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Combined with the previously mentioned background that polyurethane insulation materials will precipitate acidic substances when exposed to moisture and form a chloride-ion-containing electrolyte environment, the following are the types of metals with excellent corrosion resistance in this environment.: High-grade austenitic stainless steel such as 316L, 316LN and other molybdenum-containing low-carbon stainless steels. The molybdenum element can significantly improve the resistance to pitting corrosion and crevice corrosion. It can resist the corrosion of weakly acidic media and trace chlorine ions precipitated by polyurethane, and has extremely low corrosion rates in long-term service. A dense and stable titanium dioxide passivation film is formed on the surface of titanium and titanium alloys, and almost no corrosion occurs in the weakly acidic, chloride-ion-containing environment created by polyurethane. The performance can be maintained even under high temperature and high humidity conditions. High-nickel-based corrosion-resistant alloys such as Hastelloy and Inconel. These metals contain nickel, chromium, and molybdenum as core components. They have strong resistance to electrochemical corrosion and can withstand extreme acidic and high-chloride ion working conditions in polyurethane environments. They are often used in harsh industrial pipeline insulation scenarios. High-chromium ferritic stainless steel, such as 444 and other ultra-pure high-chromium ferritic stainless steel, has extremely low carbon and nitrogen content and a chromium content of more than 18%. Its resistance to chloride ion pitting corrosion is better than that of ordinary 304 stainless steel, and it is less prone to local corrosion in polyurethane insulation environments. The passivation films of rare corrosion-resistant metals such as zirconium and tantalum are extremely stable and are almost not corroded by various chemical media in the polyurethane system. They are only used as special components in extremely strong corrosion scenarios.