ASTM A335 Grade P91 is a specification for seamless alloy steel pipes intended for high-temperature service. Here's a detailed overview: ASTM A335 Grade P91 Alloy Steel Pipe 1. Material Type: Alloy steel, specifically a chromium-molybdenum (Cr-Mo) steel. 2. Composition: Primarily designed with about 9% Chromium (Cr) and 1% Molybdenum (Mo). Other elements typically include Carbon (C), Manganese (Mn), Silicon (Si), Nickel (Ni), and Vanadium (V), optimized for high strength and resistance to high-temperature creep. 3. Applications: Used in power plants, refineries, and petrochemical industries. Suitable for high-temperature and high-pressure services such as steam pipelines, heat exchangers, boilers, and superheaters. Excellent resistance to oxidation and creep at elevated temperatures. 4. Key Properties: High-temperature strength: Maintains strength at temperatures up to about 600–650°C (1112–1202°F). Creep resistance: Designed for long-term exposure to elevated temperature and stress. Good weldability: Can be welded using proper procedures; post-weld heat treatment (PWHT) is generally required. Corrosion resistance: Good resistance to oxidation in high-temperature environments. 5. Specification Details: ASTM standard: ASTM A335/A335M Grade: P91 Type: Seamless pipe Size range: Typically from 1/2' to 48' diameter (varies by manufacturer) Wall thickness: Various, depending on schedule