Steel plates designed for high pressure and high temperature applications are known as boiler quality plates. Boilers, storage tank and pressure vessels are all made with it. The ASTM A516 standard establishes the composition, strength and toughness requirements for these plates. Choosing the appropriate grade is important for long service life, cost, and safety. The four main grades of ASTM A516 are 55, 60, 65, and 70. The main distinctions between Grades 60, 65, and 70 are described in the blog.
Understanding ASTM A516 Standard
ASTM stands for the American Society for Testing and Materials. A516 is the code that defines carbon steel plates for moderate- and lower-temperature pressure vessels. This steel is also known worldwide with equivalents like EN 10028 P265GH, BS 1501-161-430A, and IS 2002 Grade 2. Compared to general structural steel, A516 plates offer better notch toughness and pressure resistance. These plates are most used in oil refineries, power plants, petrochemical units, and boiler manufacturing.
Overview of Boiler Quality Plate Grades
In ASTM standards, the grade number reflects the minimum tensile strength. Grade 60 steel for instance has a tensile strength of at least 60 ksi. These plates are manufactured in a wide range of thicknesses and sizes usually from 5 mm up to 200 mm thick. Each grade provides slightly different strength, weldability, and toughness levels depending on the application.
Chemical Composition Analysis
- Carbon (C): Higher carbon boosts strength but lowers weldability. Grade 70 has slightly more carbon, making it stronger but less easy to weld compared to Grade 60. Careful preheating and welding procedures are often recommended for higher grades.
- Manganese (Mn): Improves toughness and wear resistance. Manganese levels increase across the grades, helping higher grades sustain more stress. Additionally this increases hardness without sacrificing ductility.
- Phosphorus (P) and Sulfur (S): To avoid brittleness these are kept at extremely low levels. If present in excess, they can cause cracking during fabrication and reduce long-term durability.
- Silicon (Si): Leads to the deoxidation of steel and increases its strength. It also helps plates withstand higher pressures without deforming.
- Micro-Alloys: Small amount of elements like vanadium or niobium may be added in some cases. These improve grain structure, durability, and resistance to stress over time.
Mechanical Properties by Grade
- Tensile Strength: Minimum tensile strength is 60 ksi for Grade 60, 65 ksi for Grade 65, and 70 ksi for Grade 70. A material with a higher tensile strength can withstand greater stress before breaking.
- Yield Strength: Additionally yield strength increases with grade indicating that higher grades are better at withstanding deformation. Because of this, Grade 70 is perfect for boilers that run at higher pressures.
- Ductility: Grade 60 is the most ductile, making it easier to bend and shape. Grade 70, while stronger, is slightly less flexible, which may increase fabrication challenges.
- Low-Temperature Use: All grades perform well at moderate low temperatures, but Grade 60 has better toughness. It is often chosen for cold regions or when vessels operate below room temperature.
Manufacturing and Heat Treatment
- Production: Plates are made by rolling killed carbon steel using fine grain practice. This guarantees dependable strength and constant quality for large plate sizes.
- Normalizing: Plates, especially in higher grades, are often normalized to refine grain structure. Normalizing enhances toughness and reduces internal stress from rolling.
- Stress Relieving: Stress relief treatment is applied after fabrication to stop distortion or cracking. For pressure vessels and welded boilers this is crucial.
- Heat Treatment: While Grade 70 plates are more likely to undergo normalization Grade 60 plates are frequently supplied in rolled form. Heat treatment ensures performance matches the design pressure and temperature.
Detailed Differences Between Grade 60, 65 and 70
- Strength: While Grade 70 can tolerate the highest pressures Grade 60 is best suited for low pressure applications. Between the two grade 65 is widely used in situations where moderate strength is sufficient.
- Weldability: Because Grade 60 has the best weldability complex vessel fabrication is made easier. More careful welding is needed for Grade 70 to prevent cracking.
- Applications: Grade 60 works well for tanks and transport vessel. Grade 65 is common in refinery equipment. Grade 70 is the choice for high-pressure boilers and steam drums.
- Durability: Higher grades offer more resistance to stress but may lose some ductility. Engineers weigh this trade-off depending on operating conditions.
- Cost: Higher grades are more expensive, both for raw material and processing. Grade 60 is cost-effective for standard applications, while Grade 70 justifies the extra cost for demanding service.
Applications by Grade
- Grade 60: Used in storage tanks, transport tanks, and low-pressure boilers. Its ductility makes it easier to fabricate into large shapes.
- Grade 65: Found in refinery equipment, medium-pressure vessels, and process industries. It balances strength and weldability for industrial projects.
- Grade 70: Applied in steam drums, power generation boilers, and high-pressure reactors. Its higher strength support continuous high pressure service. Industries select based on required safety margins working conditions and long term durability.
Testing and Quality Requirements
- Ultrasonic Testing: Finds internal defect that could weaken the plate while it is being used such as cracks or voids.
- Impact Testing: Verifies toughness at low temperatures. This is important for vessels working in cold regions or storing cryogenic materials.
- Tensile Testing: Confirms tensile strength and yield strength of each batch. Only plates that meet ASTM requirements are approved.
- Certification: Mill test certificates (MTC) are provided with the plates. Third-party inspection by organizations like Lloyd’s or BV is essential for important projects.
Factors to Consider Before Choosing a Grade
- Operating Pressure & Temperature: While lower operating condition might only require Grade 60, higher operating conditions require stronger grade like 70.
- Fabrication Needs: Because of its greater ductility, Grade 60 is preferable for welding or forming if the vessel needs to be bent heavily.
- Corrosion Exposure: Projects in marine or chemical environments may need additional coatings or cladding, regardless of grade.
- Budget & Supply: Grade 70 may increase project costs but provides long term savings in durability. Availability of plate size and thickness may also guide the final choice.
ASTM A516 vs Other Steel Standards
Low-pressure storage tanks are the primary application for ASTM A285 plates, which are weaker. An Indian standard called IS 2002 has comparable uses though its impact requirement might be different. Similar classifications for pressure vessels are found in EN 10028, which is widely used in Europe. Because ASTM A516 complies with international codes like ASME it is frequently chosen for international projects and is a more flexible choice for cross-border applications.
Thickness, Width, and Tolerance Considerations
A516 plates are available in thicknesses from 5 mm to 200 mm, widths up to 3,500 mm and lengths up to 12,000 mm. Thicker plates provide higher pressure resistance but add cost and weight. Tighter tolerance ensures plates can be fabricated without excess machining. Precise dimensions reduce material wastage during vessel manufacturing.
Price and Market Trends
Global steel prices affect the cost of A516 plates. Grade 70 is 8–12% more expensive than Grade 60 due to its higher strength and processing requirements. In 2025, supply chain issues and rising raw material costs are influencing prices. Higher thickness plates are harder to source and carry longer lead times, making procurement planning important.
Storage, Handling, and Fabrication Tips
Plates should be stored in dry, covered areas to prevent rust. Wooden supports or pallets help avoid moisture contact. Safe lifting using spreader bars or slings prevents bending and damage. Before welding, preheating improves results and reduces cracking risk. After fabrication, stress relieving extends service life by minimizing residual stress inside the steel.
Conclusion
ASTM A516 Grade 60, 65, and 70 differ mainly in strength, weldability, and applications. Grade 60 is easier to fabricate, Grade 65 serves mid-range vessels, and Grade 70 is best for high-pressure boilers. Selection depends on working conditions, budget, and project needs. Consulting a materials engineer ensures the right balance between safety and cost.
