A516 Grade 70 is a type of pressure vessel steel plate designed for use in moderate and lower temperature service conditions. It is part of the ASTM A516 specification, which covers carbon-manganese-silicon steels suitable for fusion welding. This grade is known for its good notch toughness and strength, making it suitable for applications where pressure containment is critical. The material is commonly used in the fabrication of boilers, storage tanks, and pressure vessels that handle liquids or gases under various operating pressures. Its composition and heat treatment are optimized to provide reliable performance and resistance to brittle fracture, even in environments where temperature fluctuations may occur.
Chemical Composition
|
Element |
Composition (% by weight) |
|---|---|
|
Carbon (C) |
0.27 max |
|
Manganese (Mn) |
0.85–1.20 |
|
Phosphorus (P) |
0.035 max |
|
Sulfur (S) |
0.035 max |
|
Silicon (Si) |
0.15–0.40 |
|
Aluminum (Al) |
0.02 min (for killed steel) |
|
Iron (Fe) |
Balance |
Mechanical Properties
|
Property |
Value |
|---|---|
|
Tensile Strength |
485–620 MPa (70–90 ksi) |
|
Yield Strength (min) |
260 MPa (38 ksi) |
|
Elongation (min, 200 mm) |
17% |
|
Elongation (min, 50 mm) |
21% |
|
Hardness (HB, typical) |
140–200 HB |
|
Impact Toughness (Charpy V-notch) |
Meets ASTM requirements at -46°C |
Physical Properties
|
Property |
Value |
|---|---|
|
Density |
7.85 g/cm³ |
|
Melting Point |
~1510°C |
|
Thermal Conductivity |
50 W/m·K (at 20°C) |
|
Specific Heat Capacity |
470 J/kg·K |
processing
1. Steelmaking: Fully Killed Steel
Deoxidation: The steel must be "fully killed," typically achieved by adding silicon or aluminum during the melting process to remove oxygen.
Fine Grain Structure: This ensures a dense and uniform internal structure, providing excellent notch toughness to prevent brittle fracture under pressure.
2. Heat Treatment Processes
Heat treatment is critical for determining the mechanical properties of A516 Gr 70:
As-Rolled: Plates with a thickness of 1.5 inches (40mm) or less are usually supplied in the as-rolled condition.
Normalizing (N):
Requirement: Mandatory for plates thicker than 1.5 inches (40mm).
Process: Heating the plate above the critical temperature (approx. 900–950°C), followed by air cooling.
Effect: It refines the grain structure and significantly improves impact toughness at low temperatures. These plates are marked as A516 Gr 70N.
Stress Relieving (PWHT): Post-Weld Heat Treatment is often performed after fabrication to eliminate residual welding stresses and ensure the safety of the vessel.
3. Welding Processes
A516 Gr 70 has excellent weldability and is compatible with standard industrial methods:
Methods: Shielded Metal Arc Welding (SMAW), Submerged Arc Welding (SAW), Gas Metal Arc Welding (GMAW/MIG), and Flux-Cored Arc Welding (FCAW).
Preheating: For thick plates, preheating above 100°C is recommended to reduce the hardness of the Heat Affected Zone (HAZ) and prevent cold cracking.
Consumables: Low-hydrogen electrodes (e.g., E7018) are typically used to match the 70ksi tensile strength requirement.
4. Machining and Forming
Cutting: Commonly performed using oxy-fuel (flame) cutting, plasma cutting, or laser cutting.
Cold/Hot Forming: The material has good cold-bending properties. For heavy drum rolling, cold forming is standard; however, for extreme deformations, hot forming may be employed.
HIC Resistance Processing: For "sour service" (containing 𝐻2𝑆), specialized techniques like vacuum degassing and calcium treatment are used to minimize sulfur content and control inclusion shapes, preventing hydrogen-induced cracking.
Primary Industrial Applications
Oil, Gas, and Petrochemicals: It is the standard choice for manufacturing high-pressure storage tanks, gas separators, and distillation columns. Specialized HIC-resistant plates are used in "sour service" environments to prevent hydrogen-induced cracking caused by 𝐻2𝑆.
Power Generation: Widely utilized for high-pressure boilers, steam drums, heat exchangers, and condenser shells due to its reliability under thermal and pressure stress.
