In the recent years, China's petroleum industry needs 2 million tons of oil well pipes and 1.6 million tons of main pipelines for trunk lines and trunk lines. Oil pipeline conditions are harsh, oil and gas pipelines transport a large number of flammable and explosive media, and withstand internal pressures of tens or even hundreds of atmospheres; tubing string and casing string usually have to withstand hundreds or even thousands of atmospheric pressures or External pressure, tensile load of several hundred tons and high temperature in the well and severe corrosive medium. The performance and quality of oil pipelines are of great importance to the safety and development of the petroleum industry.
Among the steel pipes used in China's petroleum industry, most of the steel pipes are welded steel pipes; welded pipes in oil well pipes only account for 10%, while the proportion of welded pipes in oil well pipes in developed countries has reached 50%.
China has applied a large number of X70 steel grade welded pipes in gas pipelines since the West-East Gas Pipeline Project. In 2005, an 8km X80 steel pipe application section was constructed. In 2006, the domestic X100 straight seam submerged arc welded pipe was first studied.
During the "Eleventh Five-Year Plan" period, China will build the second line of the West-East Gas Pipeline and a number of transnational gas pipelines that introduce foreign natural gas, and consume more than 10 million tons of steel. The designed annual gas transmission capacity of these pipelines will increase from 12 billion m3/a in the West-East Gas Pipeline to 30 billion m3/a, the outer diameter of the steel pipe will reach 1219~1422mm, and the maximum wall thickness may be close to 40mm. To build such a huge national energy lifeline, there are extremely strict requirements on the strength, weldability, fracture toughness and corrosion resistance of pipeline steel pipes and the quality of steel pipes, and the technology and equipment for smelting, rolling, pipe making and pipeline construction. Ability is a huge test. This is a rare opportunity for China's steel industry and pipe industry, and it is a more serious challenge than the West-East Gas Pipeline Project.
Performance requirements of steel welded pipe manufacturing for steel plates
1 strength and steel grade
1) Development and application of high strength pipeline steel
In order to economically transport oil and natural gas from distant oil and gas fields to areas of use, the working pressure of long-distance oil and gas pipelines continues to increase. The working pressure of onshore natural gas pipelines has been raised to more than 15 MPa. The working pressure of the gas pipelines under construction in the Gulf of Mexico and the North Sea has reached 25 MPa; the highest working pressure of the Russian East Siberia-Pacific pipeline has been 14 MPa. Since the construction of the West-East Gas Pipeline, the working pressure of China's natural gas mains has increased from 6.4 MPa to 10 MPa. The long-distance natural gas transmission lines such as the West-East Gas Pipeline, which will be built during the 11th Five-Year Plan period, may use working pressures of 12 MPa or higher. . The use of high-grade line pipe to construct long-distance pipelines has significant economic advantages. These advantages come from the increased efficiency of pipeline transportation and the reduction in material costs. Smaller diameter, thin walled steel tubes reduce the total weight of the material itself and reduce the consumption of the ring weld material.
The Xiayan gas pipeline built in the United States in 2005 is the first X80 natural gas pipeline in the United States. It is also the longest X80 gas pipeline in the world, with a total length of 612km. The outer diameter of the main steel pipe is 914mm, the wall thickness is 11.9mm, and the maximum wall thickness of the crossing section. It is 17.2mm. On the basis of the successful completion of the Cheyenne pipeline, the United States plans to build a larger-scale US West-East Gas Pipeline, the Rockies Express Pipeline. The pipeline is the largest gas pipeline built in the United States in the past 20 years. It is made of X80 steel grade steel pipe with a diameter of 1067mm and a total length of 2130km. It will start construction in 2007. The first phase of the project (1142km) is scheduled to be completed and put into operation in 2008. The third phase of the project will be completed in 2009. The X80 will gradually become the mainstream steel grade for onshore natural gas high pressure long-distance pipelines.
Higher strength X100 and X120 grade pipeline steels have been developed and some test sections have been successfully built. The X90～X120 ultra-high strength steel grade has been included in the new pipeline steel standard jointly compiled by API and ISO and will be released soon.
Most countries in the world use API5L or equivalent pipeline steel grades, but Russia's pipeline steel grades are different. For example, Russia's Eastern Siberia-Pacific pipeline design steel grade K60 to K70 has been constructed. The lower limit of yield strength of K70 steel grade pipeline steel pipe in Russia's Eastern Siberia-Pacific oil pipeline greatly exceeds the lower limit of API5LX80 steel grade, close to the lower limit of yield strength of X90, and the lower limit of tensile strength greatly exceeds the lower limit of API5LX80 steel grade, close to X90 The lower limit of tensile strength can be regarded as the first large-scale application of X90 steel grade in oil and gas pipelines.
2) Change of tensile properties before and after steel tube manufacturing
Change in yield strength. Before and after the steel pipe, due to the combined effect of the Bauschinger effect and the cold work hardening, the yield strength of the welded pipe body and the plate is different. This difference is related to the microstructure, strength and comprehensive deformation (tube diameter, wall thickness, expansion ratio) and molding mode of different steel grades. The main difference is due to the effect of the flattening of the pipe specimen.
Spiral welded pipes generally do not use cold expansion. Since the deformation and stress direction of the rectangular tensile specimen of the tubular body are opposite to those of the forming crimp, the yield strength of the tubular body is lowered, and the yield strength is increased due to the cold hardening effect, and the final yield strength is different. It is the result of a combination of these two factors, the extent of which is related to steel grade, pipe diameter, thickness and organization. The spheroidal ferrite structure has a small effect on the steel sheet, and the yield strength of the tube may increase after the tube is produced, but the amplitude is not large.
Since the straight seam submerged arc welded pipe adopts about 1% of the cold expansion diameter, when UO molding is used, the expansion diameter is opposite to the forming compression direction, and the yield strength of the pipe body slightly rises; when JCO molding is used, since the steel plate is not formed during molding The compression occurs instead of stretching, and the stretching is again performed when the diameter is expanded. Therefore, the yield strength of the pipe body rises more significantly.
It should be noted that there is a lack of methods for estimating the change in yield strength before and after the steel tube by using the average value of the difference in yield strength between the tube and the base metal. More notable is the change in yield strength at the low end of the yield strength and the high-end sheet tube, and the average value may mask this change. The change in yield strength near the low end and near high-end sheet tube should be separately calculated. Appropriate space is provided to ensure that the final yield strength of the steel pipe is not lower than the lower limit and does not exceed the upper limit.
In order to accurately determine the yield strength of the steel pipe, the error of the flattening of the sample should be minimized. Some pipe and research institutes also use a ring expansion device to determine the true pipe yield strength, or to compare with the tube test yield strength of a hydrostatic blast test to correct and compensate for the error caused by the yield strength test.
Changes in tensile strength, yield ratio, and elongation. The pipe-sheet tensile strength will also change similarly after pipe making, but the relative yield strength will be small.
After the spiral welded control tube, the general yield ratio decreases, while the straight seam submerged arc welded tube yield ratio increases. Due to work hardening, the elongation of the steel pipe after pipe making has decreased to varying degrees. The degree of decline is related to the degree of work hardening, such as pipe making processes (such as pre-bending, forming and mechanical expansion), thickness, diameter and steel grade.
Resistance to large deformation steel pipe and strain aging. In recent years, strain-based design of high-grade pipelines has been a hot topic. In order to overcome the large displacement deformation caused by seismic activity zones and frozen land zones, and to ensure the safety of pipelines, steel pipes are required to have large resistance to large deformation. JFE Japan developed a large deformation resistant steel pipe by using steel plate online heat treatment process. These steel pipes are said to have a dome-shaped tensile stress-strain curve, high uniform elongation and low yield ratio, which can work safely under large strain conditions.
