Above Ground Pipeline Stress Analysis

[Headache2013]

Dear Specialists;

I'm asked to evaluate stresses and anchor force(at anchor block) for a pipeline laid on the ground (not buried), but I don't know how to model it using C2 or Autopipe.
For buried pipeline, there are a lot of literature explaining how to model it and how to simulate soil effect on the pipeline. However for AG lines, I couldn't find any literature.
I made some simulation using both Autopipe and Caesar II softwares and the results are abnormal.
Pipe: 6", Mat'l: API 5L X60, Design T°= 105 °C, Inst T°:15°C, Design Press: 45 BarG. Applicable code is ASME B31.8.
Pipeline shape: "L" shape, with large cold bend (40D) at the corner. An anchor block at the end of small leg of the "L". The long leg of the "L" is terminated at virtual anchor point.
I simulated two cases:
a) I assumed minimum soil cover (50mm). Stresses are Ok but the anchor forces ranges from 13KN (Autopipe) to 888KN (Caesar II).
b) I manually calculated soil springs Ki and Pi. For longitudinal and transversal, I assumed Pi as a friction force (Pipe + content weight) X friction factor (0.5). For downward, Pi and Ki calculated using ALA method.
The results are strange. Anchor forces range from 4KN (Autopipe) and 960 KN (Caesar II).
For your information, with Caesar II I changed the default post yield stiffness (K2=1) to K2=0 , otherwise the system doesn’t converge.
Something is wrong with my modeling. Could you advise the best modeling approach.

Best regards

 

[Headache2013]

BigInch;

Caesar II results says there is no upward buckle (no lift off). All displacements are in plan directions, zero in vertical direction.
To get an upward buckle, you have to introduce an initial imperfection (overbend), and this is not my case (perfectly straight).

 

[LittleInch]

Unless you're building this on a salt flat, there is no such thing as perfectly straight and flat for a pipeline. Anyway it's this 50mm burial thing that is making all your results go hay wire. What was the comparison between the programs when you modelled it as simple supports?

What are the lateral movements being predicted at the main bends?

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[BigInch]

Yes it is a headache that life isn't perfect and that Caesar does not do buckling calculations. You should.
Buckling does not require initial imperfections to initiate when the Euler buckling load is exceeded.
Initial imperfections reduce the theoretical Euler buckling load to levels more reasonable for pipeline analysis, as Little" says, there are always going to be unlevel segments, sags and overbends in pipeline installations.

Independent events are seldomly independent.