Longitudinal submerged arc welded pipe with medium-small caliber and manufacturing method

Abstract

The invention relates to a manufacturing method of a medium-and-small-caliber longitudinal submerged arc welded pipe, which adopts the scheme of combining row roller forming with high-frequency pre-welding and submerged arc finish welding and adding whole pipe heat treatment, solves the problem that the existing UOE and JCOE manufacturing processes are not suitable for producing welded pipes with the diameter of less than 508mm, expands the application range of the medium-and-small-caliber longitudinal submerged arc welded pipe, and improves the production efficiency of the medium-and-small-caliber longitudinal submerged arc welded pipe. By the adoption of the method, the medium-small-diameter longitudinal submerged arc welded pipe which is low in raw material cost, high in production efficiency and stable and reliable in performance can be manufactured and obtained, and the longitudinal submerged arc welded pipe has excellent hydrogen cracking resistance.

Description

Technical Field

[0001] The present invention relates to a longitudinally welded submerged arc welded pipe and a manufacturing method thereof, and more particularly to a medium and small diameter longitudinally welded submerged arc welded pipe and a manufacturing method thereof.

Background Art

[0002] A longitudinally welded submerged arc welded pipe is a tubular part welded by the submerged arc welding process, which has a single weld seam. When the diameter of the longitudinally welded submerged arc welded pipe is greater than 914.4, two longitudinal weld seams are allowed. Compared with other types of steel pipes, the longitudinally welded submerged arc welded pipe has the advantages of a wide product specification coverage range, high manufacturing accuracy, and stable welding performance. Currently, there are two main production processes for longitudinally welded submerged arc welded pipes at home and abroad. One is the UOE process, and the other is the JCOE process. During the forming process of these two processes, the pre-bending of the plate edge adopts die pressing forming, which is more suitable for producing medium and large diameter longitudinally welded pipes with a diameter of Φ508 - Φ1626mm, but not suitable for producing pipes with a diameter less than Φ508mm. Also, due to the small curvature radius of the steel pipe, if the wall thickness is relatively large, there is a phenomenon of local thinning of the wall thickness at the edge of the steel plate in the UOE and JCOE forming processes. And because the diameter of the steel pipe is relatively small, compared with large diameter steel pipes, the output and production efficiency are low, and the economy is poor, resulting in fewer medium and small diameter steel pipes using longitudinally welded submerged arc welded pipes. Generally, seamless pipes and HFW welded pipes are selected. At the same time, due to the influence of pipeline steel materials and the existence of processes such as welding and hydrostatic pressure in the existing steel pipe manufacturing processes, hydrogen elements will inevitably be introduced. If the hydrogen content in the steel pipe is not reduced in the subsequent processes, hydrogen embrittlement is extremely likely to occur, affecting the service safety of the pipeline.

[0003] In view of the above situation, it is necessary to develop a medium and small diameter longitudinally welded submerged arc welded pipe with low raw material cost, high production efficiency, stable and reliable performance, and a new pipe manufacturing process to give play to the pipe manufacturing advantages of the longitudinally welded submerged arc welded pipe and expand the application range of medium and small diameter longitudinally welded submerged arc welded pipes.

Summary of the Invention

[0004] The present invention provides a manufacturing method for a medium and small diameter longitudinally welded submerged arc welded pipe, which combines the forming of a row of rolls with high-frequency pre-welding and submerged arc finishing welding, solves the problem that the existing UOE and JCOE manufacturing processes cannot manufacture pipes with a diameter less than Φ508mm, and adds integral pipe heat treatment, reducing the hydrogen elements introduced due to the existence of processes such as welding and hydrostatic pressure during the manufacturing process of the longitudinally welded pipe, and reducing the probability of phenomena such as hydrogen embrittlement and hydrogen-induced cracking occurring inside the pipe material. By using this method, medium and small diameter (Φ323.9mm - Φ508mm) longitudinally welded submerged arc welded pipes with low raw material cost, high production efficiency, and stable and reliable performance can be obtained.