Many pipe mills have studied the mechanical properties of steel pipes subjected to external anti-corrosion heating. It has been found that the steel pipe anti-corrosion treatment undergoes short-time intermediate frequency heating (temperature is about 230 °C), and the shape of the tensile curve of the pipe body changes. The yield strength and yield ratio have a significant increase, which has a great influence on the strain-based pipeline design results, which may cause the strength matching of the ring weld to change from over-match to under-match. According to JFE's report, the strain resistance of large deformation resistant steel pipes is small.
2 fracture toughness of steel plate and welded pipe
1) Charpy impact toughness
Due to work hardening, the Charpy impact toughness of the steel pipe after pipe making has decreased to varying degrees compared with the plate. The degree of decline is related to the degree of work hardening, such as pipe making process such as mechanical expansion, thickness, diameter and steel grade. The Charpy impact performance of the steel sheet should be left with ample room to ensure the fracture toughness of the pipe at the lowest operating temperature of the pipeline.
2) DWTT performance
After the sheet is fabricated, the drop hammer tear (DWTT) test performance will undergo a significant change. Due to work hardening, the DWTT shear area of ​​the tube has decreased to varying degrees. The degree of decline is related to the degree of work hardening, such as pipe making process such as mechanical expansion, thickness, diameter and steel grade. For this purpose, different test temperatures are used for the steel and steel pipes to ensure the DWTT performance of the pipe. China's pipeline standards generally take the steel plate test temperature 10 ° C lower than the pipe test temperature.
During the trial production of the thick gauge (17.5mm) spiral welded pipe of the second line of Shaanxi and Beijing, the problem that the shearing area of ​​the coiled plate -15° CDWTT test was qualified, and the shearing area of ​​the pipe body -5° CDWTT test was unqualified. It shows that after the deformation amount increases, the degree of work hardening increases and the toughness loss increases. If the DWTT shearing area requirements of the coiled plate and the steel pipe are to be the same, the test temperature difference should be increased accordingly. For example, when the thickness of the coiled plate is 17.5 mm or the thickness of the steel plate is 25.4 mm, the difference between the test temperature of the steel pipe and the steel plate is preferably - 15 ° C. The DWTT test of thick gauge high-strength steel plate often also shows reverse abnormal fracture, which makes the test invalid. To this end, an evaluation method for reverse abnormal fractures has been developed, which basically solves this problem.
3 hardness of steel plate and welded pipe
Due to work hardening, the tube body has a different degree of hardness rise after the tube is formed. The degree of hardness rise is related to the degree of work hardening, such as mechanical pipe expansion and other pipe making processes, while the hardness rise is also related to the thickness, diameter and steel grade of the steel plate.
The hardness of the weld and heat affected zone is related to the welded pipe process (welding material and parameters, etc.) and the chemical composition of the steel plate. Generally, the maximum and average hardness of welded joints are higher than that of steel plates. In order to ensure that the highest hardness of the steel pipe does not exceed the standard requirements, the hardness of the plate should be 20 to 30 HV10 lower than the maximum allowable hardness of the steel pipe.
4 organization and chemical composition
1) Organization
Before the West-East Gas Transmission Project, the highest steel grade of China's oil and gas pipelines was X60, using ferrite-less pearlite structure. Since the West-East Gas Pipeline Project, acicular ferrite structure has been obtained in China's X70/X80 high-grade pipeline. A wide range of applications. The Carter's submarine pipeline (X70) in the Gulf of Mexico and the Xiayan gas pipeline (X80) in the United States use ultra-low carbon sorghum, chromium-based molybdenum and high-temperature rolling (HTP) processes, as well as high-performance needles. Ferritic pipeline steel is an example of a new generation of high performance, low cost pipeline steel.
In order to ensure the acid corrosion resistance of the steel pipe, the sulfur content should be controlled to less than 0.002%. Calcium treatment should be used to improve the form of sulfide, reduce the segregation of C and Mn, and control the hardness of the steel pipe, requiring HRC≤22, or HV260～280. Since the C and Mn contents of HTP steel are very low, the risk of segregation and the formation of banded structure are reduced, and corrosion resistance is very advantageous.
2) Chemical composition
Even if the steel grades are the same, different requirements of the pipe-making process of different pipe types should be considered.
The chemical composition of pipeline steel should not only meet the requirements of welding performance of automatic welding and repair welding process in welded pipe manufacturing, but also meet the requirements of butt welding of pipe joints.
Spiral submerged arc welded pipe. The wall thickness of the spiral welded pipe is between the ERW welded pipe and the straight submerged arc welded pipe, and the monofilament or double wire submerged arc welding method is adopted. A few special thick specifications also adopt the internal welding 3 wire, the outer welding double wire welding process, the line energy is compared low. It is required that the coil has a suitably low carbon equivalent, moderately reduces harmful elements such as C, S, P, N, H, and O, and appropriately adds elements such as Mn, Si, Ti, and Ni, which are advantageous for improving weldability. Some standard values ​​of the chemical composition of the SSAW pipe for natural gas transmission and the expected value of the pipe plant are related to the steel grade, and the chemical composition is also related to the plate thickness and the transport medium. The crude oil and the refined oil can relax relative to the natural gas.
Straight seam submerged arc welded pipe. The wall thickness of the straight seam submerged arc welded pipe is generally large, and 4-wire double-sided submerged arc welding is adopted. Because of the mechanical expansion, the toughness of the pipe body and the weld is reduced, and the strength of the pipe body is increased. Therefore, the carbon equivalent of the steel sheet is required to be as low as possible, and harmful elements such as C, S, P, N, H, and O are as small as possible, and elements such as Mn, Si, Ti, and Ni, which are advantageous for improving weldability, are appropriately added.
ERW tube. The welding method of ERW pipe and submerged arc welded pipe is significantly different. The pressure welding method without filler metal is adopted. The weld is not filled with other components, and the skin effect and the proximity effect of the high frequency current are used to instantaneously heat the edge of the plate. At the soldering temperature, the weld of the forged structure is extruded by a squeeze roll. High-quality steel pipes require on-line or off-line heat treatment of welds to refine the microstructure of the weld zone. The welds of high-quality ERW welded pipes can reach the same level of toughness as the base metal, which is not achieved by the submerged arc welding process. However, since the welding is completed instantaneously at a high speed, the difficulty in ensuring the welding quality is much higher than that in the submerged arc welding method.
The most dangerous defect in ERW welded pipes is the gray spot defects caused by cold welding and reflow inclusions. In order to reduce the weld gray spot and ensure the impact toughness of the weld, the sulfur content of the base material is particularly high, preferably S≤0.005%, while controlling Si≤0.35%, Mn/Si>5.
In order to meet the thread processing requirements of the ERW well casing, a moderate increase in C is required.
