Welded steel pipes, also known as welded pipes, are steel pipes made by welding steel plates or steel strips after curling and forming. The production process of welded steel pipes is simple, the production efficiency is high, the varieties and specifications are many, and the equipment investment is low, but the general strength is lower than that of seamless steel pipes. Since the 1930s, with the rapid development of strip steel continuous rolling production, and the advancement of welding and inspection technology, the welds have been continuously improved, the varieties and specifications of welded steel pipes have increased, and they have 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 welds.
The production process of straight seam welded pipes is simple, the production efficiency is high, the cost is low, and the development is relatively fast. The strength of spiral welded pipes is generally higher than that of straight seam welded pipes. It can produce welded pipes with larger diameters with narrower billets, and can also produce welded pipes with different diameters with billets of the same width. However, compared with straight seam pipes of the same length, the weld length increases by 30~100%, and the production speed is lower.
Therefore, most smaller-diameter welded pipes use straight seam welding, while large-diameter welded pipes mostly use spiral welding.
1. Welded steel pipe for low-pressure fluid transportation (GB/T3092-1993) is also called general welded pipe, commonly known as black pipe. It is a welded steel pipe used for conveying generally low-pressure fluids such as water, gas, air, oil heating steam, and other purposes. The wall thickness of the steel pipe joint is divided into ordinary steel pipe and thickened steel pipe; the pipe end form is divided into non-threaded steel pipe (bright pipe) and threaded steel pipe. The specifications of the steel pipe are expressed in nominal diameter (mm), which is the approximate value of the inner diameter. It is usually expressed in inches, such as 11/2. In addition to being directly used to convey fluids, welded steel pipes for low-pressure fluid transportation are also widely used as the original pipes of galvanized welded steel pipes for low-pressure fluid transportation.
2. Galvanized welded steel pipes for low-pressure fluid transportation (GB/T3091-1993) are also called galvanized electric welded steel pipes, commonly known as white pipes. 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 generally low-pressure fluids or other purposes. The wall thickness of the steel pipe joint is divided into ordinary galvanized steel pipe and thickened galvanized steel pipe; the pipe end form is divided into non-threaded galvanized steel pipe and threaded galvanized steel pipe. The specifications of the steel pipe are expressed in nominal diameter (mm), and the nominal diameter is the approximate value of the inner diameter. It is usually expressed 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 with the weld 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, etc.
5. Spiral seam submerged arc welded steel pipe for general low-pressure fluid transportation (SY5037-2000) is made of hot-rolled steel strip coil as pipe blank, spirally formed at room temperature, and made by double-sided automatic submerged arc welding or single-sided welding. It is used for water, gas, air steam, and other general low-pressure fluid transportation.
6. Spiral welded steel pipe for piles (SY5040-2000) is made of hot-rolled steel strip coil as pipe blank, spirally formed at room temperature, and made by double-sided submerged arc welding or high-frequency welding. It is used for foundation piles of civil engineering structures, docks, bridges, etc.
Advances in straight seam steel pipe rolling technology:
1) Improving hot charging temperature and hot charging ratio: Improving hot charging temperature and hot charging ratio is an important measure for energy conservation and emission reduction, and has received much attention. At present, the average hot charging temperature in my country is 500-600℃, and the highest can reach 900℃; the average hot charging ratio is 40%, and the production line reaches more than 75%. The hot charging rate of the 1780mm hot strip mill at the Fukuyama Plant of Japan Steel Pipe is 65%, the direct rolling rate is 30%, and the hot charging temperature reaches 1000℃; the direct rolling rate of the 1780mm hot strip mill at the Kashima Plant of Sumitomo Steel Pipe is 57%, the hot charging temperature is greater than 850℃, and the hot charging rate is 28%. In the future, my country should increase the hot charging ratio of continuous casting billets above 650℃ and strive to save energy by 25% to 35%.
2) Heating technologies of heating furnaces: Heating technologies include regenerative heating, automatic combustion control, combustion of low calorific value fuels, low oxidation or non-oxidation heating technologies, 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 and increasing the application of blast furnace gas and converter gas. Low oxidation heating technology for atmosphere control and non-oxidation heating technology for gas protection are important measures to reduce oxidation loss and increase the yield rate. This technology can even eliminate the pickling process. At present, the scale produced by the heating process of steel rolling is 3-3.5 kg/t, and the loss is estimated to be about 1.5 million tons of steel (about 7.5 billion yuan) per year; according to calculations by European scholars, the cost of pickling is 15-20 euros/t. If it can reduce the consumption of pickling and acid, it will have a significant effect on protecting the environment and reducing the pressure of waste acid treatment.
3) Low-temperature rolling and rolling lubrication technology: Domestic high-speed wire manufacturers have adopted low-temperature rolling technology, and their average furnace temperature has reached 950℃, and the lowest has dropped to 910℃. The power of the first rolling mill of some newly built high-speed wires has been designed and manufactured according to the rolling temperature of 850℃. The total energy consumption of low-temperature rolling is about 10%-15% lower than that of conventional rolling. According to statistics from the hot rolling mill of Kashima Steel Works in Japan, reducing the furnace temperature of steel billets by 8℃ will save 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. The temperature difference of the entire length of 130-150mm square billet should not be greater than 20-25℃. Rolling lubrication technology can reduce rolling force by 10%-30%, reduce power consumption by 5%-10%, and reduce iron oxide scale by about 1kg/t, thereby increasing the yield rate by 0.5%-1.0%, and can also reduce the acid consumption of pickling by about 0.3-1.0kg/t. Many domestic steel mills have successfully applied it to the production of stainless steel and electrical steel, with good results. In the future, while vigorously promoting rolling lubrication, we should strengthen environmentally friendly rolling lubricating media, lubrication technology, and recycling technology.
4) Controlled rolling and controlled cooling technology and its equipment: Controlled rolling and controlled cooling technology is an indispensable means for energy saving, material saving, high-performance products, and production. Representative steel materials such as DP steel, TRIP steel, TWIP steel, CP steel, AHSS steel, UHSS steel, pipeline steel, building structure steel, grain steel, and heat-free steel are all produced using controlled rolling and controlled cooling technology.
In addition to the new development of physical metallurgy as its technical basis, the controlled rolling and controlled cooling technology also benefits from new technology and equipment, such as high-power mills that can achieve low temperature and high pressure, ultra-compact mills, ultra-fast cooling (UltraFastCooling), online accelerated cooling (Super-OLAC) devices, sizing mill equipment, etc. In the future, the development of controlled rolling and controlled cooling technology will strongly rely on new technology and 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: Aug-30-2024