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Polyurethane insulation materials can cause corrosion in metals under certain conditions; there is therefore not a complete absence of corrosion risk. The main cause of corrosion is that polyurethane releases acidic substances with a pH value of 3–5 in environments containing water. Meanwhile, harmful components remaining in the material, such as chlorides, potassium oxide, and sodium oxide, form a strong electrolytic water film on the metal surface, creating conditions for electrochemical corrosion. If the insulation layer is damaged, an oxygen concentration cell is formed; the damaged area receives an adequate supply of oxygen, creating a potential difference with the surrounding oxygen-deficient areas, which accelerates local corrosion of the metal. Performance under normal operating conditions: Qualified closed-cell polyurethane insulation materials have a cell closure rate of over 90%, with extremely low water absorption. They can effectively block water and air. When used under normal conditions, they do not corrode metals; instead, they provide protection for metal pipes. Polyurethane-insulated steel pipes that are buried underground for extended periods, as long as their insulation layer remains intact, generally experience limited corrosion of the steel pipe itself; significant oxidation and rusting occur only when the waterproofing fails and moisture gets in. Methods to avoid corrosion: Give priority to polyurethane anti-corrosion insulation materials, which have good corrosion resistance and can significantly reduce the risk of corrosion. The metal surface is pre-treated with sandblasting to remove rust, followed by the application of epoxy polyurethane anti-corrosion coating, thereby creating a dual-layer anti-corrosion protection system. Ensure proper waterproof sealing of the insulation layer to prevent external moisture from penetrating it, thereby eliminating the water medium necessary for corrosion at its source.