[0005] The present invention is realized through the following technical solutions. A manufacturing method for medium and small caliber straight seam submerged arc welded pipes is provided, including the steps of: uncoiling, leveling, edge milling, forming, pre-welding, welding, full pipe body expanding, X-ray continuous inspection, hydrostatic test, ultrasonic flaw detection of weld seams and base metals, chamfering of pipe ends, radiography of pipe ends, heat treatment of the whole pipe, and finished product inspection;

[0006] The edge milling process is used to process the bevel of the steel plate into an X-shaped bevel;

[0007] The forming process is carried out by a multi-roll forming machine;

[0008] The pre-welding process uses high-frequency induction resistance welding for pre-welding;

[0009] The welding process is submerged arc welding for precise welding of the inside and outside of the pipe, and the outside of the pipe is welded first and then the inside of the pipe, so that the adjustment range of the internal welding process parameters is relatively larger, which is beneficial to improving the qualified rate of submerged arc welds;

[0010] The heat treatment process of the whole pipe needs to heat-treat the entire pipe body of the straight seam welded pipe after radiography of the pipe ends. In this way, the hydrogen element introduced due to the existence of processes such as welding and water pressure in the manufacturing process of the straight seam submerged arc welded pipe is reduced, and the probability of phenomena such as hydrogen embrittlement and hydrogen-induced cracking occurring inside the pipe material is reduced.

[0011] Particularly, the chemical composition of the steel plate is as follows:

[0012] C: 0.03 - 0.06%, Si: 0.05 - 0.45%, Mn: 0.7 - 1.25%, S ≤ 0.002%, P ≤ 0.008%, Ni: 0.01 - 0.3%, Cr: 0.01 - 0.3%, Cu: 0.01 - 0.35%, Nb: 0.01 - 0.05%, V: 0.001 - 0.05%, Ti ≤ 0.04%, Mo ≤ 0.15%, Al ≤ 0.04%, B ≤ 0.0005%, and the balance is Fe, where CE Pcm ≤ 0.15, and the levels of non-metallic inclusions of types A, B, C, D, and DS in the metallographic structure of the steel plate are not greater than 1.0 level, the banded structure is not greater than 1.5 levels, and the grain size is 9 levels and above.

[0013] Particularly, the edge milling process uses different edge milling machine tool holder shim specifications to control the root face height after semi-electric milling, and different tool holder specifications are selected to control the upper and lower bevel angles after edge milling of the plate. The upper bevel angle range is 40° - 50°, the lower bevel angle range is 30° - 40°, and the maximum processing thickness is 20 mm.

[0014] Particularly, the welding frequency of the pre-welding process is 200 kHz, the welding speed is 10 - 15 m / min, and the extrusion amount is 2 - 4 mm.

[0015] Specifically, during the welding process, external welding should be carried out first and then internal welding, and the welding speed is V = 1.2 - 1.4 m / min. Among them, external welding is carried out by double-wire submerged arc automatic welding. The first wire uses DC reverse connection, and the welding process parameters are: current I = 750 - 960 A, voltage U = 31 - 35 V. The second wire is AC, and the welding process parameters are: current I = 580 - 700 A, voltage U = 34 - 36 V. Internal welding is also carried out by double-wire submerged arc automatic welding. The first wire uses DC reverse connection, and the welding process parameters are: current I = 550 - 660 A, voltage U = 31 - 34 V. The second wire is AC, current I = 400 - 500 A, voltage U = 33 - 36 V.

[0016] Specifically, the full tube body sizing adopts a sizing module and a segmented sizing method, which can effectively solve the problems of excessive ovality and structural stress of the tube body after high-frequency pre-welding. Finally, the geometric dimension accuracy of the tube body and tube ends is high, and the straightness deviation is small. In the full tank body sizing process, the sizing length of each section is 2.5 m, each forward step length is 0.8 - 1.0 m, and the tube body sizing rate is 0.7% - 0.9%.

[0017] Specifically, the integral tube heat treatment includes two heat treatments. The temperature of the first heat treatment is controlled between 350°C and 400°C, and the holding time is between 60 min and 70 min. After the first heat treatment, the steel pipe is put into another heating furnace for the second heat treatment, the temperature is controlled between 200°C and 250°C, and the holding time is between 20 min and 30 min. After the heat treatment is completed, the steel pipe is taken out and air-cooled to room temperature.

