I need help with a column I am looking at. It is constructed with 316l the plates are 10mm thick, the welding process was stick, the vessel is used to seperate dimethly formamide (DMF) and tri-ethylamine (TEA). I cant give you any info on the welding procedure or post weld treatment The vessel in the last 6 months has had a new bottom reboiler fitted, again the materials is 316L The operating temp is 140 deg c the waste products from the process is formic acid 2-3% and water 12% "Black" products from reboiler tubes X-ray diffraction: NiO, traces Mo and Fe formate Energy dispersive analysis: Ni, Fe, Cr, Cl, S Bottom strip (waste) fluid (various analyses) Chromatography: 2-3% triethylamine, 2-3% formic acid, 10-12% water Ion chromatography: 20-120 ppm chloride; 10-50 ppm sulphate Atomic adsorption: Fe, Cr, Ni all < 5-10 ppm "Brown" products outside column X-ray diffraction: amorphous Energy dispersive analysis: Ni, Fe, Mo, Cl, S, Si, Al, Ca, Mg There has been a leak at the circ weld, (butt weld, back chipped out and re-welded) that connects the new bottom to the old column. What we have internall looks like excessive pitting, (not deep) either side of the weld around the full circumference. In addition to this there is pitting externally at the weld. The column isn't insulated or painted and open to the enviroment This is the first time we have had to deal with 316L so any help with the problem would be greatly appreciated. I have photos I can forward on that show the problems in greater detail. My apolgies if the data above seems amateurish I am not by any means an expert in corrosion

Hi Actually 316L is showed recently corrosion issue in presence of the chloride. So, the amount of the Chloride is too high and the possibility of the crack will be high and in alarm zone. What you are going to do is to coat the area that affected by the wet chloride such as Belozona coating. Thanks