The issue of pipe wall thickness
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For the wall thickness calculation of a certain pipeline, the designated thickness is 12.42 mm; the nominal thickness is 12.5 mm for SCH60 and 16 mm for SCH80. How do you guys choose when doing calculations in everyday life? Move up a level? Still level 2?
We need to analyze each specific case individually; it mainly depends on what the medium is Take factors such as corrosion, erosion, and abration into account to select an appropriate wall thickness.
Negative deviation – has the corrosion allowance been taken into account?
The wall thickness is calculated; you shouldn’t have any problems with that. However, SCH is also calculated using a formula: Sch = 1000 * (p/), where p is the design pressure of the pipe in MPa, and the allowable stress of the pipe material at the design temperature is also in MPa. The resulting value is rounded up; for example, if the calculated value is 65, then 80 is chosen. It’s not determined by using the calculated wall thickness as one might think.
I am very grateful for the reply from this moderator. One more question. We indeed move upward as you said; generally, we calculate the wall thickness of the pipes and that of the elbows. According to standard 20801, the wall thickness of elbows is definitely greater than that of pipes, so we never take into account the calculations related to the pipes – we only consider the calculations for the elbows. I just used SCH’s formula to do the calculations, and the result chosen was exactly the same as that obtained from selecting the elbow. I would like to ask about the process you follow in your design work
Generally, there is no need for elbows to be thicker than straight pipes; this is only necessary under conditions of extremely high temperature and pressure. Under normal circumstances, it is sufficient for elbows to have the same thickness as straight pipes, as there is a significant difference between the wall thickness calculated based on specific requirements and the wall thickness actually chosen. For example, if you calculate the wall thickness normally, it might be only 2 mm, but in reality the actual thickness used is much greater than that
SCH80 is the more commonly used wall thickness series. From the perspective of material availability, Sch80 should be chosen.