Those "catty" in the domestic pipe welding machine market
来源： http://tzhangli.com点击： Date: 2016-05-09 00 : 00Source : http : //tzhangli.comClick :
Most of China's oil and gas resources are distributed in the northeast and northwestern regions, and most of the consumer market is in densely populated areas such as the southeast coast and large and medium-sized cities in the central and southern regions. This severe separation of production and marketing markets makes the transportation of oil and gas products a development of oil and gas resources. And the biggest obstacle to exploitation. Pipeline transportation is the best way to overcome this obstacle. Compared with railway transportation, pipeline transportation is a large-capacity, safer, and more economical method of transporting oil and gas products. Its construction investment is half that of railways, and transportation costs are even less. one third. Therefore, the Chinese government has included the development strategy of “strengthening the construction of oil and gas pipelines and forming a pipeline transportation network” as part of the “10th Five-Year Plan”. According to the planning of related parties, in the next 10 years, China will build 14 oil and gas pipelines, forming a "two vertical, two horizontal, four hub, five gas depots" with a total length of more than 10,000 kilometers of oil and gas pipelines. This indicates that China is about to usher in the peak period of oil and gas pipeline construction.The key natural gas pipeline projects under construction and planned in China are: West-to-East Gas Transmission Project, with a total length of 4,176 kilometers and a total investment of 120 billion yuan. Construction was officially started in September this year, and the entire pipeline was opened in 2004. The Suninglan gas pipeline project The total length of 950 kilometers has been started in May 2000. It is nearing completion and the natural gas has been delivered to Xining. The Zhongxian-Wuhan gas pipeline project has a total length of 760 kilometers. Preliminary preparations have made significant progress. 4 of the 11 tunnels have been completed; the Shijiazhuang to Luzhou gas pipeline project, with a total length of 202 kilometers, was started in May 2000 and is currently nearing completion; the Shijiazhuang to Handan gas pipeline project, with a total length of about 160 kilometers ; Jingbian-Beijing gas transmission project double line in Shaanxi; Jingbian-Xi'an gas pipeline project double line in Shaanxi; Shaanxi-Ganning-Hohhot gas transmission project with a total length of 497 kilometers; Hainan Island natural gas pipeline project with a total length of about 270 kilometers; Longkou in Shandong To Qingdao gas pipeline project, a total length of about 250 kilometers; Sino-Russian gas pipeline project, a total length of 2,000 kilometers in China; Guangdong LNG project, investment promotion Completed, plans completed in 2005. The pipelines under construction and to be built are: Lanchengyu Product Oil Pipeline Project, with a total length of 1207 kilometers, which was started in May last year; the Sino-Russian Oil Pipeline Project, which is about 700 kilometers long in China; the China-Kazakhstan Oil Pipeline Project, 800 kilometers in China. In addition, a 2,000-kilometer product oil pipeline from Maoming, Guangdong to Guiyang to Kunming, and a crude oil pipeline from Zhenhai to Shanghai and Nanjing are about to start construction. In addition to the main line, large-scale urban gas pipeline network construction must also be carried out in the same period.
Facing such a huge market and such rare development opportunities, new challenges have been raised for pipeline construction technology. At the same throughput, it is more economical to build a high-pressure large-diameter pipeline than to build several low-pressure small-diameter pipelines in parallel. For example, a pipeline with a delivery pressure of 7.5 MPa and a diameter of 1,400 mm can replace three pipes with a pressure of 5.5 MPa and a diameter of 1,000 mm. However, the former can save 35% of investment and 19% of steel. Therefore, expanding the diameter of the pipeline has become Sign of scientific and technological progress in pipeline construction. Increasing the conveying pressure within a certain range can increase economic benefits. Taking a gas pipeline with a diameter of 1,020 mm as an example, the operating pressure is increased from 5.5 MPa to 7.5 MPa, the gas transmission capacity is increased by 41%, the material is saved by 7%, and the investment is reduced by 23%. Calculations show that if the working pressure of the gas pipeline can be further increased from 7.5 MPa to 10-12 MPa, the gas transmission capacity will be further increased by 33-60%. The trans-Alaska gas pipeline pressure in the United States is as high as 11.8MPa and the oil pipeline is 8.3MPa, which is the pipeline with the highest operating pressure at present.The increase in pipe diameter and the increase in conveying pressure require a higher strength of the pipe. In recent years, under the premise of ensuring weldability and impact toughness, the strength of the pipe has been greatly improved. Because pipeline laying is completely completed by welding technology, the welding quality determines the engineering quality to a large extent, and welding is the key link of pipeline construction. Pipes, welding consumables, welding processes, and welding equipment are the key factors affecting welding quality.
