X80 thick-wall high-strain straight seam steel pipe, manufacturing method and application of X80 thick-wall high-strain straight seam steel pipe

Abstract

The invention belongs to the technical field of pipeline steel pipes for oil and gas transmission pipelines, and particularly relates to an X80 thick-wall high-strain straight seam steel pipe and a manufacturing method and application thereof. The pipeline steel plate comprises the following chemical components in percentage by mass: 0.03%-0.07% of C, 1.60%-1.85% of Mn, 0.10%-0.30% of Si, less than or equal to 0.010% of P, less than or equal to 0.004% of S, 0.15%-0.30% of Cr, 0.10%-0.30% of Mo, 0.10%-0.30% of Ni, 0.03%-0.08% of Nb, 0.01%-0.05% of V, 0.008%-0.025% of Ti, 0.10%-0.30% of Cu, 0.0002%-0.001% of B, 0.003%-0.01% of N and the balance of Fe and inevitable impurity elements, the sum of Nb, V and Ti is less than or equal to 0.12%, and the cold crack sensitivity coefficient is 0.16-0.20. The steel pipe is prepared through the steps of preparing steel-making materials according to the proportion, carrying out mixed smelting on the steel-making materials, carrying out Ca treatment, carrying out external refining, carrying out vacuum degassing, carrying out continuous casting to form a thick plate blank and manufacturing the steel pipe. According to the method, the plastic deformation capacity of the pipeline steel and the steel pipe is fully utilized, so that laying of oil and gas conveying pipelines in complex working condition areas such as earthquake fault zones, landslide zones and mine goaf areas becomes possible.

Description

Technical Field

[0001] The present invention belongs to the technical field of pipeline steel pipes for oil and gas transmission pipelines, and specifically relates to an X80 thick-walled high-strain straight seam steel pipe, a manufacturing method and applications thereof. Background Art

[0002] With the increasing demand for oil and natural gas in production and daily life, the use of high-strength, large-diameter, high-pressure, long-distance pipelines has become the most economical and reasonable option for pipeline construction. These pipelines inevitably pass through complex environments such as earthquake fault zones, landslide zones, mine goafs, and subsidence zones. During service, pipelines are susceptible to high strains caused by external conditions, which can lead to buckling, instability, and ductile fractures, resulting in catastrophic accidents.

[0003] Strain-based design is a new pipeline design approach developed to address the increasingly harsh construction and service environments of pipelines. This approach fully utilizes the plastic deformation capacity of pipeline steel, allowing for deformation in harsh geological environments such as earthquake zones, goaf areas, and areas with discontinuous permafrost, where ground motion can cause the pipeline to deform. This approach addresses challenges inherent in stress-based pipeline design in specific areas, such as the seabed, polar permafrost, areas of earthquake-induced sand liquefaction and landslides, active faults, and goaf areas, while also ensuring the stability and safe and reliable operation of the pipeline structure. To ensure the safe operation of pipeline steel under strain conditions and adapt to displacement-controlled loads, strain-based design and the use of high-strain pipeline steel with enhanced strain capacity provide an effective solution. In recent years, domestically produced X70HD / X80HD high-strain pipeline steel pipe has been widely used in domestic pipeline projects, fundamentally addressing key technical challenges in pipeline construction and safe operation in complex working conditions such as earthquake fault zones, landslide zones, mine goafs, and subsidence zones in major projects such as the China-Myanmar Pipeline and the West-East Gas Pipeline.

