Thermal Load Case in ASME-SEC. VIII-DIV2 1

[Sajjad2164]

I am wondering if I want to apply the load cases involving thermal loads (such as that shown in the photo) and the design temperature is 600 degrees of centigrade (in heat exchanger) and I want to apply the 1.3 safety factor to the loads then what would be the temperature that I'm going to apply to the shell? 780? Do I need to perform the elastic-plastic analysis?

 

[BJI]

If you really needed to do this then you could factor the expansion coefficient. However, the thermal loads don't typically contribute to plastic collapse, except where they are effectively load controlled, such as in cases where elastic follow-up is present. This would be quite typical, or more likely always applicable to some degree, for restrained expansion of attached piping.

Since you are looking at limit load analysis, the latter scenario is all that is really applicable, i.e. treating your thermal loads as load controlled, no different to the 'D' category. Refer to the limitations related to the lower bound limit theory under 5.2.3.2. If you do specifically need to consider thermal stresses then you will need to run an EP analysis.

 

[NRP99]

Applying the factor on "α" (alpha) would be the way to go as explained by BJI.

However, the thermal loads don't typically contribute to plastic collapse, except where they are effectively load controlled, such as in cases where elastic follow-up is present.

BJI
Would you please explain in detail about the elastic Follow-up? This term I am encountering lot of times while reading about the analysis of pressure vessels. But its quite strange that lot of "pressure vessel" industry terms are not clearly explained or need to scan through lot of journal papers to get the grip of it.

While going through search, I stumbled on W Brock's blog here which also highlights the his frustration about finding exact explanation of this term. Further Prof. Brocks also write that "It simply says that “elastic follow-up” is a correction term in an elastic analysis incorporating plasticity."

Prof. Brocks rightly said which resonates well with me-"If terminology creates insurmountable barriers of understanding even among people having similar scientific interests and background, namely fracture mechanics and structural integrity, we have to be concerned about the language we use in our publications."

 

[TGS4]

Elastic follow-up = ratcheting.

 

[TGS4]

And yes, for the thermal load case, the appropriate method for factoring the thermal loads is to factor the coefficient(s) of thermal expansion.

 

[Sajjad2164]

Actually, I meant this one shown in the photo.
I mean if I want to do an elastic analysis and the design temperature is said to be 600 degrees of centigrade, should I still use elastic material in the analysis? Or I must take the temperature-dependent properties of the material into account?

 

[TGS4]

should I still use elastic material in the analysis?

Your material property in an elastic analysis needs to always be elastic. I'm not sure that this is the question that you wish to ask.

Or I must take the temperature-dependent properties of the material into account?

Always

The snippet of Code that you are showing is from the 2015 Edition. May I suggest that you upgrade to the current (2021) Edition. This Table has gone through several revision in the interim.

 

[cbPVme]

Review paragraph 5.1.1.3. If you don't meet the fatigue screening criteria of 5.5.2.2, you can't use this method for materials with time dependent properties.