5 Geometric requirements for steel plates for pipe making
1) Spiral welded pipe
Spiral welded pipes are generally made of hot rolled coils. According to API5L requirements, the plate width should be 0.8 to 3 times the pipe diameter. In order to obtain good molding and welding quality, the sheet width is preferably selected from 1.3 to 2.4 times the tube diameter. The actual board width must take into account the production efficiency and quality of the welded pipe and the equipment capacity of the steel mill and the pipe plant. The edge of the coil is removed by 3 to 4 times the thickness of the board edge, mainly to obtain accurate board width, reduce the moon shape and remove the edge inclusions that affect the quality of the welded pipe. The amount of removal has an effect on the yield. Some pipe-making standards impose limits on this value, requiring that the edge-side processing removal is not less than 1.5 times the plate thickness. In recent years, due to the improvement of the quality of the coil and the use of the milling process, the edge removal has been reduced to less than the thickness of the panel. Ultrasonic delamination inspection of the edge of the board should be strengthened to prevent the damage of the edge of the board to the welding. The width deviation of the uncut edge coil is usually 0 to +20 mm. The monthly curvature of the slab roll unfolding has a great influence on the circumference of the welded pipe and the quality of the wrong side, and usually requires no more than 15mm/10m. In addition to considering the thickness deviation, the thickness control also considers the amount of scratches, craters and rust. Plate thickness tolerances are typically less than 1 mm. The greater the weight of the coil, the better the efficiency and quality of the welded pipe production, but limited by the capacity of the equipment. Pipes with high quality requirements often require the removal of T-joints. Therefore, the total length of the coil directly affects the average length and minimum length of the welded pipe, which seriously affects the production cost of large-diameter thick-walled welded pipes. It is necessary to control the total length (total weight) of the coil to avoid short tubes, which is a special requirement for spiral welded pipes.
2) Straight seam submerged arc welded pipe
The width of the plate is determined by the diameter of the finished welded pipe, the wall thickness, the expansion ratio, the amount of plastic deformation, the amount of edge processing, the actual width and straightness of the steel plate, and the influence of material consumption and edge processing on production efficiency. The removal of the edge of the plate of 7 to 15 mm is to achieve a precise plate width, a straight edge, and a plate edge processing amount that satisfies the production cycle. To eliminate the non-straightness of the edge of the board, it is necessary to remove the edge of the board which is not straightened by 2 times. Straightness, flatness and tip cut of the steel plate have an impact on the production efficiency and quality of the welded pipe. When the capacity of the equipment exceeds the capacity, the steel plate will be scrapped. Generally, the board width deviation is 0 to +10 mm, the straightness is less than or equal to 10 mm, the flatness is less than or equal to 10 mm/2 m, the end cut is less than or equal to 5 mm, and the length deviation is 0 to +100 mm. In addition to considering the thickness deviation of the plate thickness control, it is also necessary to consider the amount of thinning, scratching, cratering and rusting caused by the expansion. Plate thickness tolerances are typically less than 1 mm.
3) ERW tube
The raw material used in the ERW pipe is a coiled plate, but the straight seam welded pipe is produced. Therefore, the requirements for the plate are both the characteristics of the above two welded pipes. The plate width is determined according to the diameter of the finished welded pipe, the wall thickness, the amount of deformation and the amount of extrusion, the amount of the edge of the plate, and the influence of material consumption and the amount of edge processing on the production efficiency. When the wall thickness is small, the uncut edge coil needs to remove the edge of the plate 3 to 4 times thick to obtain accurate plate width and remove the edge inclusions that affect the quality of the welded pipe. The amount of removal has an effect on the yield. The uncut edge width deviation is usually 0 to +20 mm. The moon bend has an effect on the circumference of the welded pipe and the quality of the wrong side. Usually required is no more than 15mm/10m. In addition to considering the thickness deviation, the plate thickness control also considers the amount of grinding, cratering and rusting. Plate thickness tolerances are typically less than 1 mm. The greater the weight of the coil, the better the efficiency and quality of the welded pipe production, but limited by the capacity of the equipment.
6 Surface quality requirements for steel tubes for pipe production
Modern oil and gas transmission steel pipes need to be carefully treated with anti-corrosion coatings. Gas transmission steel pipes often require coating of internal anti-resistance coatings. The inner and outer shot blasting of steel pipes is required before coating, which is the surface of the pipe-making plates. Near surface quality is a rigorous test. At the beginning of the production of the West-East Gas Pipeline, defects such as heavy skin, folding and surface pits and foreign matter indentation were found after shot blasting inside and outside. After the efforts of the steel mill, these problems have been effectively solved, and the quality of the steel pipe has been effectively improved. Got further improvement. The manufacturing process of HTP steel is different from the traditional TMCP process. How to ensure the surface quality of the sheet manufacturing process is a new problem that needs to be carefully studied.
Surface contamination of steel sheets is another type of problem. Grease pollution will contaminate the shot blasting material and reduce the adhesion of the coating. The steel sheet should be protected from oil and fat during manufacturing and transportation.
Plates used for elbow manufacturing should also avoid contamination of low melting point metals such as copper and tin to prevent cracking during the manufacturing process of the elbow.
development trend
1 spiral submerged arc welded pipe sheet
At present, Ф1016mm spiral welded pipe has been mass-produced in China, and the width of the coil is generally 1550mm, and the thickness is developed from 14.6mm to 15.3mm (X80)/17.5mm (X70). The second line of the West-East Gas Pipeline to be built and the cross-border pipelines of China, Russia, China and Kazakhstan will have a large gas transmission capacity and high toughness requirements. The toughness requirements of X70 sheets that have been used in large quantities at present are CVN (-20 °C), a single minimum of 140 J, and an average minimum of 190 J. In the future, X80 pipelines may reach a single of not less than 150 J and an average of not less than 200 J. The diameter of the pipe may be Ф1219~1422mm, and the maximum plate width may be 1800mm, but the large wall thickness comes with a large wall thickness, even if the wall thickness of the first-stage area pipe is about 18mm. Whether the DWTT performance of slab rolls can meet the requirements is a key indicator of its ability to be used in these pipelines, and it requires a difficult attack.
2 Straight seam submerged arc welded pipe sheet
1) Gas pipelines
At present, the 1016mm straight seam submerged arc welded pipe which has been mass-produced in China has a plate width of about 3100mm. The thickness is increased from 17.5 mm to 18.4 mm (X80) / 21 mm (X70) or more, and the maximum wall thickness is 30.4 mm. The diameter of the main line of the West-East Gas Pipeline to be constructed and the cross-border pipelines of China, Russia, China and Kazakhstan, etc. may be 1219~1422mm, and the maximum plate width may reach 4400mm. Whether the DWTT performance of large wall thickness steel plates can meet the requirements is also a key indicator of whether it can be used in these pipelines, and it also needs to be painstakingly tackled. At present, the toughness requirements of X70 sheets that have been used in large quantities are CVN (-20 °C), a single minimum of 140 J, and an average minimum of 190 J. In the future, X80 pipelines may reach a single of not less than 150 J, and an average of not less than 200 J.
2) Anti-corrosion tube
At present, only a few pipe factories in a few developed countries are able to produce acid-resistant steel pipes. Mainly control reduction C = 0.04, S = 0.002, P = 0.010, low Mn, moderate addition of Ni = 0.22 and Cu = 0.22, calcification, Ca / S ≥ 1.5, Low hardness, ≤250HV10, optimized inclusions ≤1.5 and banded structure ≤1.5, crack sensitivity rate (CSR)≤1.5%, crack length ratio (CLR)≤15, crack thickness rate (CTR ) ≤ 5%.
3 anti-large deformation welded pipe
Large plastic deformation of buried pipelines in seismic zones and tundra areas may occur. Linepipes require higher resistance to bending, high longitudinal strength, uniform elongation, deformation strengthening index, and low yield ratio. Strict control of the yield strength range of the pipe is equally important to maintain over-matching of the ring weld. At present, only a few pipe factories in a few developed countries are able to produce.