Cryogenic & Low-Temperature Service: Because it maintains impact toughness down to -46°C (-50°F), it is essential for LNG (Liquefied Natural Gas) storage tanks and equipment in cold climates.
Structural and Mechanical Uses
Beyond pressure vessels, its versatility leads to applications in:
Transportation: Used for the shells of railroad tank cars, heavy truck frames, trailers, and cargo containers.
Civil Infrastructure: Critical components for bridges, building structures, and transmission poles.
Manufacturing & Construction: Heavy-duty components such as construction equipment frames, structural tubing, and lighting standards.
Specialized Equipment: Fabrication of penstock pipes for hydroelectric projects, gas cylinders, and turbine volutes.
Regulatory Standards
Most applications in 2026 continue to follow ASME Boiler and Pressure Vessel Code (BPVC) Section VIII or API 650/620 for storage tanks. For plates exceeding 1.5 inches (40mm), normalizing is mandatory to ensure the required structural integrity for these high-performance roles.
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What is the dimensional tolerance standard for A516 Grade 70 steel plates?
The thickness tolerance is implemented in accordance with ASTM A6/A6M standards, and the common tolerance grades are Class A or Class B; the width and length tolerances are determined according to the delivery status (cut edge/mill edge), which must meet the requirements for dimensional accuracy in equipment manufacturing.
What are the advantages of A516 Grade 70 in natural gas storage tank manufacturing?
The advantages are good weldability, which facilitates the welding and forming of large storage tanks; excellent medium and low temperature toughness, which is suitable for the low-temperature working conditions of natural gas storage; strength meets pressure-bearing requirements, and the cost is relatively lower than that of alloy steel plates.
What is the usual delivery status of A516 Grade 70 steel plates?
The usual delivery status is hot-rolled or controlled-rolled, and normalizing treatment (N) can be performed if necessary. Normalizing treatment can refine grains, improve the toughness and uniformity of the steel plate, and meet the requirements for material stability in harsh working conditions.
What are the standard yield strength and tensile strength values of A516 Grade 70?
The minimum yield strength (σs) is 260MPa, and the tensile strength (σb) ranges from 485MPa to 655MPa. These strength indicators ensure that the steel plate is not prone to plastic deformation and fracture in pressure-bearing environments, safeguarding equipment safety.
What is the applicable temperature range of A516 Grade 70?
The applicable temperature range is -30℃ to 450℃. Within this range, it can maintain stable mechanical properties, with no risk of brittle fracture at low temperatures, and its strength and toughness meet the operating requirements of pressure-bearing equipment at high temperatures.
What are the key chemical composition requirements for A516 Grade 70?
Key components: Carbon (C) ≤0.30%, Manganese (Mn) 0.85-1.20%, Phosphorus (P) ≤0.035%, Sulfur (S) ≤0.035%, Silicon (Si) 0.15-0.40%. The content of harmful impurities is strictly controlled to ensure performance.
How to test the mechanical properties of A516 Grade 70?
The main tests include tensile test (to measure yield strength, tensile strength and elongation), impact test (Charpy V-notch, to evaluate low-temperature toughness), and hardness test. Test samples must be cut from the steel plate itself in accordance with relevant ASTM standards.
What is the elongation requirement for A516 Grade 70?
The elongation (δ5) is ≥21%. The elongation index reflects the plastic deformation capacity of the steel plate. A higher elongation allows the steel plate to be less prone to fracture when stressed and facilitates processing and forming (such as bending and stamping).
What electrode should be selected for welding A516 Grade 70?
The commonly used electrode is E7018 (low hydrogen type), which matches the strength and toughness of the base metal. During welding, the electrode needs to be dried (350-400℃, heat preservation for 1-2 hours) to avoid welding defects such as porosity and cracks, and ensure joint quality.
What is the hardness standard for A516 Grade 70?
The Brinell hardness (HB) is ≤187. Excessively high hardness will reduce the toughness and weldability of the steel plate. If the hardness exceeds the standard, tempering treatment is required to reduce the hardness to ensure that the material performance meets the equipment manufacturing requirements.
What is the difference between A516 Grade 70 and ASTM A36 materials?
A36 is a general carbon structural steel with a yield strength of 250MPa, suitable for ordinary structural parts; Grade 70 is a special steel for pressure vessels with a yield strength of 260MPa, higher low-temperature toughness and purity, suitable for pressure-bearing working conditions.