Case stories in refinery and localized corrosion testing of UNS S32707 in chlorides

摘要

UNS S32707 with a pitting resistance equivalent number, PREN≥48 is a hyper duplex stainless steel with high strength and very good localized corrosion resistance. This grade is used as heat exchanger tubing in environments that need high chloride induced corrosion resistance. In a refinery this grade has been shown to be a problem solver in seawater cooled heat exchangers. A case story shows that UNS S32707 works well in an atmospheric crude distillation unit in a refinery in Venezuela. The tubes of UNS S32707 have been used for cooling the hydrocarbon stream with seawater where it is at a high risk for localized corrosion attacks. Another case story in a vacuum distillation unit shows that UNS S32707 has very good resistance to under deposit corrosion. Recently new pitting corrosion and stress corrosion cracking experiments have been performed on UNS S32707 in both NaCl and MgCl_2. The critical crevice temperature, CCT, was determined in NaCl in modified ASTM G150.5 In the stress corrosion cracking experiments both slow strain rate test (SSRT) and constant load experiments were performed in solutions with high chloride concentration. The experimental results are discussed and compared with the results from earlier published long term testing of model heat exchangers in chlorinated seawater as well as recent case stories in the refining industry.