4 ultra-low carbon sorghum HTP pipeline steel plate
HTP pipeline steel not only reduces the amount of expensive Mo, V and other elements, but also significantly reduces the cost, and also benefits the steel pipe's corrosion resistance, heat affected zone performance and DWTT performance. However, HTP pipeline steel is not familiar to pipeline owners. Some important pipelines have not been used recently. For example, the Chuan-Shanghai gas pipeline recently constructed by Sinopec and the Russian-Siberian-Pacific oil pipeline have not used HTP pipeline steel. During the "11th Five-Year Plan" period, China will build a larger-scale gas transmission line such as the Second West-East Gas Pipeline, and the development and application of HTP pipeline steel should be advanced.
In 2006, Nangang developed a Cr-Nb microalloyed X80HTP hot rolled steel sheet with no molybdenum composition, and obtained a acicular ferrite structure with a band structure of grade 1 and a grain size of 11.6. Julong Steel Pipe Co., Ltd. used this steel plate to carry out the first trial of X80HTP straight seam submerged arc welded pipe in China. The performance of the finished steel pipe fully meets the performance requirements of the X80 grade steel pipe of Suining tie line, and confirmed the technology of HTP pipeline steel used for X80 gas pipeline. feasibility.
5 hot bending elbow parent pipe steel
The oil pipeline uses an induction heating bending process to make a large angle bend. The process of induction heating bending is actually quenching + high temperature tempering. The medium-frequency heating method is used to rapidly heat the steel to above Ac3, and the quenched structure is obtained by rapid cooling after short-term heat preservation. The metallographic structure is inevitably coarsened, the fine-grain strengthening effect is weakened, and a large number of bits obtained by lowering the finishing temperature are obtained. The wrong reinforcement effect is weakened. Therefore, to ensure the toughness of the induction heating bend, it is necessary to improve the solid solution strengthening and precipitation strengthening of the steel. The chemical composition of the main tube for induction heating elbow is different from that of straight tube. C is the strongest element for solid solution strengthening. If C is too low, the solid solution strengthening effect is insufficient, resulting in insufficient strength of the bent pipe. The C content is 0.06% to 0.09%. It is also very important to control the main alloying elements Mn, Mo, Ni and Nb. They have the following aspects in the bending and tempering of steel to improve the toughness of steel: one is to improve the hardenability of steel; the other is to dissolve in solid solution. Strengthening effect; the third is the precipitation strengthening effect of the alloy compound; the fourth is to refine the grain action. Appropriately increase the Mo and Ni content and reduce the Mn content to ensure the inductive heating bend toughness index on the basis of low Pcm and Ceq.
Steel sheets for hot-bending elbows are usually of the same size as the straight tubes. One is to increase the thickness of the steel plate in order to compensate for the decrease in the strength of the welded pipe during the heat enthalpy and the thickness reduction of the outer side wall. The other is to compensate by increasing the strength. The thickness of the X70 steel plate for the hot-bending elbow mother tube which has been used in large quantities at present is 30.4 mm. The future development trend may be X70/40.6mm, X80/35.6mm and X100/28.6mm.
3ERW tube coil
A large number of medium-diameter ERW pipes (Ф508mm and below) of X70 steel grade are used as oil and gas pipelines in Australia, and X80 medium-caliber ERW pipes are constructed. At present, the largest pipe diameter of ERW conveyor steel pipe production in China is 610mm, the plate width is 1935mm, and the steel grade and wall thickness which have been used in large quantities are X60/15.9mm, X65/14.3mm. Future development may reach X60/20mm, X65/18.4mm, and X70/17.5mm. At present, the X60 steel grade toughness that has been used in large quantities reaches a single minimum of 45J and an average minimum of 60J; the X65 grade has a single minimum of 60J and an average minimum of 90J. Future development may reach X60 single minimum 90J, average minimum 120J, X65 single minimum 120J, average minimum 160J, X70 single minimum 140J, average minimum 190J.
At present, only a few pipe factories in a few developed countries are able to produce corrosion-resistant ERW pipes. Mainly control reduction C = 0.04, S = 0.002, P = 0.010, moderate addition of Ni = 0.22 and Cu = 0.22, low Mn, calcification, Ca / S ≥ 1.5, Low hardness, ≤250HV10, optimized inclusions ≤1.5 and banded structure ≤1.5, crack sensitivity rate (CSR)≤1.5%, crack length ratio (CLR)≤15, crack thickness rate (CTR ) ≤ 5%.
Another important use of ERW welded pipes is in the manufacture of high performance oil well pipes.
At present, China can only produce J55 casings, most of which are oil well surface casings. The higher steel grade casings such as K55 and N80 have been successfully trial-produced, but the actual production and application are few, resulting in the ERW oil well pipe in China. Only about 10%, most of them still use seamless tubes. This phenomenon is in sharp contrast with the international ERW oil well pipe accounted for about 50%.
In recent years, a large number of continuous tubes and expandable tubes have been used internationally as small borehole drilling and oil recovery operations. The continuous pipe is a special small-diameter ERW welded pipe, which has broad application prospects in branch wells and small borehole drilling. Continuous tube drilling technology can save 25% to 40% of drilling costs and has been widely used in the United States and Canada. The expandable sleeve is also a special ERW welded pipe with a swellable seal at the joint. Using expansion tubes to repair damaged casings can reduce workover costs; using expansion tube completions can reduce shaft loss by 10%; establishing a single diameter oil well not only eliminates the need for complex casing series, but also reduces rock The cutting amount increases the drilling speed and the well construction speed. China cannot produce these two kinds of steel pipes. First, there is no special strip steel required for the production of these two pipes.
Prospect of demand for steel for oil and gas pipelines in China in the next 10 years
According to the planning analysis, the gap between China's natural gas supply and demand in 2010 will be nearly 100 billion m3/a. In order to meet the future natural gas demand in China, it is necessary to introduce natural gas from Russia and Central Asia and build high-pressure natural gas pipelines such as the Second West-East Gas Pipeline. The designed gas transmission capacity of these pipelines is 30 billion m3/a, which is more than twice that of the first-line pipeline of the West-East Gas Pipeline. The working pressure, pipe diameter and wall thickness are significantly improved. The use of X80 steel pipe is a realistic choice. The emergence of HTP technology has undoubtedly provided strong technical support for the application of X80 steel grade.
Compared with the boom of HTP steel development at home and abroad, China's pipeline industry has not fully understood the prospects and related technologies of HTP steel in the future long-distance natural gas pipeline, and the research and development work is relatively lagging behind. For example, some pipeline steel pipe standards (enterprise standard) have stricter restrictions on the content of bismuth, such as limiting Nb ≤ 0.08%; the related technology of HTP pipeline steel pipe application has not been included in the development project. Once the HTP pipeline steel pipe needs to be applied in the long-distance pipeline, although the US experience can be used for reference, but its steel pipe diameter and wall thickness are smaller than our future West-East Gas Pipeline and Sino-Russian gas pipeline, there is no practical experience and The development of relevant data and supporting technologies will be in a passive situation of insufficient preparation.
To this end, it is recommended that relevant departments conduct special research on the development of HTP pipeline steel, and take effective measures to accelerate the pace of development. For example, organize China's pipelines and metallurgical enterprises to conduct research and revision of relevant standards, and jointly carry out thick-walled HTP X80 pipeline steel coils and wide and thick. Development of the board, development of HTP type X80 spiral and straight seam submerged arc welded steel pipe and hot and cold bending pipe. On the basis of research and development, timely arrange a certain batch of physical production, ring seam welding and test section construction, so that the research and development results can quickly obtain the practical application of 100-kilometer scale, and prepare technical and materials for the next round of pipeline construction.