In the early 1970s, China began to construct large-caliber long-distance pipelines. The famous "eight-three" pipeline battle built oil pipelines from Daqing Oilfield to Tieling, from Tieling to Dalian, and from Tieling to Qinhuangdao, which solved the problem of crude oil export to Daqing.
The designed pipe diameter is 720mm, the steel material is 16MnR, submerged arc spiral welded pipe, and the wall thickness is 6-11mm. The welding process plan is: manual arc welding method, upward welding operation process; J506 and J507 electrodes are used for welding materials, baking at 400 ° C for 1 hour before welding, φ3.2 primer, φ4 filling, and cover surface; the welding power source uses rotating DC Arc welding machine; bevel is 60 ° V type, root is welded on one side and formed on both sides.
The pipeline constructed by the Northeast "August Three" Campaign has been in operation for 30 years and is still in service today, proving that the process plan of that year was correct and the construction quality was good.
In the early 1980s, the manual down welding process was promoted, and cellulose and low hydrogen down electrodes were developed. Compared with the traditional up welding process, down welding has the outstanding advantages of fast speed, good quality, and saving welding materials, so it has been widely used in pipe girth welding.
Since the early 1990s, the promotion of semi-automatic manual welding of self-shielded flux-cored wires has effectively overcome the shortcomings of poor wind resistance of other welding methods, and also has the characteristics of high welding efficiency, good quality and stability. The main way of welding.
The application of all-position automatic welding of pipelines has been explored for many years, and breakthroughs have been made. The West-East Gas Pipeline Project has been successfully used. Its efficiency and quality are unmatched by other welding processes, which indicates that China's oil and gas pipeline welding Technology has reached a high level.
2 Steel pipes for pipeline construction
2.1 Development history of pipeline steel
In the early pipeline steels, ordinary carbon steels of C, Mn, and Si types were always used, focusing on performance in metallurgy, and there were no strict regulations on chemical composition. Since the 1960s, with the increase in the pressure and diameter of oil and gas pipelines, low-alloy high-strength steels (HSLA) have been used, mainly supplied in hot-rolled and normalized conditions. The chemical composition of this type of steel: C ≤ 0.2%, alloy elements ≤ 3 to 5%. With the further development of pipeline steel, to the late 1960s and early 1970s, the American Petroleum Organization proposed the microalloyed controlled rolling steels X56, X60, and X65 in the API 5LX and API 5LS standards. This kind of steel breaks through the concept of traditional steel, with a carbon content of 0.1-0.14%. Nb, V, Ti and other alloying elements are added to the steel, and the mechanical properties of the steel are significantly improved through the controlled rolling process. By 1973 and 1985, X70 and X80 steels were successively added to the API standard, and then X100 pipeline steel was developed. The carbon content decreased to 0.01-0.04%, and the carbon equivalent decreased to 0.35 or less accordingly. It really appeared in a modern sense Multi-element microalloyed controlled rolling and controlled cold steel.
The application and start of pipeline steel in China is relatively late. Most of the oil and gas pipelines that have been laid in the past use Q235 and 16Mn steel. During the "Sixth Five-Year Plan" period, China began to develop X60 and X65 pipeline steel in accordance with API standards, and successfully used it with imported steel pipes for pipeline laying. In the early 1990s, Baosteel and Wuhan Iron and Steel successively developed X70 pipeline steel with high strength and high toughness, and they were successfully applied in the Seininglan pipeline project.
2.2 Main mechanical properties of pipeline steel
The main mechanical properties of pipeline steel are strength, toughness and mechanical properties in environmental media.
