SA 387 Grade 12 Class 2 is a chromium-molybdenum alloy steel plate under the ASME SA 387 standard, intended for elevated-temperature pressure vessel and boiler service. It provides good high-temperature strength, creep resistance, and oxidation resistance, and is typically used in refineries, petrochemical plants, and power generation facilities. Class 2 represents a normalized and tempered heat treatment for enhanced toughness and ductility.
Equivalents
| Designation | Nominal Chromium Content (%) | Nominal Molybdenum Content (%) |
|---|---|---|
| SA387 Grade 12 | 1.00% | 0.50% |
Chromium & Molybdenum content (according to the ASME specification):
| Designation | Requirement | Grade 12 |
|---|---|---|
| SA387 Grade 12 | Tensile strength, ksi [MPA] | 65 to 85 [450 to 585] |
| Yield strength, min, ksi [MPa]/(0.2% offset) | 40 [275] | |
| Elongation in 8 in. [200mm], min % | 19 | |
| Elongation in 2 in. [50mm], min, % | 22 | |
| Reduction of area, min % |
Tensile Requirements for Class 2 Plates
| BS | EN | ASTM/ASME | DIN |
|---|---|---|---|
| 620B | 13CrMo45 | SA387-12-2 | 13CrMo44 |
Chemical Composition of ASME SA387 Grade 12 Class 2
| Carbon (C) | % |
| Heat Analysis: Product Analysis: |
0.05 - 0.17 0.04 - 0.17 |
| Manganese (Mn) | % |
| Heat Analysis: Product Analysis: |
0.40 - 0.65 0.35 - 0.73 |
| Phosphorus (P) | % |
| Heat Analysis: Product Analysis: |
0.035 0.035 |
| Sulphur (S) (Max) | % |
| Heat Analysis: Product Analysis: |
0.035 0.035 |
| Silicon (Si) | % |
| Heat Analysis: Product Analysis: |
0.15 - 0.40 0.13 - 0.45 |
| Chromium (Cr) | % |
| Heat Analysis: Product Analysis: |
0.80 - 1.15 0.74 - 1.21 |
| Molybdenum (Mo) | % |
| Heat Analysis: Product Analysis: |
0.45 - 0.60 0.40 - 0.65 |
processing
1. Material Preparation and Cutting
Verification: Confirming heat numbers and chemical composition (Cr/Mo content) to ensure Class 2 tensile requirements.
Cutting Methods: High-precision cutting using Flame (Oxy-fuel), Plasma, or Water-jet methods.
Preheating for Cutting: Due to the hardenability of chrome-moly steel, plates thicker than 25mm usually require preheating (approx. 100°C–150°C) before flame cutting to prevent edge cracking.
2. Forming and Machining
Cold/Hot Forming: The plates are rolled into cylinders or pressed into dished ends (heads) for pressure vessels.
Edge Preparation: Beveling (V, U, or J type) is performed via machining or grinding.
Surface Inspection: Penetrant Testing (PT) or Magnetic Particle Testing (MT) is often conducted on beveled edges to check for laminations or cracks.
3. Welding Procedure (Critical Step)
SA 387 Grade 12 Class 2 requires specific welding controls to maintain its properties:
Preheating: Mandatory preheating (typically 150°C to 200°C) is required to avoid hydrogen-induced cracking.
Filler Metals: Use of low-hydrogen electrodes matching the base metal, such as E8018-B2 (SMAW) or ER80S-B2 (GTAW/GMAW).
Interpass Temperature: Must be monitored and maintained within specified limits (usually not exceeding 300°C) to preserve the grain structure.
4. Heat Treatment
The "Class 2" designation is achieved through specific thermal cycles:
Normalization & Tempering (N+T): Standard supply condition. The minimum tempering temperature for Grade 12 is 1150°F (620°C).
Post-Weld Heat Treatment (PWHT): Essential after fabrication to relieve residual stresses. This is typically done at 650°C – 700°C for a duration determined by the material thickness.
