A387 Grade 5 Class 1 is a chromium-molybdenum alloy steel plate designed for use in welded pressure vessels and high-temperature service. It offers good strength and creep resistance at elevated temperatures, along with excellent weldability and toughness. This grade is commonly employed in the oil and gas, petrochemical, and power generation industries for components that must withstand both high pressure and high temperature over extended periods.
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A387 Gr.5 CL.1 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.1 Mechanical Property |
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Thickness |
Yield |
Tensile |
Elongation |
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A387 Gr.5 Cl.1 |
mm |
Min Mpa |
Mpa |
Min % |
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t≦50 |
205 |
415-585 |
18 |
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50 |
- |
- |
- |
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processing
1. Heat Treatment (Thermal Processing)
The "Class 1" designation is achieved through specific cooling rates and tempering temperatures to prioritize ductility over high tensile strength.
Normalizing: Heating to 900°C – 950°C (1650°F – 1740°F) followed by air cooling to refine the grain structure.
Tempering: Performed at 675°C – 760°C (1250°F – 1400°F). For Class 1, the tempering duration is often longer to ensure the lower tensile range (60-85 ksi) and maximum toughness.
Annealing: Full annealing at 870°C – 930°C followed by slow furnace cooling is also an option for maximum softness.
2. Welding Procedures (WPS)
This grade is sensitive to hydrogen-induced cracking (HIC). Successful welding requires strict temperature control:
Preheating: Mandatory preheat of 150°C – 250°C (300°F – 480°F) depending on plate thickness.
Interpass Temperature: Must be maintained within the preheat range to prevent brittle martensite formation.
Post-Weld Heat Treatment (PWHT): Essential for all pressure vessel applications. Typically held at 700°C – 760°C (1300°F – 1400°F) to reduce hardness in the Heat Affected Zone (HAZ).
Filler Metal: Use low-hydrogen electrodes matching the chemistry, such as E8018-B6 or ER80S-B6.
3. Cutting and Forming
Thermal Cutting: Flame (Oxy-fuel) or Plasma cutting is standard. Due to the 5% Chromium content, the cut edges will harden significantly. It is recommended to grind away the hardened "heat-affected" edge before subsequent welding.
Cold Forming: Class 1 plates have excellent formability. However, if the strain exceeds 5%, a subsequent stress-relief or full heat treatment is often required by code (e.g., ASME BPVC).
Hot Forming: Performed between 850°C and 1050°C. If hot-formed, the plate must undergo a full Normalizing and Tempering cycle again to restore mechanical properties.
4. Surface Treatment & Inspection
Pickling or Blasting: Used to remove mill scale before fabrication to ensure high-quality welds.
Nondestructive Testing (NDT): Standard procedure for 2026 projects involves Ultrasonic Testing (UT) per ASTM A435 and Magnetic Particle Inspection (MPI) on weld seams to check for micro-cracks.
advantages
High-Temperature Stability: Designed for service between 316°C and 593°C; molybdenum provides excellent creep resistance against deformation.
Oxidation & Corrosion Resistance: 5% Chromium content prevents scaling and resists sulfidation in refinery environments.
HTHA Resistance: Highly effective against High-Temperature Hydrogen Attack, making it vital for pressurized hydrogen service.
Superior Ductility (Class 1 Benefit): Offers higher elongation than Class 2, ensuring better toughness and easier cold-forming/rolling.
Proven Weldability: A standard grade for weldable pressure vessels; ensures structural integrity when using proper PWHT (Post-Weld Heat Treatment).
Cost-Efficiency: Provides a durable, heat-resistant solution at a significantly lower cost than high-nickel alloys or stainless steel.
Contact us at beam@gneesteelgroup.com for pricing, technical support, or customized solutions. We are always ready to support your project.
What's the difference in carbon content between A387 Grade 5 Class 1 and A387 Grade 9 Class 1?
A387 Grade 5 Class 1 has a carbon content of 0.15-0.25%, while Grade 9 Class 1 is 0.05-0.15%, making the former slightly higher for better strength.
How does the tensile strength of A387 Grade 5 Class 1 compare with A36 steel?
A387 Grade 5 Class 1 has a tensile strength of 415-585 MPa, much higher than A36's 400-550 MPa, suitable for high-pressure scenarios.
What distinguishes the corrosion resistance of A387 Grade 5 Class 1 from 304 stainless steel?
304 stainless steel has better corrosion resistance due to chromium-nickel content, while A387 Grade 5 Class 1 excels in high-temperature oxidation resistance.
What is A387 Grade 5 Class 1 mainly composed of?
Its main components are iron, 4.00-6.00% chromium, 0.45-0.65% molybdenum, 0.15-0.25% carbon, with trace manganese and silicon for stability.
What is the standard specification for A387 Grade 5 Class 1?
It follows ASTM A387, a standard for chromium-molybdenum alloy steel plates used in welded pressure vessels and high-temperature services.
What is the minimum yield strength of A387 Grade 5 Class 1?
The minimum yield strength is 275 MPa (40 ksi), ensuring it can withstand high pressure and load in industrial applications without deformation.
What is the typical application of A387 Grade 5 Class 1?
It is widely used in high-pressure boilers, chemical reactors, oil refinery vessels, and pipelines that operate at elevated temperatures and pressures.
What heat treatment is required for A387 Grade 5 Class 1?
It usually undergoes normalizing (890-940°C) followed by tempering (620-705°C) to improve toughness, strength, and weldability for industrial use.
What is the elongation rate of A387 Grade 5 Class 1?
The minimum elongation rate is 18% in 50 mm, indicating good ductility to resist brittle fracture during welding and service.
Is A387 Grade 5 Class 1 a low-alloy or high-alloy steel?
It is a low-alloy steel, as its total alloy content (chromium + molybdenum) is less than 10%, balancing performance and cost.