SA 387 Grade 12 Class 1 is a low-alloy pressure vessel steel plate designed for use in elevated-temperature service. It belongs to the chromium-molybdenum steel family, which provides good strength and creep resistance at moderately high temperatures. This grade is commonly specified in refinery, petrochemical, and power generation applications where equipment must withstand both pressure and heat over extended periods. Class 1 indicates a specific set of mechanical property requirements and heat treatment conditions that ensure consistent toughness and structural integrity. The steel is typically supplied in the normalized and tempered condition, which refines the microstructure and enhances its ability to resist thermal fatigue and stress relaxation. Its weldability is generally good, though proper preheating and post-weld heat treatment are often recommended to avoid cracking and to maintain the desired mechanical properties in the heat-affected zone.
Equivalents
| BS | EN | ASTM/ASME | DIN |
| 620 B | 13 CRMO 45 | SA387-12-1 | 13 CRMO 44 |
Specifications for ASME SA387 Grade 12 Alloy Steel Plates
| Designation | Nominal Chromium Content (%) |
Nominal Molybdenum Content (%) |
| SA387 Grade 12 | 1.00% | 0.50% |
Tensile Requirements for ASME SA387 Grade 12 Alloy Steel Plates Class 1 Plates
| 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 % | ––– |
Chemical Requirements for ASME SA387 Grade 12 Alloy Steel Plates
| Element | Chemical Composition (%) | |
| ASME SA387 Grade 12 | ||
| 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: | 0.15 - 0.40 |
| Product Analysis: | 0.13 - 0.45 | |
| Chromium: | Heat Analysis: | 0.80 - 1.15 |
| Product Analysis: | 0.74 - 1.21 | |
| Molybdenum: | Heat Analysis: | 0.45 - 0.60 |
| Product Analysis: | 0.40 - 0.65 |
processing
1. Steel Making & Casting
Melting: Produced via Electric Arc Furnace (EAF) or Basic Oxygen Furnace (BOF).
Refining: Usually undergoes Ladle Metallurgy Furnace (LMF) treatment and Vacuum Degassing (VD) to minimize impurities like sulfur, phosphorus, and dissolved gases (hydrogen/oxygen), which prevents hydrogen-induced cracking.
Casting: Cast into ingots or continuous slabs.
2. Hot Rolling
The slabs are reheated to approximately 1100°C – 1250°C.
They are rolled to the target thickness. Rolling parameters are controlled to ensure a uniform grain structure throughout the plate.
3. Heat Treatment (Critical Phase)
As per ASME SA 387, Class 1 material must undergo specific heat treatments to achieve its mechanical properties:
Normalizing: Heating the plate to a temperature above the critical range (typically 900°C - 950°C) and cooling in air. This refines the grain structure.
Tempering: Reheating to a minimum of 1150°F (620°C). This reduces brittleness and stabilizes the microstructure for high-temperature service.
Note: Accelerated cooling (quenching) followed by tempering is also permitted if specified.
4. Mechanical & Chemical Testing
Before fabrication, the plate must pass several quality gates:
Chemical Analysis: Verifying Cr (0.80–1.25%) and Mo (0.45–0.65%) content.
Tensile Testing: Ensuring Tensile Strength is within 55–80 ksi (380–550 MPa).
Impact Testing: Charpy V-Notch tests to ensure toughness at low temperatures.
Nondestructive Examination (NDE): Ultrasonic Testing (UT) per SA 435 or SA 578 to detect internal laminations or defects.
5. Fabrication Processing (Welding & Forming)
Cutting: CNC Flame or Plasma cutting.
Cold/Hot Forming: If the plate is heavily cold-worked (strained), a stress-relief heat treatment may be required.
Preheating for Welding: Mandatory preheating (usually 120°C to 200°C) is required to prevent cold cracking in the heat-affected zone (HAZ).
Welding: Using compatible filler metals like E8018-B2 or ER80S-B2.