[0004] Strain-based design methods can fully utilize the plastic deformation capacity of high-grade steel pipelines, making it possible to lay oil and gas pipelines through complex operating conditions such as earthquake fault zones, landslide zones, mine goafs, and subsidence zones. To improve gas transmission efficiency, reduce steel usage and the associated logistics and construction costs, and ensure efficient and safe oil and gas transportation, the steel grade of steel pipe used in strain-based areas has been upgraded to X80 and above, with diameters exceeding 1219 mm and wall thicknesses exceeding 30 mm. The West-East Gas Pipeline IV, which crosses active fault zones, also employs strain-based pipeline design. The design utilizes X80M φ1219×33mm high-strain longitudinal submerged arc welded steel pipe, the largest steel grade, diameter, and wall thickness currently designed in China. This presents new challenges for pipeline design, materials, and construction. Therefore, research on key manufacturing technologies and product development for X80 steel grade, wall thicknesses exceeding 30 mm, are urgently needed for high-strain pipeline steel pipe. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention provides an X80 thick-walled high-strain straight seam steel pipe, a manufacturing method and applications thereof.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] An X80 thick-walled high-strain straight seam steel pipe uses pipeline steel plates whose chemical composition, calculated by mass percentage, is as follows:

[0008] C: 0.03%~0.07%, Mn: 1.60~1.85%, Si: 0.10%~0.30%, P: ≤0.010%, S: ≤0.004%, Cr: 0.15%~0.30%, Mo: 0.10%~0.30%, Ni: 0.10%~0.30%, Nb: 0.03%~0.08%, V: 0.01%~0.05%, Ti: 0.008%~0.025%, Cu: 0.10%~0.30%, B: 0.0002%~0.001%, N: 0.003%~0.01%, the balance is Fe and unavoidable impurity elements, Nb+V+Ti≤0.12%, cold crack sensitivity coefficient 0.16~0.20.

[0009] The pipeline steel plate adopts a "ferrite + bainite" dual-phase structure design, with a ferrite content of 30% to 60%, a grain size of more than 10 levels, a grain size of less than 10 μm, and a banded structure of less than 2 levels.

[0010] The transverse yield strength control range of the steel plate is 480MPa~600MPa, the tensile strength control range is 640MPa~760MPa, the yield strength ratio is ≤0.88, and the elongation is ≥28%; the longitudinal yield strength control range is 430MPa~550MPa, the tensile strength control range is 630MPa~765MPa, the yield strength ratio is ≤0.80, the elongation is ≥28%, the uniform elongation is ≥10%, and the tensile curve is "vault type".

[0011] A method for manufacturing an X80 thick-walled high-strain straight seam steel pipe comprises the following steps:

[0012] Step 1: Prepare steelmaking materials according to the proportion of pipeline steel plates;

[0013] Step 2: mixing the steelmaking materials prepared in step 1 and then melting them;

[0014] Step 3: Ca treatment;

[0015] Step 4: refining outside the furnace;

[0016] Step 5: vacuum degassing;

[0017] Step 6: Continuously casting into thick slabs;

[0018] Step 7: Steel pipe manufacturing

[0019] Steel pipe manufacturing is completed through forming, welding and pipe expansion processes.

[0020] The steel pipe is formed in step seven by using the JCO forming process, double-sided submerged arc welding of "four wires for internal welding + four wires for external welding" and mechanical cold expansion of the entire steel pipe body.

[0021] The transverse yield strength of the steel pipe body is 575MPa~675MPa, the tensile strength is 685MPa~765MPa, and the yield strength ratio is ≤0.90; the longitudinal yield strength of the pipe body is 530MPa~610MPa, the tensile strength is 675MPa~765MPa, the yield strength ratio is ≤0.85, and the uniform elongation is ≥7%; at -60°C, the single value of the impact energy of the pipe body is ≥285J, the single value of the impact energy of the weld is ≥120J, and the impact energy of the heat-affected zone is ≥100J; at -20°C, the DWTT shear area of ​​the pipe body is ≥85%.

[0022] The steel pipe forming process adopts small step multi-pass pressing, with a step length of ≤150mm and a pressing number of ≥21 times. The steel pipe is pressed to a preset curvature by adjusting the pressing amount; the opening of the steel pipe after forming is controlled at 130mm~180mm, the difference between the two ends is ≤30mm, the axial misalignment of the pipe end is ≤6mm, and the ovality of the steel pipe after pre-welding is controlled within 15mm.

