51314-4053-Case Story in Refinery and Localised Corrosion Testing of UNS S32707 in Chlorides

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Product Number: 51314-4053-SG

ISBN: 4053 2014 CP

Author: Ulf Kivisakk

Publication Date: 2014

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UNS S32707 with a PRE?48 is a hyper duplex stainless steel with high strength and very good localised corrosion resistance. This grade is used as heat exchanger tubing in environments that needs high chloride induced corrosion resistance. In refinery this grade has showed 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 in UNS S32707 have been used for cooling the hydrocarbon stream with seawater where it is high risk for localised corrosion attacks.Recently new pitting corrosion and stress corrosion cracking experiments have been performed in both NaCl and MgCl2. The critical pitting temperature in modified ASTM G150 was determined at several chloride concentrations. In the stress corrosion cracking experiments both SSRT and constant load experiments were performed in solutions with high chloride concentration.As indicated by earlier results and the high PRE value the results show that CPT and CCT are higher for UNS S32707 than UNS S32750. Further the stress corrosion cracking resistance is equal or better for UNS S32707 than UNS S32750. No cracking was found in saturated NaCl at boiling temperature in both SSRT and constant load. In MgCl2 UNS S32707 for example experienced no cracking at 110°C in 7.5 M Cl- at a load at 90% of Rp0.2.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 refinery.