6. Post-Weld Heat Treatment (PWHT)
After welding is completed, the entire component (or the weld seam) undergoes PWHT (typically 620°C - 700°C).
This process relieves residual stresses caused by welding and ensures the weld zone has similar ductility and toughness to the base metal.
7. Surface Treatment
Shot Blasting: To remove mill scale.
Priming/Coating: Application of heat-resistant primers if specified for corrosion protection during transport and storage.
Core Applications
The material is predominantly used in the petrochemical, oil and gas, and power generation industries for equipment operating at temperatures up to approximately 600°C (1112°F). Typical components include:
Pressure Vessels & Boilers: For safe containment of pressurized gases and liquids in industrial boilers and thermal power plants.
Heat Exchangers & Reactors: Critical in refining processes for efficient heat transfer and chemical reactions.
Sour Service Equipment: Ideal for environments containing hydrogen sulfide (𝐻2𝑆), common in oil and gas extraction.
Piping Systems: Used for high-temperature process pipework in refineries and chemical plants.
Storage Tanks: For storing volatile liquids and gases at elevated temperatures.
Key Advantages
As a Class 1 material, it offers a specific balance of properties compared to the higher-strength Class 2 variant:
Superior Ductility & Toughness: Class 1 provides better ductility and impact resistance, making it less prone to brittle fracture under dynamic loads.
Enhanced Weldability: Because it has lower tensile strength than Class 2, it typically exhibits better weldability and requires less stringent pre-heating in some moderate-thickness applications.
Corrosion & Oxidation Resistance: High chromium content (approx. 1.00%) provides excellent resistance to oxidation and many acids (sulfuric, nitric), while molybdenum (approx. 0.50%) improves resistance to pitting and chloride stress cracking.
Creep Resistance: The addition of molybdenum increases the steel's high-temperature tensile strength and creep resistance, ensuring it maintains structural integrity under prolonged heat exposure.
Cost-Effectiveness: Although more expensive than standard carbon steel, its longer service life and reduced maintenance requirements in harsh environments make it more economical over its lifecycle.
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Can SA 387 Grade 12 Class 1 be used in corrosive environments?
It resists mild corrosion but not severe media. Additional coatings or alloy upgrades are needed for harsh corrosive environments.
What is the difference between Class 1 and Class 2 of SA 387 Grade 12?
Class 1 has lower carbon for better weldability; Class 2 has higher carbon for higher strength, suitable for less critical welds.
What testing methods are required for SA 387 Grade 12 Class 1?
Mandatory tests include tensile, bend and Charpy V-notch impact tests. Ultrasonic testing is required for thickness over 12.5 mm.
What is the creep resistance performance of SA 387 Grade 12 Class 1?
It has good creep resistance at high temperatures, minimizing deformation under long-term constant load, crucial for high-temperature pressure vessels.
Can SA 387 Grade 12 Class 1 be cold-formed?
Limited cold forming is feasible with preheating to prevent cracking; hot forming at 900-1100°C is preferred for complex shapes.
What is the density of SA 387 Grade 12 Class 1?
Its density is about 7.85 g/cm³ (0.283 lb/in³), same as most carbon and low-alloy steels, facilitating weight calculation.
What is the thermal conductivity of SA 387 Grade 12 Class 1?
Its thermal conductivity is around 42 W/(m·K) at 20°C, enabling efficient heat transfer, ideal for heat exchangers and boilers.
Is SA 387 Grade 12 Class 1 magnetic?
Yes, it is ferromagnetic due to iron-based composition, which is important for non-destructive testing and magnetic separation.
What is the melting point range of SA 387 Grade 12 Class 1?
Its melting point ranges 1425-1455°C (2597-2651°F), guiding hot working and heat treatment to avoid overheating.
Can SA 387 Grade 12 Class 1 be normalized and tempered?
Yes, normalizing (920-980°C, air-cooled) and tempering (600-700°C) enhance its strength and toughness, optimizing mechanical properties.