At present, China has become a major producer of oil well pipes in the world, but the application ratio of ERW pipes in oil well pipes is only 10%, which is quite different from that of ERW oil well pipes in developed countries. Each increase of one percentage point means that the production of ERW oil well pipes has increased by 20,000 tons. CNPC is organizing the research of ERW oil well pipe. It can be expected that the application of ERW high-end oil well pipe in China's petroleum industry will have a great development, and high-quality hot-rolled strip is a necessary condition to achieve this goal.
Among the steel pipes used in China's petroleum industry, most of the steel pipes are welded steel pipes; welded pipes in oil well pipes only account for 10%, while the proportion of welded pipes in oil well pipes in developed countries has reached 50%.
China has applied a large number of X70 steel grade welded pipes in gas pipelines since the West-East Gas Pipeline Project. In 2005, an 8km X80 steel pipe application section was constructed. In 2006, the domestic X100 straight seam submerged arc welded pipe was first studied.
During the "Eleventh Five-Year Plan" period, China will build the second line of the West-East Gas Pipeline and a number of transnational gas pipelines that introduce foreign natural gas, and consume more than 10 million tons of steel. The designed annual gas transmission capacity of these pipelines will increase from 12 billion m3/a in the West-East Gas Pipeline to 30 billion m3/a, the outer diameter of the steel pipe will reach 1219~1422mm, and the maximum wall thickness may be close to 40mm. To build such a huge national energy lifeline, there are extremely strict requirements on the strength, weldability, fracture toughness and corrosion resistance of pipeline steel pipes and the quality of steel pipes, and the technology and equipment for smelting, rolling, pipe making and pipeline construction. Ability is a huge test. This is a rare opportunity for China's steel industry and pipe industry, and it is a more serious challenge than the West-East Gas Pipeline Project.
Performance requirements of steel welded pipe manufacturing for steel plates
1 strength and steel grade
1) Development and application of high strength pipeline steel
In order to economically transport oil and natural gas from distant oil and gas fields to areas of use, the working pressure of long-distance oil and gas pipelines continues to increase. The working pressure of onshore natural gas pipelines has been raised to more than 15 MPa. The working pressure of the gas pipelines under construction in the Gulf of Mexico and the North Sea has reached 25 MPa; the highest working pressure of the Russian East Siberia-Pacific pipeline has been 14 MPa. Since the construction of the West-East Gas Pipeline, the working pressure of China's natural gas mains has increased from 6.4 MPa to 10 MPa. The long-distance natural gas transmission lines such as the West-East Gas Pipeline, which will be built during the 11th Five-Year Plan period, may use working pressures of 12 MPa or higher. . The use of high-grade line pipe to construct long-distance pipelines has significant economic advantages. These advantages come from the increased efficiency of pipeline transportation and the reduction in material costs. Smaller diameter, thin walled steel tubes reduce the total weight of the material itself and reduce the consumption of the ring weld material.
The Xiayan gas pipeline built in the United States in 2005 is the first X80 natural gas pipeline in the United States. It is also the longest X80 gas pipeline in the world, with a total length of 612km. The outer diameter of the main steel pipe is 914mm, the wall thickness is 11.9mm, and the maximum wall thickness of the crossing section. It is 17.2mm. On the basis of the successful completion of the Cheyenne pipeline, the United States plans to build a larger-scale US West-East Gas Pipeline, the Rockies Express Pipeline. The pipeline is the largest gas pipeline built in the United States in the past 20 years. It is made of X80 steel grade steel pipe with a diameter of 1067mm and a total length of 2130km. It will start construction in 2007. The first phase of the project (1142km) is scheduled to be completed and put into operation in 2008. The third phase of the project will be completed in 2009. The X80 will gradually become the mainstream steel grade for onshore natural gas high pressure long-distance pipelines.
Higher strength X100 and X120 grade pipeline steels have been developed and some test sections have been successfully built. The X90～X120 ultra-high strength steel grade has been included in the new pipeline steel standard jointly compiled by API and ISO and will be released soon.
Most countries in the world use API5L or equivalent pipeline steel grades, but Russia's pipeline steel grades are different. For example, Russia's Eastern Siberia-Pacific pipeline design steel grade K60 to K70 has been constructed. The lower limit of yield strength of K70 steel grade pipeline steel pipe in Russia's Eastern Siberia-Pacific oil pipeline greatly exceeds the lower limit of API5LX80 steel grade, close to the lower limit of yield strength of X90, and the lower limit of tensile strength greatly exceeds the lower limit of API5LX80 steel grade, close to X90 The lower limit of tensile strength can be regarded as the first large-scale application of X90 steel grade in oil and gas pipelines.
2) Change of tensile properties before and after steel tube manufacturing
Change in yield strength. Before and after the steel pipe, due to the combined effect of the Bauschinger effect and the cold work hardening, the yield strength of the welded pipe body and the plate is different. This difference is related to the microstructure, strength and comprehensive deformation (tube diameter, wall thickness, expansion ratio) and molding mode of different steel grades. The main difference is due to the effect of the flattening of the pipe specimen.
Spiral welded pipes generally do not use cold expansion. Since the deformation and stress direction of the rectangular tensile specimen of the tubular body are opposite to those of the forming crimp, the yield strength of the tubular body is lowered, and the yield strength is increased due to the cold hardening effect, and the final yield strength is different. It is the result of a combination of these two factors, the extent of which is related to steel grade, pipe diameter, thickness and organization. The spheroidal ferrite structure has a small effect on the steel sheet, and the yield strength of the tube may increase after the tube is produced, but the amplitude is not large.
Since the straight seam submerged arc welded pipe adopts about 1% of the cold expansion diameter, when UO molding is used, the expansion diameter is opposite to the forming compression direction, and the yield strength of the pipe body slightly rises; when JCO molding is used, since the steel plate is not formed during molding The compression occurs instead of stretching, and the stretching is again performed when the diameter is expanded. Therefore, the yield strength of the pipe body rises more significantly.
It should be noted that there is a lack of methods for estimating the change in yield strength before and after the steel tube by using the average value of the difference in yield strength between the tube and the base metal. More notable is the change in yield strength at the low end of the yield strength and the high-end sheet tube, and the average value may mask this change. The change in yield strength near the low end and near high-end sheet tube should be separately calculated. Appropriate space is provided to ensure that the final yield strength of the steel pipe is not lower than the lower limit and does not exceed the upper limit.
In order to accurately determine the yield strength of the steel pipe, the error of the flattening of the sample should be minimized. Some pipe and research institutes also use a ring expansion device to determine the true pipe yield strength, or to compare with the tube test yield strength of a hydrostatic blast test to correct and compensate for the error caused by the yield strength test.
Changes in tensile strength, yield ratio, and elongation. The pipe-sheet tensile strength will also change similarly after pipe making, but the relative yield strength will be small.
After the spiral welded control tube, the general yield ratio decreases, while the straight seam submerged arc welded tube yield ratio increases. Due to work hardening, the elongation of the steel pipe after pipe making has decreased to varying degrees. The degree of decline is related to the degree of work hardening, such as pipe making processes (such as pre-bending, forming and mechanical expansion), thickness, diameter and steel grade.
Resistance to large deformation steel pipe and strain aging. In recent years, strain-based design of high-grade pipelines has been a hot topic. In order to overcome the large displacement deformation caused by seismic activity zones and frozen land zones, and to ensure the safety of pipelines, steel pipes are required to have large resistance to large deformation. JFE Japan developed a large deformation resistant steel pipe by using steel plate online heat treatment process. These steel pipes are said to have a dome-shaped tensile stress-strain curve, high uniform elongation and low yield ratio, which can work safely under large strain conditions.
