What is the difference between stress analysis of newly installed pipelines and stress analysis of pipelines in service for 3 years or longer?
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What is the difference between stress analysis of newly installed pipelines and that of existing pipelines? Additionally, what is the role of stress analysis in the risk assessment of pressure pipelines? Why is it necessary to perform stress analysis to check both primary and secondary stresses on pipelines after several years of use? Thank you!
I haven’t studied it in detail; you can take a look at the two standards, ASME B31G and API 579.
Reply 2#: The power API579 is a recommended standard for fitness for service; it seems this issue is not relevant. Evaluate issues such as whether defects will propagate based on the principles of fracture mechanics.
In service pipes, the wall thickness may vary, especially those for which a corrosion margin was specified in the original design； If the service life does not exceed the limit specified in the original design, parameters such as the allowable stress of the material should remain unchanged ； Of course, there may be some special cases: for example, after a certain stop, the pipeline fails to return to its original installation position due to certain factors (it might be stuck by some pipe supports or other similar issues). Upon reanalysis, the situation was different from when the new pipeline was first installed.
I read an article recently. For units that have been in operation beyond their design life, the mechanical properties of pipeline materials also change accordingly; thus, the allowable stress at the operating temperature cannot be simply determined based on manuals. It should be selected based on the performance test data of the materials. In that case, the allowable stress was divided by 1.5. But the operating time was 250,000 hours. Personally, I believe that after two or three years of operation, provided there are no major design issues, the allowable stress should not change significantly!