5. Non-Destructive Testing (NDT) & Quality Control
Volumetric Inspection: 100% Ultrasonic Testing (UT) or Radiographic Testing (RT) to ensure the integrity of the welds and base material.
Mechanical Testing: Tensile tests (to confirm Class 2 range of 65–85 ksi), Yield tests (min 40 ksi), and Charpy V-Notch impact tests.
Hardness Testing: Conducted to ensure the PWHT was successful and the material hasn't become too brittle.
6. Finishing
Surface Protection: Blasting and coating with high-temperature resistant primers.
Documentation: Issuance of the Material Test Report (MTR) including chemical analysis, heat treatment charts, and NDT results.
Core Industrial Applications
Oil & Gas and Petrochemical: Extensively used for fabricating refinery equipment, separator vessels, and storage tanks. Its chromium content makes it ideal for sour service applications, which involve exposure to corrosive hydrogen sulfide (𝐻2𝑆).
Power Generation: Essential for high-stress components in thermal and nuclear power stations, including boiler drums, steam pipelines, and turbine components. It is also used in Heat Recovery Steam Generators (HRSG).
Pressure Vessel Fabrication: A standard material for weldable pressure vessels and industrial boilers designed for internal pressures significantly different from atmospheric pressure.
Chemical Processing: Used to construct reactors and vessels that handle corrosive media at raised temperatures.
Component-Specific Uses
The material is processed into various specialized industrial parts, including:
Piping Systems: High-temperature ducting, pipe supports, and large-diameter steam work.
Fittings and Valves: Flanges, pipe clamps, and specialized valves for high-pressure gas control.
Storage Solutions: Large metallic tanks and heavy-duty oxygen cylinders.
Industrial Liners: Chutes, tubs, and bins in mining or waste recycling where durability is required.
Emerging and Specialty Sectors
Aerospace and Defense: Applied in military vehicles, naval ships, and aircraft components due to its resistance to thermal fatigue.
Renewable Energy: Integrated into waste-to-energy and biomass power plant boiler systems.
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What post-weld heat treatment (PWHT) is used for this grade?
Typical PWHT is tempering at 620°C to 675°C (1150°F to 1250°F). It reduces residual stresses and improves the material's toughness and ductility.
What is the main application of SA 387 Grade 12 Class 2?
It is widely used in welded boilers, pressure vessels, and heat exchangers. Ideal for high-temperature, high-pressure industrial processes like oil refining and power generation.
Can this material be used in cryogenic environments?
No, it is not suitable for cryogenic use. Its ductility decreases at temperatures below -29°C (-20°F), increasing the risk of brittle fracture.
What is the density of SA 387 Grade 12 Class 2?
Its density is approximately 7.85 g/cm³ (0.284 lb/in³), the same as most low-alloy steels, facilitating weight calculation in component design.
What is the thermal conductivity of this material at room temperature?
At room temperature, its thermal conductivity is about 42 W/(m·K). This property is crucial for heat transfer calculations in heat exchanger design.
Does SA 387 Grade 12 Class 2 have good creep resistance?
Yes, it has excellent creep resistance. The chromium-molybdenum alloying prevents permanent deformation under long-term high-temperature and pressure loads.
What is the elongation requirement of this grade?
It requires a minimum elongation of 22% in 50 mm (2 inches). This ensures sufficient ductility for forming and absorbing load variations.
What is the Brinell hardness (HB) range of this material?
Its Brinell hardness ranges from 130 to 180 HB. This moderate hardness balances wear resistance and machinability for industrial fabrication.
Is this material resistant to hydrogen attack?
Yes, it has good resistance to hydrogen attack when properly heat-treated. It is suitable for environments with hydrogen at elevated temperatures and pressures.
What is the maximum thickness available for SA 387 Grade 12 Class 2 plates?
Plates are available up to 200 mm (7.87 inches) thick. Thicker plates may require special heat treatment to ensure uniform mechanical properties.