[0018] The present invention also provides a small and medium-sized diameter straight seam submerged arc welded pipe manufactured by the above method. The diameter deviation of the pipe end of the small and medium-sized diameter straight seam submerged arc welded pipe is -0.1%D - +0.2%D, and the out-of-roundness of the pipe end < 0.7%D; the diameter deviation of the pipe body is -0.15%D - +0.2%D, and the out-of-roundness of the pipe body < 1.0%D; the full-length straightness deviation does not exceed 0.06% of the length of the steel pipe. This straight seam submerged arc welded pipe can fully meet the requirements of on-site circumferential welding butt joints of pipelines.

[0019] The present invention provides a small and medium-sized diameter straight seam submerged arc welded pipe and its manufacturing method, which has the following beneficial effects:

[0020] 1. The method gives full play to the pipe manufacturing advantages of high-frequency resistance welding for efficient pre-welding and straight seam submerged arc welding, and adds the process of integral tube heat treatment, which can effectively solve the problems of low production efficiency and poor economy of small and medium-sized diameter straight seam welded pipes. The straight seam welded pipe manufactured by this method has the characteristics of low raw material cost, high production efficiency, stable and reliable weld performance, and low diffusible hydrogen content.

[0021] 2. The welding process adopted is external welding first and then internal welding, which makes the adjustment range of the internal welding process parameters relatively larger, facilitating the improvement of the qualified rate of submerged arc welds;

[0022] 3. The segmented full-tube body expanding process is adopted, effectively solving the problems of excessive ovality and structural stress of the tube body after high-frequency pre-welding. Finally, the manufactured tube body and tube end have high geometric dimension accuracy and small straightness deviation. Among them, the diameter deviation of the tube end is -0.1%D to +0.2%D, and the out-of-roundness of the tube end is <0.7%D; the diameter deviation of the tube body is -0.15%D to +0.2%D, and the out-of-roundness of the tube body is <1.0%D; the straightness deviation of the full length of the steel pipe does not exceed 0.06% of the length of the steel pipe, which can meet the requirements of on-site circumferential welding butt joints of pipelines;

[0023] 4. By adding the process of full-tube heat treatment, the hydrogen element introduced during processes such as welding and hydrostatic pressure in the manufacturing process of straight seam welded pipes is reduced, and the probability of phenomena such as hydrogen embrittlement and hydrogen-induced cracking inside the pipe materials is reduced;

[0024] 5. When the tube body and welds of medium and small diameter straight seam welded pipes manufactured by this method are subjected to the HIC test using the A solution of the NACE TM0284 standard, the crack length rate (CLR) = 0, the crack thickness rate (CTR) = 0, and the crack sensitivity rate (CSR) = 0 for three cross-sections, indicating that the welded pipes have excellent hydrogen-induced cracking resistance.

Specific Embodiment

[0025] In order to make the purpose, technical solution and advantages of the present invention clearer, the following further elaborates on the present invention in combination with specific embodiments.

[0026] Embodiment 1

[0027] The present invention takes the manufacture of a straight seam submerged arc welded pipe with a specification of Φ323.9×10.8mm as an example.

[0028] (1) Raw materials: Hot-rolled coil plates of X52M with a wall thickness of 10.8mm are used, and its chemical composition is shown in Table 1 (wt%).

[0029] Table 1 Chemical composition (wt%) of hot-rolled coil plates for Φ323.9×10.8mm straight seam submerged arc welded pipes of X52M

[0030] C Mn Si S P Cu Al B Nb V Ti Ni Cr Mo 0.06 1.15 0.3 0.002 0.007 0.15 0.035 0.0004 0.05 0.03 0.03 0.1 0.25 0.08

[0031] (2) Pipe manufacturing process: Uncoiling, leveling, edge milling, forming, pre-welding, welding, full-tube body expansion, continuous X-ray detection, hydrostatic pressure test, ultrasonic flaw detection of welds and base metals, chamfering of pipe ends, radiography of pipe ends, full-tube heat treatment, and finished product inspection.

[0032] (3) Edge milling: Using the pressure roller device of a skateboard - type edge milling machine, process the edge of a 10.8 - mm plate into an X - type groove. The groove angle is 55° for the upper - slope single - side and 37.5° for the lower - slope single - side, with a root face of 4 mm.

