51314-4441-Field testing of twelve corrosion resistant alloys in forced-oxidation wet flue ga

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Product Number: 51314-4441-SG

ISBN: 4441 2014 CP

Author: Brett Tossey

Publication Date: 2014

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The recent epidemic of localized corrosion in alloy wet flue gas desulfurization (WFGD) absorbers led to an industry-wide effort to reexamine the material selection for WFGD service. This paper presents the results of field cyclic potentiodynamic polarization testing (CPP) in free immersion coupon testing in flowing WFGD slurry. Free immersion test coupons were exposed for three months. CPP data was collected in situ at two power plants in the in-service absorber slurry. The absorber slurry was routed from an operating absorber into a novel side-tank test platform. 12 alloys were tested; UNS N10276 (C276) UNS N06625 (A625) UNS N06200 (C2000) UNS N08031 (UR31) UNS S32750 (2507 duplex) UNS S31254 (254SMO) UNS S32205 (2205) UNS S32550 (F255) UNS S34565 (UR4565) and UNS S31266 (UR66). Two coupon surface conditions were examined; an as-received surface and a rough ground surface. The rough ground surface was tested based on the findings of a root-cause analysis and to simulate grind marks that were left in place after fabrication of the absorber shell wall and floor. Using a categorization scheme developed in this study the results of the CPP curves were interpreted based on characteristic potential such as the open circuit potential and the repassivation potential and their overall shape. The results showed that surface preparation and alloy content have a dramatic effect on the alloys resistance to localized corrosion. Many of the alloys that were tested exhibited classic localized corrosion behavior during the CPP test.