Seamless pipes are produced by punching a steel ingot or solid pipe and then undergoing hot rolling, cold rolling, or cold drawing. In China's steel pipe industry, seamless pipes hold a significant position. According to incomplete data, there are approximately 240 enterprises engaged in the production of seamless pipes, with around 250 sets of production units. These facilities have an annual capacity of about 4.5 million tons. From a size perspective, pipes with diameters less than φ76 account for 35%, while those between φ159 and φ650 make up 25%. In terms of product types, general-purpose pipes amount to 1.9 million tons, representing 54% of total output. Petroleum pipes reach 760,000 tons, or 5.7%, while hydraulic supports and precision pipes together reach 150,000 tons, or 4.3%. Stainless steel pipes, bearing pipes, and automotive pipes combined total 50,000 tons, accounting for 1.4%.
The raw material used in the production of seamless tubes is a round billet. This billet is cut into pieces of approximately 1 meter in length using a cutting machine and then transported via a conveyor belt to the furnace for heating. The billets are heated to around 1,200 degrees Celsius, typically using hydrogen or acetylene as fuel. Precise temperature control in the furnace is critical to ensure quality.
Once heated, the billets are fed into a piercing machine. The most commonly used type is the conical roller piercer, which offers high efficiency, excellent product quality, and the ability to handle various steel grades. After piercing, the billet undergoes rolling, rolling again, or extrusion through three rolls. Following this, the sizing process begins, where a cone-shaped tool is rapidly inserted into the die to form the final pipe shape. The inner diameter of the pipe is determined by the outer diameter of the sizing tool.
After sizing, the pipe is sent to a cooling tower, where it is cooled by water spraying. Once cooled, the pipe must be straightened to ensure it meets quality standards. After straightening, the pipe is conveyed to a metal detector or subjected to a hydraulic pressure test for internal inspection. Any internal defects, such as cracks or air bubbles, will be identified during this stage.
Finally, after passing all quality checks, the pipes undergo manual sorting. Each pipe is then marked with its serial number, specifications, and batch number before being lifted into storage by a crane. This entire process ensures that only high-quality seamless pipes reach the market.
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