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The concept of noble metal chemical addition technology for IGSCC mitigation of structural materials
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1995
Year
Igscc MitigationNoble MetalsEngineeringNoble MetalChemistryMineral ProcessingStructural MaterialsChemical EngineeringCorrosionHydrogen Water ChemistryCorrosion ResistanceMaterials EngineeringMaterials ScienceSurface TreatmentHydrogenInorganic SynthesisCorrosion TechnologySurface ScienceHigh-performance MaterialHydrogen EmbrittlementMetal Processing
Hydrogen Water Chemistry (HWC) has been successfully employed to mitigate the IGSCC of BWR components in the recent years. However, to mitigate SCC in some vessel internals requires the use of high levels of feed water hydrogen, which results in high main steam radiation dose rate increases. Recent studies have shown that the presence of noble metals on these surfaces, by alloying or surface deposition by plating or various thermal spray coating techniques significantly reduced the hydrogen demand necessary to achieve the IGSCC protection potential of {minus}0.230 V(SHE). These techniques, although attractive, have some limitations because accessibility to individual components is a requirement for their successful application. This paper describes the concept of a novel method of applying noble metals potentially to all in-core wetted components by employing the reactor coolant water as the medium of transport for depositing noble metal on in-core metal surfaces. The concept of noble metal chemical addition (NMCA) technology has been successfully used in numerous laboratory tests to create a ``noble metal like`` (catalytic) surface on four of the major structural materials, Type 304 SS, Inconel 600, Alloy 182 weld metal and low alloy steel. The success of this technology has been tested using constantmore » extension rate tensile (CERT) tests, crack growth rate (CGR) tests and electrochemical corrosion potential (ECP) response tests. The NMCA technology has successfully decreased the ECP of surfaces below {minus}0.230 V(SHE), prevented crack initiation and mitigated crack growth rates in stoichiometric excess hydrogen in simulated boiling water reactor (BWR) environments, even at high oxygen or hydrogen peroxide levels. The NMCA treatment of surfaces has minimized the hydrogen demand necessary for IGSCC protection of the materials tested. Tests are in progress to qualify this process for operating BWRs.« less