Flange bolts preload stress: ASME II Part D vs. PCC-1 1

[Skatemav86]

Hi,

According to ASME II Part D Table 3, the Maximum Allowable Stress S for a Section VIII Div. 1 bolting material is Su/5.
However, the default preload stress of a flange bolt according to ASME PCC-1 is 50%Sy, well above the Allowable Stress S.
Thus, if preload is applied correctly, the bolt is experiencing in operation a stress which is significantly greater than its allowable.
How this can be explained?

Thank you in advance

 

[TGS4]

The bolt "allowable" stresses are used only to size/design the flange. Following the stress levels in PCC-1 will lead to a well-functioning joint.

Do not, under any circumstances, use the "allowable" bolt stress in assembly - your joint WILL leak.

 

[SnTMan]

And please, do some reading...

You can learn a lot about the Code just by reading it

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

 

[Skatemav86]

Thank you very much for your replies.

The components I design are not required to be compliant with ASME VIII Div. 1 so I am using this code just as a first guess for thickness and bolt selection of the main components.
All components are then verified with FE analysis so the sloppy work in the end might be more accurate than a simple code calculation.
So when the code is saying "The maximum allowable stress value is the maximum unit stress permitted in a given material used in a vessel constructed under these rules" it is not referred to bolts preloading. In operation, the stress on the bolt will be significantly higher than S, at least greater than 50%Sy.

 

[TGS4]

Please also read Appendix S.