What is the minimum tensile strength of SA 387 Grade 12 Class 2?

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.

SA 387 GR.12 Equivalent Grades :

Other Types :

Chemical Composition of SA387 GR.12 CL.2 Plate

Mechanical Properties of SA 387 GR.12 CL.2 Plate

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.

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applications

Core Industrial Sectors

Oil, Gas, and Petrochemicals: This is the primary application area. It is used for refinery equipment, separator vessels, and storage tanks for high-pressure gases. Its chromium content provides excellent resistance to sour service (environments containing 𝐻2𝑆).

Power Generation: Essential for industrial boilers, boiler drums, and steam pipelines. It is also used in Heat Recovery Steam Generators (HRSG) and components for both gas and steam turbines.

Nuclear Energy: Utilized in the fabrication of nuclear reactor pressure vessels and related heat exchange systems due to its mechanical reliability at high temperatures.

Chemical Processing: Used for reactors and pressure vessels that handle corrosive media and liquefied petroleum.

Specialized Components

Beyond large vessels, SA 387 Grade 12 Class 2 is processed into various critical parts:

Heat Transfer: Heat exchangers, condensers, and superheaters.

Piping Systems: High-temperature ducting, pipe supports, and large-diameter pipe work.

Hardware Fittings: Specialized valves, flanges, pipe clamps, and fittings.

Storage & Transport: Oxygen cylinders and large metallic tanks.

Other Industrial Uses

Aerospace & Defense: Military vehicles, naval ships, and aircraft components due to its resistance to thermal fatigue.

Mining & Construction: Liners for chutes, tubs, and bins, as well as specialized equipment like arcoplate cyclones.

Manufacturing: Used in fertilizer plants, paper mills, and cement industries for high-stress processing equipment.

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What is the modulus of elasticity of this grade?

Its modulus of elasticity is about 200 GPa (29×10⁶ psi) at room temperature, consistent with most low-alloy steels for structural design.

Can SA 387 Grade 12 Class 2 be formed by bending?

Yes, it can be bent with proper procedures. Preheating may be needed for thick sections to avoid cracking, and bending radius should be controlled.

What is the service life expectation of this material in typical applications?

With proper maintenance and operation, it can serve 20 to 30 years. Service life depends on temperature, pressure, and corrosiveness of the working environment.

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.

Is SA 387 Grade 12 Class 2 magnetic?

Yes, it is ferromagnetic. As a low-alloy steel, it retains magnetic properties at room temperature, which is important for non-destructive testing.

What non-destructive testing (NDT) methods are used for this material?

Common NDT methods include ultrasonic testing (UT), radiographic testing (RT), and magnetic particle testing (MT) to detect internal and surface defects.

Can this material be normalized?

Yes, normalization is a common heat treatment. It involves heating to 899°C to 954°C (1650°F to 1750°F) and air cooling to refine grain structure.

What is the difference between Class 1 and Class 2 of SA 387 Grade 12?

Class 2 has stricter impact toughness requirements than Class 1. It is suitable for more severe service conditions with higher stress and temperature fluctuations.

Can this material be used in oil and gas refineries?

Absolutely. It is widely used in oil and gas refineries for reactors, boilers, and heat exchangers, enduring high temperatures and corrosive media.

What is the melting point range of SA 387 Grade 12 Class 2?

Its melting point ranges from 1427°C to 1455°C (2600°F to 2650°F). This high melting point supports its use in high-temperature applications.

Does this material require corrosion protection?

It depends on the environment. In mild conditions, it resists corrosion, but in harsh corrosive media, coatings or linings may be needed to extend service life.