post heating of weld for 9 Cr material 1

[lahane1443]

I have to fabricate 20 identical tags in which a single spool piece of 4.2 meter long is having 16[1.5" sch160] nozzles welded on a 4" sch120 pipe [A335 P9] material.

My weld procedure calls for post heating at 300 deg C for min 1 Hr.
I will weld 4 nozzles at a time. what is the best method available for post heating of this nozzles? i do not want to use manual way of heating these by gas burner or cutting torch?

A quick response is highly appreciated.

 

[stanweld]

To what Code are you welding? The 300 C PWHT is only a dehydrogenation procedure and would not be accepetd under most Codes as the final PWHT. The spool should be post weld heat treated in a furnace.

 

[vpl]

stanweld,

For my own edification, would you only do one PWHT after all 16 nozzles were welded? The OP's comment about "doing 4 nozzles at a time" had me wondering if he thought he needed to do separate PWHT after each set of 4.

Patricia Lougheed

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[stanweld]

I would make all branch attachments and then PWHT in a furnace. This is done all the time on low alloy steel headers where multiple branches are installed.

 

[lahane1443]

stanweld,

sorry for late response.

Design code is B31.3 & yes, i will be doing PWHT also at 740 deg C for 3 Hrs. job thickness is 11.13 mm.

one of the consultant advised me that you will need to do PWHT of whole unit at a time within 72 hours from weld completion & if you delay the PWHT beyond 72 hrs. it will have adverse effect on the material. Is it tru?

Can you advise me how to go about it . will it be okay if i weld 4 branch at a time ,do post heating for those 4 branch joint at a time then move on to second lot of 4 branch joint, complete it & post heat it. And after completing all 4 sets go for complete PWHT of spool piece by electric resistance method.

but to complete welding of all 4 sets will take 4 days time, so i have fear that PWHT of whole unit will not take place in 72 hrs.

Awating your quick response

 

[stanweld]

The 72 hr issue pertains to the potential for delayed hydrogen cracking. If you locally or furnace dehydrogenation heat treat and use low hydrogen welding processes and maintain preheat at 400F, you should have no problems with delayed cracking. You can also maintain the 400 F preheat throughout the spool fabrication and disregard the dehydrogenation process.