ASME II Part D - Allowable Stress 1

[Design-Engineer]

Hi everyone I'm new on this thread.
Thanks in advance to all people who will give me their valuable feedback.

Regarding allowable stresses stated in ASME II Part D 2021 Edition,
I'm trying to understand when values tabulated into tables shall be used and when it is possible to calculate values with the criteria stated in the Mandatory Appendix.

Specifically, I'm looking at how to determine allowable stress for ASTM A193 B7M bolts.

ASME II Part D Table 3 (applicable for ASME VIII Div.1) states the allowable stress of 138 MPa,
but applying the criteria described in Mandatory Appendix 2 Table 2-100(b) the calculated value is 172.5 MPa.

Since the Mandatory Appendix 2 gives the criteria to establish values for ASME II Part D Table 3,
I'm not understanding why values are different and what is the reason to use one or the other.

thanks again for your help

 

[Cobra17]

I believe B7M is heat treated.

I have the customary tables, but.


(b) For materials whose strength has been enhanced
by heat treatment or by strain hardening, the allowable
stress value shown at any temperature in Table 3 is the
least of the following, unless these values are lower than
the annealed values, in which case the annealed values
shall be used:
(1) one‐fifth of the specified minimum tensile
strength at room temperature;
(2) one‐fourth of the tensile strength at
temperature;
(3) one‐fourth of the specified minimum yield
strength at room temperature;
(4) two‐thirds of the yield strength at temperature.

 

[SnTMan]

Design-Engineer, it'd be helpful to know which Code you are interested in, but in general you may not calculate allowables, you must use the tabulated values in the relevant table in Sec II, Part D, Subpart 1. For example, Sec VIII, Div 1, refer to UG-23 and in turn the the other tables referenced by it, e.g. UCS-23.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[weldstan]

B7M is a low strength bolt generally specified in sulphide stress corrosion environments.

 

[Design-Engineer]

SnTMan, thanks for your reply, really helpful.
I'm still trying to understand why the calculated value seems different from the tabulated one even if the criteria should be the same.

B7M tabulate value (allowable) is 138MPa (20'000 psi)
B7M calculated value (allowable) 172.5MPa (20'000 psi)

I'm working with ASME VIII Div.1 and I'm checking allowable for ASTM A193 B7M to calculate a flanged connection (ASME VIII Div.1 - Appendix 2)

Regards

Manuele