Corrosion Enhancement for FGM Coolant Pipes Subjected to High-Temperature and Hydrostatic Pressure

Abstract

The objective of this paper is to enhance the corrosion resistance of coolant pipes in high temperature and lateral hydrostatic pressure in critical engineering environment, especially for circular coolant pipes under hydrostatic pressure of LBE (lead-bismuth eutectic) applications in nuclear power plants. The resistance against corrosion caused by LBE liquid is mainly formed by Fe-12Cr-2Si solid solutions coatings on the pipe. The silicon concentration in Fe-12Cr-2Si can interact with LBE as an effective oxidized compound such as SiO2 and Fe2SiO4 when the silicon concentration is higher than 1.25 wt.%. The oxide film formed on the coating can resist the LBE corroding in the Fe-12Cr-2Si structure. The primary material of a constructing coolant pipe is T91 ferritic-martensitic alloys, and the surface anti-corrosion coating is Fe-12Cr-2Si solid solution. With a high strength structure, FGC (functionally graded composite material), ensures that the pipe resists the corrosion from LBE liquid. In this study, both the steady-state stress values and silicon concentration are evaluated at 700, 1000, and 1200 °C to know the fatigue problems. The research result indicates the FGM (functionally graded material) structure performs better in promoting the margin of safety on stress distribution and reserving the silicon concentration on the inner surface higher than 1.25 wt.% over 60 years as compared to the FGC structure with 34 μm thickness of Fe-12Cr-2Si coating in a high temperature environment.

Studies on In Situ Alloy Formation Using Mild Steel–Inconel 625 Twin Filler Wire Gas Tungsten Arc Weld Deposition

“…A few examples of FGM are the SS321/IN 625 FGM fabricated by Mohan et al for aerospace application by the WAAM technique [9] and Inconel 718/SS 316L FGM, successfully printed by Sang Hoon Kim et al via DED, the chemical composition of the FGM being varied in steps of 10 wt% for the two materials across their build [10,11]. Kai-Chien Lo et al created an FGM that enhances the corrosion resistance of coolant pipes at high temperature and under hydrostatic pressure of LBE (lead-bismuth eutectic) applications in nuclear power plants by the 3D laser printing technique [12]. This work focused on printing a mild steel (E7018)-Inconel 625 FGM on an in house fabricated dual filler GTAW-WAAM setup.…”