Two cases involving failure by corrosion of lead linings in sulfuric evaporators are reported. Case 1 involved an investigation of the reasons for a difference in service life of almost four to one between sheet supplied by two plants of the same manufacturer. The investigation showed the sheet failing in 18 months had a crystalline structure in which some crystals were 50 to 60 times greater in surface area than others. The smaller crystals appeared to be anodic to the large ones as pinholes in the sheet appeared to be at the location of the small crystals. The other sheet, which lasted seven years, was found to lack crystalline structure almost completely, indicating proper cooling technique.
Case 2 involved rapid disintegration of the lining of an evaporator into which prevailing winds introduced abrasive dusts from a nearby steel mill. It was postulated and proved in laboratory tests that the abrasive continuously removed the protective lead sulfate coating. When the evaporator was enclosed to exclude the dust, the trouble disappeared.
