Dear All

I am trying to undertake an investigation for a pipeline with the following properties:

- 400m length of DN1050 18.68mm WT pipe either side of a 45deg 5D 22.4mm WT hot induction bend with 1000mm transition sections to girth welds, all buried
-1200mm soft soil cover
-Installation temperature 17 C
-Maximum temperature 55 C
-Maximum Pressure 13500 kPa

The results of the sustain case loads seem to be strange as all come up as zero in the report!!!

Comparing the results to another software which they are not zero, Would you kindly advise why am I having this problem?

Confirming that I am using version 8, 2016

It cannot be zero.
you can share input file to check.

If the entire system was "buried" using the program's buried pipe modeler, all densities will be set to zero (to eliminate bending moments caused by weight load on those point supports). If you are calling this a sustained analysis, I guess your only other load component is pressure and that should generate a stress.

Thanks Dave! You are correct; I have stresses in the system but no loads.

I am trying to understand how mush load do I have on the girth weld close to the 45° bend. The entire system is buried and there is no above ground piping. Is the analysis going to be incorrect if I add the weight back in the system?

Thanks!!

If the system rests in a properly prepared and properly filled-in trench what loads are you expecting on the weld? The weight is supported by the trench bottom and the system should see little distortion (and load) from weight. In CAESAR II, buried pipe is analyzed to evaluate the effects of (thermal) strain. Even though the temperature change may be low, buried pipe runs can be quite long and you can accumulate a lot of bending at your changes in direction. It's (thermal) strain that loads your weld.

No, do not re-define your densities.The soil stiffnesses that the buried pipe processor adds to your model are not pre-loaded to carry deadweight so your added loads will deflect the entire system downward based on x=F/k.

So If I understand correctly the effects of the pressure in the buried system are neglected by CAESAR II?

When I do my analysis with the other programs I can see the bending moments and the pressure effect which are quite big and not ignored!!

can you also confirm what is the effect of building your pipeline from small length of pipe rather than a long run when it gets converted to underground?

Oh, yes.
Typically, structural response to pressure (except for XJ's) is not considered. The general exception is FRP pipe and long transportation piping.
Be sure that the translational "Bourdon" effect is activated. See Special Execution settings. With this you should see your response.

Thanks Dave, problem solved!

Much appreciated!

Hi Dave

Can I open this case with another question about displacement? Including the Pressure elongation and bourdon effect solved the problem of the stress while increasing the displacements in the bend with the highest stress.

The other program seems not to include the Bourdon effect in displacement calculation as when I turn it off the displacements are the same.

Thanks