ASTM A516 Grade 70 is a popular, high-strength carbon steel plate for welded pressure vessels and tanks. It is valued for its excellent strength and toughness in moderate to lower-temperature service and is commonly used in the oil, gas, and chemical industries, with applications ranging from bridges to boilers. The grade offers higher tensile strength than the other A516 grades, such as 55, 60, and 65, and it is known for good weldability and notch toughness. The material contains controlled levels of manganese, phosphorus, sulfur, and silicon, and it is commonly supplied to pressure vessel quality requirements with documented mill test reports.
Material Properties
The principal mechanical requirements of A516 Grade 70, as defined by the ASTM specification, are:
Minimum yield point: 38 ksi, equal to about 260 MPa.
Tensile strength: 70 to 90 ksi, equal to 485 to 620 MPa.
Minimum elongation in 8 inches: 17 percent.
These values are the specification minimums and are confirmed on the mill test report of each delivered plate. The strength of the grade makes it suitable for pressure-bearing components where higher loading requires a stronger plate than the lower A516 grades.
Chemical Composition
The chemical composition of A516 Grade 70 is controlled within tight limits:
Carbon: maximum 0.27 percent for plates up to 1/2 inch thick, 0.28 percent over 1/2 inch to 2 inches, 0.30 percent over 2 to 4 inches, and 0.31 percent over 4 inches thick.
Manganese: 0.85 to 1.20 percent.
Phosphorus: maximum 0.025 percent.
Sulfur: maximum 0.025 percent.
Silicon: 0.15 to 0.40 percent.
The low carbon content supports weldability, while the manganese and silicon provide the strength and deoxidation required for a pressure vessel plate.
Heat Treatment, Welding, and Fabrication
Heat treatment is critical for achieving the required mechanical properties, especially for thicker plates:
Normalizing: mandatory for plates over 1.5 inches, about 38 mm, thick. The plate is heated to approximately 900 to 950 degrees Celsius and air cooled to refine the grain structure and improve toughness.
Stress relieving: post-weld heat treatment is typically performed at approximately 620 degrees Celsius, with a common rule of holding the material at this temperature for one hour per inch of thickness.
Plates up to 1.5 inches thick are usually supplied in the as-rolled condition, while normalizing can be specified for improved toughness and uniformity where required by the application.
A516 Grade 70 is highly weldable but requires care to prevent hydrogen-induced cracking, particularly in cold environments or thick sections. Preheating is recommended for thick sections, typically between 95 and 150 degrees Celsius. Common filler metal choices include ER70S-6 type electrodes for root passes and low-hydrogen fill and cap electrodes, and fabrication must often follow the requirements of the governing pressure vessel code.
The material can be processed by precision cutting methods such as bandsaw, plasma, or laser cutting. It is easily formed, although aggressive forming can lead to thinning, so gradual, controlled rolling is preferred over single deep draws to maintain wall thickness.
Supplementary Testing
During processing, plates may undergo additional testing to ensure they meet the demands of the service environment:
Charpy V-notch testing: measures impact toughness at low temperatures, for example at about minus 50 degrees Fahrenheit, where the application requires verified fracture resistance.
Hydrogen-induced cracking testing: required for sour service environments containing hydrogen sulfide, to confirm the plate's resistance to cracking.
Ultrasonic examination: used to detect internal flaws or laminations in the plate.
For sour service applications, plates with controlled hardness and verified hydrogen-induced cracking resistance can be specified, in line with the applicable industry requirements for hydrogen sulfide environments.
Typical Applications
A516 Grade 70 is used in a wide range of pressure-bearing equipment:
Oil, gas, and petrochemical: high-pressure components such as separators, distillation columns, reactors, and pipelines, including sour service variants for environments containing hydrogen sulfide.
Power generation: industrial boilers, steam drums, and heat exchangers, as well as nuclear pressure vessel and piping components where fracture toughness is required.
Storage and transport: large-scale storage tanks for liquids at moderate temperatures, railroad cars, cargo containers, and truck frames.
Renewable energy: hydroelectric penstock pipes and specialized components for cryogenic environments such as LNG storage.
The grade's combination of strength, toughness, and weldability makes it a dependable, economical choice for moderate to lower-temperature pressure vessel construction.
Frequently Asked Questions
What is A516 Grade 70? It is a carbon structural steel plate under ASTM A516, mainly used for manufacturing medium and low-temperature pressure vessels. It has good strength, toughness, and weldability, with a minimum yield strength of about 260 MPa and a tensile strength of 485 to 620 MPa.
What are the core applications of A516 Grade 70? It is mainly used to manufacture pressure-bearing equipment such as storage tanks, boilers, pressure vessels, and pipelines, and is widely applied in the petroleum, chemical, natural gas, and electric power industries.
What is the difference between A516 Grade 70 and A516 Grade 60? The core difference lies in strength: Grade 70 has a minimum yield strength of about 260 MPa, while Grade 60 is about 205 MPa, and Grade 70 also has higher tensile strength. Grade 70 is suitable for more stringent pressure-bearing conditions, while Grade 60 is used for lower-load scenarios.
What is the usual delivery status of A516 Grade 70 plates? The usual delivery status is hot-rolled or controlled-rolled, and normalizing can be performed where required. Normalizing refines the grains and improves the toughness and uniformity of the plate.
How is the weldability of A516 Grade 70? It has excellent weldability. No complex preheating is required before welding except for thick plates or low-temperature environments, and conventional methods such as shielded metal arc welding and gas metal arc welding can be used.
What are the low-temperature impact requirements for A516 Grade 70? Where impact testing is specified, for example at about minus 30 degrees Celsius, a minimum Charpy V-notch impact energy of 27 J on average, with a single-sample minimum of 20 J, is a common requirement to ensure resistance to brittle fracture in low-temperature service.