Question about Ratcheting (ASME Sec. VIII Div.2)

[victor6397]

Hello mates, I have some doubts regarding ratcheting, and I hope you can help me a bit.

As I have read, and as can be seen in the Bree diagram, for ratcheting to take place a source of sustained primary stresses and a source of cyclic secondary loads is necessary. In that case, why is it mandatory to evaluate this failure mode always according to ASME Sec. VIII Div. 2? Based on the above, if we only have internal pressure in a cylindrical shell, regardless of whether it is cyclic or not, ratcheting would not be possible, would it?

Also, one of the criteria to verify this failure mode from the ASME Sec. VIII Div. 2 limit load method is the following:
"There is an elastic core in the primary-load-bearing boundary of the component".

Is this location the same as the location where the primary membrane stress (Pm), also called "structural element", occurs?

If so, the effect of a cyclic bending moment in a nozzle on a pressurised cylindrical shell, for example, could not lead to ratcheting on the latter, as the stresses would be considered secondary, right?
The only case I can understand is that of a cyclic temperature gradient. Could you give me another example?

I'm aware that I'm probably misunderstanding some concepts, and that the questions can be a bit silly, so please don't be too hard on me, I'm trying to learn

 

[IdanPV]

Hi,

I rocommend to start with reading the below articles, it can give you better understanding:

ASME Section VIII, Division 2 Elastic Analysis Discussion: Collapse vs Ratcheting

So, you think you know what load case combinations to use for your ASME Section VIII, Division 2, Part 5 analysis to satisfy Protection Against? Common sense says to follow to Code rules in Table 5.3 – but do you fully understand what that means? And, what loads should you use to satisfy Protection

becht.com

My notes on ratcheting failure and local failure criteria

Codes or standards for pressurized components requires design and analysis engineers to asses the component design for ratcheting and local failure modes. It’s very important to understand the physical phenomenon of the failure modes to correctly apply it during design and analysis.

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