Please refer Para 419.6.4 of B31.4 which differentiates between the restrained portion and unrestrained portion of a pipeline for the calculation and evaluation of the stresses resulting from temperature and pressure changes in the line. For unrestrained portion the longitudinal compressive stress is added directly to the hope stress according to max shear stress theory and compared with 0.9 times of SMYS to ensure safety against general yielding
B31.8 on the other hand, though addressing piping systems subjected to similar failure mechanisms as that of B31.4, does not even touch this topic and don't explicitly impose any limit on the combined stress intensity for the restrained (buried) portion of the pipe line. Can someone of the fellow members comment on the intent and philosophy of B31.8 regarding the stress evaluation in restrained portion of pipeline. It would be of great help for me to know the design practice of other members while designing pipelines following B31.8
Thanks for your valuable comments.
B31.8 on the other hand, though addressing piping systems subjected to similar failure mechanisms as that of B31.4, does not even touch this topic and don't explicitly impose any limit on the combined stress intensity for the restrained (buried) portion of the pipe line. Can someone of the fellow members comment on the intent and philosophy of B31.8 regarding the stress evaluation in restrained portion of pipeline. It would be of great help for me to know the design practice of other members while designing pipelines following B31.8
Thanks for your valuable comments.
