P22 vs P91- The 565°C Decision

Side-by-side comparison of ASTM A335 Grade P22 and Grade P91 seamless alloy steel pipes at Nakoda Steel Industry’s Mumbai works. The P22 pipe shows the heavy wall thickness required for main steam service near 565°C, while the vanadium-strengthened 9Cr-1Mo P91 pipe achieves the same pressure rating with roughly half the wall — illustrating why power plants above 565°C specify P91 despite its stricter welding and heat-treatment demands. Both pipes carry stamped heat numbers traceable to EN 10204 3.1 mill test certificates.