ASTM A662 Grade C is a carbon-manganese-silicon steel plate used for welded pressure vessels, boilers, and storage tanks, particularly where moderate to lower temperatures are involved and improved low-temperature toughness is needed. It is the strongest of the three grades in the A662 specification, with a higher manganese content that raises strength without sacrificing weldability. This combination makes Grade C a practical choice for pressure-containing equipment that must resist brittle fracture in cold service.
What Is A662 Grade C
ASTM A662 covers carbon-manganese-silicon steel plates for pressure vessels, and the specification defines three grades, A, B, and C, with increasing strength. Grade C has the highest manganese range, about 1.00 to 1.60 percent, which gives it a minimum yield strength of 295 MPa and makes it suitable for more demanding designs. Plates thicker than about 40 mm are normally supplied in the normalized condition to guarantee the specified toughness through the thickness.
Chemical Composition
The chemical composition of A662 Grade C is controlled to balance strength and weldability. Carbon is limited to a maximum of 0.20 percent, manganese is 1.00 to 1.60 percent, and silicon is 0.15 to 0.40 percent. Phosphorus and sulfur are each limited to 0.025 percent. The relatively low carbon content keeps the steel readily weldable, while the manganese provides the strength increase that distinguishes Grade C from the lower grades.
Mechanical Properties
A662 Grade C plate requires a tensile strength of 485 to 620 MPa and a minimum yield strength of 295 MPa. Minimum elongation is 18 percent in 200 mm gauge length and 22 percent in 50 mm gauge length. The strength level is comparable to many common pressure vessel grades, and the ductility supports cold forming of shells and heads without cracking.
Why Choose Grade C
Grade C is chosen when the design needs higher strength than Grades A and B but the project still uses a simple carbon-manganese steel without expensive alloying elements. The steel offers good low-temperature toughness, especially in the normalized condition, and it welds with standard procedures using low-hydrogen consumables. For applications such as large storage tanks and vessels that operate at moderate or lower temperatures, Grade C delivers the required strength and fracture resistance at a controlled cost.
Typical Applications
Welded pressure vessels for moderate and lower temperature service
Boilers and boiler-related pressure parts
Above-ground and underground storage tanks
Process vessels in chemical and petrochemical plants
Equipment requiring improved low-temperature toughness
Frequently Asked Questions
What is ASTM A662 Grade C? It is a carbon-manganese-silicon steel plate for welded pressure vessels and storage tanks, with higher strength than Grades A and B.
What is the yield strength of A662 Grade C? The minimum yield strength is 295 MPa and the tensile strength is 485 to 620 MPa.
What is the difference between Grades A, B, and C of A662? The grades increase in strength, mainly through higher manganese content, with Grade C being the strongest.
Is A662 Grade C good for low-temperature service? Yes, it offers improved low-temperature toughness, especially when supplied in the normalized condition.
Is A662 Grade C weldable? Yes, its low carbon content gives it good weldability with standard procedures and low-hydrogen consumables.
When is normalization required for A662 Grade C? Plates thicker than about 40 mm are normally normalized to guarantee the specified toughness.