Hot-expanded Seamless Steel Pipe Process – Development History and Current Situation
Development History and Current Situation of Medium and High Frequency Heat-Expanded Seamless Steel Pipe Process
The development of the Guanzhong medium-high frequency thermal expansion seamless steel pipe technology can be roughly divided into three stages: the initial formation stage, the rapid development stage, and the upgrading and optimization stage. After years of development, the technology has gradually matured and formed a relatively complete industrial system in the Guanzhong region of Shaanxi Province, becoming an important part of my country’s seamless steel pipe industry. Based on the research and materials consulted during my internship, the development history and current status of this technology are detailed below.
2.1 Initial Formation Stage (1980s – 1990s)
In the 1980s, with the acceleration of China’s industrialization process, the demand for large-diameter seamless steel pipes in petroleum chemical industry and municipal construction began to appear. At that time, China’s seamless steel pipe production mainly relied on the hot-rolled process, which was limited by equipment and technology, and it was difficult to produce large-diameter seamless steel pipes. Under this background, some enterprises in Guanzhong region of Shaanxi Province began to try to use the medium frequency induction heating technology to carry out secondary processing of seamless steel pipes, and initially formed the Guanzhong medium and high frequency heat expansion process.
During this period, the Guanzhong medium and high frequency heat expansion process was still in the initial exploration stage, with relatively simple production equipment and backward technology. Most enterprises used simple medium frequency heating furnaces and manual expansion equipment, without systematic process parameters control and quality inspection means. The production process mainly relied on the experience of operators. The main raw materials were ordinary carbon steel seamless steel pipes, and the products were mainly used in low-end fields such as rural water supply and drainage and small-scale municipal pipe networks. The product specifications were relatively single, the diameter was generally below DN500, the wall thickness deviation was large, the surface quality was poor, and the product qualification rate was only about 70% – 80%.
I learned from the old engineers in the internship enterprise that during this period, the production conditions of the enterprise were very simple. The medium frequency heating furnace was a simple structure built by the enterprise itself, which could not realize accurate temperature control. The expansion speed and pressure were completely controlled by the operator’s experience. Sometimes, due to the improper control of parameters, the mother pipe would break during the expansion process, resulting in the waste of raw materials. At the same time, the industry awareness of the process was relatively low, and many enterprises and users did not recognize the process, believing that the performance of the heat-expanded seamless steel pipe was not as good as that of the hot-rolled seamless steel pipe, which restricted the initial development of the process.
Despite the many shortcomings, the initial formation of the Guanzhong medium and high frequency heat expansion process filled the gap of China’s large-diameter seamless steel pipe secondary processing technology, and laid a foundation for the subsequent development of the process. During this period, some enterprises began to accumulate production experience, optimize the production process, and gradually improve the product quality and production efficiency.
2.2 Rapid Development Stage (2000s – 2015)
Entering the 21st century, with the rapid development of China’s economy, the demand for large-diameter seamless steel pipes in petroleum chemical industry, municipal pipe network, energy power and other fields has increased sharply. At the same time, the state has increased the support for the equipment manufacturing industry, and the technology of medium and high frequency induction heating and expansion equipment has also made great progress, which has provided a good opportunity for the rapid development of the Guanzhong medium and high frequency heat expansion process.
During this period, the Guanzhong medium and high frequency heat expansion process has achieved rapid development in terms of production scale, technical level and product quality. First of all, the number of enterprises adopting this process has increased significantly. A number of medium and high frequency heat-expanded seamless steel pipe enterprises have emerged in Guanzhong region of Shaanxi Province, forming an industrial agglomeration effect. The production scale has been continuously expanded, and the annual output of heat-expanded seamless steel pipes has increased from tens of thousands of tons in the initial stage to millions of tons. Secondly, the production equipment has been continuously upgraded. Enterprises have gradually eliminated simple manual equipment and introduced semi-automatic medium and high frequency heating furnaces, hydraulic expansion equipment and simple online detection equipment, which has improved the automation level of production and the accuracy of process parameter control. Thirdly, the product quality has been significantly improved. Through the optimization of process parameters and the improvement of quality control means, the product qualification rate has increased from 70% – 80% in the initial stage to 90% – 95%, the product specifications have become more diversified, the diameter can reach DN1500, and the wall thickness range is 3 – 30mm, which can meet the needs of different fields.
