Protection Against Local Failure, Weld Joint Efficiency 1

[Ray6]

Hello all,
For Protection Against Local Failure, ASME Sec VIII Div 2 has two methods. The less recommend one is using "Elastic Analysis Method" that I am using. My question is regarding the Weld Joint Efficiency.
My design is based on ASME B31.4 so I am using the concept of API 597 for the factors. API 597 has a section to explain what to do for "Treatment of the Weld Joint Efficiency" on Protection Against Plastic Collapse.
But it does not say how to treat weld joint efficiency for other failure modes such as Local Failure. The elastic criteria for local failure is that (s1+s2+S3)<4s. Should I consider Weld Joint Efficiency when calculating S or just ignore it?

 

[DriveMeNuts]

The joys of mixing codes.

API 579 says change (s1+s2+S3)<4s to (s1+s2+S3)<4s/RFS[sub]a[/sub]. I would say that if you choose to use the elastic analysis method to assess local failure then the "Treatment of weld efficiency" rules need to be used with that elastic analysis, i.e. (s1+s2+S3)<4s/E/RFS[sub]a[/sub]

The Div 2 rules are based on 100% weld efficiency, so you need to make some adjustment.

ASME VIII Div 1, Appendix 46, Section 46-2(b)(2) might be helpful.

 

[TGS4]

Weld joint efficiency is really only applicable to the failure mode of Plastic Collapse. It does not have meaning in Protection Against Local Failure, which is why it is not referenced in API 579-1/ASME FFS-1. (And if this emphatic and definitive statement seems a little forward, I say it only in the context of being the author and technical project manager of the Code item that incorporated the weld joint efficiency rules into API 579-1/ASME FFS-1. I have researched this topic extensively and have published on the subject).

There are no rules in ASME Section VIII, Division 2, Part 5 for partial weld joint efficiencies because the ASME Code Committee has decided that DBA per Part 5 requires an effective weld joint efficiency of 1. (See the above parenthetical note - I have been extensively involved in this topic at the ASME Code Committees for many years)

I agree with DriveMeNuts - see 46-2(b)(2).

 

[DriveMeNuts]

I understand that the reason why a weld efficiency is applied to plastic collapse is not applicable to Local Failure because they are fundamentally different failure modes.

However, I would have thought local failure would need some sort of weld imperfection factor because as the material approaches and exceeds its local failure limit it behaves like a brittle material.
If there is a slag inclusion or some other sharp weld imperfection in the weld, I would have thought that local failure would occur sooner.