The Effect of Microstructural Variation on the Hydrogen Environment-Assisted Cracking of Monel K-500
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L K-500 is a Ni-Cu-Al superalloy commonly used in marine applications due to its excellent combination of corrosion resistance, strength, and fracture toughness. For such applications, environment-assisted cracking (EAC) is historically evaluated via a wide- and
ZACHARY D. HARRIS, Graduate Student, BRENDY C. RINCON TROCONIS, Research Associate, JOHN R. SCULLY, Charles Henderson Chaired Professor of Materials Science and Engineering, and JAMES T. BURNS, Assistant Professor, are with the Center for Electrochemical Science and Engineering, Department of Materials Science and Engineering, University of Virginia, Charlottesville, VA 22904. Contact e-mail: [email protected] JUSTIN D. DOLPH, formerly Graduate Student with the Center for Electrochemical Science and Engineering, Department of Materials Science and Engineering, University of Virginia, is now Staff Engineer with Elzly Technology Corporation, Reston, VA 20190. GREGER L. PIOSZAK, formerly Graduate Student with the Center for Electrochemical Science and Engineering, Department of Materials Science and Engineering, University of Virginia, is now Senior Materials Engineer with Exxon Mobil Corporation, Houston, TX 77386. Manuscript submitted December 21, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS A
diverse-range of testing approaches (e.g., NACE MR0175 and ASTM G30, G39, G129, E1681, and F1624[1–6]). Material selection engineers will often use data from such tests in a ‘‘go/no-go’’ paradigm where the long-term EAC resistance is inferred by empirical material testing. Specifically, if testing indicates that the service environment and loading conditions are below a threshold level of severity, it is then assumed that cracking will not occur over the lifetime of the component. Such an approach is codified in NACE MR0175 which outlines guidelines for the selection of ‘‘cracking resistant materials’’ in H2S environments (of note is that this specification does state that materials meeting this standard are ‘‘not necessarily’’ immune under all service conditions). The inadequacy of this ‘‘go/no-go’’ approach is demonstrated by isolated long-time (~10 year) service failures of Monel K-500 components on North Sea oil and gas platforms, deep gas wells, and US Navy sea vessels.[7–13] In each of these cases, the Monel K-500 components were immersed in seawater and cathodically polarized to protect adjacent carbon and low alloy steel structures. This service environment, combined with the observation of fracture surfaces that exhibited intergranular (IG) with small amounts of transgranular (TG) crack growth,[7,8,11–13] suggests that
the failure of these components can be attributed to EAC—an assessment corroborated by laboratory testing of Ni-based superalloys.[14–18] These service failures expose critical, nonconservative flaws in the existing approach to EAC management for current- and next-generation materials. Specifically, current EAC characterization techniques, material selection criteria, and structural integrity prognosis approaches fail to fully account for condit
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