ASTM A106 Grade C is a specification for seamless carbon steel pipe designed specifically for high-temperature service, often used in applications involving the transportation of fluids and gases under elevated temperatures and pressures. This grade is part of the ASTM A106/ASME SA106 standard, which covers seamless carbon steel pipes suitable for bending, flanging, welding, and similar forming operations. It is produced from killed steel (fully deoxidized) using processes like open-hearth, basic-oxygen, or electric-furnace melting, potentially with degassing or refining. Steel can be cast in ingots or strand cast.

Unlike welded pipes, these are seamless, meaning they are manufactured from a single piece of steel without joints, providing higher strength and reliability in demanding environments. Pipes in NPS 1-1/2" and under may be hot-finished or cold-drawn, while NPS 2" and larger are typically hot-finished unless specified otherwise.

Key Applications

ASTM A106 Grade C pipes are widely used in industries requiring robust performance at high temperatures (up to around 750°F or 400°C, depending on specific conditions) and pressures. Common uses include:

Oil and gas refineries and petrochemical plants for transporting hot fluids or gases.

Power plants and boilers for steam and superheated water lines.

Shipbuilding and pressure vessels.

High-temperature pipelines in chemical processing and mineral slurry transmission.

This grade is preferred over lower grades (A or B) when higher strength is needed for more severe service conditions.

Chemical Composition

The chemical requirements for Grade C emphasize higher carbon content for enhanced strength, with limits on impurities like phosphorus and sulfur to ensure weldability and ductility. The composition (maximum percentages unless noted) is as follows:

Note: The combined content of Cr, Cu, Ni, Mo, and V shall not exceed 1%. For every reduction of 0.01% below the maximum carbon, an increase of 0.06% Mn above the maximum is permitted, up to 1.35% max Mn.

Mechanical Properties

Grade C offers superior tensile and yield strengths compared to Grades A and B, making it suitable for higher-stress applications. Minimum values at room temperature are:

These properties ensure the pipe can withstand significant stress without deformation. For comparison with other grades in the A106 family:

Dimensions and Tolerances

Sizes: Nominal Pipe Size (NPS) 1/8" to 48" (DN6 to DN1200), with wall thicknesses per ASME B36.10M (Schedules 10 through XXS, or custom).

Outside Diameter (OD) Tolerance: ±1% for pipes matching A53 OD standards (industry practice for A106).

Wall Thickness Tolerance: ±12.5% for NPS 1.5" and under; varies by size for larger pipes.

Weight Tolerance: -3.5% to +10% of nominal weight.

Lengths: Single random (17–24 ft), double random (36–44 ft), or as specified (no jointers unless ordered).

Ends: Plain, threaded, or beveled; suitable for welding.

Pipes must meet general requirements of ASTM A530/A530M for carbon and alloy steel pipes.