ASTM A387 Grade 5 Class 2 (also designated as ASME SA 387 Grade 5 Class 2) is a high-quality chromium-molybdenum alloy steel plate designed for use in welded boilers and pressure vessels operating at elevated temperatures.
Standard Specification For ASTM A387 Gr.5 Class 2 Alloy Steel Plate
Specifications : ASTM A387 / ASME SA387
Standard : ASTM, ASME and API
Thickness : 5mm-150mm
Specialize : Shim Sheet, Perforated Sheet, B. Q. Profile.
Form : Coils, Foils, Rolls, Plain Sheet, Shim Sheet, Perforated Sheet, Chequered Plate, Strip, Flats, Blank (Circle), Ring (Flange)
Finish : Hot rolled plate (HR), Cold rolled sheet (CR), 2B, 2D, BA NO(8), SATIN (Met with Plastic Coated)
Hardness : Soft, Hard, Half Hard, Quarter Hard, Spring Hard etc.
Equivalent Grades Alloy Steel ASTM A387 Grade 5 Class 2 Plate
| GRADE | UNS NO | DIN | GOST | EN |
| Gr 5 Class 2 | S50200 | - | 15KH5M | X12CrMo5 |
Chemical Composition of ASTM A387 Gr.5 Class 2 Alloy Steel Plate
| Grade | C | Mn | P | S | Si | Cr | Mo |
| Gr 5 | 0.15 max. | 0.25 - 0.66 | 0.035 | 0.030 | 0.55 max. | 0.40 - 0.7 | 3.9 - 6.1 |
Mechanical Properties of Alloy Steel Grade 5 Class 2 Plate
| Tensile Strength | Yield Strength | Elongationin 50mm (%) | Reduction of area in % |
| 75-100 ksi, 515-690 MPa | 45 Ksi, 310 MPa | 18 | 45 |
Tensile Requirements for Alloy Steel Grade 5 Class 2 Plate
| Designation: | Requirement: | Grade 5 |
|
A387 Grade 5 |
Tensile strength, ksi [MPA] | 75 to 100 [515 to 690] |
| Yield strength, min, ksi [MPa]/(0.2% offset) | 45 [310] | |
| Elongation in 8 in. [200mm], min % | ... | |
| Elongation in 2 in. [50mm], min, % | 18 | |
| Reduction of area, min % | 45 (measured on round specimen) 40 (measured on flat specimen) |
Sizes of ASTM A387 Grade 5 Class 2 Plate
| Size (in inches) | Size (in mm) |
| .125" | 3.18mm |
| .134" | 3.40mm |
| .156" | 3.96mm |
| .187" | 4.75mm |
| .250" | 6.35mm |
| .312" | 7.92mm |
| .375" | 9.53mm |
| .500" | 12.7mm |
| .600" | 15.9mm |
| .750" | 19.1mm |
| .875" | 22.2mm |
| 1" | 25.4mm |
| 1.125" | 28.6mm |
| 1.250" | 31.8mm |
| 1.500" | 38.1mm |
| 1.750" | 44.5mm |
| 2" | 50.8mm |
| 2.500" | 63.5mm |
| 3" | 76.2mm |
Processing
1. Primary Heat Treatment (Crucial for Class 2)
As per 2026 technical requirements, the mechanical properties of Class 2 are achieved through controlled thermal cycles:
Normalizing: Heating the plates to an austenitizing temperature and cooling in air to refine the grain structure.
Tempering: Reheating to a minimum temperature of 1300°F [705°C]. This relieves internal stresses and achieves the specific tensile strength of 75–100 ksi.
Accelerated Cooling: If specified, liquid quenching followed by tempering is used to enhance toughness in thicker plates.
2. Mechanical Processing (Fabrication)
Hot Rolling: The process of reducing steel thickness while maintaining high temperatures to ensure uniform alloy distribution.
Edge Preparation: Beveling or machining plate edges to ensure proper fit-up and penetration during the welding stage.
Cold/Hot Forming: Shaping the plates into "shells" or "heads" for pressure vessels using hydraulic presses or rollers.
3. Welding & Thermal Conditioning
Preheating: Essential for Grade 5 (5% Cr) to minimize the risk of hydrogen-induced cracking during welding.