[0033] (4) Pre - welding: Carry out high - frequency pre - welding using high - frequency resistance welding. The welding frequency is 200 kHz, the welding speed is 13 m / min, and the extrusion amount is 2 mm.

[0034] (5) Welding: The welding process is a precision welding process. Adopt the welding process of welding from the outside to the inside. The outside - welding process is as follows: Carry out welding using twin - wire submerged - arc automatic welding. The first wire uses DC reverse connection, and the welding process parameters are: current I = 800 A, voltage U = 34 V; the second wire is AC, current I = 620 A, voltage U = 35 V; the welding speed V = 1.3 m / min. The inside - welding process is as follows: Carry out welding using twin - wire submerged - arc automatic welding. The first wire uses DC reverse connection, and the welding process parameters are: current I = 580 A, voltage U = 33 V; the second wire is AC, current I = 430 A, voltage U = 34 V; the welding speed V = 1.3 m / min.

[0035] (6) Full - pipe body expanding: According to the pipe diameter size of the welded pipe, adopt a special expanding module and the way of segmented expanding. The expanding length of each segment is about 2.5 m, each forward step length is 0.8 m - 1.0 m, and the pipe body expanding rate is 0.8%.

[0036] (7) Whole - pipe heat treatment: The heat treatment process adopts two - stage heat treatment. The temperature of the first heat treatment is controlled between 350°C and 400°C, and the holding time is 60 min. The temperature of the second heat treatment is controlled at 225°C, and the holding time is 30 min. After the heat treatment is completed, take out the steel pipe and air - cool it to room temperature to finally obtain a longitudinally - submerged - arc - welded pipe.

[0037] In order to confirm that the longitudinally - submerged - arc - welded pipe manufactured by the method described in the present invention meets the design requirements, the following is to conduct tests on physical and chemical properties, geometric dimension measurement, and corrosion resistance.

[0038] 1) Physical and chemical properties: According to CDP - S - NGP - PL - 006 - 2019 - 4 "Technical Specification for Steel Pipes for Natural Gas Pipeline Projects", conduct physical and chemical property tests on the welded pipe. The mechanical properties all meet the standard requirements, and the test results are as follows: The yield strength R t0.5 of the pipe body: 400 - 450 MPa; The tensile strength R m of the pipe body: 500 - 550 MPa; The yield - strength ratio R t0.5 / R m: 0.82 to 0.88; elongation rate A of the pipe body: 40 to 45%; tensile strength Rm of the weld: 530 to 570 MPa; transverse impact energy of the pipe body at -10°C: 280 to 320 J; impact energy of the weld at -10°C: 160 to 240 J; impact energy of the heat-affected zone at -10°C: 230 to 290 J; hardness of the welded joint: 175 to 190 HV10; the springback amount of the pipe body of the longitudinally welded pipe measured by cutting the pipe ring is -20 mm, and the residual stress is low.

[0039] 2) Geometric dimensions: The geometric dimensions of the welded pipe were detected according to CDP-S-NGP-PL-006-2019-4 "Technical Specification for Steel Pipes for Natural Gas Pipeline Projects", and the results all met the standard requirements. The test results are as follows: the diameter deviation of the pipe end is +0.3 mm, and the out-of-roundness of the pipe end is 1 mm; the diameter deviation of the pipe body is +0.3 mm, and the out-of-roundness of the pipe body is 0.8 mm; the straightness deviation of the entire length of the steel pipe does not exceed 0.06% of the length of the steel pipe, which can meet the requirements of on-site circumferential welding butt joint of the pipeline.

[0040] 3) HIC corrosion resistance: According to NACE TM0284 standard solution A, the HIC test was carried out. The crack length rate (CLR) of three cross-sections = 0, the crack thickness rate (CTR) = 0, and the crack sensitivity rate (CSR) = 0, indicating excellent resistance to hydrogen-induced cracking.

[0041] Example 2

[0042] Taking the production of longitudinally welded submerged arc welded pipe with a specification of Φ508×19.6 mm as an example.

