Allowable stress values in ASME sec.II D & ASME B31.3

[stesw90]

Dear all,
My concern is about allowable stress values mentioned in table-1A of ASME secII D and one that is mentioned table A-1 of ASME B31.3,

I was checking allowable stress value for SA-106 gr.b in sec-II D and in ASME B31.3 and i found different values in both place,

In ASME sec2 pard D it is mentioned as 17100 psi for lowest to 100°c,
and 20000psi in ASME B31.3.

All I want to know is what is the difference and which should be used when,
Reason i m asking this if i can use higher allowable stress values for design i can design for lower thickness.

 

[metengr]

Allowable stress values are determined based on factors determined by the code committee associated with the specific code of construction. ASME Section II provides the requirements for determination of allowable stress values, which are used in Boiler and Pressure Vessel Codes.

However, ASME B31.1 or B31.1 or B31.8 are standards committees and they can provide their own factors that are more conservative than Section II. If the allowable stress values are more conservative than Section II valves, you are required to use the more conservative values IF the code of construction requires more conservative values.

 

[marty007]

You must use the allowable stresses dictated by the code of construction you are building to.

If you're building piping to ASME B31.3, use the allowables from ASME B31.3.

If you're building an ASME VIII-1 pressure vessel, use the allowables from ASME IID.

Simple as that.

 

[stesw90]

@metengr
can i find some were in the code factors considered for allowable stress

 

[davefitz]

The allowable stress for low temp materials is also correlated to the code's max overpressure during hydrotest. Some codes use 1.30 * MAWP and other codes use 1.5* MAWP, and it is necessary to ensure that the low temp allowable stress used for design does not lead to system failure during hydrotest.

"Whom the gods would destroy, they first make mad "

 

[metengr]

stesw90;
Review Mandatory Appendix I in Section II Part D and review Note 1 of Appendix A Tables in B31.3.

 

[AmoorSaleh]

Sometimes there is no different in the type name, but the values is totally different, i suggest to you to find the UN number.