Causes for Surface Corrosion of 1Cr18Ni9Ti Stainless Steel Globe

Corrosion pits were found at the surface of a 1Cr18Ni9Ti stainless globe after acid pickling. The causes for the corrosion pits were analyzed by using scanning electron microscopy(SEM), energy dispersive spectrum(EDS), and metallographic microscopy. The results show that the globe became locally sensitized in the welding process. The grain size of the globe was smaller than that of the out nut, and consequently, the corrosion resistance of the globe was weaker than that of the out nut. In the acid pickling process, the gaps formed between the out nut and the globe weld zone as well as between the out nut and the mouth weld zone. The moving of positive and negative ions in the pickling solution was blocked, causing serious corrosion in the gaps. As a result, pitting corrosion was present at the surface of the globe. Periodic replacement of the pickling bath, reducing Cl ion concentration, and moving parts in the pickling process can reduce the generation of such corrosion.