In a number of chemical processes, apparatus made from stainless steels undergo dangerous types of pitting corrosion: intercrystalline corrosion, corrosion cracking, and corrosion fatigue. As an example of the substantial effects of the process parameters, the corrosion failure of cyclohexane oxidation reactors is cited. A detailed inspection showed that on the inner surfaces of the reactors a large number of areas appeared from which surface defects on the sheet were removed before operation, followed by welding on and trimming. These rewelded parts of the basic metal, as well as the longitudinal and annular welds, were strongly etched and underwent pitting corrosion. The considerable residual stresses in the welded joints and the rewelded areas promoted the formation and development of intense corrosion cracking. After repairing the unit, it was operated under conditions which did not permit an increase in temperature above 140/sup 0/C. Inspection of the reactors over 10 years operation showed that only at individual sites of the welds that had not been annealed had the weld metal undergone structure-selective corrosion. The equipment should therefore be fabricated taking into account that it is desirable to lower the residual stresses, to remove the strengthening of welded joints, and to polish themore » internal surface followed by subsequent light etching« less