Solution annealing of 304H S.S.

[vesselguy]

All,

I would like to hear some opinions and advise on doing solution annealing of Type 304H aust. S.S. in the field.

I have a 43" ID x 3/4" thk. pipe section (line) in an FCCU operation. 50 psi design pressure, 1385 F design temp. Portions of the line has an elbow made from 304 material piping dating back to 1970 and some 304H piping from the 1990 & 1993 refitting.

It is known the aged elbow from 1970 has suffered from sigmatization and thus is embrittled. No metallograph was done for the newer stuff so I don't know. I'm sure they have been senitized, but it does not matter since this service is only flue gas.

I susgested to cut away the stuff from 1970 and some parts from the 1990 and weld on new replacements for other mechanical reasons which I don't need to discuss here. All the future field weld joints will be at the newer materials (1990 and onward).

The questions is, after cutting off the piping parts must I do field solution annealing to bring back the mechanical properties of the S.S. (to almost like new condition) before I weld on the new parts?

A study done before my work suggests it needs to be done otherwise, the welder will be "chasing cracks" after welding. I say, we don't have to solution anneal for the joints at the "newer" (1990 onward) materials. I have my reason for that but I will keep it to myself for now until I hear any respondent.

Thanks for reading and hope to hear some expert opinion and past experiences.

 

[stanweld]

Your question really is based on whether the 1990 material has suffered sufficient embrittlement to cause cracking. I can only say that we have made repairs to 304H with similar exposures without resorting to solution treating the weld area in the exposed material prior to welding.

Have you checked these areas for sigma? It would appear that you would have no trouble doing so? In any event, you will find out quickly enough when you make the first welds.

You may wish to butter the old material, rebevel and then make the strength weld. I have used this method in the past for weld repairing other embrittled materials.

 

[vesselguy]

Stanweld,

Your interpretation is right on. The concern is with the "newer" 1990 material. The area of concern is in operation right now and is under insulation. Can one do the metallographic etching when the metal temp is around 1300F? I don't think so right? If so, I have to wait till next year's shut down, however, I have to make the recommendation and planning way before that.

My understanding for buttering a joint is used for joining disimilar metals. How will buttering the "old" joint make for any improvement here? Please help me lite the dim lamp for me.

 

[stanweld]

You are correct, you cannot check it now.

Buttering puts the base metal under it in compression. When you subsequently make the butt weld, the primary residual tension stress is in the ductile deposited weld metal not the embrittled metal. I have used this in a number of similar repairs where standard repair techniques failed.

 

[vesselguy]

Thanks for sharing that bit of info, Stanweld. I've not heard of that before. If the point is to let the buttering pass take some of the shrinkage stresses then I would say the buttering pass should be at least 1/4" final thickness.

 

[stanweld]

Agree