Corrosion And Failure Analysis Of Welding Joint Between Austentic Stainless Steels Used For Petrochemical Equipment

Molecular sieve catalyst is one of the most important catalytic cracking catalysts in the process of petroleum refining and its production and preparation process are very complex. The temperature and pH of the process fluctuate large and this does harm to equipment. Carbon steel can not meet the requirement of process, so stainless steel, for example, 0Cr18Ni9Ti, 1Cr18Ni9Ti and 0Cr25Ni20, are used for molecular sieve equipments.Although stainless steel has excellent corrosion resistance, the lifespan of joint will be damnified after welding and using in the bad conditions. Serious corrosion may occur and causes the device to leak, or even rupture in petrochemical equipment because of its unique operation environment. Field research found that the failure concentrate on weld bead. The process engineer take remedial measures against equipment leak. To some extent, it is ease corrosion. But corrosion and leak could not be eliminated from the root. After a period of working, the problem occurs again.In this paper, the equipment material is sampled. The result shows that the corrosion mechanism is very complex. Forms of corrosion include pitting corrosion, crevice corrosion, stress cracking corrosion, intergranular corrosion and so on. In order to solve this corrosion problem, welding parameters is optimized and ENiCrMo-3 is chosen as welding electrode. The angle of groove weld and other parameters is changed. Welding procedure qualification of old and new procedures and their mechanical test, intergranular corrosion test, stress cracking corrosion test, coupon test are studied. The results show that the intergranular corrosion and stress cracking corrosion resistance of new welding procedure are better than old one. Metallographic examination shows that the size of grain of weld joint is fine and homogeneous for new procedure.