Post-Weld Heat Treatment (PWHT): A mandatory thermal cycle performed after welding to restore ductility and reduce hardness in the Heat Affected Zone (HAZ).
Simulated PWHT (SPWHT): A test procedure where samples are subjected to additional heat cycles to predict the final mechanical properties of the finished vessel.
4. Surface & Integrity Processing
Shot Blasting: Removing mill scale to provide a clean surface for inspection and coating.
Pickling and Passivation: Chemical cleaning to enhance the chromium-oxide protective layer for better corrosion resistance.
Vacuum Degassing: A refining process during the melting stage to eliminate trapped gases like hydrogen and oxygen.
5. Inspection & Verification
Non-Destructive Testing (NDT): Includes Ultrasonic Testing (UT) for internal flaws and Magnetic Particle Inspection (MPI) for surface cracks.
Charpy V-Notch Impact Testing: Evaluating the material's toughness at specific temperatures.
Positive Material Identification (PMI): Verifying the 5% Chromium and 0.5% Molybdenum content before shipment.
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What standards govern the testing of ASTM A387 Grade 5 Class 2?
Testing of ASTM A387 Grade 5 Class 2 is governed by ASTM standards, including tensile, bend, and impact tests. Additional requirements may be specified by ASME Boiler and Pressure Vessel Code when used in certified pressure vessel construction.
What is the density of ASTM A387 Grade 5 Class 2?
The density of ASTM A387 Grade 5 Class 2 is approximately 0.284 lb/in³, similar to other carbon and low-alloy steels. This density is used in weight calculations for pressure vessel components and structural designs.
What is the difference between ASTM A387 Grade 5 Class 2 and ASTM A387 Grade 22?
ASTM A387 Grade 5 Class 2 has a lower alloy content compared to Grade 22, which contains higher amounts of chromium and molybdenum. Grade 22 offers superior creep strength and is used in more aggressive high-temperature environments, while Grade 5 Class 2 is used in less severe thermal service conditions.
How does ASTM A387 Grade 5 Class 2 compare to ASTM A387 Grade 91?
ASTM A387 Grade 5 Class 2 has significantly lower chromium and molybdenum than Grade 91, a high-strength ferritic alloy steel. Grade 91 provides excellent creep resistance at very high temperatures, while Grade 5 Class 2 is suitable for moderately elevated-temperature pressure vessel applications.
What is the modulus of elasticity of ASTM A387 Grade 5 Class 2?
The modulus of elasticity for ASTM A387 Grade 5 Class 2 is about 29,000 ksi at room temperature. This value is typical for carbon and low-alloy steels and is used in structural and pressure vessel design calculations.
What is the coefficient of thermal expansion for ASTM A387 Grade 5 Class 2?
ASTM A387 Grade 5 Class 2 has a coefficient of thermal expansion similar to other low-alloy steels, approximately 6.5 × 10⁻⁶ per °F between 70°F and 600°F. This property is important for designing components subject to thermal cycling.
What is the thermal conductivity of ASTM A387 Grade 5 Class 2?
The thermal conductivity of ASTM A387 Grade 5 Class 2 is around 25 Btu/(hr·ft·°F) at room temperature, decreasing slightly at higher temperatures. This property influences heat transfer efficiency in boilers and heat exchangers.
What post-weld heat treatment is required for ASTM A387 Grade 5 Class 2?
Post-weld heat treatment for ASTM A387 Grade 5 Class 2 usually involves tempering at temperatures between 1100°F and 1200°F. This relieves residual stresses, improves toughness, and restores the material's mechanical properties after welding.
What is the electrical resistivity of ASTM A387 Grade 5 Class 2?
ASTM A387 Grade 5 Class 2 has an electrical resistivity similar to other low-alloy steels, approximately 20 × 10⁻⁸ ohm-meters at room temperature. This property is generally not a primary consideration for its typical pressure vessel applications.
What are the storage and handling recommendations for ASTM A387 Grade 5 Class 2?
ASTM A387 Grade 5 Class 2 plates should be stored in a dry, covered area to prevent corrosion. They should be handled with care to avoid surface damage, and proper lifting equipment should be used to prevent bending or deformation. Plates should be inspected before fabrication to ensure they meet specification requirements.