ASME VIII, Div 2 Part 5 1

[engpes]

Section 5.7.2 in ASME VIII, Div II Part 5, states that the "service stresses" in bolts for a flange design may be higher than the "allowable stresses" of Annex 3-A (ie ASME IID). It states that the max service stress value may be 2.0 times the allowable stress values listed in Annex 3-A / IID.

1.) Does this mean that the allowable bolt Sb stress value can be multiplied by 2.0 when designing a flange to part 5 (as opposed to part 4)?

2.) Does the term "service stress" in part 5.7.2 indicate a design stress value for the flange? Or is this only for assembly procedures?

I was under the impression that this X2 multiple was a less conservative part 5 approach as opposed to part 4 (by rules).

Any help would be greatly appreciated. Thanks in advance!

 

[TGS4]

The bolt rules in Part 5 are a mess. I recommend submitting a Request for Interpretations from the ASME Committee responsible for this mess.

 

[prex]

Actual service stress in bolts, such as those produced by the combination of preload, pressure, and
differential expansion, may be higher...

This is clear to me and has nothing to do with assembly procedures or design stress values. Calculation of such service stresses requires a model of the flange assembly accounting for residual preload stress after applying pressure and for differential expansion effects.

prex
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[engpes]

I am assuming you mean modeling the studs and nuts in the flange assembly?

Is there an exert in division 2 that clearly describes this as an acceptable approach? We have done this in the past, but I am curious to see if there is any specific reference to this being a valid analysis method. Thanks!

 

[TGS4]

You asked for a Division 2 expert. Here I am. I have answered already above. I am a member of the WG-DBA (VIII) Code Committee. I honestly mean that the rules are a mess. Please please please submit a request for inquiry.

 

[engpes]

How long would this take? Surely I can't be the first person to ask this question?

Thanks for your help!

 

[TGS4]

It won't be fast. But, the more people we have asking this question, the more impetus there is for us to deal with this. If you are interested in assisting us with fixing these rules, that would be much appreciated.