Carbon steel piping is most often used in chemical, petrochemical and oil and gas industry applications. It has the benefits of wide availability, high strength and a wide variety of connection types and fittings. Carbon steel piping is used for many liquid and gas services. It is widely used for water, air and steam systems.
Carbon steel pipe is widely available in a wide range of grades, sizes, wall thicknesses, lengths. Carbon steel pipe is economically priced compared to other non-ferrous materials, resulting in lower material costs and requires no special handling. A key advantage to carbon steel is its ability to be rolled, formed, bent or fabricated, allowing it to be manufactured into various sizes, shapes, and configurations. The elongation properties of steel allow it to withstand stresses and strains without breaking under shocks from surges, water hammer and other man-made disturbances.
Carbon steel can be broadly classified into the following broad groups:
- Low Carbon Steels - 0.05% to 0.25% Carbon
- Medium Carbon Steels - 0.25% to 0.5% Carbon
- High Carbon Steels - 0.5% and greater
Weldability of Carbon Steel
Low carbon steel grades are easily weldable. As percentage of carbon increases, its weldability decreases. Medium carbon steel grades are also easily weldable and may require application of appropriate preheating and post weld heat treatment. High grades of carbon steel are difficult to weld and require preheating and post weld heat treatment. Effects of carbon and other elements on the weldability of steel can be estimated by equating them to an equivalent amount of carbon.
Carbon Equivalent Ceq = C + Mn/6 + (Cr+Mo+V)/5 + (Cu+Ni)/15
Forgeability of Carbon Steel
Carbon steel forgings are used for manufacture of flanges, socket weld and threaded fittings, valves in sizes up to two inches. Carbon steels have excellent forgeability at the appropriate forging temperatures. As the carbon content increases the maximum forging temperature decreases.
The P-Number
This number is used to group similar Base Metals, allowing welding qualification of an entire selection versus qualification of just one. These base metals are grouped by material and assigned P-Numbers based on what material they are. P-Number 1 is assigned to Carbon Manganese or Low Carbon Steel base metals.