Heat Treatment Issues on Stainless Steel Heat Exchanger Tubes

Proper heat treatment on stainless steel (SS) heat exchanger tubes is very important to obtaining the expected stress corrosion cracking (SCC) and corrosion resistance of the material in-service. This paper will discuss three recent issues arising on this topic.  The first involved a review of whether 321 SS Twisted Tubes ™ required heat treatment after twisting, and the results of chloride SCC tests are presented.  The second issue involves heat treatment recommendations on duplex SS u-bends, and it is generally not recommended on all except the tightest bends.  A case history where heat treating appears to have contributed to cracking in-service is discussed.  The third topic is on the differences between furnace and electric capacitance heat treatment for austenitic u-bends.