[0023] The welding adopts an X-shaped welding groove design, the groove design angle of the internal welding and the external welding is 60°, the welding wire adopts a welding material matching method of H08C welding wire and high-alkalinity CHF102GX flux; the internal welding four-wire process parameters are: the first wire current I=1120~1180A, voltage 30~33V, the second wire current I=820~880A, voltage 34~37V, the third wire current I=670~730A, voltage 37~40V, the fourth wire current I=580~64 0A, voltage 39~42V, welding speed V=110~140cm / min; external welding four-wire process parameters are: first wire current I=1120~1180A, voltage 30~33V, second wire current I=820~880A, voltage 34~37V, third wire current I=720~780A, voltage 38~40V, fourth wire current I=620~680A, voltage U=39~42V; welding speed V=120~150cm / min.

[0024] The expansion rate of the entire steel pipe is 0.6% to 1.0%.

[0025] A manufacturing method for an X80 thick-walled high-strain straight seam steel pipe is applied to the manufacture of X80 steel grade high-strain pipeline steel pipes with a wall thickness of 30 mm or more for strain-based pipeline design in areas with complex and harsh geographical environments such as earthquake fault zones, landslide zones, and subsidence zones.

[0026] Beneficial effects:

[0027] 1. This invention utilizes a low-carbon, high-manganese alloy as its foundation, adding complex microalloying elements such as Nb, Cr, Ni, Mo, Ti, and Cu to create an alloy system. This design controls the nitrogen content and strictly controls the contents of harmful elements such as S, P, O, and H. Furthermore, through clean steel metallurgy, ultrafine grain control technology, and a rational TMCP production process, this achieves a balanced balance of strength, toughness, plasticity, and weldability for X80 thick-walled pipeline steel. Furthermore, a "ferrite + bainite" dual-phase microstructure is employed, where the soft ferrite phase ensures sufficient plasticity for the pipeline steel, while the hard bainite phase ensures the necessary strength.

[0028] 2. This invention fully considers the impact of work hardening on sheet strength, uniform elongation, and other mechanical properties during the pipemaking process, optimizing the control ranges for transverse and longitudinal performance indicators of the steel plate. By optimizing the process parameters for forming, welding, and expanding the steel pipe, the pipe body not only meets mechanical properties such as transverse tensile strength, Charpy impact toughness, and DWTT, but also exhibits excellent longitudinal mechanical properties. The strain curves are all "vault-shaped," and the welded joints exhibit high strength and excellent, stable low-temperature toughness, possessing the essential characteristics of high-strain line pipe.

[0029] 3. The main mechanical properties of the X80 thick-walled high-strain straight seam steel pipe involved in the present invention are: transverse yield strength R t0.5 The tensile strength is 640MPa~675MPa, and the tensile strength R m 710MPa~765MPa, yield strength ratio R t0.5 / R m ≤0.90, elongation after break A f ≥24%; Transverse tensile strength of weld R m ≥682MPa; before aging: longitudinal yield strength of pipe body R t0.5 525MPa~610MPa, tensile strength R m 685MPa~765MPa, yield strength ratio R t0.5 / R m ≤0.81, elongation after fracture A f ≥54%, uniform elongation UEL ≥7.6%, stress ratio R t1.5 / R t0.5 ≥1.154, stress ratio R t2.0 / R t1.0≥1.055; after aging: longitudinal yield strength R t0.5 560MPa~630MPa, tensile strength R m 690MPa~765MPa, yield strength ratio R t0.5 / R m ≤0.84, elongation after fracture A f ≥53%, uniform elongation UEL ≥7.1%, stress ratio R t1.5 / R t0.5 ≥1.106, stress ratio R t2.0 / R t1.0 ≥1.052. At -60℃, the transverse impact energy value of the pipe body is ≥289J, the longitudinal impact energy value of the pipe body is ≥326J, the weld impact energy value is ≥153J, and the heat-affected zone impact energy value is ≥102J. At -10℃, the transverse DWTT shear area value of the pipe body is ≥85%, and the longitudinal DWTT shear area value of the pipe body is ≥98%. The actual hardness of the pipe body is 206HV 10 ~221HV 10 ;The actual hardness of the welded joint is 212HV 10 ~254HV 10 All performance characteristics of the steel pipe meet the relevant technical index requirements for X80M high-strain pipeline steel pipes designed based on strain for the West-East Gas Pipeline IV crossing active fault zones, and meet the demand for steel pipes in areas with strain-based pipeline design, such as earthquake fault zones, subsidence zones, permafrost zones, and landslide zones.

