Does the SCH wall thickness chart include a corrosion allowance?
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Regarding the wall thickness determined according to the SCH table, is it necessary to add an allowance for pipe corrosion as well? For example: SCH20, DN30 – the wall thickness determined is 2.3 mm. The corrosion allowance for 20# carbon steel is 1.5 mm. So, should the final wall thickness of the pipe be 2.3 mm, 3.8 mm, or something else?
The pipe wall thickness is a value determined through calculations based on the process conditions, and after rounding, a standard pipe wall thickness is selected. The so-called pipeline corrosion allowance should be included in the calculations
Why can’t we directly calculate the SCH value and then select the wall thickness?
What you mean is to calculate the SCH number and then choose between the standard version or the reinforced version based on the pressure, is that right?
First, it is necessary to calculate the wall thickness required for the pipeline in accordance with the process requirements. The calculation of this wall thickness takes into account the thickness needed to withstand pressure, corrosion allowance, erosion allowance, manufacturing tolerances, etc.; for details, refer to 20801. Once the wall thickness is determined, the appropriate SCH grade that meets this thickness requirement can be identified.