China's seamless steel pipe industry process development trend

Seamless steel pipe are mainly produced by hot-rolled steel pipes. In addition to hot rolling, there are still cold-rolled or cold-drawn hot-rolled piers to produce small-size seamless steel pipes. The proportion of seamless steel pipes in steel pipes has stabilized at 42 in recent years. %-45%, the welded pipe has a rising trend. Seamless steel tubes and welded steel tubes are more reliable and adaptable to the materials, especially for the production of thick-walled and alloy steels. The main problems are high investment, high costs, complex manufacturing processes, and large wall thickness and ovality tolerances. The welded pipe is actually a deep-processed plate product. Its cost and price mainly depend on the cost and price of the plate. Under the condition of similar prices, the market competitiveness of the seamless steel pipe is improved due to its strong reliability, with the quality of the steel plate. The continuous improvement and the improvement of the technical level of welded pipe, some of the seamless pipe market may be replaced by welded pipe, but this is only a very limited area.

(1) The hot rolling process is the main manufacturing method for seamless steel pipes, accounting for 80% of the seamless pipe production. At present, China has 41 sets of Ф100mm hot-rolled tube units, including 9 sets of hot-rolling mills with a capacity of 4.45 million tons; 5 sets of precision rolling tube units with a capacity of 600,000 tons. The production capacity of hot strip mills accounts for 45%-50% of the total capacity of seamless pipes. In addition to the technical level of the mill itself, the type and quality level of hot-rolled tube mill production are largely constrained by smelting and continuous casting. Therefore, the advanced process flow should refer to the complete process from smelting to tube processing. Internationally renowned seamless companies are mostly complete professional steel pipe mills or iron and steel joint ventures. Enterprises that rely on outsourcing billets to manufacture seamless pipes are difficult to occupy positions in fierce market competition. The use of electric arc furnace or converter smelting, LF furnace refining, VD vacuum processing, full protection casting continuous casting tube hot strip mill (MPM, PQF) tube processing, is considered to be the current international advanced seamless steel pipe production process, using The above process can produce such as petroleum-specific pipes, high-pressure boiler pipes, middle and low alloy pipes, and the like. The quality level of steel can reach higher standards, generally S ≤ 0.015%, deep desulfurization can reach 0.005% or less, 15-20ppm, [H] ≤ 2ppm, C can be controlled at ± 0.02%, continuous casting temperature is controlled at +10- 15°C. Tianjin Pipe Company, Baosteel Trading (Pipe) Company, Angang Seamless Factory, and Baotou Seamless Plant have all achieved the above-mentioned process flow. Pancheng Steel Seamless and Hengyang Steel Pipe Co., Ltd. are also stepping up their supporting project construction. The above process flow can be realized in the near future.For smelting equipment, the electric arc furnace or converter capacity should not be less than 70-100t, which creates conditions for ladle refining. It must pay full attention to the on-line detection means and automatic control system of the continuous rolling mill, and be equipped with an advanced inspection system to locate oil pipes and high-pressure boilers. The production line of the pipe should be equipped with a high level of heat treatment and processing system, and gradually realize the processes of billet hot charging, heat transfer, on-line normalization, and controlled rolling air cooling.

The difference between the existing other rolling mills is adjusted:

——The automatic rolling mill is the earliest rolling mill used at home and abroad. No matter the quality or efficiency lags behind the continuous rolling mill, due to the low cost and the high rate of finished products, it is especially suitable for the Ф250mm and above, and still has market competitiveness. Technological transformation will be eliminated in a planned manner for medium and small mills and will not be newly constructed.

——Pirgall mill has a hundred years of history, is a backward equipment, only in the production of large-size and special steel pipe has advantages, such as Ф426mm large diameter, thick-walled high-pressure boiler tubes and other small-batch alloy pipe, according to market demand to retain 1- 2 sets of pilger mills, retrofitted with advanced technology, specializing in the production of these products.

——For other types of hot rolling mills, they should form their own market based on the location and product orientation, continuously improve in quality and variety, reduce energy consumption and material consumption, and form low-cost advantages. Of course, with the development of market economy, especially in the situation of oversupply, there will be a group of mills with high cost and poor quality that will be eliminated naturally. Independent rolling mills that have not completely implemented tube blanks should take long-term strategic alliances with metallurgical enterprises as an important measure to stabilize raw materials, production, and product quality.

(2) About 20% of domestic cold-drawn (rolled) seamless steel tubes are produced by cold-drawing or cold-rolling after the perforation of small punchers with a diameter of 100 mm or less. According to incomplete statistics, there are more than 110 sets of perforating machines for thousands of cold-drawn tube units and nearly a thousand cold-rolled tube units in China, mainly for the following cold-rolled (rolled) piercers, which are mainly Ф100mm-sized, cold drawn (rolled) tubes and heat. Rolling pipes have the disadvantages of low product rate, high energy consumption and low labor productivity. Most of the small business equipment is backward and the degree of automation is low. Most of its specifications can be completely produced by hot-rolled steel pipe units. It is necessary to gradually realize the industrial policy of eliminating the seamless rolling mills below Ф76mm by replacing them with heat, reducing costs and resource consumption. For small-size steel tubes that cannot be addressed in special applications and hot rolling, if they are still solved by cold-drawing and cold-rolling techniques, hydraulic automatic cold-drawing units with a higher degree of automation and high-speed and ultra-long-stroke cold-rolling tube machines should be used today.

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