[0030] 4. The present invention relates to the X80 high-strain pipeline steel pipe with the largest steel grade, diameter, and wall thickness currently designed in China. It overcomes the new challenges posed by X80 thick-walled high-strain pipeline steel and steel pipes in design, materials, and construction, fills a domestic gap, effectively reduces pipeline construction costs, and generates huge social and economic benefits.

[0031] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the following is a detailed description of the preferred embodiments of the present invention with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0033] Figure 1 Flowchart of the present invention.

[0034] Figure 2 This is the microstructure diagram of the X80M high strain pipeline steel plate of the present invention.

[0035] Figure 3 FIG. 1 is a longitudinal tensile curve diagram of the X80M high strain pipeline steel pipe before aging in the present invention.

[0036] Figure 4 FIG. 1 is a longitudinal tensile curve diagram of the X80M high strain pipeline steel pipe after aging according to the present invention. DETAILED DESCRIPTION

[0037] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0038] Example 1:

[0039] according to Figure 1-Figure 4 The chemical composition of the pipeline steel plate used in the X80 thick-walled high-strain straight seam steel pipe shown in the figure is as follows:

[0040] C: 0.03%~0.07%, Mn: 1.60~1.85%, Si: 0.10%~0.30%, P: ≤0.010%, S: ≤0.004%, Cr: 0.15%~0.30%, Mo: 0.10%~0.30%, Ni: 0.10%~0.30%, Nb: 0.03%~0.08%, V: 0.01%~0.05%, Ti: 0.008%~0.025%, Cu: 0.10%~0.30%, B: 0.0002%~0.001%, N: 0.003%~0.01%, the balance is Fe and unavoidable impurity elements, Nb+V+Ti≤0.12%, cold crack sensitivity coefficient 0.16~0.20.

[0041] The basis for the chemical composition design of the pipeline steel plate for the X80 high-strain thick-walled straight seam steel pipe involved in the present invention is described as follows:

[0042] Carbon (C): Carbon is a key element in ensuring the strength of low-alloy pipeline steel. It significantly increases the strength of steel through solid solution strengthening and precipitation strengthening. However, increasing the C content negatively impacts the ductility, toughness, and weldability of pipeline steel. Reducing the C content not only helps improve the toughness of the steel, but also improves its weldability. When the carbon content is below 0.03%, the strength is low, and the precipitation strengthening effects of elements like Nb cannot be fully realized. When the C content is below 0.11%, the pipeline steel exhibits good weldability. For pipeline steels requiring even higher toughness, ultra-low C content designs with less than 0.07% C are often used. In the present invention, the C content is designed to be within the range of 0.03% to 0.07%.

[0043] Mn: Manganese is a solid solution strengthening element, which delays the transformation of austenite to ferrite in the steel, and is beneficial to refining ferrite and improving strength and toughness. When the manganese content is lower than 1.50%, the above effect is not significant, resulting in low strength and toughness. Increasing the Mn content increases the hardenability of the steel. When the content increases to a certain level, it will lead to a decrease in welding performance, especially a serious deterioration in the toughness of the weld heat affected zone. In addition, an excessively high Mn content can easily cause severe central segregation in hot-rolled thick-walled steel plates, and increase the anisotropy of the steel plate properties. In order to ensure a balance between strength and low-temperature toughness as well as higher plate quality, the present invention designs the Mn content to be within the range of 1.60% to 1.85%.

