Steel is classified according to the chemical composition contained in it. Steel pipes and fittings are an alloy of iron (Fe) and carbon (C), and contain less than 1.7% carbon. Steel classifications are in three groups, namely: Carbon steel, low alloy steel and high alloy steel.
Carbon steel consists of iron, carbon less than 1.7%, manganese less than 1.65%, a certain amount of silicon (Si), aluminum (Al), and a limit of contaminants such as sulfur (S), oxygen (O), nitrogen (N ), and no minimum limits have been defined for elements such as Al, Cr, Co, Ni, Mo, Ni [ASM, ASTM A 941].
Carbon steel is the most common pipe material in the power plant, chemical, process, hydrocarbon and industrial plumbing industries. Specifications for carbon steel pipes commonly used in steam, water or air operations include ASTM A106 and ASTM A53. Common carbon steel for pipeline applications is API 5L pipe. Mild steel is carbon steel with a carbon content of less than 0.30%. Medium carbon steels have 0.30% to 0.60% carbon. High carbon steels have carbon above 0.6%.