SA387 Grade 11 Class 2 is a chromium-molybdenum alloy steel plate for high-temperature pressure vessels and boilers, offering good strength and corrosion resistance due to its ~1% Chromium (~Cr) and ~0.5% Molybdenum (~Mo) content, with the 'Class 2' designation indicating higher tensile strength (75-100 ksi) compared to Class 1. It's used in oil, gas, and chemical industries for elevated temperature service, providing resistance to oxidation and sour gas environments, and is certified to both ASME and ASTM standards.
Equivalents
| BS | EN | ASTM/ASME | DIN |
| 621 B | ––– | SA387-11-2 | ––– |
Specifications for ASME SA387 Grade 11 Alloy Steel Plates
| Designation | Nominal Chromium Content (%) |
Nominal Molybdenum Content (%) |
| SA387 Grade 11 | 1.25% | 0.50% |
Tensile Requirements for ASME SA387 Grade 11 Alloy Steel Plates Class 2 Plates
| Designation: | Requirement: | Grade 11 |
| SA387 Grade 11 | Tensile strength, ksi [MPa] | 75 to 100 [515 to 690] |
| Yield strength, min, ksi [MPa]/(0.2% offset) | 43 [310] | |
| Elongation in 8 in. [200mm], min % | 18 | |
| Elongation in 2 in. [50mm], min, % | 22 | |
| Reduction of area, min % | ––– |
Chemical Requirements for ASME SA387 Grade 11 Alloy Steel Plates
| Element | Chemical Composition (%) | |
| SA387 Grade 11 | ||
| Carbon: | Heat Analysis: | 0.05 - 0.17 |
| Product Analysis: | 0.04 - 0.17 | |
| Manganese: | Heat Analysis: | 0.40 - 0.65 |
| Product Analysis: | 0.35 - 0.73 | |
| Phosphorus: | Heat Analysis: | 0.035 |
| Product Analysis: | 0.035 | |
| Sulphur (max): | Heat Analysis: | 0.035 |
| Product Analysis: | 0.035 | |
| Silicon: | Heat Analysis: | 0.50 - 0.80 |
| Product Analysis: | 0.44 - 0.86 | |
| Chromium: | Heat Analysis: | 1.00 - 1.50 |
| Product Analysis: | 0.94 - 1.56 | |
| Molybdenum: | Heat Analysis: | 0.45 - 0.65 |
| Product Analysis: | 0.45 - 0.70 |
processing
1. Material Preparation & Cutting
Supply Condition: Usually delivered in Normalized and Tempered (N+T) or Quenched and Tempered (Q+T) condition.
Cutting: CNC Plasma or Oxy-fuel cutting is standard. Mechanical cutting is preferred for thin plates to avoid Heat Affected Zones (HAZ).
2. Forming
Cold/Hot Forming: Plates are rolled into cylinders or pressed into heads. If hot forming exceeds the lower critical temperature, re-normalization and tempering are required to restore mechanical properties.
3. Welding (Critical Phase)
As a P-No. 4 group material, it is sensitive to hydrogen-induced cracking.
Preheating: Mandatory preheating to a minimum of 121°C (250°F) is required per ASME Section VIII.
Consumables: Use matching low-hydrogen electrodes (e.g., E8018-B2 or ER80S-B2).
Interpass Temperature: Must be strictly controlled (typically 150°C–300°C).
4. Post-Weld Heat Treatment (PWHT)
PWHT is essential to reduce hardness and relieve residual stresses.
Holding Temperature: Minimum 620°C (1150°F) per ASME code.
Industrial Practice: Often performed between 675°C and 705°C to ensure ductility and prevent Stress Orientation Hydrogen Induced Cracking (SOHIC).
5. Inspection and Testing
NDT: 100% Radiographic Testing (RT) or Ultrasonic Testing (UT) for weld seams. Magnetic Particle Testing (MT) is used to check for surface cracks after PWHT.
