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what next

what next

what next

(OP)
severe uniform Corrosion  in Amine Stripper column at a gas sweeting plant
after few years of service the amine stripper columns (A516-Gr70) started leaking from different points mainly near nozzle welds and seams of the tower.these leakages were stoppped by placing patches with mechanical binding.  now during shutdown when these defects were being repaired by welding (preheating was looked after with care), they posed a tough problem , that was; lot of tranverse cracks about (1") started appearing (in radiography) where the seam was repaired. after rewelding we couldnt get rid of all the defects. one of the seam of 132" dia got its 45% length repaired. now the question why these defects appeared and how many times and how much area of the weld we can repair ? severe uniform corrosion was observed inside the shell.   
Now the status is that shutdown of the plant is over. all repairs havebeen made.As i told you, and you can well imagine the repairs by one example that one of the seam of the stripper having 132" circumferential length has got 60" (in total) at different locations repaired, which also contains re-repairs. this seam is about bottom half of the almost 20 meter amine stripper column. well that is the worst example but other welds are getting towards the situation.(How much repair welding can be done and how many times on the same location?)
Hardness (175-210 HB) and Thickness (18-20 mm; at some points there is reduction of 1 to 2mm ) measurement at different locations havebeen made and found satisfactory.
The issue is how we can assess the fitness of the stripper for further operation because we know that there were lot of leakages earlier, so in future, we can expect the same as the material has degraded(we have yet to prove it). Can you kindly advice how to proceed for the evaluation for hydrogen or sulfide (as stripping of H2S) induced damage.Probably Metallography (details or reference from net), strain rate test,  fracture analysis or some kind of ultrasonic inspection.(we can get 2-3 meter removed part of vapor return line of the same conditions.)
what would be remedial actions? (not going to use surface coating inside the shell, neither using nor have any plan of using inhibitors).
    
Hoping to get answer

RE: what next

The ASMI "Metals Handbook"  Volume 13, Corrosion tackles the amine regenerator (stripper) corrosion problems and suggests solutions.

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