NOTICE

Forums are temporarily disabled while we are working on a new login procedure.

When migrating the old forums over to our new forums we were unable to retain the identity of the authors, so the old posts will show up as "anonymous". All NEW posts will show up credited to their authors. So please participate and share knowledge just as you have in the past.

You must log in if you are an existing user or register if you are a new user in order to contribute to the discussions.

Discussion Forums - The Hendrix Group
HomeHomeDiscussionsDiscussionsGeneral Corrosi...General Corrosi...HELP!!!  PittingHELP!!! Pitting
Previous
 
Next
New Post
9/11/2006 9:00 AM
 
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
 
New Post
9/15/2006 9:00 AM
 
Sounds like the weld was not passivated. With the Cl present this could easily cause pitting in the heat affected zone. Once the pits are formed it is VERY difficult to remove the rust, as it keeps bleeding out of the pits and "feeding on itself". If it is possible at this stage, you need to grind off the corroded material, passivate the surface and then you should be good as long as the chloride content is not too high. If this does not resolve the problem for the chemistry involved, you should go to a Duples grade.
 
New Post
9/16/2006 9:00 AM
 
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
 
New Post
11/8/2006 9:00 AM
 
Steve The best advice i can give is to re read the the learning objectives. What ever topics you have covered will lead you to the ones you haven't. Here lies the answer. Failing that read the main failure modes of stainless steel due to corrosion. Look again at the pictures and you will also have the answer.
 
Previous
 
Next
HomeHomeDiscussionsDiscussionsGeneral Corrosi...General Corrosi...HELP!!!  PittingHELP!!! Pitting


  

News

With a little delay, our Calculation of Ammonium Salt Deposition Temperatures...read more
Our sulfidic corrosion calculators are now available at hghouston.com/calcula...read more

Stay Current

Sign up for our quarterly newsletter

covering updates on corrosion

Sign Up