[0044] Si: Silicon is an essential element for steelmaking deoxidation and also has a certain solid solution strengthening effect. However, if excessive Si is added, the toughness of the base metal and its weld heat-affected zone will be significantly reduced, and field weldability will deteriorate. The present invention designs the Si content to be within the range of 0.10% to 0.30%.

[0045] P, S: Impurity elements in steel, such as phosphorus and sulfur, can seriously impair the low-temperature toughness of the steel and the weld zone. Therefore, the present invention limits the P and S contents to P≤0.010% and S≤0.004%, respectively.

[0046] Cr, Mo: Chromium and molybdenum are elements that improve the hardenability of steel. They can inhibit the formation of polygonal ferrite and pearlite, increase the stability of austenite, promote the transformation of low-temperature microstructure bainite, and improve the strength of steel. In addition, the coexistence of Mo and Nb effectively inhibits the recrystallization of austenite during controlled rolling, refines the austenite structure, and has the effect of improving low-temperature toughness. However, too high a Cr content will affect the toughness of the steel and cause temper brittleness. In order to achieve a reasonable combination of strength, plasticity and toughness, the present invention designs the Cr content to be within the range of 0.15% to 0.30%, and the Mo content to be within the range of 0.10% to 0.30%.

[0047] Ni, Cu: Nickel and copper can increase steel strength through solid solution strengthening. Adding Ni primarily improves the hot brittleness often caused by Cu in steel and also benefits low-temperature toughness. Cu also improves corrosion resistance. Adding Ni and Cu to thicker-gauge pipeline steel can also compensate for the strength loss associated with increased thickness. The present invention aims to maintain a Ni content within the range of 0.10% to 0.30% and a Cu content within the range of 0.10% to 0.30%. The effects are even better when Ni and Cu are added in equal proportions.

[0048] Nb: Niobium is one of the most important microalloying elements in pipeline steel, significantly contributing to grain refinement. The solute drag effect of trace amounts of niobium and the pinning effect of Nb (C, N) on austenite grain boundaries inhibit recrystallization of deformed austenite. Through controlled rolling and controlled cooling, ferrite grains can be refined, resulting in high strength and toughness. However, excessive niobium levels can promote surface cracking in continuous casting slabs. The present invention specifies a Nb content within the range of 0.03% to 0.08%.

[0049] Vanadium combines with carbon or nitrogen in steel to produce a strong precipitation strengthening effect, which helps increase steel strength. However, adding less than 0.01% vanadium does not achieve these benefits, and adding more than 0.05% may reduce field weldability. The present invention contemplates a vanadium content within the range of 0.01% to 0.05%.

[0050] Titanium (Ti): Titanium is used to bind nitrogen in steel. Under appropriate conditions, titanium and nitrogen form titanium nitride, which prevents grain growth during heating, rolling, and welding. This helps increase the solid solubility of Nb and V in austenite, improving the impact toughness of the base metal and the weld heat-affected zone. Below 0.005%, titanium has a poor nitrogen-binding effect. Above 0.03%, the nitrogen-binding effect reaches saturation, and excess titanium degrades the steel's low-temperature toughness. The present invention contemplates a Ti content within the range of 0.008% to 0.025%.

[0051] Boron (B): Boron improves hardenability and facilitates the formation of a continuous cooling transformation structure. Furthermore, B enhances the hardenability-enhancing effect of Mo and, in combination with Nb, synergistically increases hardenability. Therefore, it is added as needed. However, a content of less than 0.0002% is insufficient to achieve this effect, and additions exceeding 0.001% can cause slab cracking. Therefore, the amount of boron added must be limited to a very narrow range. The present invention contemplates a B content within the range of 0.0002% to 0.001%.

