ASME SA387 Grade 11 Class 2, also designated ASTM A387 Grade 11 CL2, is a chromium-molybdenum alloy steel plate intended for elevated temperature applications, commonly associated with pressure vessels and heat exchangers. The nominal chromium content is 1.00 to 1.50 percent and the molybdenum content is 0.45 to 0.65 percent. This composition provides good strength, oxidation resistance, and creep resistance at high temperatures, which makes the grade a standard choice for oil and gas, power, and chemical plant equipment.
Chemical Composition
The chemical composition of SA387 Grade 11 is controlled to deliver the elevated-temperature performance. Carbon is limited to 0.17 percent on heat analysis, manganese is 0.40 to 0.65 percent, and silicon is 0.50 to 0.80 percent. Phosphorus is limited to 0.035 percent and sulfur to 0.035 percent. Chromium is specified at 1.00 to 1.50 percent and molybdenum at 0.45 to 0.65 percent, with heat analysis and product analysis limits defined in the specification.
Mechanical Properties for Class 2
SA387 Grade 11 Class 2 requires a tensile strength of 515 to 690 MPa, 75 to 100 ksi, and a minimum yield strength of 310 MPa, 45 ksi at 0.2 percent offset. Minimum elongation is 18 percent in 200 mm gauge length and 22 percent in 50 mm gauge length, and the minimum reduction of area is 45 percent on round specimens and 40 percent on flat specimens. These values are higher than the Class 1 requirements and are intended for applications that demand greater performance under higher stress and temperature.
Heat Treatment of Class 2
The Class 2 condition is achieved by normalizing and tempering. The plate is heated to the austenitizing temperature and cooled in air to refine the grain structure, then tempered to develop the specified strength and toughness. The controlled heat treatment distinguishes Class 2 from Class 1, which is supplied at a lower strength level, and the resulting microstructure provides the creep resistance needed for long-term elevated-temperature service.
General Requirements and Quality
Plates to this specification are governed by the general requirements of ASTM A20 and A20M, which cover the permitted tolerances, test methods, and marking. Mechanical testing is performed in accordance with ASTM A370, and ultrasonic examination per A435 or A578 is specified when required by the order. These controls ensure that each plate is traceable and verified for pressure vessel service.
Typical Applications
Pressure vessels in the oil and gas industry
Boilers and boiler-related pressure parts
Heat exchangers and process equipment
Pipelines and equipment operating at elevated temperatures
Vessels for storing oil, gas, and liquids in various industries
Frequently Asked Questions
What is ASME SA387 Grade 11 Class 2? It is a chromium-molybdenum alloy steel plate for elevated temperature pressure vessels and heat exchangers, with higher strength than Class 1.
What is the tensile strength of SA387 Grade 11 Class 2? The tensile strength is 515 to 690 MPa and the minimum yield strength is 310 MPa.
What is the chromium content of SA387 Grade 11? The nominal chromium content is 1.00 to 1.50 percent, with molybdenum of 0.45 to 0.65 percent.
What heat treatment does Class 2 require? Class 2 is supplied in the normalized and tempered condition, which gives it higher strength than Class 1.
What is the difference between Class 1 and Class 2? Class 2 has a higher minimum yield and tensile strength and is intended for more demanding high-temperature service.
Where is SA387 Grade 11 Class 2 used? In pressure vessels, boilers, heat exchangers, and elevated-temperature piping in the oil and gas and power industries.