[0043] (1) Raw materials: Hot-rolled coil plates of X52M with a wall thickness of 19.6 mm were used, and its chemical composition is shown in Table 2 (wt%).

[0044] Table 2 Chemical composition of hot-rolled coil plates for longitudinally welded submerged arc welded pipes of X52M Φ508×19.6 mm (wt%)

[0045] C Mn Si S P Cu Al B Nb V Ti Ni Cr Mo 0.06 1.15 0.3 0.002 0.007 0.15 0.035 0.0004 0.05 0.03 0.03 0.1 0.25 0.08

[0046] (2) Pipe manufacturing process: Uncoiling, leveling, edge milling, forming, pre-welding, welding, full-pipe body expanding, continuous X-ray detection, hydrostatic test, ultrasonic flaw detection of welds and base metals, chamfering of pipe ends, radiography of pipe ends, heat treatment of the whole pipe and finished product inspection.

[0047] (3) Edge milling: Using the pressure roller device of a slide-type edge milling machine, the 19.6 mm plate edge was processed into an X-shaped groove, the groove angle was 50° for the single side of the upper groove and 37.5° for the single side of the lower groove, and the root face was 8 mm.

[0048] (4) Pre-welding: High-frequency resistance welding was used for high-frequency pre-welding, the welding frequency was 200 kHz, the welding speed was 13 m / min, and the extrusion amount was 4 mm.

[0049] (5) Welding: The welding process is the fine welding process. The welding process from outside to inside is adopted. The outside welding process is as follows: Double-wire submerged arc automatic welding is used for welding. The first wire is connected with reverse direct current. The welding process parameters are: current I = 960 A, voltage U = 35 V; the second wire is alternating current, current I = 700 A, voltage U = 36 V; welding speed V = 1.3 m / min. The inside welding process is as follows: Double-wire submerged arc automatic welding is used for welding. The first wire is connected with reverse direct current. The welding process parameters are: current I = 660 A, voltage U = 34 V; the second wire is alternating current, current I = 500 A, voltage U = 35 V; welding speed V = 1.3 m / min.

[0050] (6) Full tube body expanding: According to the pipe diameter size of the welded pipe, a special expanding module and the way of segmented expanding are adopted. The expanding length of each segment is about 2.5 m, and each forward step length is 0.8 m - 1.0 m. The tube body expanding rate is 0.8%.

[0051] (7) Whole tube heat treatment: The heat treatment process adopts two heat treatments. The temperature of the first heat treatment is controlled between 350 °C and 400 °C, and the heat preservation time is 60 min. The temperature of the second heat treatment is controlled at 225 °C, and the heat preservation time is 30 min. After the heat treatment is completed, the steel pipe is taken out and air-cooled to room temperature, and finally the longitudinal submerged arc welded pipe is obtained.

[0052] In order to prove that the longitudinal submerged arc welded pipe manufactured by the method described in the present invention meets the design requirements, the following is to conduct tests on physical and chemical properties, geometric dimension measurement and corrosion resistance.

[0053] 1) Physical and chemical properties: According to CDP-S-NGP-PL-006-2019-4 "Technical Specification for Steel Pipes Used in Natural Gas Pipeline Engineering", the physical and chemical properties of the welded pipe are tested. The mechanical properties all meet the standard requirements. The test results are as follows: The yield strength R t0.5 of the pipe body: 400 - 470 MPa; the tensile strength R m of the pipe body: 510 - 550 MPa; the yield ratio R t0.5 / R m of the pipe body: 0.82 - 0.87; the elongation rate A of the pipe body: 40 - 45%; the tensile strength Rm of the weld: 530 - 600 MPa; the transverse impact energy of the pipe body at -10 °C: 280 - 330 J; the impact energy of the weld at -10 °C: 170 - 250 J; the impact energy of the heat affected zone at -10 °C: 240 - 300 J; the hardness of the welded joint: 175 - 190 HV10; The springback amount of the pipe body of the longitudinal welded pipe measured by cutting the pipe ring is -15 mm, and the residual stress is low.