[0052] N: Nitrogen can be partially used in steel to strengthen solid solution and improve hardenability. It also combines with other elements in steel to produce precipitation hardening. The present invention aims to use N in an amount within the range of 0.003% to 0.01%.

[0053] Nb, V, Ti: Nb, V, and Ti are the most important microalloying elements for pipeline steel. Adding trace amounts of Nb, V, and Ti to steel can ensure that, when the carbon equivalent is low, the steel refines the grains through the dispersion and precipitation of carbon and nitride particles and the solid solution of Nb, V, and Ti, greatly improving the strength and toughness of the steel, especially its low-temperature toughness, and giving the steel good weldability and applicability. When the sum of the weight percentages of Nb, V, and Ti is ≤0.12%, the refining effect on high-temperature austenite grains is the strongest, not only achieving excellent toughness, but also enabling high-energy-wire welding of more than 30 kJ / cm. The present invention designs the sum of the weight percentages of the three elements Nb, V, and Ti to be no higher than 0.12%, allowing for fine-tuning of the content of individual elements.

[0054] Cold Crack Sensitivity Index (Pcm): The Pcm value reflects, to a certain extent, the difficulty of welding a material; the smaller the value, the easier the material is to weld. When the Pcm value does not exceed 0.22%, the pipeline steel exhibits excellent weldability, with minimal cold crack sensitivity and minimal hot crack sensitivity. The present invention aims for a Pcm value within the range of 0.16% to 0.20%.

[0055] According to the above-mentioned pipeline steel plate composition design and rolling process, X80M high-strain thick-walled straight seam steel pipe steel plate is manufactured. Compared with the existing ordinary X80M pipeline steel plate, the X80M high-strain thick-walled straight seam steel pipe steel plate has the advantages of lower yield strength ratio, higher uniform elongation, better strength and toughness matching, small performance difference between the same plates, high thickness direction uniformity, and low banding level. It is suitable for the production of large-diameter straight seam submerged arc welded pipes for use in strain-based design areas.

[0056] Furthermore, the pipeline steel plate adopts a dual-phase microstructure of "ferrite + bainite," with a ferrite content of 30% to 60%, a grain size above Grade 10, a grain size below 10μm, and a banded structure below Grade 2. The plate's transverse yield strength is controlled within a range of 480MPa to 600MPa, its tensile strength is controlled within a range of 640MPa to 760MPa, its yield strength ratio is ≤0.88, and its elongation is ≥28%. The longitudinal yield strength is controlled within a range of 430MPa to 550MPa, its tensile strength is controlled within a range of 630MPa to 765MPa, its yield strength ratio is ≤0.80, its elongation is ≥28%, its uniform elongation is ≥10%, and its tensile curve is a "vault-shaped" structure. The plate's microstructure and mechanical properties meet the target design requirements.

[0057] Example 2:

[0058] according to Figure 1-Figure 4 The manufacturing method of the X80 thick-walled high-strain straight seam steel pipe shown in the figure comprises the following steps:

[0059] Step 1: Prepare steelmaking materials according to the proportion of pipeline steel plates;

[0060] Step 2: mixing the steelmaking materials prepared in step 1 and then melting them;

[0061] Step 3: Ca treatment;

[0062] Step 4: refining outside the furnace;

[0063] Step 5: vacuum degassing;

[0064] Step 6: Continuously casting into thick slabs;

[0065] Step 7: Steel pipe manufacturing

[0066] Steel pipe manufacturing is completed through forming, welding and pipe expansion processes.