The tensile strength and yield strength of steel are determined by the chemical composition and rolling process of the steel. When selecting the material for gas pipelines, steel grades with higher yield strength should be selected to reduce the amount of steel. But not the higher the yield strength, the better. Too high yield strength reduces the toughness of the steel. In the selection of steel types, the ratio of yield strength to tensile strength of the steel—yield ratio should also be considered to ensure the quality of pipe forming and welding performance.
After repeated tensile and compression of steel, the mechanical properties will change, the strength will decrease, and the strength will be severely reduced by 15%, which is the Bauschinger effect. This factor must be considered when ordering steel plates for pipe making. It can be taken to improve the minimum yield strength of this grade of steel by 40-50MPa.
The fracture toughness of steel is related to chemical composition, alloying elements, heat treatment process, material thickness and directionality. The content of C, S, P in steel should be reduced as much as possible, and alloying elements such as V, Nb, Ti, Ni, etc. should be appropriately added, and controlled rolling and controlled cooling should be used to improve the purity of steel, uniform material and fine grain. , Can improve the toughness of steel. At present, many methods are adopted to reduce C and increase Mn.
In the pipeline steel in the oil and gas environment containing hydrogen sulfide, hydrogen caused by corrosion invades the steel and causes hydrogen-induced cracking. Therefore, pipeline steels for acid oil and gas transportation should have low sulfur content, effectively control the morphology of non-metallic inclusions, and reduce segregation of microscopic components. The hardness value of pipeline steel also has an important influence on HIC. In order to prevent hydrogen-induced cracks in steel, it is generally believed that the hardness should be controlled below HV265.
2.3 Weldability of pipeline steel
With the reduction of the carbon equivalent of pipeline steel, the sensitivity of welding to hydrogen-induced cracks decreases, the number of technological measures required to avoid cracks decreases, and the degree of performance damage in the heat-affected zone of welding decreases. However, pipeline steel undergoes a series of complex non-equilibrium physical and chemical processes during welding, which may cause defects in the welding zone or reduce the performance of the joint, mainly due to welding cracks and embrittlement of the heat-affected zone.
Due to the low carbon content of pipeline steels, the quenching tendency is reduced and the cold cracking tendency is reduced. However, as the strength level increases and the thickness of the plate increases, it still has a certain tendency to cold crack. When welding on site, cellulose welding electrodes, self-shielded flux-cored welding wires and other high-hydrogen welding materials are often used. The line energy is small, the cooling rate is fast, and the sensitivity of cold cracks is increased. It is necessary to take necessary welding measures, such as welding Before warming up.
The brittleness of the welding heat affected zone is often the source of pipeline fractures and catastrophic accidents. There are mainly two areas of local embrittlement, that is, the coarse-grained zone in the heat-affected zone is caused by the excessive growth of grains in the superheated zone and the formation of poor structures. The coarse-grained zone is again critically embrittled during multi-layer welding. That is, the coarse grain region of the front bead is caused by the reheating of the two-phase region of the subsequent bead. This can improve the toughness by adding a certain amount of Ti and Nb microalloying elements in the steel and controlling the cooling rate after welding to obtain a suitable t8 / 5.
2.4 Steel Pipe for West-East Gas Pipeline Project
The steel pipe used for the West-East Gas Pipeline Project is X70 grade pipeline steel with specifications of Φ1 016mm × 14.6 ～ 26.2mm, of which spiral welded pipe accounts for about 80%, straight seam submerged arc welded pipe accounts for about 20%, and pipeline steel consumption is about 1.7 million tons.
In addition to Nb, V, and Ti, X70 pipeline steel also contains a small amount of Ni, Cr, Cu, and Mo, which delays the formation of ferrite to a lower temperature, which is beneficial to the formation of acicular ferrite and lower bain body. Therefore, X70 pipeline steel is essentially an acicular ferritic high-strength, high-toughness pipeline steel. The chemical composition and mechanical properties of steel pipes are shown in Tables 1 and 2.
