I'll been asked to calculate the MAOP of our pipelines and risers. my concern is some line have a combination of flexible hose and carbon steel pipe. I can give the lowest MAOP base on the hose rating base on the design pressure.I have gather some UT inspection of wall thickness of the pipe and some of them are 30 years of age I have given 3mm corrosion allowance for is it the right thing to calculate
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MAOP
- Thread starter OilHunter
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The MAOP for the flexible might not be the MAOP for the steel pipeline. In no way can you ascribe a 3 mm corrosion allowance without detailed knowledge of the current integrity status of the system. Try a Google search on: pipeline integrity, pipeline fitness for service; pipeline rerating
Steve Jones
Materials & Corrosion Engineer
Steve Jones
Materials & Corrosion Engineer
"Corrosion allowance" is something you assign at the beginning of life (or at the time of re-rating) to determine an effective life of the pipe. So, if you are designing a pipeline using 0.322 inch wt 8-inch nominal pipe, you have to subtract your corrosion allowance from the actual wall thickness to determine the metal mass that participates in the strength calculation.
You pick that corrosion allowance based on expected wastage per year times the number of years you are planning for the pipe to last. Let's say that the expected life was 30 years and the corrosion allowance was 3 mm. That says that your current pipe wall thickness should be assumed to be 3 mm thinner than original (i.e., the corrosion allowance is gone).
Now if you are re-rating the pipe for another 30 years, you can either measure the current wall thickness in a large number of places (take readings all around the pipe at every place you anticipate higher-than-normal corrosion rates) and then use the minimum value measured (not the average) as your new wall thickness. Subtract the corrosion allowance from that and calculate the new MAWP based on the remaining metal mass.
David
You pick that corrosion allowance based on expected wastage per year times the number of years you are planning for the pipe to last. Let's say that the expected life was 30 years and the corrosion allowance was 3 mm. That says that your current pipe wall thickness should be assumed to be 3 mm thinner than original (i.e., the corrosion allowance is gone).
Now if you are re-rating the pipe for another 30 years, you can either measure the current wall thickness in a large number of places (take readings all around the pipe at every place you anticipate higher-than-normal corrosion rates) and then use the minimum value measured (not the average) as your new wall thickness. Subtract the corrosion allowance from that and calculate the new MAWP based on the remaining metal mass.
David
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