Dear Experts We have experienced a leak in the Non Phenolic Waste water stripper boiler outlet header (24”) in our Sulfur unit in the month of April 2010 .Leak is in the form of Pin hole in 2 O Clock and 10 O clock position.(Localized thickness loss near leaky portion).No thickness loss was observed in the other part of the header. Shell side : Stripped Water Tube Side : Steam Bundle Moc : Carbon Steel- U Tube bundle. We went for a patch plate welding in the leaky portion .Also the exchanger was pulled out and found severe thinning in the top three row s of the bundle. Three top row were chopped off. After 8 months of service we experienced another leak near to the patched location. Thickness loss is observed in area of 3”* 3” patch. Other area of header have no thickness reduction. Last times RCA was concluded as Low PH Acidic corrosion. I would like to know any body have experienced similar problem and what could be the probable cause of localized thickness loss and leak in the outlet header. Regards