ONERLAY ABOUT ENiCrFe-3 ON 1Cr-1/2Mo

Date 07-30-2004 17:06

We preheat all of our welds on 1 1/4Cr-1/2Mo (B2 type metal) to 300F. However, most of our welds are on metal that is fairly thick. You may be able to get away without preheat or a lower preheat if your base metal is relatively thin. The other slight advantage you have is that nickel based fillers will not put as much hydrogen into the HAZ, where cracking is most likely. If it is a one time project, it is probably worth it to just preheat and be on the safe side. If you do it all the time, you would probably be better off to devise a series of experiments to determine the minimum preheat level.

By jiweiming (**)

Date 07-31-2004 04:01

Its very kind of you ,GRoberts, for ur response.
The wall thickness of the pressure vessel(coke drum in an oil refinery )is 28mm,1Cr-1/2Mo(B2 type metal) ,and the thickness of the overlay is 3mm,ENiCrFe-3.It is said when u r using the electrode of ENiCrFe-3,u have to keep the interpass temperature no higher than 100Ž,otherwise, it is easy to make a hot cracking.is it?if so,is it necessary to preheat before overlaying on 1Cr-1/2Mo(28mm)?

By GRoberts (***)

Date 08-01-2004 03:17

I have not heard about causing hot cracking with an interpass temp over 100(C?), but that does not mean it does not happen. Your application, however, seems to be ideal for requiring preheat. Thick plate, high residual stresses, and an application where a soft HAZ is essential. A good preheat would help all these circumstances. Is this a new fabrication or a repair? If it is a repair, the base metal could already have a high hydrogen content, and a pre &/or post weld hydrogen bake would also help.

By MBSims

Date 08-01-2004 03:48

Very wise words indeed! I've heard of a case where boiler waterwall tubes were overlayed with nickel-base material and, unknown to the contractor, there was some hydrogen damage to the tubes. After the unit started back up they experienced so many tube failures that all of the waterwall panels had to be replaced.