Failure of drain valve reducer in de-sulfurisation unit

Abstract

The amount of sulfur in various crude fractions used as fuel or internal combustion engineis to be reduced to avoid pollution hazard. This requires removal of sulfur as H2S, which is accomplished by reactinga mixture of HC + H2 in presence of a catalyst at high temperature and pressure. In the process any chlorine and nitrogen compound present are also converted into HCl and NH3, which in turn along with H2S form polythionic acid, ammonium bi sulfide and ammonium chloride. Of these,austenitic stainless steels are susceptible to stress corrosion cracking inpolythionic acid and chlorides. The paper presents a case study of cracking of drain valve reducer in atmospheric residue desulfurizer(ARDS) unit. DP test confirmed that the cracking was initiated and propagated from inner surface and propagated outward. Optical and SEM metallography and fractographic examination confirmed the cracking to be a case of chloride stress corrosion cracking, presence of chloride being confirmed on the basis of EDAX analysis of cracked surface. The source of chloride in all probability was neutralizing solution, wash water and possible process side chloride deposits on the surface of various equipment.