ASME SA387 Grade 11 Class 1 is a chromium-molybdenum alloy steel plate formulated for critical high-temperature service applications. It is primarily designed for the fabrication of welded boilers and pressure vessels, and the combined effect of its chromium and molybdenum content delivers a balanced set of performance attributes including elevated-temperature strength, creep resistance, and corrosion resistance. This article reviews the composition, mechanical properties, and applications of the grade.
Chemical Composition
The heat analysis of SA387 Grade 11 Class 1 is limited to carbon 0.04 to 0.17%, silicon 0.44 to 0.86%, manganese 0.35 to 0.73%, phosphorus 0.035% maximum, sulfur 0.035% maximum, chromium 0.94 to 1.56%, and molybdenum 0.40 to 0.70%. The chromium content provides oxidation and corrosion resistance at elevated temperature, while molybdenum improves high-temperature strength and creep resistance. The controlled carbon and manganese levels support welding, and the steel is intended for service in welded boilers and pressure vessels designed for elevated temperature operation.
Mechanical Properties
For plates up to 50 mm thick, the minimum yield strength of SA387 Grade 11 Class 1 is 240 MPa and the tensile strength is 415 to 585 MPa, with a minimum elongation of 22%. For plates above 50 mm, the minimum yield strength remains 240 MPa and the tensile strength 415 to 585 MPa, with a minimum elongation of 19%. The Class 1 designation defines the lower strength level of the two classes; Class 2 has higher tensile and yield strength achieved by enhanced heat treatment, while Class 1 offers higher elongation. The minimum tempering temperature for Grade 11 is 620 C, which relieves internal stress and restores toughness after heat treatment.
Pressure Vessel and Boiler Applications
The grade serves as a staple material for fabricating welded pressure vessels and industrial boilers that operate under continuous elevated-temperature conditions. Its excellent thermal stability and creep resistance ensure long-term structural integrity, even when the equipment is exposed to cyclic heating and cooling processes. Superheater headers, reheater tubes, and other boiler components benefit from the material's ability to maintain strength under sustained temperature, and the plate is also used for heat exchangers and reactor shells where pressure and temperature act together.
Oil, Gas and Power Applications
In the oil and gas industry, the alloy is widely adopted in upstream, midstream, and downstream operations. It is used for key equipment in refineries, petrochemical plants, and offshore drilling platforms, especially for systems handling sour gas and high-temperature hydrocarbon fluids, because of its resistance to sulfide stress cracking and chloride corrosion. In the power generation sector, the material is used to produce core components of boiler systems such as superheater headers and reheater tubes, as well as heat recovery steam generators, where it withstands high-temperature flue gases and superheated steam.
Chemical and Industrial Applications
In chemical and pharmaceutical industries, SA387 Grade 11 Class 1 is a preferred choice for fabricating reactors, heat exchangers, and storage tanks. Its corrosion resistance against various acidic and alkaline media makes it suitable for handling aggressive process fluids at elevated temperatures. The plate is also applied in the construction of high-temperature processing equipment in pulp and paper mills and fertilizer production plants, where it resists the corrosive effects of chemical reagents and maintains reliable performance under harsh operating conditions.
Frequently Asked Questions
What is the difference between SA 387 Grade 11 Class 1 and Class 2?
The two classes share the same chemical composition but differ in mechanical properties. The tensile and yield strengths of Class 2 are higher than Class 1, while the elongation of Class 1 is higher than Class 2.
What is the tempering temperature for SA 387 Grade 11?
SA 387 Grade 11 has a minimum tempering temperature of 620 C, and the plates can be provided in the normalized and tempered or quenched and tempered condition, in either Class 1 or Class 2.
What is SA387 Grade 11 material?
SA387 is the ASME specification for pressure vessel plates of alloy steel, chromium-molybdenum, intended primarily for welded boilers and pressure vessels designed for elevated temperature service. Grade 11 refers to the 1.25Cr-0.5Mo composition.
Is SA387 Grade 11 Class 1 suitable for sour gas service?
Yes. The grade offers resistance to sulfide stress cracking and chloride corrosion, making it suitable for systems handling sour gas and high-temperature hydrocarbon fluids in refineries and offshore platforms.
What are the typical applications of SA387 Grade 11 Class 1?
Typical applications include welded pressure vessels and industrial boilers, superheater headers, reheater tubes, heat recovery steam generators, reactors, heat exchangers, and storage tanks in the oil, gas, power, chemical, and pharmaceutical industries.
Is SA387 Grade 11 Class 1 weldable?
Yes. As a chromium-molybdenum steel, it is weldable with proper procedures including preheat and post-weld heat treatment, which are essential to prevent hydrogen-induced cracking and to restore the toughness of the heat-affected zone.