Chkara & John Helical coil bending is not a new process or new technology either for low alloy steel and for S.S materials in a refinery or chemical plant . Helical coil designs are used widely for fired heaters. Helical coil bending in cold formed state is in existence for the last 40 years at least. Your question whether helical coil needs PWHT after cold forming and the formed stresses are allowed to be continued in process fired heaters. Cold formed bending if it exceeds > 10% cold work. some process designs and piping designers prefer to carry out PWHT as an abundant caution to prevent future SCC in cold formed S.S 347. We (Luis and me) have understood your question correctly and only replied in a general way as we do not know the process design conditons and temperature conditions. I again repeat that if your process design calls for PWHT for S.S 347 for cold formed helical coils for your fired heater, whether as an abundant caution and also to meet piping code , for this prcess ervice design pressure and design temperature , you have to perform the same. Trust this clarifies your querry. We have fully understood the code and process design requiremetns and posted our replies. C.V.Srinivasan Nishi Engineers Pvt Ltd Chennai India April 21 E-mail:nishi@vsnl.com >Chakra, > >You are correct. We are going to build a heater with a >helical coil, 8" 0.311 wall bent to 12'-2" diameter (1 >pass). I knew the straight tube would be anealed before >sent from the mill, but wasn't sure if it required >stabilization by the mill due to the high service >temperature (skin temps could get close to 500 C. The other >question was if, after bending, would it require PWHT to >relieve bending stresses? Thanks for your prompt attention.