Your question is very general... some things you would have to consider would be thermal deformation, thermal cycling, mat'l type, fluid material in pipe, burial depth, pipe connections (galvanic series), hydrogen embrittlement, burst strength, etc. What you should do first is better define the problem, then evaluate what needs to be calculated.
We are using 40" cement lined pipe(inside) with 3 layer polyethylene coated (outside)pipe. The pipe is for water in take from sea and that water will used for heating purpose of LNG vaporiser. Now we did not install CP system for this buried pipe. According to NACE generally we consider 16 mpy for corrosion rate if there is any defect. I want to calculat the effect of load on the thickness variation which can predict the chances of rupture or leak.
I would try to consider load as a result of soil weight above the pipeline, shear as the result of possible soil shift in the lateral plane and then longitudinal or axial loading as the result of thermal expansion/contraction. This would give you three principle stresses.
Note also you have to consider stresses as the result of internal pressurization, model the pipeline as an infinite pressure vessel (i.e. no longitudinal stress due to end cap reaction) with the above mentioned EXTERNAL stresses.
Finally, depending on material constituting the pipe, worry about degragation, the change in material properties which would lead to performance capability variation.
Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada
Guideline for the Design of Buried Steel Pipe - July 2001
This guideline presents design provisions to evaluate the integrity of Buried steel pipe for a range of applied loads. It applies to new or existing buried pipe made of carbon or alloy steel; welded pipe; piping designed, fabricated, inspected and tested in accordance with an ASME B31 pressure piping code; and buried pipe and its interface with buildings and equipment.
