ASME Sec. VIII, Div. 2, Annex 3-F, Eqn. 8

[LS_SMS]

Folks, I found another thread HERE about Sec. VIII, Div. 2, Annex 3-F, Eqn. 8. The equation has something wrong with it. That old thread was dated from 2018. In the 2023 version of the Code, the problem still exists. Does anyone have a status update on when they plan to fix this?

Additionally, I would like to know if there is any official ASME errata documentation acknowledging the error so I can cite it in my deliverable.

 

[IdanPV]

Same issue as here:

Damage >1 For Low Stress Location || v2017 BPVC, Sec. VIII, Div. 2, Eqn 3-F.8 - Boiler and Pressure Vessel engineering

Please see the attached PDF. I'm assessing fatigue for a stress cut line in a low stress location using ASME v2017, Sec. VIII, Div. 2, Eqn 3-F.8. The PDF lists the calculations for this stress cut line. I've double/triple checked the calculations, but am getting number of allowable cycles, N...

www.eng-tips.com

What is the value of Sa?

 

[LS_SMS]

Is the Code Committee planning to fix the equations? Or was the added excerpt (quote below) supposed to act as the fix? It seemed insinuated HERE that they were actually fixing the equations themselves.

...and for 93.7 MPa (13.6 ksi) ≤ Sa ≤ 6000 MPa (870 ksi)

 

[TGS4]

I have the equations graphed. The S/N curve is smooth and continuous. I fail to see the issue. Please provide a value of S_a that doesn't give a valid N.

 

[LS_SMS]

Please provide a value of Sa that doesn't give a valid N.

See the Mathcad image below for 2000 psi for 316 stainless at room temperature. Please also peek at my previously shared link HERE. The person graphed the natural log equation and it is going haywire as it goes below the fatigue limit.

*edit* My screenshot does not show n_k, which was earlier in Mathcad worksheet assigned as 5000.

 

[IdanPV]

2000psi are 2ksi.
Equations 3-F.6 to 3-F.8 are applicable for 13.6ksi ≤ Sa ≤ 870ksi.
For Sa values below 13.6ksi (93.7MPa) you are just below the design life curve which result in infinite number of design cycles.

 

[LS_SMS]

2000psi are 2ksi.
Equations 3-F.6 to 3-F.8 are applicable for 13.6ksi ≤ Sa ≤ 870ksi.
For Sa values below 13.6ksi (93.7MPa) you are just below the design life curve which result in infinite number of design cycles.

Yes agreed. What prompted my original post is that I blindly assumed the equation would output valid answers all the way down to 0 ksi. But if I understand correctly from your feedback, it seems that the equations are only applicable down to 13.6 ksi. Thanks for helping me see that.