Bending moment constraint for pipe with internal pressure during creep

[Dyson993]

I've got a section of a straight pipe with internal pressure loading, for with I have applied elastic-creep steps. One end is fixed and to the other, through a continuum distributing constraint, I've applied a bending moment to simulate power plant system loading conditions. Under elastic conditions the results look reasonable but during the creep step there is excessive compression on the bottom half of the pipe causing a von mises stress that is far larger than the maximum principal stress. The maximum principal stress is also not distributed uniformly at the top surface of the pipe as expected. The moment applied is about the x-axis, can someone help with my constraints? An image of the FE model is shown below

 

[TGS4]

For creep analyses you should be performing elasto-visco-plastic analysis. This is not a constraint issue but a more fundamental analysis issue. There are approaches in API 579-1/ASME FFS-1, Part 10 that describe how to perform such an analysis.

 

[Dyson993]

What I've done is a elastic-viscoplastic analysis and I'll have a look at the codes