Many pipe mills have studied the mechanical properties of steel pipes subjected to external anti-corrosion heating. It has been found that the steel pipe anti-corrosion treatment undergoes short-time intermediate frequency heating (temperature is about 230 °C), and the shape of the tensile curve of the pipe body changes. The yield strength and yield ratio have a significant increase, which has a great influence on the strain-based pipeline design results, which may cause the strength matching of the ring weld to change from over-match to under-match. According to JFE's report, the strain resistance of large deformation resistant steel pipes is small.
2 fracture toughness of steel plate and welded pipe
1) Charpy impact toughness
Due to work hardening, the Charpy impact toughness of the steel pipe after pipe making has decreased to varying degrees compared with the plate. The degree of decline is related to the degree of work hardening, such as pipe making process such as mechanical expansion, thickness, diameter and steel grade. The Charpy impact performance of the steel sheet should be left with ample room to ensure the fracture toughness of the pipe at the lowest operating temperature of the pipeline.
2) DWTT performance
After the sheet is fabricated, the drop hammer tear (DWTT) test performance will undergo a significant change. Due to work hardening, the DWTT shear area of ​​the tube has decreased to varying degrees. The degree of decline is related to the degree of work hardening, such as pipe making process such as mechanical expansion, thickness, diameter and steel grade. For this purpose, different test temperatures are used for the steel and steel pipes to ensure the DWTT performance of the pipe. China's pipeline standards generally take the steel plate test temperature 10 ° C lower than the pipe test temperature.
During the trial production of the thick gauge (17.5mm) spiral welded pipe of the second line of Shaanxi and Beijing, the problem that the shearing area of ​​the coiled plate -15° CDWTT test was qualified, and the shearing area of ​​the pipe body -5° CDWTT test was unqualified. It shows that after the deformation amount increases, the degree of work hardening increases and the toughness loss increases. If the DWTT shearing area requirements of the coiled plate and the steel pipe are to be the same, the test temperature difference should be increased accordingly. For example, when the thickness of the coiled plate is 17.5 mm or the thickness of the steel plate is 25.4 mm, the difference between the test temperature of the steel pipe and the steel plate is preferably - 15 ° C. The DWTT test of thick gauge high-strength steel plate often also shows reverse abnormal fracture, which makes the test invalid. To this end, an evaluation method for reverse abnormal fractures has been developed, which basically solves this problem.
3 hardness of steel plate and welded pipe
Due to work hardening, the tube body has a different degree of hardness rise after the tube is formed. The degree of hardness rise is related to the degree of work hardening, such as mechanical pipe expansion and other pipe making processes, while the hardness rise is also related to the thickness, diameter and steel grade of the steel plate.
The hardness of the weld and heat affected zone is related to the welded pipe process (welding material and parameters, etc.) and the chemical composition of the steel plate. Generally, the maximum and average hardness of welded joints are higher than that of steel plates. In order to ensure that the highest hardness of the steel pipe does not exceed the standard requirements, the hardness of the plate should be 20 to 30 HV10 lower than the maximum allowable hardness of the steel pipe.
4 organization and chemical composition
1) Organization
Before the West-East Gas Transmission Project, the highest steel grade of China's oil and gas pipelines was X60, using ferrite-less pearlite structure. Since the West-East Gas Pipeline Project, acicular ferrite structure has been obtained in China's X70/X80 high-grade pipeline. A wide range of applications. The Carter's submarine pipeline (X70) in the Gulf of Mexico and the Xiayan gas pipeline (X80) in the United States use ultra-low carbon sorghum, chromium-based molybdenum and high-temperature rolling (HTP) processes, as well as high-performance needles. Ferritic pipeline steel is an example of a new generation of high performance, low cost pipeline steel.
In order to ensure the acid corrosion resistance of the steel pipe, the sulfur content should be controlled to less than 0.002%. Calcium treatment should be used to improve the form of sulfide, reduce the segregation of C and Mn, and control the hardness of the steel pipe, requiring HRC≤22, or HV260～280. Since the C and Mn contents of HTP steel are very low, the risk of segregation and the formation of banded structure are reduced, and corrosion resistance is very advantageous.
2) Chemical composition
Even if the steel grades are the same, different requirements of the pipe-making process of different pipe types should be considered.
The chemical composition of pipeline steel should not only meet the requirements of welding performance of automatic welding and repair welding process in welded pipe manufacturing, but also meet the requirements of butt welding of pipe joints.
Spiral submerged arc welded pipe. The wall thickness of the spiral welded pipe is between the ERW welded pipe and the straight submerged arc welded pipe, and the monofilament or double wire submerged arc welding method is adopted. A few special thick specifications also adopt the internal welding 3 wire, the outer welding double wire welding process, the line energy is compared low. It is required that the coil has a suitably low carbon equivalent, moderately reduces harmful elements such as C, S, P, N, H, and O, and appropriately adds elements such as Mn, Si, Ti, and Ni, which are advantageous for improving weldability. Some standard values ​​of the chemical composition of the SSAW pipe for natural gas transmission and the expected value of the pipe plant are related to the steel grade, and the chemical composition is also related to the plate thickness and the transport medium. The crude oil and the refined oil can relax relative to the natural gas.
Straight seam submerged arc welded pipe. The wall thickness of the straight seam submerged arc welded pipe is generally large, and 4-wire double-sided submerged arc welding is adopted. Because of the mechanical expansion, the toughness of the pipe body and the weld is reduced, and the strength of the pipe body is increased. Therefore, the carbon equivalent of the steel sheet is required to be as low as possible, and harmful elements such as C, S, P, N, H, and O are as small as possible, and elements such as Mn, Si, Ti, and Ni, which are advantageous for improving weldability, are appropriately added.
ERW tube. The welding method of ERW pipe and submerged arc welded pipe is significantly different. The pressure welding method without filler metal is adopted. The weld is not filled with other components, and the skin effect and the proximity effect of the high frequency current are used to instantaneously heat the edge of the plate. At the soldering temperature, the weld of the forged structure is extruded by a squeeze roll. High-quality steel pipes require on-line or off-line heat treatment of welds to refine the microstructure of the weld zone. The welds of high-quality ERW welded pipes can reach the same level of toughness as the base metal, which is not achieved by the submerged arc welding process. However, since the welding is completed instantaneously at a high speed, the difficulty in ensuring the welding quality is much higher than that in the submerged arc welding method.
The most dangerous defect in ERW welded pipes is the gray spot defects caused by cold welding and reflow inclusions. In order to reduce the weld gray spot and ensure the impact toughness of the weld, the sulfur content of the base material is particularly high, preferably S≤0.005%, while controlling Si≤0.35%, Mn/Si>5.
In order to meet the thread processing requirements of the ERW well casing, a moderate increase in C is required.
5 Geometric requirements for steel plates for pipe making
1) Spiral welded pipe
Spiral welded pipes are generally made of hot rolled coils. According to API5L requirements, the plate width should be 0.8 to 3 times the pipe diameter. In order to obtain good molding and welding quality, the sheet width is preferably selected from 1.3 to 2.4 times the tube diameter. The actual board width must take into account the production efficiency and quality of the welded pipe and the equipment capacity of the steel mill and the pipe plant. The edge of the coil is removed by 3 to 4 times the thickness of the board edge, mainly to obtain accurate board width, reduce the moon shape and remove the edge inclusions that affect the quality of the welded pipe. The amount of removal has an effect on the yield. Some pipe-making standards impose limits on this value, requiring that the edge-side processing removal is not less than 1.5 times the plate thickness. In recent years, due to the improvement of the quality of the coil and the use of the milling process, the edge removal has been reduced to less than the thickness of the panel. Ultrasonic delamination inspection of the edge of the board should be strengthened to prevent the damage of the edge of the board to the welding. The width deviation of the uncut edge coil is usually 0 to +20 mm. The monthly curvature of the slab roll unfolding has a great influence on the circumference of the welded pipe and the quality of the wrong side, and usually requires no more than 15mm/10m. In addition to considering the thickness deviation, the thickness control also considers the amount of scratches, craters and rust. Plate thickness tolerances are typically less than 1 mm. The greater the weight of the coil, the better the efficiency and quality of the welded pipe production, but limited by the capacity of the equipment. Pipes with high quality requirements often require the removal of T-joints. Therefore, the total length of the coil directly affects the average length and minimum length of the welded pipe, which seriously affects the production cost of large-diameter thick-walled welded pipes. It is necessary to control the total length (total weight) of the coil to avoid short tubes, which is a special requirement for spiral welded pipes.
