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

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m_ridzon

Mechanical
Sep 18, 2020
80
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, is <1 and damage > 1. These results do not seem to make sense to me, but I don't know what went wrong in the calculations.

Are there singularity problems in the v2017 equations, as was the case in v2013?
 
 https://files.engineering.com/getfile.aspx?folder=c90257bf-cce7-4fd2-bcf5-2946923ddf58&file=Mathcad_-_10_Fatigue_Hand_Calc_.pdf
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Please check your units. In Imperial units, the units of stress is ksi, not psi.
 
It has nothing to do with UNITS. As long as the elastic modulus and the stress are in the same units (psi for both) he is ok.

The thing is that the Eq. in 3-F.7 and 3-F.8 are for Sa which is larger than 13.6 ksi and smaller than 870ksi.

The 2017 Edition doesn't include this exemption but the 2019 does.
2017-2019_fi3qwj.png


The stress is low and hence, you may not use the Eq. you better take a look at Figure 3-F.3

P.S
The Code do states that units shall be in KSI but from Mathematical point of view, it doesn't really matter.
 
Thank you. Yes, I double-checked my units and concluded that PSI was acceptable to use since they cancel out in the calculations. Everything from the FEA model was PSI, which is why I used that in my calculations. And yes, for my reporting in the project documents, I'm using KSI as is the custom.

Thank you for sharing the excerpt added in v2019. That clears it up.
 
It is not a responsible engineering practice to work with an old code edition.

Regards
 
r6155 said:
It is not a responsible engineering practice to work with an old code edition.
Wow, that was uncalled for! There's much to the story you do not know. I've done tons of BPVC work where the customer, regulator, or municipality MANDATED an older version. I've yet to have a regulator come back on me for a bad one. There's plenty of valid reasons to use other versions of the Code when the situation calls for it. Please don't chastise someone's commitment to good engineering practices by assuming pieces of the story that you don't have.
 
I don't think you have a 2019 edition.
If you have the 2019 edition then why do you ask a question if the answer is in it.
Try to give all the information next time.

Regards
 
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