A516 Gr.65 steel VS Gr.70

A516 is a standard specification for carbon steel plates intended for pressure vessel service. Grades 65 and 70 are two different tensile strength categories within this specification. The primary difference between A516 Gr.65 and A516 Gr.70 lies in their chemical composition and mechanical properties, which affect their performance in various pressure vessel applications.

1. Tensile Strength and Yield Strength:
A516 Grade 65 has a tensile strength range of 70-90 ksi (485-620 MPa) and a yield strength of ≥ 450 MPa (65 ksi).
A516 Grade 70 has a tensile strength range of 70-95 ksi (485-655 MPa) and a yield strength of ≥ 485 MPa (70 ksi).
Grade 70 generally has a higher yield strength, making it more suitable for higher-pressure environments compared to Grade 65.

2. Chemical Composition:
Both grades are primarily composed of carbon, with small amounts of manganese, phosphorus, sulfur, and other elements to improve strength and toughness.
The difference in strength and toughness can be attributed to subtle variations in the carbon content and alloying elements. Grade 70 may have slightly higher levels of carbon and manganese than Grade 65 to achieve its higher tensile and yield strength.

3. Thickness and Weldability:
Both grades are available in a variety of thicknesses, but A516 Grade 70 tends to be preferred in thicker plates because of its higher strength and greater resistance to pressure.
Weldability: Both grades are considered highly weldable, with proper preheating and post-weld heat treatment (PWHT) for thicker sections. However, Grade 70’s higher carbon content can make it slightly more sensitive to welding issues like cracking, which may require more attention during welding procedures.

4. Application:
A516 Gr.65 is typically used in moderate-temperature pressure vessels, including those found in the petrochemical, oil, and gas industries, but at slightly lower pressure than where Grade 70 would be used.
A516 Gr.70 is often used in applications requiring higher strength, such as in high-pressure steam systems, boilers, and pressure vessels subject to high temperatures or pressure.

5. Charpy Impact Toughness:
Both grades are required to meet Charpy V-notch impact tests, but Grade 70 typically offers better toughness at lower temperatures due to its higher alloy content and processing.

In summary, A516 Grade 70 has slightly superior mechanical properties and is better suited for higher-pressure, higher-temperature applications compared to A516 Grade 65. However, A516 Gr.65 is still an excellent material for moderately high-pressure and temperature environments where cost or availability is a consideration.