If the pipe is buried, there are different methods to solve the problem, without doubt, the calculation with caesar II is the one I recommend.

Assuming that the pipe is buried, the problem of calculation of flexibility becomes a meticulous study of soil-pipe interaction. There are different methods to address the problem of modeling of the springs that simulate the elasticity of the soil, I recommend the use of L. Peng model for its simplicity.

If the pipe is not welded and the joints are flexible or type coupling, the input and design of the pipe does not require calculation of flexibility, and if you base your design on the introduction and design of pressure thrust block.