Post weld heat treatment on 4140 H ?

By nateprice215 Date 07-31-2007 12:41

Hello:

Have any welders out there had experience with not post weld heat treating 4140H? We have some 4" threaded pipe 0.4" thick. It is like drill pipe, but used in a refinery. We have sprung a little leak and some had the idea of seal welding the threads, but I am under the impression that PWHT would be required.

Have any of you welders out there had similar experience?
Thanks,
Nate

By DaveBoyer (*****)

Date 08-01-2007 05:32

I don't have experience, but without post weld heat treat, there is going to be hardened but untempered material in and around the weld. This will be suseptable to cracks, and depending on the circumstances they could propagate beyond the HAZ. That is My opinion, YMMV [Your mileage may vary]

By RonG

Date 08-01-2007 12:21

Just curious but what is the product and pressure to require 4140H pipe?

By nateprice215 Date 08-01-2007 19:09

Thanks for your replies;

The service is actually water at 4000 psi. Outside the pipe is coke, H2s, hydrocarbons, steam, water, and I think that is about it. Regarding the untempered martensite; wouldn't the high preheat (400°F) not allow the cooling to go below the transformation temperature? I know there would be a hardened area, but maybe not completely from martensite?

These are not normally welded at all since they are threaded, but this was just a small fillet weld to seal the mating surface of the threads.

Thanks,
Nate

By RonG

Date 08-01-2007 21:08

From the question I am guessing you do not have access to PQR or WPS to work from which is not a good practice.

My thoughts on the subject that are sure to open the flood gates and you will most likely be inundated with more information than you can process in a short time.

The preheat is critical as you aware but a full PWHT could be detrimental because you may need the as welded properties which depending on what PWHT temp you use could lose.

I know of similar situations where a 600'F/8-16 hours Hydrogen bake out process was used versus a high temp PWHT.

I am not a Engineer or Metallurgist but I have preformed the above process in the field more than a couple times 20 years ago with out problems.