First of all john, I need to apologize. I don't know what the hail I was thinkin. The primary thing, IMO, that needs to be done is INCREASING the cooling rate to prohibit the transformation of ferrite to austenite. Clearly you recognized this as evidenced by your forced air cooling statement, but were perhaps to polite to correct me.
I understand your 37kj/in and 212 interpass is low, and under normal circumstances would be well adequate. But I'm thinking this isn't normal circumstances. And the response from engineering that somehow 4% or 5% ferrite is critical to SCC is revealing. Not about the service "in my opinion", but the people responsible for the engineering. After all, continued testing is not going to be at their expense. It would be interesting however to see if they have definitive data stating the criticality of their ferrite % choice.
The way I see it you really only have two choices; change the filler (and thereby the chemistry) or speed up the cooling. Thats really all there is.
And here is another issue that could perhaps be used as ammunition. By speeding up the cooling rate too much N does not have time to diffuse to the austenite and can form Chromium nitrides(CrN and Cr2N), which are detrimental to corrosion as well.
No, it is my belief, that without definitive data proving the criticality of the 35% ferrite standard (which I believe they don't have, and have created the requirement right out of the duplex handbook), the responsible engineering and metallurgical thing to do is reduce the requirement for ferrite just a little. Thats always been the problem with duplex. Its a window. And going too far one way to avoid problems from the other just creates a whole new set of problems.
And one other thing, if you run your heat inputs too low, what is going to happen to your HAZ? The chemistry of the BM is not designed to handle that fast of a cooling rate. You might find your weld metal ferrite rising, but your base metal ferrite will rise as well. Perhaps to a level that is too high. I am assuming of course that your spec has a top side as well as a bottom side. Have the engineers given any thought to service difficulties if the HAZ ferrite is too high? Your weld metal ferrite might, I say might, increase by 4% or 5%, but your HAZ ferrite might increase by 15% or 20%. Or more.
John,
This is too little, too late, but I always recommend addressing the ferrite issue anytime 2209 stick electrodes are used on a job. Any time I'm asked to review a bid package, I always recommend the fabricator either directly talk to the Owner or some way of clarifying the issue of the almost certainty of lower ferrites when using stick electrodes. This can definitely eliminate a lot of cost (and grief) down the line. It should be perfectly clear to both the fabricator and the Owner of this issue. Of course I'm preaching to the choir in this case. But, a little communication can go a long way. P.S. The Avesta "How to Weld Avesta 2205" states that a minimum of 25% ferrite is adequate for strength and corrosion resistance.