[0054] 2) Geometric dimensions: The geometric dimensions of the welded pipe were detected according to the Technical Specification for Steel Pipes for Natural Gas Pipeline Engineering CDP-S-NGP-PL-006-2019-4, and the results all met the standard requirements. The test results are as follows: the diameter deviation at the pipe end is +0.7 mm, and the out-of-roundness at the pipe end is 1.5 mm; the diameter deviation of the pipe body is +0.5 mm, and the out-of-roundness of the pipe body is 1 mm; the straightness deviation of the entire length of the steel pipe does not exceed 0.06% of the pipe length, which can meet the requirements of on-site circumferential welding butt joint of the pipeline.

[0055] 3) HIC corrosion resistance: The HIC test was carried out according to the standard A solution of NACE TM0284. The crack length rate (CLR) of the three cross-sections = 0, the crack thickness rate (CTR) = 0, and the crack sensitivity rate (CSR) = 0, indicating excellent resistance to hydrogen-induced cracking.

[0056] Comparative Example 1

[0057] Take the straight seam submerged arc welded pipe with a manufacturing specification of Φ323.9×12.7 mm as an example.

[0058] (1) Raw materials: Hot-rolled coil plates of X52M with a wall thickness of 12.7 mm were used, and their chemical compositions are shown in Table 3 (wt%).

[0059] Table 3 Chemical Compositions of Hot-rolled Coil Plates for Straight Seam Submerged Arc Welded Pipes of X52M Φ323.9×12.7 mm (wt%)

[0060] C Mn Si S P Cu Al B Nb V Ti Ni Cr Mo 0.13 1.45 0.3 0.015 0.007 0.05 0.035 0.0004 0.001 0.03 0.03 0.005 0.05 0.08

[0061] (2) Pipe manufacturing process: Uncoiling, leveling, edge milling, forming, pre-welding, welding, full-pipe body expanding, continuous X-ray detection, hydrostatic test, ultrasonic flaw detection of welds and base metals, chamfering of pipe ends, radiography of pipe ends, and finished product inspection.

[0062] (3) Edge milling: A roller device of a skateboard type edge milling machine was used to process the 12.7 mm plate edge into an X-shaped groove. The groove angle is 55° for the single side of the upper groove and 30° for the single side of the lower groove, and the root face is 5 mm.

[0063] (4) Pre-welding: High-frequency resistance welding was used for high-frequency pre-welding. The welding frequency was 200 kHz, the welding speed was 13 m / min, and the extrusion amount was 3 mm.

[0064] (5) Welding: The welding process is the fine welding process. The inside-out welding process is adopted. The outside welding process is as follows: Double-wire submerged arc automatic welding is used for welding. The first wire is connected with reverse direct current. The welding process parameters are: current I = 1100 A, voltage U = 36 V; the second wire is alternating current, current I = 660 A, voltage U = 35 V; welding speed V = 1.3 m / min. The inside welding process is as follows: Double-wire submerged arc automatic welding is used for welding. The first wire is connected with reverse direct current. The welding process parameters are: current I = 620 A, voltage U = 34 V; the second wire is alternating current, current I = 450 A, voltage U = 34 V; welding speed V = 1.3 m / min.

[0065] (6) Full tube body sizing: According to the pipe diameter size of the welded pipe, a special sizing module is used for overall sizing. The segmented sizing method is not adopted. The tube body sizing rate is 0.8%.

[0066] It can be seen from the chemical composition and manufacturing process of the steel plate for welded pipes above that the contents of C, Mn, and S elements in the steel plate chemical composition in Comparative Example 1 are all higher than the composition ranges specified in the present invention, while Nb and Ni are lower than the composition ranges specified in the present invention. C is the main solid solution strengthening element. The higher its content, the greater the hydrogen embrittlement sensitivity of the steel pipe; Mn is an element prone to segregation and is likely to cause segregation in the center of the steel plate during manufacturing, so its content should not be too high; S easily causes hydrogen atoms infiltrating into the steel to accumulate at the tips of sulfides, and the hydrogen internal pressure formed induces hydrogen-induced cracks, so its content should not be too high either. At the same time, in Comparative Example 1, the whole pipe heat treatment is not adopted in the manufacturing process. Through experiments, it is found that the manufacturing method of the welded pipe used in Comparative Example 1 cannot effectively reduce the diffusible hydrogen content of the welded pipe. In addition, the welding process parameters in Comparative Example 1 are too large, and in the groove design, a large uphill groove angle and a small downhill groove angle are adopted. In the actual welding process, it will cause too much wire filling amount for the uphill groove and too little wire filling amount for the small groove, which will make the weld bead morphology prone to poor forming and is likely to cause welding defects such as undercut, affecting the weld quality. Again, Comparative Example 1 does not adopt the full tube body sizing process of segmented sizing. Compared with Example 1 and Example 2, the situation of poor geometric dimensions of the welded pipe is likely to occur.

