Carbon Steel Pipe – Chemical Composition, Standards, Specifications, Applications

From the above introduction, we already know that carbon steel pipe is iron + controlled carbon content + small amount of unavoidable impurities. But do you know how much iron is in carbon steel pipe? What are those unavoidable impurities?

• Iron (Fe): Iron is the real main body of steel. Whether it is carbon steel pipe or other types of steel pipe, iron usually accounts for more than 98%. The iron content in low carbon steel is as high as 99.2%. Iron constitutes the structural skeleton of carbon steel pipe.
• Carbon (C): Carbon is the most important element in carbon steel pipe, typically ranging from 0.06% to 0.8%. The carbon content affects the overall performance of the pipe. A high carbon content increases the pipe’s strength and hardness, but reduces its plasticity, toughness, and workability.
• Manganese (Mn): Manganese content ranges from 0.3% to 1.0%, though 0.8% to 1.0% is less common. The more common range is 0.3% to 0.8%. Manganese acts as a strengthening and deoxidizing element, increasing the strength and hardness of pipes while reducing hot brittleness.
• Phosphorus (P): Phosphorus is a harmful element. While a small amount can enhance pipe strength and corrosion resistance, it significantly impairs plasticity and toughness. Therefore, the phosphorus content must be strictly controlled, typically requiring ≤ 0.040%.
• Sulfur (S): Sulfur is also a harmful impurity that requires strict control. It forms manganese sulfide inclusions, which can reduce the pipe’s ductility, toughness, fatigue strength, weldability, and corrosion resistance. Therefore, the sulfur content is typically required to be ≤ 0.050%.
• Silicon (Si): Silicon primarily deoxidizes the pipe. While residual silicon slightly reduces toughness and plasticity, it increases strength and hardness. Its content is typically between 0.10% and 0.35%.
• Other elements: Nickel (Ni), molybdenum (Mo), vanadium (V), chromium (Cr), etc. are called residual elements. Their source is scrap steel and ore as raw materials. The standard will set an upper limit for the total content or a certain content.