ASME VIII Saddles Stress Analysis - Material Allowable Stress 3

[FPPE]

Hi,

I'm performing a stress analysis of the saddles of an heat exchanger with FEA. The whole heat exchanger is designed according to ASME VIII Div. 1, but for covering the case of the saddles (due to them geometry) I cannot use div.1.

My doubt is about the material allowable stress of the saddles, because (for SA516-70) at ambient temperature the allowable is 138 MPa according to ASME VIII-1, but for ASME VIII div. 2 is 175 MPa (Table 5A).

In the case of protection against plastic collapse i'm performing the operating conditions analysis, so i think that the higher portion of the saddle is at a higher temperature than the ambient temperature (the channel in operating is at 377°C). How do I consider this fact?

Moreover I have a doubt for the properties of the material to insert in the software, specifically the Young's modulus. This decreases with temperature, but in part D it is not tabulated, should I take it from the catalogs of the material?

Going back to the first question about which admissible code to use (in the specific case of saddles also because they are not a pressurized part), if I use another code that is not div.1 (when this represents the main calculation code for most of the vessel) should I use the admissible codes tabulated in part D for div. 1 or can I use in this specific case those of div. 2?

 

[IdanPV]

If the construction Code is VIII-1 you shall use the allowable stress as shown on Table 1A.
See App.46.

 

[Christine74]

IdanPV, that's a reasonable approach but nowhere in the ASME code does it state that the allowable stresses provided for pressure components must also be used for non-code, non-pressure components like saddle supports.


-Christine

 

[SnTMan]

Correct, for non Code, non pressure parts, the allowable may whatever the designer is comfortable with...

Regards,

Mike


The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[Christine74]

Back to the original question, see Table TM-1 in Section II Part D for Young's Modulus for ferrous materials. It goes all the way up to 650°C/1200°F.


-Christine

 

[DriveMeNuts]

I assume you are doing an elastic FEA.
PD5500 Appendix C is a good resource for stress design margins at different locations around the saddle.

 

[IdanPV]

It is true that for non Code parts the allowable may whatever the designer is comfortable with, it is engineering judgement.

 

[FPPE]

Thank you all for the excellent responses!