Study on the Stainless Steel Used for Fractionator in Crude Oil Distillation Unit

Abstract

The environment is highly corrosive in the top section of fractionator in the crude oil distillation unit. SUS27 (18-8 steel) was failured due to stress corrosion cracking in 3 months and SUS38 (13Cr-Al steel) due to severe general corrosion. Corrosion resistance of typical austenitic and ferritic stainless steels and the developed 17Cr-Mo steel were compared in such an environment. Then, corrosion resistance of these steels in a few mineral acid solutions and of their weld joints were compared in laboratory.The results were as follows:(a) In the top section of fractionator, 17Cr-Mo steel (containing 0.5-2%Mo) is most resistant to general or pitting corrosion and/or stress corrosion cracking.(b) In laboratory tests, 17Cr-Mo steel shows the lowest corrosion rate in hydrochloric acid solution of 0.1% concentration or less.(c) Austenitic steel containing Mo also shows low corrosion rate in dilute hydrochloric acid solution, but it appears to be susceptible to stress corrosion cracking in dilute hydrochloric acid solution saturated with hydrogen sulfide, judging from test results with SUS27 (18-8).(d) Weld joint of 17Cr-Mo steel is resistant to corrosion as well as the base sheet or plate itself.