During the internship, I saw the old production equipment retained by the enterprise, including the semi-automatic medium frequency heating furnace and hydraulic expansion equipment introduced in 2010. The old engineer told me that after the introduction of these equipment, the production efficiency of the enterprise has been increased by 50% compared with the initial stage, and the product qualification rate has also been increased by nearly 20%. At the same time, the application field of the product has also been continuously expanded, from the initial rural water supply and drainage, small-scale municipal pipe network to petroleum chemical industry, energy power, engineering machinery and other fields. For example, the heat-expanded seamless steel pipes produced by the enterprise have been widely used in the oil and gas transmission pipelines in Northern Shaanxi and the municipal heating pipelines in Guanzhong region, and have been recognized by users.
In addition, during this period, the industry’s understanding of the Guanzhong medium and high frequency heat expansion process has also been continuously improved. Relevant enterprises and research institutions have carried out research on the process principle and technical characteristics, and initially formed a set of relatively complete production process specifications. Some local enterprises in Shaanxi have also established industry associations to strengthen communication and cooperation, promote the exchange of technology and experience, and promote the healthy development of the industry. However, during this period, the Guanzhong medium and high frequency heat expansion process still has some problems, such as the large gap in technical level between enterprises, the serious homogenization of products, the high energy consumption of the process, and the lack of core technology, which have laid hidden dangers for the subsequent development of the industry.
2.3 Upgrading and Optimization Stage (2016 – Present)
Since 2016, with the continuous advancement of China’s manufacturing industry transformation and upgrading, the implementation of the “double carbon” goal and the increasingly strict environmental protection policies, the Guanzhong medium and high frequency heat expansion process has entered a critical stage of upgrading and optimization. Enterprises have increased investment in technology research and development, equipment upgrading and environmental protection transformation, and the process has gradually moved towards intelligence, greenization and high-endization, and the industry development level has been significantly improved.
Intelligent upgrading is an important direction of this stage. A large number of enterprises have introduced intelligent production equipment and control systems, such as PLC control systems, infrared thermometers, online ultrasonic thickness gauges and other equipment, to realize the automatic adjustment and real-time monitoring of core parameters such as heating temperature, expansion speed and plug pressure.
Let me give an example I saw with my own eyes during the internship: on the intelligent production line, the staff only need to input the product specification model (such as DN800, wall thickness 10mm) into the control system, and the system will automatically call the preset process parameters. The intermediate frequency heating furnace will automatically adjust the heating power according to the data fed back by the infrared thermometer to ensure that the steel pipe heating temperature is uniform and stable; the expansion equipment will automatically adjust the plug advancing speed and expansion pressure according to the wall thickness data fed back by the online ultrasonic thickness gauge to ensure that the wall thickness deviation of the steel pipe is controlled within the allowable range; all data during the production process will be uploaded to the enterprise’s production management system in real time. The staff can check the production progress and product quality at any time through computers or mobile phones. Once parameter abnormalities occur, the system will automatically alarm and adjust in time, which effectively reduces the error of manual operation and improves the product qualification rate and production efficiency. According to the enterprise statistics, after the intelligent upgrading, the product qualification rate has increased from 92% to more than 98%, the production efficiency has increased by 30%, and the labor cost has decreased by 25%.
Green production is another important development direction of this stage. With the increasingly strict environmental protection policies, high-energy-consuming and high-pollution production processes have been gradually eliminated, and the Guanzhong medium and high frequency heat expansion process has also been continuously optimizing the energy consumption structure and reducing pollutant emissions. On the one hand, enterprises have upgraded and transformed the heating furnaces, adopted new energy-saving heating furnaces, improved energy utilization efficiency and reduced electric energy consumption. For example, the energy consumption of the original intermediate frequency heating furnace was 800kWh/ton of steel pipe, and the energy consumption of the upgraded energy-saving heating furnace was reduced to 650kWh/ton of steel pipe. Each ton of steel pipe can save 150kWh of electric energy. In one year, only the energy consumption cost can be saved by several million yuan. On the other hand, enterprises have established a complete waste gas and residue treatment system, which purifies the waste gas generated during the production process before emission, and recycles the waste residue to realize “turning waste into treasure”. For example, the oxide scale waste residue generated during the production process can be used as raw material for building materials after crushing and screening, which not only reduces environmental pollution, but also creates certain economic benefits.