[0067] The straight seam submerged arc welded pipes produced are subjected to physical and chemical performance testing, geometric dimension measurement, and corrosion resistance testing.

[0068] 1) Physical and chemical properties: According to CDP-S-NGP-PL-006-2019-4 "Technical Specification for Steel Pipes for Natural Gas Pipeline Projects", the physical and chemical properties of the welded pipes are tested, and the results are as follows: The yield strength R t0.5 of the pipe body: 410 - 480 MPa; the tensile strength R m of the pipe body: 520 - 580 MPa; the yield ratio R t0.5 / R m: 0.82 to 0.91; Elongation rate A of the pipe body: 42 to 46%; Tensile strength Rm of the weld: 542 to 583 MPa; Transverse impact energy of the pipe body at -10°C: 270 to 330 J; Impact energy of the weld at -10°C: 55 to 150 J; Impact energy of the heat affected zone at -10°C: 58 to 170 J; Hardness of the welded joint: 188 to 210 HV10; The springback amount of the pipe body of the longitudinally welded pipe measured by cutting the pipe ring is +20 mm.

[0069] 2) Geometric dimensions: The geometric dimensions of the welded pipe were detected according to CDP-S-NGP-PL-006-2019-4 "Technical Specification for Steel Pipes Used in Natural Gas Pipeline Projects", and the results are as follows: The diameter deviation of the pipe end is +2.4 mm, and the out-of-roundness of the pipe end is 2.6 mm; The diameter deviation of the pipe body is +3.3 mm, and the out-of-roundness of the pipe body is 4 mm; Although the straightness deviation of the full length of the steel pipe exceeds 0.06% of the steel pipe length, there are certain difficulties in the on-site girth welding butt joint of the pipeline.

[0070] 3) HIC corrosion resistance: The HIC test was carried out according to the standard A solution of NACE TM0284. The crack length rate (CLR) of the three cross-sections = 20, the crack thickness rate (CTR) = 8, and the crack sensitivity rate (CSR) = 5, which cannot meet the requirements for transportation in acidic or hydrogen service conditions.

[0071] It can be seen from the test results of the physical and chemical properties, geometric dimensions and HIC corrosion resistance of the welded pipe in Comparative Example 1 that due to some differences in the chemical composition and manufacturing process of the steel plate used for the welded pipe and the present invention, the performance of the weld of the welded pipe has decreased extremely, seriously affecting the weld quality; The geometric dimension accuracy has also decreased to a certain extent, and there are difficulties in the on-site girth welding butt joint of the pipeline; In the HIC corrosion resistance test, the crack length rate, crack thickness rate and crack sensitivity rate are higher than the requirements of acidic or hydrogen service environments and cannot be used in acidic or hydrogen service conditions.

[0072] It can be seen from the above examples and comparative examples that the method of the present invention can be used to manufacture longitudinally welded submerged arc pipes with medium and small diameters, and the manufactured longitudinally welded submerged arc pipes have excellent physical and chemical properties and HIC corrosion resistance, and their geometric dimensions more meet the requirements of on-site girth welding butt joint of the pipeline.

Claims

1. A manufacturing method for medium and small diameter longitudinally submerged arc welded pipes, comprising the steps of: uncoiling, leveling, edge milling, forming, pre-welding, welding, full pipe body expanding, continuous X-ray inspection, hydrostatic test, ultrasonic flaw detection of welds and base metals, chamfering of pipe ends, radiography of pipe ends, and finished product inspection. It is characterized in that it further includes: Full pipe heat treatment, and this treatment process needs to perform heat treatment on the entire pipe body of the longitudinally welded pipe after radiography of the pipe ends; The edge milling process is used to process the bevel of the steel plate into an X-shaped bevel; The forming process is formed by a row of roll forming machines; The pre-welding process uses high-frequency induction resistance welding for pre-welding; The welding process is submerged arc welding for precise welding of the inside and outside of the pipe, and the outside of the pipe is welded first and then the inside of the pipe.

