Bigpond There is no theoretical limitation so long as you do proper PWHT for F22 after repair welding. Variation in profile hardness should indicate if the PWHT had been done properly. Most users do not take the aspect of complete profile hardness across accessible areas of the exchanger forgings and assume / rely on the temperature record profile given by the PWHT record. However, the point to be remembered is: Why a second time repair is warranted / necessitated if the original PWHT after first repair had been done properly? This aspect has to be studied by you thoroughly. Most of the time, for heavy wall thick F 22 forgings - F22 forgings used for ex: for Syn Gas WHB service in Ammonia synthesis services, variation in hardness profile may occur - both across thickness section and also for the diameter that is being PWHT after repair welding. If this aspect of a complete profile hardness measurement is well controlled, success in PWHT is ensured to avoid a second or third time repair in F 22 forgings. Hope this helps C.V.Srinivasan Nishi Engineers Pvt Ltd India April 17, 2009 E-mail: nishi@vsnl.com >Hi, >We have an inservice exchanger made in F22 which is being >repaired for the second time, each repair is followed by >PWHT. The question being asked on whether is there any >limitation on the number of times a metal can be heat >treated. I would like to understand which way it will affect >its tensile strength and how. Theoritically the exchagners >gets back to its nomral properties after each post weld heat >treatment. Secondly if it does how can we make sure that the >metal doesnt loose its properties. >regards

Bigpond Think of a lower attainable but sustainable temp for all components so that variation effects are minimized to a large extent if wide variation in wall thickness exists in forging or components attached to forging. At lower temp, you may have to hold for a longer time , to meet Code practices for PWHT, but that may improve in reducing hardness variations as well as improving tempering conditions Hope this helps C.V.Srinivasan Nishi Engineers Pvt Ltd India April 29, 2009 E-mail: nishi@vsnl.com >Thanks, this was very useful and informative. The problem in >this case was with vessel components of varying thicknesses >which poses restricitons to what max temperature you can go, >especially in repair cases. >regards