3 Welding process
3.1 Characteristics of field welding
Because the discovered and exploited oil and gas fields are located in remote areas, the geographical, climatic, and geological conditions are poor, and the social support conditions are poor, which brings a lot of difficulties to construction, especially the lowest temperature.
When welding on-site, the nozzle is used to match the nozzles. In order to improve efficiency, foundation beams or mounds of earth are usually placed under a good pipe opening, and the next butt joint preparation work is started while welding the previous butt joint. This will cause greater additional stress. At the same time, due to the thermal expansion and contraction of the steel pipe, when the dead end is hit, the problem is most likely due to the additional stress.
The on-site welding position is the horizontal fixed or inclined fixed butt joint of the pipe, including welding positions such as flat welding, vertical welding, overhead welding, and horizontal welding. Therefore, higher and stricter requirements are imposed on the operation techniques of the welder.
Today's pipeline industry requires pipelines to have higher delivery pressures and larger pipeline diameters and to ensure their safe operation. A variety of welding methods, welding materials and welding processes have emerged in order to adapt to the high strengthening, high toughness, pipe diameter enlargement and thickening of the pipe wall.
3.2 Welding methods for pipeline construction
Pipe welding construction abroad has experienced the development of manual welding and automatic welding. Manual welding mainly consists of cellulose electrode downward welding and low hydrogen electrode downward welding. In terms of automatic pipe welding , there is a pipeline flash butt welder developed by the former Soviet Union, which accumulated tens of thousands of kilometers of large-caliber pipes during the former Soviet Union. Its distinctive features are high efficiency and strong adaptability to the environment. The CRC multi-head gas protection pipeline automatic welding system developed by the American CRC company is composed of three parts: a pipe end beveling machine, a combination system of an internal mouthpiece and an internal welding machine, and an external welding machine. So far, the total length of welded pipes in the world has exceeded 34,000km. France, the former Soviet Union and other countries have also researched and applied similar automatic welding technology inside and outside the pipeline. This technology has become the mainstream of large-caliber automatic welding technology in the world today.
China ’s steel pipe girth welding technology has undergone several major changes. In the 1970s, traditional welding methods were used. Manual arc welding of low-hydrogen electrodes was used for upward welding. In the 1980s, manual arc welding was used for downward welding. Cellulose electrodes were used. And low-hydrogen type electrode downward welding, the use of self-shielded flux-cored wire semi-automatic welding technology in the 1990s, to this day began to fully promote the all-position automatic welding technology.
Manual arc welding includes the application of cellulose electrodes and low hydrogen electrodes. The manual arc welding upward welding technology is the main welding method in the past in China's pipeline construction. It is characterized by a large gap between the nozzle group and the arc welding method during the welding process. The thickness of each welding layer is large and the welding efficiency is low. . Manual arc welding downward welding is a welding technology introduced from abroad in the 1980s. It is characterized by a small gap between the nozzle group and the welding process using high current, multi-layer, fast welding operation method. It is suitable for flowing operations, welding Higher efficiency. Because the thickness of each welding layer is relatively thin, the toughness of the girth welding joint can be improved by the heat treatment of the front welding layer by the back welding layer. The manual arc welding method is flexible, simple, and highly adaptable. The organic combination of the two methods of down welding and up welding and the good root welding adaptability of cellulose electrodes are still irreplaceable in many cases.
Self-shielded flux-cored wire semi-automatic welding technology was applied to pipeline construction in the 1990s, and is mainly used for filling and covering. It is characterized by high deposition efficiency, good all-position forming, strong environmental adaptability, and easy for welders to master. It is an important welding process method for current pipeline construction.
With the increase of the strength grade of steel pipes for pipeline construction, the increase of pipe diameter and wall thickness, automatic welding technology has gradually begun to be applied in pipeline construction. Pipeline automatic welding technology has great potential in the application of large-caliber, thick-walled pipeline construction due to its advantages such as high welding efficiency, low labor intensity, and small human influence on the welding process. However, China's pipeline automatic welding technology is in its infancy, the root automatic welding problem has not been solved, and the supporting facilities such as pipe end beveling machines are not yet mature, which has limited the large-scale application of automatic welding technology.
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