we were allowed to take the less conservative allowables from a design code that required extremely rigorous analysis and use these with a design code that applied simplified and only approximately accurate design rules.