High-end upgrading is also an important trend of this stage. With the continuous upgrading of market demand, ordinary carbon steel heat-expanded seamless steel pipes can no longer meet the needs of petroleum chemical industry, deep-sea oil and gas, high-end equipment and other fields. Enterprises have begun to increase investment in the research and development of production technology for high-strength, corrosion-resistant alloy heat-expanded seamless steel pipes, broken through a series of core technologies, and realized the localization of high-end products. For example, by optimizing process parameters and improving heating methods, enterprises have successfully produced high-strength heat-expanded seamless steel pipes such as Q355 and Q460, as well as stainless steel heat-expanded seamless steel pipes such as 304 and 316L. The performance of these products has reached the international advanced level, broken the monopoly of foreign enterprises, and been widely used in deep-sea oil and gas transmission, high-end chemical equipment and other fields. In 2017, China Iron and Steel Industry Association issued the group standard T/CISA 002-2017 “Intermediate Frequency Heat-Expanded Seamless Steel Pipes for High Pressure Boilers”. In 2023, the GB 5310 standard officially included intermediate frequency heat-expanded steel pipes, marking that the development of intermediate frequency heat expansion process has entered a new stage.
In addition, during this stage, the application scope of the Guanzhong medium and high frequency heat expansion process has also been continuously expanded, gradually extending from traditional fields such as petroleum chemical industry and municipal pipe network to emerging fields such as deep-sea oil and gas, new energy and high-end equipment. According to the latest data from China Steel Structure Association Steel Pipe Branch in 2025, the output of China’s high-end heat-expanded seamless steel pipes reached 3.2 million tons in 2024, a year-on-year increase of 15.4%, accounting for 17.2% of the total output of heat-expanded seamless steel pipes. Among them, the proportion of high-end products of Guanzhong medium and high frequency heat expansion reached more than 90%, showing a good development prospect. At the same time, the technical understanding of the intermediate frequency heat expansion process has been continuously improved. The industry has gradually realized that although the intermediate frequency induction heating push-type heat expansion process is local heating, compared with the overall heating expansion process, it has no obvious impact on the expansion deformation. As long as the quality control is strengthened, the product quality can be guaranteed.
However, I also noticed that although the Guanzhong medium and high frequency heat expansion process has made great progress during this stage, the gap in technical level between different enterprises is still large. Large enterprises, relying on their capital and technological advantages, have realized intelligent and green production, with strong product quality and competitiveness; while some small and medium-sized enterprises, due to insufficient capital and backward technology, still use traditional production equipment and processes, with uneven product quality, excessive energy consumption and pollutant emissions, facing the risk of being eliminated by the market. This polarized situation also restricts the overall development level of China’s Guanzhong medium and high frequency heat-expanded seamless steel pipe process.
High Frequency Heat-Expanded Seamless Steel Pipes – Technology, Application and Development Trend
Hot-expanded Seamless Steel Pipe Process – Development History and Current Situation
Heat-Expanded Seamless Steel Pipe – Process Core Principle and Technical Analysis
ERW BLACK Pipes. Electric Resistance Welded (ERW) Pipes are manufactured from Hot Rolled Coils / Slits. All the incoming coils are verified based on the test certificate received from steel mill for their chemistry and mechanical properties. ERW pipe is cold-formed into a cylindrical shape, not hot-formed.
Seamless pipe is manufactured by extruding the metal to the desired length; therefore ERW pipe have a welded joint in its cross-section, while seamless pipe does not have any joint in its cross-section through-out its length. In Seamless pipe, there are no welding or joints and is manufactured from solid round billets.
The 3 elements of pipe dimension Dimension Standards of carbon and stainless steel pipe (ASME B36.10M & B36.19M) Pipe Size Schedule (Schedule 40 & 80 steel pipe means) Means of Nominal Pipe Size (NPS) and Nominal Diameter (DN) Steel Pipe Dimension Chart (Size chart) Pipe Weight Class Schedule (WGT)
Seamless pipes are manufactured using a piercing process, where a solid billet is heated and pierced to form a hollow tube. Welded pipes, on the other hand, are formed by joining two edges of steel plates or coils using various welding techniques.
Carbon steel pipe is highly resistant to shock and vibration which making it ideal to transport water, oil & gas and other fluids under roadways. Dimensions Size: 1/8″ to 48″ / DN6 to DN1200 Thickness: Sch 20, STD, 40, XS, 80, 120, 160, XXS Type: Seamless or welded pipe Surface: Primer, Anti rust oil, FBE, 2PE, 3LPE Coated Material: ASTM A106B, A53, API 5L B, X42, X46, X52, X56, X60, X65, X70 Service: Cutting, Beveling, Threading, Grooving, Coating, Galvanizing
Type A- Used where ample head room is available. Specific elevation is desirable. Type B- Used where headroom is limited. Head attachment is a single lug. Type C- Used where headroom is limited. Head attachment is side by side lugs
