Max.principal stress theory in ASME III ND 2

[Umar107]

I am using DBA approach and design code is ASME III ND, should I use maximum principal stress theory or tresca theory?
ND refers to 1A and it uses the maximum principal stress but material is ductile and I want to find a reference in ND to use tresca theory.Any helP?

 

[1503-44]

Generally you must use the method quoted by the code unless the code specifically states alternative methods are also acceptable.

“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"

 

[DriveMeNuts]

My recollection is that the maximum principal stress (MPS) theory is non conservative when it comes to shear stresses (where you have positive and negative principal stresses at a specific location).

Tresca provides identical results to MPS where principal stresses at a location are all positive or all negative. Tresca provides safe/conservative results compared to MPS, for areas experiencing shear.

In that sense, if you design in accordance with Tresca, you are automatically designing in accordance with MPS, with the addition that you are taking a more cautious approach with regions experiencing shear. It can be easily proved mathematically (and using wikipedia ) that Tresca is identical in tension/compression and is always safer in shear. If the AI understands the difference between Tresca, MPS and Von Mises, they won't reject your design because you decide to be more cautious with shear stresses.

I can only assume that all geometries in ND are non-shear.

 

[TGS4]

Section III uses Tresca. End of story. See Mandatory Appendix XIII.

 

[Umar107]

@TGS4 ,Mandatory appendix XIII refers to NC-3200 but I'm looking for a reference in ND.

 

[TGS4]

Appendix XIII is referenced 12 times in ND. What are you evaluating in ND?

 

[Umar107]

It is a horizontal storage tank (size 2.2m dia and L 4m, atmospheric pressure). Client requested to design it as per ND-3900 (Design of 0 psi to 15 psi storage tanks).
I'm trying to link ND-3900 with Appendix XIII but in ND-3900 there's no guideline regarding design by analysis.
This is my first project and it'll be helpful if you comment on the choice of code as well.
Sorry for late reply @TGS4

 

[TGS4]

Why do you need Design By Analysis in ND-3900? The rules are rather comprehensive.

 

[Umar107]

It is the requirement of the client. @TGS4

 

[TGS4]

Then it would be best to inquire with your client about how they want to work this within the limits of the Code.