EN 13445 Progressive Plastic Deformation

[SiggiN]

Hi all!

I'm having a hard time understanding when Progressive Plastic Deformation is a relevant design check

At the moment i'm calculating a subsea valve according to the EN 13445 Direct Route

The valve will not be subject to pressure cycles greater than 500, so my understanding is that fatigue check will not be required. Temperature during life/operation 4degC. pressure rating 250bar

When is Progressive Plastic Deformation (ratcheting?) a relevant failure mode?

From litteratur i see that ratcheting = cyclic creep, so is it temperature dependent? Is there a defined limit for when I must consider Progressive Plastic Deformation

Thank you!

 

[TGS4]

In both EN 13445 and ASME Section VIII, Division 2, Part 5, demonstrating that ratcheting doesn't occur is critical. One reason for that is that if ratcheting does occur, then the fatigue checking thresholds are not valid.

Your understanding of ratcheting with respect to creep is incorrect - it is simply progressive plastic deformation. Creep-ratcheting is also a real and relevant failure mode.