SA387 Grade 11 Class 1 is a chromium-molybdenum alloy steel plate specifically designed for use in welded boilers and pressure vessels operating at elevated temperatures.it remains a critical material in the oil, gas, and petrochemical industries due to its resistance to oxidation, corrosion, and high-temperature creep.
Chemical Composition
| C | Mn | P | S | Si | Cr | Mo |
|---|---|---|---|---|---|---|
| 0.04 – 0.17 | 0.35 – 0.73 | ≤0.035 | ≤0.035 | 0.44 – 0.86 | 0.94 – 1.56 | 0.40 – 0.70 |
Mechanical Properties
| Grade | Thickness (in / mm) | Yield Strength (ksi) | Tensile Strength (ksi) | Elongation in 2" (%) | Elongation in 8" (%) |
|---|---|---|---|---|---|
| Grade 11 Class 1 | 0.185 – 3.60 / 4.70 – 91.4 | 35 | 60 – 85 | 22 | 19 |
Dimension Range – SA387 Grade 11 Class 1 Plates
| Grade | Product Type | Thickness (in / mm) | Width (mm) | Length (mm) |
|---|---|---|---|---|
| Grade 11 | Plate | 0.185 – 3.60 / 4.70 – 91.4 | 1500 – 3350 | 1900 – 15000 |
Tensile Requirements
| Requirement | Value |
|---|---|
| Tensile Strength | 75 – 100 ksi (515 – 690 MPa) |
| Yield Strength (0.2% offset) | ≥ 43 ksi (310 MPa) |
| Elongation in 8 in. (200 mm) | ≥ 18% |
| Elongation in 2 in. (50 mm) | ≥ 22% |
| Reduction of Area | Not specified |
workflow
1. Pre-Processing & Cutting
Material Verification: Ensure the plate is supplied in a Normalized and Tempered (N+T) condition with a valid Mill Test Certificate (MTC).
Preheated Cutting: To prevent edge cracking in the Heat Affected Zone (HAZ), plates should be preheated to 250°F - 300°F (120°C - 150°C) before oxy-fuel or plasma cutting.
2. Forming (Cold vs. Hot)
Cold Forming: Permissible for large radii. If the fiber elongation exceeds 5%, a subsequent stress-relief or full heat treatment is required per ASME Section VIII.
Hot Forming: Performed at temperatures between 1650°F and 1925°F (900°C - 1050°C).
Crucial Requirement: If the material is heated above its original tempering temperature, it must undergo a complete re-heat treatment (Normalizing & Tempering) to restore Class 1 mechanical properties.
3. Welding Operations (P-Number 4)
As a P-No. 4 material, Grade 11 requires rigorous thermal control during welding:
Preheating: Mandatory preheat of 300°F - 500°F (150°C - 260°C) depending on thickness to avoid hydrogen-induced cracking.
Interpass Temperature: Should be maintained above the preheat temperature but typically below 600°F (315°C).
Filler Metals: Use matching low-hydrogen consumables such as E8018-B2 electrodes or ER80S-B2 wires.
Dehydrogenation (DHT): If PWHT cannot be performed immediately after welding, a post-heat "bake-out" at 600°F (315°C) for 2+ hours is recommended.
4. Post-Weld Heat Treatment (PWHT)
This is the most critical stage for pressure vessel safety:
Temperature Range: Typically 1200°F to 1300°F (650°C - 705°C).
Holding Time: Usually 1 hour per inch of thickness (minimum 15-30 minutes).
Function: It reduces residual stresses, lowers weld hardness, and stabilizes the microstructure for high-temperature service.
5. Inspection and Quality Control (NDT)
Surface Inspection: Magnetic Particle Testing (MT) is performed after PWHT to detect any delayed surface cracking.
Volumetric Inspection: Ultrasonic Testing (UT) or Radiographic Testing (RT) to ensure weld internal soundness.
Mechanical Testing: Tensile tests must confirm the Class 1 range: 60–85 ksi (415–585 MPa).
Key Applications
Oil & Gas:
Pressure vessels, storage tanks, reactors, and piping for processing and storing high-temperature liquids and gases.
Petrochemical Industry:
Equipment in refineries and chemical plants that operates under extreme thermal conditions.
Power Generation:
Components in thermal power plants, boilers, and steam piping systems.
Heat Exchangers:
Used where high temperatures and corrosive media are present.
Why It's Used
High-Temperature Service:
Specifically designed for elevated temperature applications.
Corrosion Resistance:
Chromium content provides excellent resistance to oxidation and sour gas environments.
Creep Resistance:
Molybdenum enhances its ability to resist deformation under sustained stress at high temperatures.
Industries
Oil & Gas
Petrochemical
Chemical Processing
Power Generation
For more details about GNEE's steel products, contact us at beam@gneesteelgroup.com. We look forward to working with you.
What is the maximum service temperature of SA387 Grade 11 Class 1?
Its maximum continuous service temperature is around 593°C (1100°F). Beyond this, its strength and structural stability will decrease significantly.
What is the hardness range of SA387 Grade 11 Class 1?
After heat treatment, its Brinell hardness (HB) is usually between 137-187, balancing strength and machinability for industrial processing.
Which industry is this steel grade most commonly used in?
It is widely applied in the petrochemical, refinery and power generation industries, especially for pressure vessels, boilers and heat exchangers.
What post-weld heat treatment (PWHT) is required for this steel?
Common PWHT is tempering at 620-675°C, held for a certain time to relieve welding stress, improve toughness and stabilize mechanical properties.
How to prevent corrosion of this steel grade in service?
Regular inspection, anti-corrosion coatings and controlling service environment (avoiding strong acids/bases) can effectively prevent corrosion and extend service life.
What is the tensile strength range of SA387 Grade 11 Class 1?
Its tensile strength is typically between 415-585 MPa. This range ensures it can withstand high pressure in harsh working environments.
Can SA387 Grade 11 Class 1 be machined easily?
It has moderate machinability. Using high-speed steel or carbide tools with proper cutting parameters ensures smooth machining without excessive tool wear.
What is the elongation rate of this steel grade?
The minimum elongation rate is 22% (in 50mm). This indicates good ductility, allowing slight deformation without fracture under external force.
How to improve the weldability of this steel grade?
Preheating to 150-200°C before welding and post-weld heat treatment (PWHT) can reduce welding stress and prevent cold cracks, enhancing weldability.