Warm or hot rolling of SA387 Gr22 cladded plates

[teokal]

Hi all,
I am facing the following problem: We are building a hydrocracker reactor from SA387 Gr22 plates, cladded with 347 (T=84+3mm). The plates have been normalized and tempered in the mill. The welds are to suffer DHT and finally PWHT. Our rolling machine can barely roll those pieces, but if you consider that they are of a big quantity, the time delay will be disasterous. I have been thinking of warm rolling (up to 593 deg C) in the furnace, and immediately rolling. This is something familiar to us, we tried it on the same plates' remains, and it works. Of course, productivity is extremely better when warm rolling. PT, MT, UT thickness, tensile and impact tests seem to be OK. Nowhere in the literature is mentioned if I am allowed to do it or not, or what are the precautions. Applicable job specs and codes (API 934, UOP 3-12-5, ASME VIII div1) do not refer to this. On the other hand, a colleague told me that if the plates are normalized, I should re-normalize them, if I intent to perform warm rolling...
Does anyone have an idea?
Thanks a lot...

 

[metengr]

teokal;
Based on my experience with Cr-Mo steels, it would be wise to hot form the plate into the desired shape followed by a complete re-heat treatment in accordance with the proper material specification. The concept of hot working is to reduce the flow stress of the material to enable lower loads for forming. The upside is this, the downside is re-heat treatment is usually necessary for N&T formed plate.

Hot working versus warm working has more to do with recrystallization temperature. However, in this case, I would consider it hot working and as such re-heat treatment is necessary to achieve the desired final mechanical properties.

 

[metengr]

teokal;
One follow-up comment after re-reading the OP, since the carbon steel plates are already clad with stainless this results in a more complex problem. If the CS plates were bare, my initial response would be the best approach to assure complete removal of all tensile fiber strains during forming and a uniform grain structure.

If you have evaluated the effects of hot working on cut outs of the same plate at or below the original tempering temperature of the plate from the mill, and the mechanical properties are still acceptable in accordance with the original plate specification for a N&T heat treatment, this should suffice. You always want to minimize exposure of any stainless steel cladding to thermal treatments during fabrication.