SA 387 GR 91 CL 1 / CL 2 – High-Strength Cr-Mo-V Steel for Severe Thermal Conditions SA 387 Grade 91 Class 1 and Class 2 represent a high-grade alloy steel containing 9% chromium, 1% molybdenum, and vanadium, tailored for extreme temperature and pressure applications. Thanks to its tempered martensitic structure, it delivers outstanding creep strength and oxidation resistance—ideal for ultra-supercritical boilers, steam piping, and long-term thermal service. Class 2 is used where higher strength is a must, while Class 1 suits standard heavy-duty thermal applications. Key Highlights: Exceptional High-Temperature Strength: Withstands sustained thermal loads and creep at 600–675°C. Creep and Oxidation Resistance: Ideal for long-term service in aggressive thermal cycling environments. Advanced Alloy Composition: Vanadium addition enhances mechanical properties under heat stress. Strong but Fabrication-Ready: Weldable with correct preheat/post-weld procedures. Mechanical Properties Overview: Property SA 387 Gr 91 Cl 1 SA 387 Gr 91 Cl 2 Yield Strength ≥ 310 MPa ≥ 415 MPa Tensile Strength 585–760 MPa 620–795 MPa Elongation ≥ 20% ≥ 18% Max Temperature Up to ~675°C Up to ~675°C Typical Applications: Ultra-supercritical and advanced thermal boilers High-pressure steam lines and turbine piping Hydrogen-rich service in refineries Components in nuclear and fossil fuel energy systems