As the most widely used and widely used basic pipe in the industrial system, carbon steel pipes have become core materials in energy transmission, machinery manufacturing, construction engineering and other fields due to their excellent mechanical properties, easy processability and high cost performance. From municipal water supply pipelines to long-distance oil and gas pipelines, from mechanical parts processing to boiler and pressure vessel manufacturing, the model selection and quality control of carbon steel pipes are directly related to project safety and operational efficiency. This article will systematically sort out the classification system, core characteristics, purchase points and typical applications of carbon steel pipes, providing professional reference for industry selection and daily understanding.
1. Classification system of carbon steel pipes

Carbon steel pipes have rich classification dimensions. The core can be divided according to carbon content, production process and usage scenarios. Different classifications correspond to differentiated performance characteristics and application scope, forming a product matrix covering multiple fields.

(1) Classification according to carbon content

Carbon content is the core factor that determines the mechanical properties of carbon steel pipes. According to this, it can be divided into three major categories. The performance changes regularly with the increase or decrease of carbon content:

1. Low carbon steel pipe: carbon content ≤0.25%, typical materials such as Q235, 10#, 20#. It has good plasticity, toughness and welding properties, strong adaptability to hot and cold processing, low hardness but excellent ductility, and is not prone to welding cracks. It is widely used in municipal water supply and drainage, gas transmission, low-pressure fluid pipelines and general mechanical structural parts.

2. Medium carbon steel pipe: The carbon content is between 0.25% and 0.60%, and the representative materials are 35# and 45#. Carbon steel with lower strength and hardness is significantly improved, and the comprehensive mechanical properties are balanced, but the welding performance and plasticity are slightly inferior to low carbon steel. The welding quality needs to be improved through preheating, post-weld heat treatment and other processes. It is often used to manufacture gears, shafts, connecting rods and other mechanical parts that bear moderate loads.

3. High carbon steel pipe: carbon content ≥0.60%, such as 65#, 70#. It has extremely high hardness and strength, and excellent wear resistance, but has extremely poor plasticity and toughness, poor welding performance, and is prone to brittleness. It is usually strengthened by heat treatment such as quenching and tempering. It is suitable for manufacturing knives, molds, springs, etc. that require extremely high hardness and wear resistance, and is rarely used in transportation pipelines.

(2) Classification by production process

The production process directly affects the accuracy, surface quality and internal structure of carbon steel pipes. The mainstream is divided into two categories: seamless steel pipes and welded steel pipes. The applicable scenarios are obviously different:

1. Seamless carbon steel pipe: processed through hot rolling, cold rolling or cold drawing process, no weld structure, the core process is round steel perforation and then rolling. It has high dimensional accuracy, uniform wall thickness, strong pressure resistance, dense internal structure, and can withstand high pressure and high temperature conditions. Common specifications include an outer diameter of 6mm-630mm and a wall thickness of 2mm-70mm. According to the processing accuracy, it can be divided into hot-rolled seamless pipes (relatively rough surface, suitable for medium and low pressure working conditions) and cold-drawn/cold-rolled seamless pipes (smooth surface, high precision, suitable for high-pressure equipment and precision mechanical parts). They are widely used in oil and gas transportation, boiler heating surfaces, high-pressure hydraulic systems and aerospace parts manufacturing.

2. Welded carbon steel pipe: made of steel plate or steel strip as raw material, curled and then welded. According to the welding method, it can be divided into straight seam welded pipe and spiral welded pipe. The production process of straight seam welded pipes is simple, the cost is low, and the dimensional accuracy is moderate. It is suitable for low-pressure fluid transportation (such as municipal water supply, drainage, and low-pressure gas pipelines); spiral welded pipes have high welding strength and uniform weld stress, and can produce large-diameter pipes (outer diameter can reach more than 3000mm). Their crack resistance and pressure resistance are better than straight seam welded pipes. They are often used in long-distance oil and gas transportation, municipal engineering pipe networks, and steel structure supports. Although the cost of welded steel pipes is lower than that of seamless pipes, the performance of the welds is slightly affected, and they need to be selected with caution in high temperature, high pressure, and highly corrosive working conditions.