Hi all,

this is not specifically a PVElite question, but more a piping/PV question in general.
I'm looking for information about how to bend a straight pipe to form for example a heating coil and how to take this into account when doing strength-analysis.
I know the strain by bending can be calculated as strain = pipe diameter/coil diameter * 100%. This however creates a high strain which will make the pipe unsuitable. I've checked different codes (EN-13445, EN-13480, ASME VIII, B31.3) but none of these give information about how to handle this during design.
Is this because the bending of the pipe needs to be done in combination with an extra threatment to get ride of the bending stresses introduced? And is it possible to calculate the thinning of the wall due to bending?

Thanks in advance for your replies.

Hello corne

A simple rule of thumb is to use the strain of the outer fibres of the pipe, and use this for the thinning percentage of the pipe. However, usually the coil diameter is very much larger than the pipe diameter, and generally the amount of thinning can be ignored. If you use the 12-1/2% mill undertolerance, that should more than cover it. High strain is not really a problem. If you are worried about high strain, then PWHT should give you peace of mind. Many coils are made without regard to strain.

If you are worried about strain hardening, that should not be a problem either as once the coil is wound, it is not strained again beyond the yield point, and you will not lose much ductility.