A contractor is going to make a repair, in a hydro power plant, on the weld between a 15 feet diameter runner outer cover made of stainless steel to a carbon steel draft tube, because there are cracks and corrosion at the joint.
-The contractor proposes to do the welding with E309L-16 with a 200 deg F preheat, because there are indications that that's probably what was done 20 years ago
- An expert we've consulted believes welding with ENiCrFe3 with a 500 deg F preheat would be better. This expert says that this material and level of preheat temperature is needed to avoid future cracking, which may happen with the E309 because we are not sure of what kind the stainless steel is, so he's proposing a 'silver bullet". In this case there is concern about distortion with such a large diameter piece.
I'd appreciate your comments and advise on kind of electrode to use and level of preheat.
Thanks
jemayen
I too would be hesitant to apply that much heat to a cover like that.
I am guessing this is a horizontal, or some tilt axis type unit?
Anyway, my two cents- I'd keep the 309L and keep the preheat to a minimum. One would think an "expert" would get some drillings for the stainless analysis if he is concerned about it. If the original 309L lasted 20 yrs. why re-invent the wheel now?
(Ask the Army Corps. what happened at Truman Dam when too much heat was applied to a cover).
Tnamks for your prompt advise Bill.
This is a large vertical shaft unit and the weld will be horizontal along the circumference
Tnaks again
jemayen
I looked at one of these just before Thanksgiving while repairing a cracked blade. The carbon steel is not likely to be thick enough to require preheat, but considering the cold temperatures this time of year some preheat is warranted. The 309 will not be any more likely to contribute to the corrosion problem than Inconel. I would repair the cracks and corrosion with 309 (preferably FCAW or solid wire GMAW). It may also be helpful to drill holes into the liner after the repair and pump urethane sealer into the gap between the liner and the concrete to help seal it off from water and slow the corrosion. I would also consider grit blasting a band 6" above the weld down to 18" below the weld and applying an epoxy coating.
Forum
