What Is ASME SA387 Grade 11 Class 2
ASME SA387 Grade 11 Class 2 is a chromium-molybdenum alloy steel plate for high-temperature pressure vessels, boilers, and heat exchangers. The steel contains approximately 1.25% chromium and 0.50% molybdenum, which provide strength, heat resistance, and oxidation resistance. Class 2 indicates higher tensile strength, 75–100 ksi, compared with Class 1, achieved through a more stringent heat treatment, making the grade ideal for demanding elevated-temperature applications in the oil, gas, and petrochemical industries.
Temperature Range
ASME SA387 Grade 11 Class 2 is typically used in the medium-temperature range of 350°C to 480°C (660°F to 900°F). Maximum use temperatures vary by ASME code but generally reach up to around 649°C (1200°F) in some applications, while lower limits apply under other code sections. During manufacturing, the minimum tempering temperature is around 1150°F (620°C), which develops the enhanced mechanical properties of the Class 2 condition. Designers should confirm the allowable stress values for the exact operating temperature with the governing code.
Chemical Composition and Mechanical Properties
The heat analysis chemical composition of SA387 Grade 11 Class 2 is: carbon 0.05–0.17%, manganese 0.40–0.65%, phosphorus 0.035% maximum, sulfur 0.035% maximum, silicon 0.50–0.80%, chromium 1.00–1.50%, and molybdenum 0.45–0.65%. Product analysis allows slightly wider tolerances. The chromium and molybdenum additions provide the elevated-temperature strength and corrosion resistance that make the grade suitable for sour gas and other demanding services.
For Class 2 plates, the tensile strength is 75–100 ksi (515–690 MPa), the minimum yield strength at 0.2% offset is 43 ksi (310 MPa), and the minimum elongation is 18% over 8 inches (200 mm) and 22% over 2 inches (50 mm). Class 1 and Class 2 share the same chemical composition; the Class 2 designation refers to the higher-strength mechanical requirements.
Welding and Heat Treatment
When welding ASME SA387 Grade 11 Class 2, mandatory preheating and post-weld heat treatment are required to prevent hydrogen cracking by reducing hardness and avoiding the formation of brittle martensite. Specific filler metals such as E8018-B2 are used, and strict interpass temperature control is required. A typical manufacturing heat treatment for the plate is quenching at 870–900°C followed by tempering at 620–650°C, which optimizes the heat resistance of the material.
Typical Applications
ASME SA387 Grade 11 Class 2 is commonly used in pressure vessels in the oil and gas industry, boilers, heat exchangers, and pipelines and other equipment operating at elevated temperatures. Its oxidation resistance and creep strength make it a preferred choice for refinery and petrochemical service, including applications handling sour gas.
Frequently Asked Questions
What temperature can ASME SA387 Grade 11 Class 2 withstand? The grade is typically used in the range of 350°C to 480°C (660°F to 900°F), with maximum use temperatures generally up to around 649°C (1200°F) in some ASME code applications.
What is ASME SA387 Grade 11 Class 2 equivalent to? It is equivalent to ASTM A387 Grade 11 Class 2, with identical chemistry and mechanical properties. In British standards it is similar to BS 621B; European and German standards relate to similar designations rather than direct equivalents.
What is the P number of SA387 Gr. 11? ASME SA387 Grade 11 is a 1.25Cr-0.5Mo-Si steel with UNS designation K11789 and belongs to P-Number 5A in ASME Section IX.
What is the difference between Class 1 and Class 2? Class 1 and Class 2 share the same chemical composition but differ in mechanical properties and heat treatment. Class 2 has higher tensile and yield strength and requires a more stringent heat treatment, making it suitable for higher-stress and higher-temperature applications.
What precautions should be taken when welding SA387 Grade 11 Class 2? Mandatory preheating and post-weld heat treatment, low-hydrogen filler metals such as E8018-B2, strict interpass temperature control, and proper ventilation and fire safety measures are required.
What are common testing requirements? Common testing includes tensile tests for strength, yield, and elongation, chemical analysis, impact tests that are often optional but project-dependent, plus radiographic, hydrostatic or pneumatic testing, and visual and non-destructive inspections of the finished vessel.