2. The manufacturing method for medium and small diameter longitudinally submerged arc welded pipes according to claim 1, It is characterized in that The chemical composition of the steel plate is: C: 0.03 - 0.06%, Si: 0.05 - 0.45%, Mn: 0.7 - 1.25%, S ≤ 0.002%, P ≤ 0.008%, Ni: 0.01 - 0.3%, Cr: 0.01 - 0.3%, Cu: 0.01 - 0.35%, Nb: 0.01 - 0.05%, V: 0.001 - 0.05%, Ti ≤ 0.04%, Mo ≤ 0.15%, Al ≤ 0.04%, B ≤ 0.0005%, the balance being Fe, where CE Pcm ≤ 0.15, the levels of non-metallic inclusions of types A, B, C, D, and DS in the metallographic structure of the steel plate are all not greater than grade 1.0, the banded structure is not greater than grade 1.5, and the grain size is grade 9 or above.

3. The manufacturing method for medium and small diameter longitudinally submerged arc welded pipes according to claim 1, It is characterized in that The edge milling process uses different edge milling machine tool holder shim specifications to control the root face height after milling, and different tool holder specifications are selected to control the upper and lower bevel angles after edge milling of the plate. The upper bevel angle range is 40° - 50°, the lower bevel angle range is 30° - 40°, and the maximum processing thickness is 20mm.

4. The manufacturing method for medium and small diameter longitudinally submerged arc welded pipes according to claim 1, It is characterized in that The welding frequency of the pre-welding process is 200kHz, the welding speed is 10 - 15m / min, and the extrusion amount is 2 - 4mm.

5. The manufacturing method for medium and small diameter longitudinally submerged arc welded pipes according to claim 1, It is characterized in that During welding in the welding process, external welding is required first and then internal welding, and the welding speed is V = 1.2 - 1.4m / min; among them, external welding is carried out by double-wire submerged arc automatic welding. The first wire uses DC reverse connection, and the welding process parameters are: current I = 750 - 960A, voltage U = 31 - 35V. The second wire is AC, and the welding process parameters are: current I = 580 - 700A, voltage U = 34 - 36V; internal welding is also carried out by double-wire submerged arc automatic welding. The first wire uses DC reverse connection, and the welding process parameters are: current I = 550 - 660A, voltage U = 31 - 34V; the second wire is AC, current I = 400 - 500A, voltage U = 33 - 36V.

6. The manufacturing method for medium and small diameter longitudinally submerged arc welded pipes according to claim 1, It is characterized in that The full pipe body expanding uses an expanding module and a segmented expanding method. The expanding length of each segment is 2.5m, each forward step length is 0.8 - 1.0m, and the pipe body expanding rate is 0.7% - 0.9%.

7. The manufacturing method for medium and small diameter longitudinally submerged arc welded pipes according to claim 1, It is characterized in that The overall tube heat treatment includes two heat treatments. The temperature of the first heat treatment is controlled between 350°C and 400°C, and the heat preservation time is between 60 min and 70 min. After the first heat treatment, the steel pipe is placed in another heating furnace for the second heat treatment, with the temperature controlled between 200°C and 250°C and the heat preservation time between 20 min and 30 min. After the heat treatment is completed, the steel pipe is taken out and air-cooled to room temperature.

8. A small and medium-sized diameter longitudinally submerged arc welded pipe manufactured by the manufacturing method according to any one of claims 1-7, characterized in that the diameter deviation of the pipe end of the small and medium-sized diameter longitudinally submerged arc welded pipe is -0.1% D to +0.2% D, and the out-of-roundness of the pipe end < 0.7% D; the diameter deviation of the pipe body is -0.15% D to +0.2% D, and the out-of-roundness of the pipe body < 1.0% D; the overall straightness deviation does not exceed 0.06% of the length of the steel pipe.