2) Straight seam submerged arc welded pipe
The width of the plate is determined by the diameter of the finished welded pipe, the wall thickness, the expansion ratio, the amount of plastic deformation, the amount of edge processing, the actual width and straightness of the steel plate, and the influence of material consumption and edge processing on production efficiency. The removal of the edge of the plate of 7 to 15 mm is to achieve a precise plate width, a straight edge, and a plate edge processing amount that satisfies the production cycle. To eliminate the non-straightness of the edge of the board, it is necessary to remove the edge of the board which is not straightened by 2 times. Straightness, flatness and tip cut of the steel plate have an impact on the production efficiency and quality of the welded pipe. When the capacity of the equipment exceeds the capacity, the steel plate will be scrapped. Generally, the board width deviation is 0 to +10 mm, the straightness is less than or equal to 10 mm, the flatness is less than or equal to 10 mm/2 m, the end cut is less than or equal to 5 mm, and the length deviation is 0 to +100 mm. In addition to considering the thickness deviation of the plate thickness control, it is also necessary to consider the amount of thinning, scratching, cratering and rusting caused by the expansion. Plate thickness tolerances are typically less than 1 mm.
3) ERW tube
The raw material used in the ERW pipe is a coiled plate, but the straight seam welded pipe is produced. Therefore, the requirements for the plate are both the characteristics of the above two welded pipes. The plate width is determined according to the diameter of the finished welded pipe, the wall thickness, the amount of deformation and the amount of extrusion, the amount of the edge of the plate, and the influence of material consumption and the amount of edge processing on the production efficiency. When the wall thickness is small, the uncut edge coil needs to remove the edge of the plate 3 to 4 times thick to obtain accurate plate width and remove the edge inclusions that affect the quality of the welded pipe. The amount of removal has an effect on the yield. The uncut edge width deviation is usually 0 to +20 mm. The moon bend has an effect on the circumference of the welded pipe and the quality of the wrong side. Usually required is no more than 15mm/10m. In addition to considering the thickness deviation, the plate thickness control also considers the amount of grinding, cratering and rusting. Plate thickness tolerances are typically less than 1 mm. The greater the weight of the coil, the better the efficiency and quality of the welded pipe production, but limited by the capacity of the equipment.
6 Surface quality requirements for steel tubes for pipe production
Modern oil and gas transmission steel pipes need to be carefully treated with anti-corrosion coatings. Gas transmission steel pipes often require coating of internal anti-resistance coatings. The inner and outer shot blasting of steel pipes is required before coating, which is the surface of the pipe-making plates. Near surface quality is a rigorous test. At the beginning of the production of the West-East Gas Pipeline, defects such as heavy skin, folding and surface pits and foreign matter indentation were found after shot blasting inside and outside. After the efforts of the steel mill, these problems have been effectively solved, and the quality of the steel pipe has been effectively improved. Got further improvement. The manufacturing process of HTP steel is different from the traditional TMCP process. How to ensure the surface quality of the sheet manufacturing process is a new problem that needs to be carefully studied.
Surface contamination of steel sheets is another type of problem. Grease pollution will contaminate the shot blasting material and reduce the adhesion of the coating. The steel sheet should be protected from oil and fat during manufacturing and transportation.
Plates used for elbow manufacturing should also avoid contamination of low melting point metals such as copper and tin to prevent cracking during the manufacturing process of the elbow.
development trend
1 spiral submerged arc welded pipe sheet
At present, Ф1016mm spiral welded pipe has been mass-produced in China, and the width of the coil is generally 1550mm, and the thickness is developed from 14.6mm to 15.3mm (X80)/17.5mm (X70). The second line of the West-East Gas Pipeline to be built and the cross-border pipelines of China, Russia, China and Kazakhstan will have a large gas transmission capacity and high toughness requirements. The toughness requirements of X70 sheets that have been used in large quantities at present are CVN (-20 °C), a single minimum of 140 J, and an average minimum of 190 J. In the future, X80 pipelines may reach a single of not less than 150 J and an average of not less than 200 J. The diameter of the pipe may be Ф1219~1422mm, and the maximum plate width may be 1800mm, but the large wall thickness comes with a large wall thickness, even if the wall thickness of the first-stage area pipe is about 18mm. Whether the DWTT performance of slab rolls can meet the requirements is a key indicator of its ability to be used in these pipelines, and it requires a difficult attack.
2 Straight seam submerged arc welded pipe sheet
1) Gas pipelines
At present, the 1016mm straight seam submerged arc welded pipe which has been mass-produced in China has a plate width of about 3100mm. The thickness is increased from 17.5 mm to 18.4 mm (X80) / 21 mm (X70) or more, and the maximum wall thickness is 30.4 mm. The diameter of the main line of the West-East Gas Pipeline to be constructed and the cross-border pipelines of China, Russia, China and Kazakhstan, etc. may be 1219~1422mm, and the maximum plate width may reach 4400mm. Whether the DWTT performance of large wall thickness steel plates can meet the requirements is also a key indicator of whether it can be used in these pipelines, and it also needs to be painstakingly tackled. At present, the toughness requirements of X70 sheets that have been used in large quantities are CVN (-20 °C), a single minimum of 140 J, and an average minimum of 190 J. In the future, X80 pipelines may reach a single of not less than 150 J, and an average of not less than 200 J.
2) Anti-corrosion tube
At present, only a few pipe factories in a few developed countries are able to produce acid-resistant steel pipes. Mainly control reduction C = 0.04, S = 0.002, P = 0.010, low Mn, moderate addition of Ni = 0.22 and Cu = 0.22, calcification, Ca / S ≥ 1.5, Low hardness, ≤250HV10, optimized inclusions ≤1.5 and banded structure ≤1.5, crack sensitivity rate (CSR)≤1.5%, crack length ratio (CLR)≤15, crack thickness rate (CTR ) ≤ 5%.
3 anti-large deformation welded pipe
Large plastic deformation of buried pipelines in seismic zones and tundra areas may occur. Linepipes require higher resistance to bending, high longitudinal strength, uniform elongation, deformation strengthening index, and low yield ratio. Strict control of the yield strength range of the pipe is equally important to maintain over-matching of the ring weld. At present, only a few pipe factories in a few developed countries are able to produce.
4 ultra-low carbon sorghum HTP pipeline steel plate
HTP pipeline steel not only reduces the amount of expensive Mo, V and other elements, but also significantly reduces the cost, and also benefits the steel pipe's corrosion resistance, heat affected zone performance and DWTT performance. However, HTP pipeline steel is not familiar to pipeline owners. Some important pipelines have not been used recently. For example, the Chuan-Shanghai gas pipeline recently constructed by Sinopec and the Russian-Siberian-Pacific oil pipeline have not used HTP pipeline steel. During the "11th Five-Year Plan" period, China will build a larger-scale gas transmission line such as the Second West-East Gas Pipeline, and the development and application of HTP pipeline steel should be advanced.
