Dear All

this is a practical problem for which I need a quick solution/advice..in our naphtha cracker unit there is material of composition 35Cr45Ni(bal Fe,etc). These are statically cast austenitic Wye pieces from Paralloy. We need to repair weld some puctures. metallurgists from paralloy/doncasters have advised to preheat the piece to 400degC and maintain the same interpass temp . This condition will be highly uncomfortable for the welder. Being a young metallurgist myself I am keen know why such high preheat temp is reqd. Is it absolutely necessary? We will be using Inconel 617 filler wire. In this context I would like to mention that for centrifugally cast tubes of same material we donot do any preheat during welding. Please suggest some good URLs where useful informations is available.