A387 Grade 5 Class 2 is a chromium-molybdenum pressure vessel steel plate intended for service at elevated temperatures. It offers good strength and resistance to creep and oxidation, making it suitable for boilers and pressure vessels operating under harsh thermal conditions. The material is processed with controlled chemistry and heat treatment to ensure reliable mechanical properties.
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A387 Gr.5 CL.2 Chemical Composition |
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Grade |
The Element Max (%) |
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C |
Si |
Mn |
P |
S |
Cr |
Mo |
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A387 Gr.5 Cl.1 |
0.15 |
0.55 |
0.25-0.66 |
0.035 |
0.035 |
3.90-6.10 |
0.40-0.70 |
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Grade |
A387 Gr.5 CL.2Mechanical Property |
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Thickness |
Yield |
Tensile |
Elongation |
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A387 Gr.5 Cl.2 |
mm |
Min Mpa |
Mpa |
Min % |
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t≦50 |
310 |
515-690 |
18 |
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50<t≦200 |
- |
- |
- |
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processing
1. Steelmaking & Primary Processing
Electric Arc Furnace (EAF) Melting: Primary melting of scrap and alloys.
Ladle Refining (LRF): Precise chemistry adjustment for Chromium (4.0–6.0%) and Molybdenum (0.45–0.65%).
Vacuum Degassing (VD): Removal of dissolved gases (Hydrogen, Oxygen, Nitrogen) to prevent internal hydrogen-induced cracking.
Continuous Casting: Casting the molten steel into slabs.
2. Rolling & Slab Treatment
Reheating: Heating slabs to standardized rolling temperatures (approx. 1150°C–1250°C).
Hot Rolling: Multi-pass reduction to achieve the final plate thickness.
Controlled Cooling: Managing the cooling rate to prepare the microstructure for heat treatment.
3. Heat Treatment (Critical for Class 2 Properties)
To achieve the specific mechanical properties of Class 2 (75-100 ksi tensile strength), the material undergoes:
Normalizing: Heating to a specific temperature above the transformation range and cooling in air to refine grain structure.
Tempering: Reheating to a temperature below the transformation range (min. 1150°F / 620°C) to achieve the required ductility and toughness.
Accelerated Cooling (Optional): Sometimes used if the thickness requires faster cooling to meet yield specifications.
4. Fabrication & Machining
Oxy-Fuel / Plasma Cutting: Profiling the plates to required dimensions.
Edge Preparation (Milling): Creating U-groove or V-groove bevels for welding.
Bending/Rolling: Cold or hot forming into cylindrical shells for vessels.
5. Welding & PWHT (Post-Weld Heat Treatment)
Preheating: Mandatory preheating (typically 200°C–300°C) is required before welding to prevent Martensite formation and cracking.
Welding Process: Common methods include Submerged Arc Welding (SAW) or Gas Tungsten Arc Welding (GTAW) using matching Cr-Mo fillers.
Post-Weld Heat Treatment (PWHT): Mandatory thermal soak to relieve residual stresses and soften the Heat Affected Zone (HAZ).
6. Testing & Quality Control (QC)
Ultrasonic Testing (UT): Performed per ASTM A435 or A578 to detect internal laminations.
Mechanical Testing: Tensile, Yield, and Charpy V-Notch impact tests.
PMI (Positive Material Identification): Verification of alloy content before shipment.
Hardness Survey: Ensuring the material does not exceed specified Brinell limits.
7. Finishing
Shot Blasting: Removing mill scale and oxidation.
Surface Coating: Application of temporary rust preventatives or primers.
applications
Weldable Pressure Vessels and Industrial Boilers:
It is extensively applied in manufacturing weldable pressure vessels and industrial boilers, core equipment for petrochemical, power generation and chemical sectors. Its excellent high-temperature resistance guarantees stable operation under long-term thermal loads, preventing deformation or failure from extreme temperature and pressure.
Sour Service Environments:
This alloy steel plate excels in sour environments containing hydrogen sulfide. It resists hydrogen-induced cracking and sulfide stress corrosion, ensuring safe equipment operation in harsh oil and gas extraction and processing scenarios.
Numerous Applications:
Beyond core industries, it is used in thermal processing equipment, high-temperature pipelines and chemical reaction vessels. It adapts to diverse harsh working conditions, becoming a preferred material for high-temperature and high-pressure industrial applications.
Gas Applications:
It is suitable for gas transmission, storage and processing equipment. For natural gas, coal gas and other industrial gases, it withstands media corrosion and pressure, ensuring efficient and safe gas transportation and utilization.
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How does ASTM A387 Grade 5 Class 2 compare to ASTM A387 Grade 11 Class 2?
ASTM A387 Grade 5 Class 2 has lower chromium and molybdenum content than Grade 11 Class 2, resulting in lower high-temperature strength and creep resistance. Grade 11 Class 2 is better suited for higher-temperature and higher-pressure applications, while Grade 5 Class 2 is used in moderately severe conditions.
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.
What thickness range is ASTM A387 Grade 5 Class 2 available in?
ASTM A387 Grade 5 Class 2 is commonly produced in thicknesses from 1/4 inch to several inches. Thicker plates may require additional heat treatment to ensure uniform mechanical properties throughout the section, especially for pressure vessel applications.
What are the key chemical elements in ASTM A387 Grade 5 Class 2?
ASTM A387 Grade 5 Class 2 contains chromium and molybdenum as primary alloying elements, which enhance its high-temperature strength and corrosion resistance. Carbon, manganese, silicon, and small amounts of other elements are also present to optimize weldability and mechanical performance during fabrication and service.
What is the typical tensile strength range of ASTM A387 Grade 5 Class 2?
ASTM A387 Grade 5 Class 2 generally has a tensile strength between 60 ksi and 80 ksi. This range provides a good balance of strength and ductility, making it suitable for pressure vessel components that operate under moderate to high-temperature conditions.
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 typical tensile strength range of ASTM A387 Grade 5 Class 2?
ASTM A387 Grade 5 Class 2 generally has a tensile strength between 60 ksi and 80 ksi. This range provides a good balance of strength and ductility, making it suitable for pressure vessel components that operate under moderate to high-temperature conditions.
What is the minimum yield strength requirement for ASTM A387 Grade 5 Class 2?
The minimum yield strength for ASTM A387 Grade 5 Class 2 is typically 30 ksi. This ensures that the material can withstand significant internal pressures and loading without undergoing excessive deformation in high-temperature service environments.
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.