Production process of hot rolled seamless stainless steel pipe
In recent years, with the development of China’s oil, natural gas, chemical and other industrial fields, the working performance and technical requirements of the equipment are more and more stringent. In the production process of seamless steel pipe, if we want to improve the smelting quality of stainless steel, we need to operate the production equipment carefully, according to the precise process flow, and reduce the error rate. This paper mainly analyzes the selection of seamless stainless steel pipe production process equipment and the production technology of hot-rolled seamless stainless steel pipe, aiming to improve the quality control of stainless steel pipe.
The production level of seamless stainless steel pipe is an important indicator to measure the overall production level of steel in a country. With the development of social economy, the requirements for corrosion resistance of stainless steel are becoming higher and higher. In the production process of seamless steel pipe, modern finishing equipment must be equipped, and the quality control shall be strengthened according to the accurate process flow.
Selection and analysis of hot rolled seamless steel pipe production process equipment
Selection and analysis of Piercer
At present, the more widely used piercers in China are pressure piercer, PPM push rolling piercer and cross rolling piercer. In the process of piercing and rolling, the elongation coefficient of the former two is small, and the stretcher must be equipped after piercing, so the equipment investment is large, and they are rarely used now. According to the analysis of seamless pipe deformation, compared with the continuous casting billet, the continuous casting round billet can better reduce the tool wear, reduce the uneven deformation, and then reduce the production cost. Due to the limitation of their own production and use of raw materials, the pressure piercer and ppm piercer can not meet the development requirements of reducing production cost and improving product quality, so they have been gradually abandoned. As the raw material of continuous casting round billet, the cross rolling piercer has been widely used.
Selection and analysis of pipe mill
The pipe mills used in China include pilger pipe mill, automatic pipe mill, CPE pipe mill, new three roll pipe mill, accu roll pipe mill, MPM pipe mill and PQF pipe mill. Pilger pipe mill uses ingot as raw material for rolling large diameter thick wall steel pipe, so it is mainly used to produce hot rolled large diameter thick wall seamless pipe.
The automatic pipe rolling mill is mainly used to roll the thick wall pipe into thin-walled pipe. Generally, the finished wall thickness can be rolled through 2-3 passes in order to produce hot-rolled thick wall seamless pipe. CPE pipe mill uses larger tube blank, For the production of longer pipes, the yield is relatively higher, but still lower than that of other processes, which can be used for the production of thin-walled steel pipes; the three roll pipe mill has high dimensional accuracy, less tool consumption, but low productivity, and needs to use high-quality billet as raw material, so it is difficult to produce thin-walled pipe; accu roll The MPM pipe mill is similar to the two roll cross rolling piercer, but the fixed guide plate is changed into the active guide plate. In addition, its production cost is high and the capillary length is short, so the utilization rate is low. MPM pipe mill belongs to the two roll continuous pipe rolling mill, with high technical level and many mill specifications and models. It can be used in the production of medium and thin-walled seamless steel tubes. Up to now, it is the main selection machine for continuous pipe rolling in the world PQF pipe mill is a three roll continuous pipe mill, which can be used to roll thin-walled pipes and difficult to deform steel grades. At present, China’s seamless pipe rolling mill is in the situation of coexistence of various rolling mills, and its application prospect should be determined according to the product structure and production scale of the enterprise. Because of its large scale, high yield and wide range of products, the continuous pipe mill is recognized as the most promising pipe mill.
Type and analysis of stretch reducing mill
There are two types of stretch reducing mill: two rolls and three rolls. According to the actual production experience, the frame spacing of three roll stretch reducing machine is smaller than that of two roll stretch reducing machine, and the slip of steel pipe in the empty line of three roll stretch reducing machine is also smaller than that of two roll stretch reducing machine. Therefore, the use of three roll reducing mill to produce steel pipe has good surface quality, less cutting head, large diameter reduction and wall reduction, which has become the main selection of stretch reducing machine at present.
In short, any equipment has its own technical and background advantages. At the same time, considering the advanced nature of the equipment, the equipment should be considered and analyzed according to the specific conditions of the enterprise, such as the production scale, product structure and capital status.
Production process of hot rolled seamless steel pipe
Hot rolled seamless pipe can be divided into general steel pipe, low and medium pressure boiler steel pipe, high pressure boiler steel pipe, alloy steel pipe, stainless steel pipe, oil cracking pipe, etc. The main production process of hot-rolled seamless steel pipe is as follows: preparation and inspection of tube blank → heating of tube blank → piercing → pipe rolling → reheating of raw pipe → sizing (reducing) diameter → heat treatment → straightening of finished pipe → finishing → inspection (nondestructive, physical and chemical, bench inspection) → warehousing. The round tube blank is the raw material for rolling seamless steel pipe. The round tube blank is cut by the cutting machine and processed into a billet with a length of about 1 m, and then transported to the furnace for heating through the conveyor belt. The tube blank is sent into the furnace and heated to about 1200 ℃. The heat release tube blank is fueled by hydrogen or acetylene. The temperature control in the furnace is the key. After the tube is discharged from the furnace, it needs to pass through the piercing machine for piercing. One of the most widely used piercer is the cone-shaped roller piercer, which has the advantages of high-efficiency production, good product quality and large hole expansion, which can be used for piercing of various steel grades. After piercing, the tube blank is successively rolled by three rollers. After extrusion, the tube should be removed for sizing. The sizing machine rotates the conical drill bit into the billet to drill holes at high speed to form a steel pipe (the inner diameter of the steel pipe is determined by the outer diameter length of the drill bit of the sizing machine). After sizing, the steel pipe enters the cooling tower for spray cooling, and then straightens after cooling. Then it is sent to the metal flaw detector through the conveyor belt for internal flaw detection. If there are cracks and bubbles inside the steel pipe, they will be detected immediately. Quality inspection also needs to select the process by hand, after passing the paint spray brush number and specification, etc., and then put into storage.
Problem analysis of stainless steel pouring
In the process of pouring stainless steel, a small amount of elements are easily oxidized, resulting in oxide doping. Due to the high viscosity of molten steel, it is easy to cause nozzle blockage. Due to the poor thermal conductivity of molten steel and the complex solidification morphology of stainless steel, the continuous casting billet is prone to crack. Therefore, the cooling and drawing speed of continuous casting billet are required to ensure the accuracy of operation. In addition, a series of new technologies are adopted in the process, such as pouring without oxidation protection, automatic control of liquid level and electromagnetic stirring, etc The quality has been greatly improved.
Size and position detection technology and automatic control technology. The finishing process and its equipment setting is an important link in the quality control of stainless steel pipe, in which non-destructive testing is the most important means of quality inspection. With the development of technology, more and more manufacturers adopt eddy current and ultrasonic combined flaw detection units, and ultrasonic thickness measuring and laser diameter measuring devices are equipped in the flaw detection units. Before the steel pipe leaves the factory, the factory should control the product quality from several links. This kind of combined flaw detection unit has advanced and superb processing system. All the measured signals are processed and stored by computer after being digitized. The degree of automation and production efficiency are quite high.
The weakest link in China’s machinery industry is detection and technology control, which greatly hindered the improvement of China’s industrial level. Domestic and foreign seamless steel pipe production, has gradually from the early pursuit of output to improve product quality, reduce production costs, and then constantly appear new equipment and technology. This requires our steel enterprises in the premise of updating equipment, bold to improve the implementation of new technology and technology, better improve the quality and level of steel pipe.
Source: China Stainless Steel Seamless Pipe Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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