Three questions about Chinese steel pipe industry

It is estimated that the annual consumption of steel pipe and cold bending steel in our country is about 2265 tons ( of which steel pipe is 1860 tons and cold bending section is 405 tons ). The market of steel pipe industry is focused on the application of steel pipe in the energy field ( oil and gas and coal electricity ). in recent years, it has been closely watched the vigorous development of steel pipe and cold bending steel in the field of steel structure, so some hot issues have appeared.

The market research report published in 2014 shows that the national welded pipe capacity of the year was 6,500 tons, and the actual output of welded pipe reached 7016 million tons in 2016, because the former counted the capacity of welded pipe production line, while the statistics of the latter included the total output of all complete and incomplete production lines.

With regard to the problem of crack in corner of thick wall rectangular pipe in the cold bending steel industry, the residual stress can be eliminated by hot forming process. For high strength thin - walled cold-formed steel products, hot stamping forming is a developing direction.

The downward pressure of the oil casing and the boiler tube market, the welded pipe also occupied the equivalent of the market share of seamless steel pipe, the production of seamless steel pipe industry appears to decline, so as to play the advantages of thick wall, batch and thermal forming of seamless steel pipe, the products are personalized and customized.

Q: how can the capacity of Chinese steel pipe be counted?
According to the statistical data of China steel pipe industry and market research report published by China steel structure association in 2014, the total capacity of seamless steel pipe in China is about 4,300 tons, and the total capacity of welded pipe is about 6,500 tons. This is based on the production capacity of the welded pipe complete production line. However, the actual production of welded pipe reached 7016 million tons in 2016. The author believes that this is the total production of welded pipe production line and incomplete production line in the oil industry, steel structure industry, cold bending steel industry, iron tower industry, stainless steel industry, boiler industry, shipbuilding industry, machinery industry and other industries.

For the non - petroleum system welded pipe function, some parts of the steel structure need to be produced by the complete production line. For example, tokyo Japan tokyo eye empty tower ( the world's highest self - supporting electric wave tower ), its main steel pipe position is with uoe welded pipe, its large diameter thick steel tube Ф 2300 mm × 100 mm is made by the Rb method ( not taking pipe-expansion shaping ), but after the heat treatment; China's heavy construction steel structure, such as the main steel pipe structure of Beijing Olympic venues, also uses uoe welded pipe, some of which are produced by Panyu Zhujiang steel pipe company, some of which are made by Baosteel's uoe unit. Again, the UHV transmission tower requires uoe, jcoe welded pipe, or hfw high frequency straight seam welded pipe with medium frequency heat treatment; For example, the steel pipe for the overload boom of the offshore giant floating crane vessel is Ф 850 mm× 30 mm, Ф 650 mm× 24 mm, Ф 550 mm × 20 mm, using seamless steel tube or uoe ( jcoe ) pipe, or hfw high frequency straight seam welded pipe after intermediate frequency heat treatment.

But in some steel structure, the non - main steel pipe structure can be used with jco, UO2 or high frequency welded pipe without intermediate frequency heat treatment, such as steel pipe pile, highway guardrail pipe, cable casing, low pressure water pipe, lamp post tube, etc.

China is a big country of steel pipe production in the world, steel pipe production enterprises are distributed in all walks of life, but not built can represent the national steel pipe enterprises of the industry association, therefore, at present, the statistics of the national welded pipe production of 70m tons of production capacity is still very difficult.

Q: what is the development direction of cold - formed steel processing?
How to solve the problem of corner cracking due to the increase of plate thickness in the manufacturing process of cold formed steel rectangular pipe? In this regard, some experts put forward the countermeasure is " the angle line heating + necking secondary forming" process, in short, the cold formed steel to the hot forming process. According to the calculation, the annual consumption of rectangular steel pipe in China reaches to million tons, and the automobile manufacturing enterprises are prepared to use the hot-rolled seamless square steel tube to produce the driving axle of the truck. This paper presents the challenge to the cold-formed steel enterprises in China to accelerate the development of thick wall square rectangular pipe.

From the development of the cold - formed steel, the process of the foreign production square steel tube is first formed into a circular pipe, then heated to the normalizing temperature, and the rectangular tube is transformed from the circular pipe to rectangular tube in the sizing process. The advantage is that the residual stress of the finished steel pipe is small, and the radius of the corner is small. Until now, the UK has been using this process. However, because of the high energy consumption and cost, the cold bending steel process at home and abroad gave up the normalizing process, which was converted from high frequency welding. The domestic cold bending steel mill uses the direct set of the production line.

