Discontinuity stresses.(ASME section VIII Div-2)

[MDKARMD]

can anyone pls clarify below queries about discontinuity stresses:-
Pm-General membrane stress - its because of pressure loading and it is limited to S.
PL-Local membrane stress- what is this stress actually??? and why it is limited to 1.5S
Pb-primary bending stress - what is this??? also this stress not limited to any allowable value ,why??

As per Figure 5.15 of ASME section 8 div-2,
PL+Pb limited to 1.5S
and Pm+Pb not comparing with any one allowable.why??

what are the stresses generated because of local load of nozzle???
what is stress linearization and why it is required???

 

[TGS4]

Please refer to ASME PTB-1. That references the important papers in the literature with respect to stress linearization. If I recall correctly, PTB-1 also includes the old "Criteria" document, which was published with the original Division 2 and contains much of the rationale.

This is an incredibly complex and complicated topic that requires some reading on your part before having a discussion here. I would recommend that you read these documents, and then come back here with specific questions.

 

[MDKARMD]

Thanks TGS4..I m going thru the document..

can u pls explain below query.

1. The local membrane stress(PL) is the membrane stress at very near to the discontinuity,(sqrt(T)),
Why this is limited to 1.5S... more specifically i m not understanding where this stresses will come and when??
2. Why primary bending stress(Pb) always combined with local primary membrane stress(PL)?? why not to the general membrane stress(Pm).??
Is internal pressure cause bending stress(Pb)?? or this is only from other local loads??

 

[TGS4]

1. The 1.5S limit was used to approximately limit the local membrane stresses to yield, in order to prevent gross yielding. In this way, it is similar to having no explicit margin against yield (compared to that of Pm), but the limit on locality - that the membrane stress must be less than 1.5S and greater than 1.1S for a distance in the meridional direction of 1*sqrt(rt).

2. Pb occurs in conjunction with Pl, and it is the summation of the two that is important. See Table 5.6 for a description/examples of the loads and locations where different classification s can be found.