Welded pressure vessel operating limit 2

[Hajakala]

Hello. I have a thin flat square shaped container that is welded around the edges and filled with water.
After welding it induces tensile residual stress approaching the material's yield strength around the weld seam.
When I pressurise the vessel to more than 2 bar, what is going to happen?
Will the maximum allowable stress value according to section 8 of asme code be: tensile residual stress + applied 2 bar pressure?

I am not sure how to model in abaqus and what to look for when checking if the component is safe when pressurised after welding.

Could anyone please tell me the correct approach and how to go about modelling this? How can I tell if it is safe? Which field output should I look at? Like Peeq pemag? Should I look at ductile damage using Gurson? The operating temp is low and its ss so i dont think creep is an issue.

For now I have modelled the welding process and then just pressurised the component in the next step. Now I get very high direct stresses way above the yield strength.

Thanks.

 

[FEA way]

Can you say more about the analysis that you’ve performed for now ? How was the welding process simulated ? Which type of analysis, modeling technique and material model did you choose ?

 

[Hajakala]

I have modelled the welding process (laser using dflux subroutine with a gaussian distribution) via 3D uncoupled thermal mechanical model with uniaxial true tensile properties incl. elastic, plastic (annealing temp), and other thermal properties with thermal and mechanical bcs.

Once I simulate the residual stress in the component, I then introduce a static step and apply a pressure load and prescribed temperature. The direct stresses become very high beyond yield strength but mises below. It shows some plastic strain. I am not sure if I have modelled the pressurised condition properly.
I would like to know how to assess whether the component is safe to use under this pressure and temperature.
By the way the component is a heat pipe for electronics.

 

[FEA way]

This approach seems correct. But make sure that you include enough time for cooling in thermal simulation and that the model is not overconstrained in mechanical steps.

 

[Hajakala]

Sorry but my question wasn't regarding the welding process. Could you please let me know if you have some idea about pressure testing as written in post?
I want to know what to do after the welding.

 

[FEA way]

My suggestion is related to pressure testing too - if you suspect that stresses in mechanical analysis might be too high then you should make sure that thermal aspects are properly modeled and that the model is not overconstrained (common reason of high thermal stresses). To evaluate the results of mechanical simulation, check Mises stress and PEEQ contours but also take a closer look at deformations.

 

[TGS4]

There are design by analysis procedures in ASME Section VIII, Division 2, Part 5. Follow those rules.

(Hint: weld residual stresses are not part of the equation)