ASTM A106 is a specification for seamless carbon steel pipes used for high-temperature applications. The standard covers three grades: Grade A, Grade B, and Grade C, with each grade differing in terms of mechanical properties, particularly in strength.

Here’s a comparison between ASTM A106 Grade B and Grade C:

1. Chemical Composition

• Grade C has a slightly higher carbon content, which increases the strength of the steel but can make it slightly less ductile compared to Grade B.

2. Mechanical Properties

• Grade C has a higher tensile and yield strength, making it stronger than Grade B. However, this also results in less elongation, meaning Grade C is less ductile and more brittle than Grade B.

3. Applications

• Grade B: This is the most common grade used in general applications like boilers, piping systems, and pressure vessels where strength is important but ductility is also needed for forming and bending.
• Grade C: It is typically used in more demanding applications that require higher strength, such as higher-pressure pipelines and steam lines where toughness is critical.

4. Weldability and Formability

• Grade B: Easier to weld and form due to its lower carbon content and better elongation properties.
• Grade C: While it is still weldable, it requires more attention during welding to avoid cracking due to the higher carbon content. The increased hardness also makes it more difficult to form compared to Grade B.

5. Cost

• Grade C is usually more expensive than Grade B because of the increased strength and higher carbon content.

Summary

• ASTM A106 Grade B is more versatile, with good balance between strength, ductility, and weldability. It's often used in general piping systems, boilers, and industrial applications.
• ASTM A106 Grade C offers higher strength but sacrifices some ductility and formability, making it suitable for higher-pressure applications where strength is a priority.

Choosing between the two depends on the specific mechanical and chemical demands of the project.