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Discussion Forums - The Hendrix Group
HomeHomeDiscussionsDiscussionsGeneral Corrosi...General Corrosi...Heat Treatment and side effectsHeat Treatment and side effects
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9/5/2008 9:00 AM
 
We have recently replaced a BFW preheater (U tube cnst.) with F22 channel, all connected piping to it are F22 due to presence of hydrogen gas at higher temperature. While welding the connected piping (P22 10" Sch 160) , there are concerns with the temp gradient of the nozzle which is 107mm and was not heated completely. There are thoughts that due to relatively cooler forging, the entire nozzle may be stressed and may be favorable site for hydrogen attack. I request your expert opinon on these queries: 1. How do these forgnings are welded where differential thicknesses are involved. 2. How do we know that forging / nozzles are affected, if yes that whether these are stressed and to what extent. (will FEA will help) 3. Will doing the entire pwht of entire channel including nozzle will help. 3. The pwht was done at 690 Deg C and distance of nozzle to piping weld is 400 m from the shell. 4. Is there any NDT which can bring some confidence to what we have done. cheers
 
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9/6/2008 9:00 AM
 
Bigpond 1.Welding F 22 forged nozzle with P 22 - 10" Sch 160 pipe, joint preparation should match the lower thickness like what is normally done for a WN flange. 2.You can wrap up the F 22 nozzle during welding to avoid the temperature differential. FEA is not needed. 3.PWHT - both the F 22 and the P 22 joint and with thorough insulation of the joint and that of the F 22 forging, PWHT temp is usually 720 deg + or minus 10 deg cent. If you are not able to attain this temp due to heat dissipation or some other factor, you can keep at 690+/- 10 deg cent for a slighter longer time. This will reduce the stresses in weld and in the forging and piping. 4. NDT: Radiograph the weld joint or do UT Flaw check of the weld joint. Take hardness after PWHT on the joint /HAZ/parent forging /piping Hope this helps C.V.Srinivasan Nishi Engineers Pvt Ltd India Sept 06. 2008 E-mal: nishi@vsnl.com >We have recently replaced a BFW preheater (U tube cnst.) >with F22 channel, all connected piping to it are F22 due to >presence of hydrogen gas at higher temperature. While >welding the connected piping (P22 10" Sch 160) , there are >concerns with the temp gradient of the nozzle which is 107mm >and was not heated completely. There are thoughts that due >to relatively cooler forging, the entire nozzle may be >stressed and may be favorable site for hydrogen attack. I >request your expert opinon on these queries: >1. How do these forgnings are welded where differential >thicknesses are involved. >2. How do we know that forging / nozzles are affected, if >yes that whether these are stressed and to what extent. >(will FEA will help) >3. Will doing the entire pwht of entire channel including >nozzle will help. >3. The pwht was done at 690 Deg C and distance of nozzle to >piping weld is 400 m from the shell. >4. Is there any NDT which can bring some confidence to what >we have done. >cheers >
 
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