Mechanical Properties: Verification of Class 2 tensile strength (515–690 MPa or 75–100 ksi).
Hardness Testing: Hardness is typically limited to ≤ 225 HBW to ensure resistance to sulfide stress cracking (SSC) in sour service.
Key Applications:
Oil & Gas:
Refining, processing, and storage of high-temperature liquids and gases, especially in sour (hydrogen sulfide) service.
Petrochemical Plants:
Reactors, vessels, and piping for chemical processing.
Power Generation:
Boilers, heat exchangers, and other components in thermal power plants.
General Industrial:
Pressure vessels, heat exchangers, and steam piping systems.
Why it's Used :
High Temperature Service:
Designed for applications with elevated temperatures and pressures.
Corrosion/Oxidation Resistance:
Higher chromium content provides excellent resistance, vital for harsh environments.
Strength & Toughness:
Class 2 provides higher strength than Class 1 due to enhanced heat treatment, making it suitable for critical, high-stress equipment like reactors and high-pressure vessels.
Weldability:
Good weldability for fabrication into complex equipment.
Key Benefits & Characteristics:
High-Temperature Service:
Specifically designed for equipment operating at elevated temperatures, like boilers, heat exchangers, and pipelines.
Corrosion & Oxidation Resistance:
Higher chromium content provides superior resistance to corrosion and oxidation, crucial in harsh environments.
Enhanced Strength (Class 2):
The "Class 2" designation means it receives additional heat treatment, resulting in higher tensile and yield strength compared to Class 1.
Superior Mechanical Properties:
Offers better performance under higher stress and temperature conditions than standard carbon steels or its Class 1 counterpart.
Reliable in Sour Service:
Its composition makes it suitable for sour gas environments (containing hydrogen sulfide).
Industry Standard:
Widely used in the oil, gas, and petrochemical industries for safe and long-term operation.
For more details about GNEE's steel products, contact us at beam@gneesteelgroup.com. We look forward to working with you.
What maintenance measures are needed for SA387 Grade 11 Class 2 components?
Regular non-destructive testing (NDT), corrosion inspection, and heat treatment if needed. Clean components to prevent scale buildup.
What is the difference between SA387 Grade 11 Class 1 and Class 2?
Class 2 has stricter impact test requirements and finer grain structure, making it more suitable for critical high-temperature applications than Class 1.
Does SA387 Grade 11 Class 2 require certification?
Yes, it usually requires MTC (Material Test Certificate) to confirm chemical composition, mechanical properties, and heat treatment compliance.
What material category does SA387 Grade 11 Class 2 belong to?
It is a low-alloy chromium-molybdenum steel, mainly used for pressure vessel applications. It has excellent high-temperature strength and corrosion resistance, suitable for harsh working environments.
What is the main chemical composition of SA387 Grade 11 Class 2?
Its key components include 0.05-0.17% carbon, 0.40-0.65% manganese, 1.00-1.50% chromium, and 0.45-0.65% molybdenum, ensuring its mechanical properties.
Can SA387 Grade 11 Class 2 be formed by bending?
Yes, it can be bent cold or hot. Hot bending at 925-1040°C improves formability and reduces the risk of cracking during the process.
What is the maximum bending radius for SA387 Grade 11 Class 2?
The minimum bending radius depends on thickness, usually 3-5 times the material thickness for cold bending, smaller for hot bending.
Is SA387 Grade 11 Class 2 compliant with ASME standards?
Yes, it meets ASME Boiler and Pressure Vessel Code Section II, making it acceptable for use in ASME-certified equipment.
Can SA387 Grade 11 Class 2 be repaired after damage?
Yes, welding repair is feasible. Follow proper preheating and post-weld heat treatment procedures to restore performance.
What factors affect the service life of SA387 Grade 11 Class 2?
Temperature, pressure, corrosive media, and maintenance frequency. Proper operation within design limits extends service life.