When joining by welding SS316 there is no need for (PWHT) post weld heat treatment. Is required a stress relieving after cold bending SS316 materials. Luis Marques

Jayaan Piping codes/ Fabrication code for S.S to S.S - pipe joints or vessel joints have not made it as a mandatory practice to carry PWHT for S.S joints. In general, cold Formed SS ( due to formed stresses) are highly susceptible for SCC. As a precaution, formed bends of S.S are given PWHT during fabrication stages. In some cases, joints with high heat input and joint design restrictions tend to develop SCC due to built-in residual stresses - unknowingly introduced during fabrication or error in joint design - even without forming stresses. Such left over residual stresses could promote SCC for S.S materials under specific corroding or process medium. PWHT consideration is normally decided by the user based on process system parameters, mechanical designer on weld geometry and design, welding speed and welding process. If trends of SCC are anticipated and are likely after a few years in service for a particular process system using S.S, PWHT would greatly help in controlling the SCC trend. For Ex: in a simple case of providing steam tracing for S.S piping or equipment, leaching of chlorides can cause SCC after some years for S.S materials whether formed bends or even without forming. Most users / designers / fabricators do not take this aspect into consideration while doing steam tracing. Many plants have experienced this problem after some years. Another Ex: If repeated condensation and evaporation is likely in weld joints in process systems with steam injection, SCC is likely after some years. Heat sink for welding and as a part of WPS for S.S joints, suggested by Debasis, is followed only by those who anticipate problems in future. This is not done as a routine during WPS or during field welding. in most fabrication at shop or in the field. Trust this is of help to you C.V.Srinivsan Nishi Engineers Pvt Ltd India Sept 06 E-mail:nishi@vsnl.com >Sir, > >I have one clarification on Stainless steel material heat >treatment. >Is there any international std which requires stress >releiving for SS316 material or weld joints.Under What >circumstances stress releiving requires for SS 316 welding. > > >Please reply to jayaashree@hotmail.com