Now, because of the extension of the building steel structure to the high strength of thick wall, the hot forming process has been resumed in foreign countries, and our country has not yet made the rectangular cold bending steel products, the new capital museum and other engineering projects use hot forming cold formed steel, both imported from abroad at high price. For example, Japan JFE know high frequency welded pipe Ф 26in ( Ф 660 mm ) unit produces the rectangular tube diameter of 250 mm ￣ 550 mm, the wall thickness of 6 mm ￣ 25 mm, the square rectangular tube diameter of the east Japan Keihin high frequency welding pipe Ф 24in ( Ф 610 mm ), the diameter of the square rectangular tube is 200 mm ￣ 550 mm, the wall thickness is 4.5 mm ￣ 22 mm. They not only have the intermediate frequency normalizing process, but also have the ability of secondary heat treatment. The high frequency welded pipe 610 unit of Baosteel in China also has such capability.

At normal temperature, the square tube of cold bending forming is easy to crack at the fillet of thick wall, the residual stress is large, and the weld seam is easy to form grooving corrosion. Due to the Package effect, the strength and hardness are improved, which is not conducive to the secondary processing of users. At present, cold - formed steel mill in China can only process products with thickness ≤ 14 mm. In the process of " round square ", if the material elongation is low, even if the wall thickness is small, it is easy to cause longitudinal cracking at the fillet. The cold push process for seamless steel pipe is made in the northeast of China. the " round variant" is made into 160 mm× 60 mm× 6.5 mm rectangular tube, because the material is 20 # steel, the elongation is only 16 %, some batches of rectangular steel pipe after delivery delay the corner of the corner cracking serious, causing user quality objection. Later, the seamless steel pipe of the factory adopts the normalizing process for " round variation ", and the qualified products are obtained, and the normalizing temperature is at 850 ℃ ~ 900 ℃. For the process of " corner line heating" cold - formed square steel rectangular tube, the author thinks it is worth discussing. The experimental results of induction heating bend in the west - to - east gas transmission project show that the performance of the bended pipe is improved, but the performance of the curved section is not stable. Therefore, the author believes that the rectangular tube should be heated by the whole induction. This means that the cold bending process is more suitable for the hot forming process by the " circle" production line.

The main steel pipe structure of Shanghai oriental art center uses the oval tube DP × 126mm 12 12 mm, after the cold bending of the stainless steel thin wall elliptical tube, the elliptical port can rebound easily in the subsequent processing due to the residual stress. The cold stamping die solves the problem of port rebound in the production of dongyang Alien steel pipe plant in Shenyang, which leads to the development of high strength, thin wall and light weight of cold bending steel, that is, hot stamping forming. Domestic enterprises are also developing in this direction. Baosteel precision cold bending forming RF production line is put into operation by the end of 2016. the cold bending profiled bar is processed into various sections with high precision and complex structure. the material is light and lightweight, and the steel, stainless steel and coated steel coil are used as raw materials for profile processing.

The author believes that the design of CAD / cam / CAE technology for the forming design of cold - formed steel has many kinds of square rectangular tubes, elliptical tubes and complicated special-shaped sections. the intelligent design of the CAD / cam / CAE technology is a major subject, and should be used as the target of the industry during the 13th five - year plan period.
　
Q: what is the matter with the decline in production and the seamless steel pipe industry?
The annual production of seamless steel pipe has been gradually declining in recent years, it has dropped to 2743 tons in 2016, down 4.15 %, what is the matter with the seamless steel pipe industry?

From the perspective of market demand. On the one hand, because of the decline of the international oil price, the growth rate of oil field exploitation is declining, and the oil well pipe market of seamless steel pipe is shrinking; On the other hand, the entry into force of the Paris agreement makes the environmental protection of industrial enterprises increasingly serious, restricting the development of coal electricity, resulting in the use of boiler tubes reduced year by year; Seamless steel tube two major market pillar products are not free.

From a competitive point of view. With the improvement of the quality of plate materials and the development of welded pipe technology, the high frequency straight seam welded pipe ( hfw ) is increasingly replacing the seamless steel pipe in some middle and high end parts of steel pipe. For example, the welded pipe has entered the hydraulic cylinder, the overweight machine hanging wall steel pipe and other market.

Therefore, the author believes that seamless steel tube enterprises should exert their own product advantages, such as thick wall, batch and hot forming advantages, products to personalized and customized direction.