In 2006, Nangang developed a Cr-Nb microalloyed X80HTP hot rolled steel sheet with no molybdenum composition, and obtained a acicular ferrite structure with a band structure of grade 1 and a grain size of 11.6. Julong Steel Pipe Co., Ltd. used this steel plate to carry out the first trial of X80HTP straight seam submerged arc welded pipe in China. The performance of the finished steel pipe fully meets the performance requirements of the X80 grade steel pipe of Suining tie line, and confirmed the technology of HTP pipeline steel used for X80 gas pipeline. feasibility.
5 hot bending elbow parent pipe steel
The oil pipeline uses an induction heating bending process to make a large angle bend. The process of induction heating bending is actually quenching + high temperature tempering. The medium-frequency heating method is used to rapidly heat the steel to above Ac3, and the quenched structure is obtained by rapid cooling after short-term heat preservation. The metallographic structure is inevitably coarsened, the fine-grain strengthening effect is weakened, and a large number of bits obtained by lowering the finishing temperature are obtained. The wrong reinforcement effect is weakened. Therefore, to ensure the toughness of the induction heating bend, it is necessary to improve the solid solution strengthening and precipitation strengthening of the steel. The chemical composition of the main tube for induction heating elbow is different from that of straight tube. C is the strongest element for solid solution strengthening. If C is too low, the solid solution strengthening effect is insufficient, resulting in insufficient strength of the bent pipe. The C content is 0.06% to 0.09%. It is also very important to control the main alloying elements Mn, Mo, Ni and Nb. They have the following aspects in the bending and tempering of steel to improve the toughness of steel: one is to improve the hardenability of steel; the other is to dissolve in solid solution. Strengthening effect; the third is the precipitation strengthening effect of the alloy compound; the fourth is to refine the grain action. Appropriately increase the Mo and Ni content and reduce the Mn content to ensure the inductive heating bend toughness index on the basis of low Pcm and Ceq.
Steel sheets for hot-bending elbows are usually of the same size as the straight tubes. One is to increase the thickness of the steel plate in order to compensate for the decrease in the strength of the welded pipe during the heat enthalpy and the thickness reduction of the outer side wall. The other is to compensate by increasing the strength. The thickness of the X70 steel plate for the hot-bending elbow mother tube which has been used in large quantities at present is 30.4 mm. The future development trend may be X70/40.6mm, X80/35.6mm and X100/28.6mm.
3ERW tube coil
A large number of medium-diameter ERW pipes (Ф508mm and below) of X70 steel grade are used as oil and gas pipelines in Australia, and X80 medium-caliber ERW pipes are constructed. At present, the largest pipe diameter of ERW conveyor steel pipe production in China is 610mm, the plate width is 1935mm, and the steel grade and wall thickness which have been used in large quantities are X60/15.9mm, X65/14.3mm. Future development may reach X60/20mm, X65/18.4mm, and X70/17.5mm. At present, the X60 steel grade toughness that has been used in large quantities reaches a single minimum of 45J and an average minimum of 60J; the X65 grade has a single minimum of 60J and an average minimum of 90J. Future development may reach X60 single minimum 90J, average minimum 120J, X65 single minimum 120J, average minimum 160J, X70 single minimum 140J, average minimum 190J.
At present, only a few pipe factories in a few developed countries are able to produce corrosion-resistant ERW pipes. Mainly control reduction C = 0.04, S = 0.002, P = 0.010, moderate addition of Ni = 0.22 and Cu = 0.22, low Mn, calcification, Ca / S ≥ 1.5, Low hardness, ≤250HV10, optimized inclusions ≤1.5 and banded structure ≤1.5, crack sensitivity rate (CSR)≤1.5%, crack length ratio (CLR)≤15, crack thickness rate (CTR ) ≤ 5%.
Another important use of ERW welded pipes is in the manufacture of high performance oil well pipes.
At present, China can only produce J55 casings, most of which are oil well surface casings. The higher steel grade casings such as K55 and N80 have been successfully trial-produced, but the actual production and application are few, resulting in the ERW oil well pipe in China. Only about 10%, most of them still use seamless tubes. This phenomenon is in sharp contrast with the international ERW oil well pipe accounted for about 50%.
In recent years, a large number of continuous tubes and expandable tubes have been used internationally as small borehole drilling and oil recovery operations. The continuous pipe is a special small-diameter ERW welded pipe, which has broad application prospects in branch wells and small borehole drilling. Continuous tube drilling technology can save 25% to 40% of drilling costs and has been widely used in the United States and Canada. The expandable sleeve is also a special ERW welded pipe with a swellable seal at the joint. Using expansion tubes to repair damaged casings can reduce workover costs; using expansion tube completions can reduce shaft loss by 10%; establishing a single diameter oil well not only eliminates the need for complex casing series, but also reduces rock The cutting amount increases the drilling speed and the well construction speed. China cannot produce these two kinds of steel pipes. First, there is no special strip steel required for the production of these two pipes.
Prospect of demand for steel for oil and gas pipelines in China in the next 10 years
According to the planning analysis, the gap between China's natural gas supply and demand in 2010 will be nearly 100 billion m3/a. In order to meet the future natural gas demand in China, it is necessary to introduce natural gas from Russia and Central Asia and build high-pressure natural gas pipelines such as the Second West-East Gas Pipeline. The designed gas transmission capacity of these pipelines is 30 billion m3/a, which is more than twice that of the first-line pipeline of the West-East Gas Pipeline. The working pressure, pipe diameter and wall thickness are significantly improved. The use of X80 steel pipe is a realistic choice. The emergence of HTP technology has undoubtedly provided strong technical support for the application of X80 steel grade.
Compared with the boom of HTP steel development at home and abroad, China's pipeline industry has not fully understood the prospects and related technologies of HTP steel in the future long-distance natural gas pipeline, and the research and development work is relatively lagging behind. For example, some pipeline steel pipe standards (enterprise standard) have stricter restrictions on the content of bismuth, such as limiting Nb ≤ 0.08%; the related technology of HTP pipeline steel pipe application has not been included in the development project. Once the HTP pipeline steel pipe needs to be applied in the long-distance pipeline, although the US experience can be used for reference, but its steel pipe diameter and wall thickness are smaller than our future West-East Gas Pipeline and Sino-Russian gas pipeline, there is no practical experience and The development of relevant data and supporting technologies will be in a passive situation of insufficient preparation.
To this end, it is recommended that relevant departments conduct special research on the development of HTP pipeline steel, and take effective measures to accelerate the pace of development. For example, organize China's pipelines and metallurgical enterprises to conduct research and revision of relevant standards, and jointly carry out thick-walled HTP X80 pipeline steel coils and wide and thick. Development of the board, development of HTP type X80 spiral and straight seam submerged arc welded steel pipe and hot and cold bending pipe. On the basis of research and development, timely arrange a certain batch of physical production, ring seam welding and test section construction, so that the research and development results can quickly obtain the practical application of 100-kilometer scale, and prepare technical and materials for the next round of pipeline construction.
At present, China has become a major producer of oil well pipes in the world, but the application ratio of ERW pipes in oil well pipes is only 10%, which is quite different from that of ERW oil well pipes in developed countries. Each increase of one percentage point means that the production of ERW oil well pipes has increased by 20,000 tons. CNPC is organizing the research of ERW oil well pipe. It can be expected that the application of ERW high-end oil well pipe in China's petroleum industry will have a great development, and high-quality hot-rolled strip is a necessary condition to achieve this goal.
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