What are the main chemical components of ordinary carbon steel pipes?
Ordinary carbon steel pipes are mainly composed of iron (Fe) and carbon (C), and the carbon content is usually between 0.06% and 1.5%. In addition, it may contain small amounts of impurities such as silicon (Si), manganese (Mn), sulfur (S) and phosphorus (P). Low carbon steel (such as Q235) has a lower carbon content, and high carbon steel (such as 45# steel) has a higher carbon content. The ratio of these elements directly affects the strength, hardness and weldability of the steel pipe. Sulfur and phosphorus, as harmful elements, need to be strictly controlled to avoid increased brittleness.
What is the core difference between carbon steel pipes and other steel pipes (such as stainless steel pipes)?
Carbon steel pipes use carbon as the main alloying element, while stainless steel pipes use chromium (Cr) as the main alloying element (usually ≥10.5%) and have corrosion resistance. Carbon steel pipes are cheaper, but they are prone to rust and require surface treatment (such as galvanizing). Stainless steel pipes are suitable for corrosive environments, such as the chemical or food industry, while carbon steel pipes are mostly used for structural support or low-pressure fluid transportation. The two also differ in mechanical properties (such as tensile strength), and carbon steel pipes are easier to process and weld.
What is the density of ordinary carbon steel pipes? How does it affect its weight calculation?
The density of ordinary carbon steel pipes is about 7.85 g/cm³, which is close to pure iron. When calculating the weight, the outer diameter, wall thickness and length must be combined. The formula is: weight (kg) = (outer diameter-wall thickness) × wall thickness × length × 0.02466. For example, a DN50 pipe (outer diameter 60mm, wall thickness 3mm, length 6 meters) weighs about 25.3kg. Constant density makes weight proportional to volume, which is convenient for logistics and cost estimation.
Why does carbon steel pipe need to distinguish between hot rolling and cold rolling processes?
Hot-rolled steel pipes are formed at high temperatures, with a rough surface but good toughness, suitable for large-diameter thick-walled pipes; cold-rolled steel pipes are processed at room temperature, with precise dimensions and smooth surfaces, but with large residual stress. Hot-rolled pipes are low-cost and often used in building structures; cold-rolled pipes are used for precision machinery or thin-walled requirements. The two differ in mechanical properties (such as yield strength) and subsequent processing (such as bending).
What are the common hardness indicators of carbon steel pipes? How to test?
Common hardness indicators include Brinell hardness (HB), Rockwell hardness (HRB/HRC) and Vickers hardness (HV). During the test, Brinell hardness is calculated by indentation diameter and is suitable for softer materials; Rockwell hardness is divided into B scale (soft steel) and C scale (hardened steel). The hardness of carbon steel pipes is usually HB120-160 (such as Q235), and high carbon steel can reach HRC20 or above. Hardness affects wear resistance, but too high may reduce toughness.
