Welded steel pipe, also known as welded pipe, is a steel pipe made of steel plate or steel strip after crimping and welding. Welded steel pipe has a simple production process, high production efficiency, many varieties and specifications, and less equipment investment, but its general strength is lower than that of seamless steel pipe. Since the 1930s, with the rapid development of continuous strip rolling production and the advancement of welding and inspection technology, the weld seam has been continuously improved, and the varieties and specifications of welded steel pipes have increased day by day and replaced seamless steel pipes in more and more fields. Welded steel pipes are divided into straight seam welded pipes and spiral welded pipes according to the form of the weld seam.
The production process of straight seam welded pipe is simple, the production efficiency is high, the cost is low, and the development is rapid. The strength of the spiral welded pipe is generally higher than that of the straight seam welded pipe, and the welded pipe with a larger diameter can be produced with a narrower billet, and welded pipes with different diameters can be produced with the same width billet. But compared with the straight seam pipe of the same length, the weld length is increased by 30~100%, and the production speed is lower. Therefore, most of the welded pipes with smaller diameters adopt straight seam welding, and most of the large diameter welded pipes adopt spiral welding.
1. Welded steel pipes for low-pressure fluid transportation (GB/T3092-1993) are also called generally welded pipes, commonly known as clarinet pipes. It is a welded steel pipe used for conveying water, gas, air, oil, heating steam, and other general lower-pressure fluids and other purposes. The wall thickness of the steel pipe is divided into ordinary steel pipe and thickened steel pipe; the form of the pipe end is divided into unthreaded steel pipe (light pipe) and threaded steel pipe. The specification of the steel pipe is expressed by the nominal diameter (mm), and the nominal diameter is an approximate value of the inner diameter. It is customary to express in inches, such as 11/2, etc. In addition to being directly used to transport fluids, welded steel pipes for low-pressure fluid transportation are also widely used as raw pipes for galvanized welded steel pipes for low-pressure fluid transportation.
2. Galvanized welded steel pipe for low-pressure fluid transportation (GB/T3091-1993) is also called galvanized electric welded steel pipe, commonly known as a white pipe. It is a hot-dip galvanized welded (furnace welded or electrically welded) steel pipe used for conveying water, gas, air oil, heating steam, warm water, and other general lower-pressure fluids or other purposes. The wall thickness of the steel pipe is divided into ordinary galvanized steel pipe and thickened galvanized steel pipe; the form of the pipe end is divided into non-threaded galvanized steel pipe and threaded galvanized steel pipe. The specification of the steel pipe is expressed by the nominal diameter (mm), and the nominal diameter is an approximate value of the inner diameter. It is customary to express in inches, such as 11/2, etc.
3. Ordinary carbon steel wire casing (GB3640-88) is a steel pipe used to protect wires in electrical installation projects such as industrial and civil buildings, and installation of machinery and equipment.
4. Straight seam electric welded steel pipe (YB242-63) is a steel pipe whose weld seam is parallel to the longitudinal direction of the steel pipe. It is usually divided into metric electric welded steel pipe, electric welded thin-walled pipe, transformer cooling oil pipe, and so on.
5. The spiral seam submerged arc welded steel pipe (SY5037-2000) for general low-pressure fluid transportation is made of hot-rolled steel strip coils, spirally formed at normal temperature, and made by double-sided automatic submerged arc welding or single-sided welding. Submerged arc welded steel pipes for general low-pressure fluid transportation such as water, gas, air, and steam.
6. Spiral welded steel pipe for piles (SY5040-2000) is made of hot-rolled steel strip coils, spirally formed at normal temperature, and made by double-sided submerged arc welding or high-frequency welding. It is used for civil construction structures, wharves Steel pipes for foundation piles such as bridges and bridges
Technical progress of straight seam steel pipe rolling:
1) Increase the thermal charging temperature and thermal charging ratio: Increasing the thermal charging temperature and thermal charging ratio is an important measure for energy saving and emission reduction, and has attracted much attention. At present, the average hot charging temperature in my country is 500-600°C, and the highest temperature can reach 900°C; the average hot charging ratio is 40%, and the production line reaches more than 75%. The hot charging rate of the 1780mm hot strip rolling mill in Fukuyama Works of Japan Steel Tube is 65%, the direct rolling rate is 30%, and the hot charging temperature reaches 1000°C; , The hot charging rate is 28%. In the future, my country should increase the hot charging ratio of continuous casting slabs above 650 °C, and strive to save energy by 25% to 35%.
2) Various heating technologies of the heating furnace: Heating technologies include regenerative heating, automatic combustion control, combustion of low calorific value fuel, low oxidation or non-oxidation heating technology, etc. According to statistics, more than 330 steel rolling heating furnaces in my country have adopted regenerative combustion technology, and the energy-saving effect can reach 20% to 35%. Energy consumption can be further reduced by optimizing combustion. This requires work on the use of low-calorific-value fuels, increasing the application of blast furnace gas and converter gas. The low-oxidation heating technology of atmosphere control and the non-oxidation heating technology of gas protection are important measures to reduce oxidation burning loss and increase yield. The technology even eliminates the need for pickling. At present, the oxide scale produced in the steel rolling heating process is 3-3.5kg/t, and the annual loss is estimated to be about 1.5 million tons of steel (about 7.5 billion yuan);
3) Low-temperature rolling and rolling lubrication technology: Some domestic high-speed wire manufacturers have adopted low-temperature rolling technology, and their average furnace temperature has reached 950°C, and the lowest has dropped to 910°C. The power has been designed and manufactured according to the rolling temperature of 850°C. The total energy consumption of low-temperature rolling is reduced by about 10% to 15% compared with conventional rolling. According to the statistics of the hot rolling plant of Kashima Iron Works in Japan, reducing the billet temperature by 8°C will save energy by 4.2kJ/t, and the energy saving effect is 0.057%. However, low-temperature rolling has strict requirements on the uniformity of billet heating temperature, and the temperature difference over the entire length of a 130-150mm billet should not be greater than 20-25°C. Rolling lubrication technology can reduce rolling force by 10% to 30%, reduce power consumption by 5% to 10%, reduce iron oxide scale by about 1kg/t, thereby increasing yield by 0.5% to 1.0%, and can also reduce pickling acid The consumption is about 0.3～1.0kg/t. Many domestic rolling mills have successfully applied it to the production of stainless steel and electrical steel, with excellent results. In the future, while vigorously promoting rolling lubrication, we should strengthen the research and development of environmentally friendly rolling lubrication media, lubrication technology, and recycling technology.
4) Controlled rolling and cooling technology and its equipment: Controlled rolling and cooling technology are indispensable means for energy saving, high-performance products, and production. Representative steel materials such as DP steel, TRIP steel, TWIP steel, CP steel, AHSS steel, UHSS steel, other pipeline steel, building structure steel, grain steel, and heat-free steel are all produced by controlled rolling and controlled cooling technology. Controlled rolling and controlled cooling technology is not only based on the new development of physical metallurgy, but also benefits from new technology and equipment, such as high-pressure rolling mills that can achieve low temperature and high pressure, ultra-compact rolling mills, and ultra-fast cooling ( UltraFastCooling), – Online Accelerated Cooling (Super-OLAC) device, reducing and sizing machine equipment, etc. In the future, the development of controlled rolling and controlled cooling technology will strongly rely on new technical equipment. This is an important feature of the development of controlled rolling and controlled cooling technology, which needs to be paid attention to.
Post time: Jun-09-2023