[0067] Furthermore, the steel pipe formed in step seven utilizes the JCO forming process, double-sided submerged arc welding using four internal welding wires and four external welding wires, and mechanical cold expansion of the entire pipe body. The JCO process is used to form the steel plate used for the X80M high-strain, thick-walled straight seam steel pipe produced above. After pre-bending, the straight edge width of the plate is less than the wall thickness of the steel plate. The steel pipe forming process utilizes multiple pressing passes with small step lengths (≤150mm) and ≥21 pressing passes. The desired curvature of the steel pipe is achieved by adjusting the pressing reduction. After forming, the opening of the steel pipe is controlled between 130mm and 180mm, with a difference of ≤30mm between the two ends and an axial misalignment of ≤6mm between the pipe ends. The ovality of the pre-welded steel pipe is controlled within 15mm.

[0068] An X-shaped welding groove design is adopted, and the groove design angles of internal and external welds are both 60°. After welding process tests and welding process assessments, the welding material matching method of H08C welding wire with high strength and high toughness and high basicity SJ102G inert sintered flux was optimized, and the double-sided multi-wire submerged arc welding process parameters of "four wires for internal welding + four wires for external welding" were optimized and designed. The welded joint has a good macromorphology, the height of the internal and external welds, and the overlap of the internal and external welds are effectively controlled, the welded joint has high strength, and the weld and heat-affected zone positions have stable and excellent low-temperature impact toughness.

[0069] The specific welding process parameters are: the internal welding four-wire process parameters are: the first wire current I = 1120 ~ 1180A, the voltage 30 ~ 33V, the second wire current I = 820 ~ 880A, the voltage 34 ~ 37V, the third wire current I = 670 ~ 730A, the voltage 37 ~ 40V, the fourth wire current I = 580 ~ 640A, the voltage 39 ~ 42V, and the welding speed V = 110 ~ 140cm / min; the external welding four-wire process parameters are: the first wire current I = 1120 ~ 1180A, the voltage 30 ~ 33V, the second wire current I = 820 ~ 880A, the voltage 34 ~ 37V, the third wire current I = 720 ~ 780A, the voltage 38 ~ 40V, the fourth wire current I = 620 ~ 680A, the voltage U = 39 ~ 42V; the welding speed V = 120 ~ 150cm / min.

[0070] The mechanical cold expansion process is used to expand the entire steel pipe. Taking into account the influence of the expansion rate on the transverse and longitudinal mechanical properties of the pipe body and the influence of the expansion rate on the ovality of the steel pipe, the expansion rate control range of the entire steel pipe body is optimized to be 0.6% to 1.0%, eliminating the residual stress of the steel pipe forming and welding, and effectively improving the dimensional accuracy of the steel pipe.

[0071] The X80 thick-walled, high-strain straight seam steel pipe manufactured according to the above process has the characteristics of low yield ratio, high uniform elongation, high and low-temperature toughness and stable performance. The main mechanical properties are as follows: the transverse yield strength of the pipe body is 575MPa~675MPa, the tensile strength is 685MPa~765MPa, and the yield ratio is ≤0.90; the longitudinal yield strength of the pipe body is 530MPa~610MPa, the tensile strength is 675MPa~765MPa, the yield ratio is ≤0.85, and the uniform elongation is ≥7%; at -60℃, the single value of the impact energy of the pipe body is ≥285J, the single value of the impact energy of the weld is ≥120J, and the impact energy of the heat-affected zone is ≥100J; at -20℃, the DWTT shear area of ​​the pipe body is ≥85%.

[0072] The performance of the steel pipe meets the performance index requirements of steel pipes used in pipeline construction in strain-based design areas. The steel pipe can be used in areas with complex and harsh geographical environments such as earthquake fault zones, landslide zones, and subsidence zones, and must also meet on-site welding requirements.

[0073] Example 3:

[0074] The present invention will be further described in detail below in conjunction with the manufacture of X80Mφ1219×33mm JCOE straight seam submerged arc welded steel pipe for regional natural gas pipeline engineering based on strain design.

[0075] (1) Steel grade X80M, 33mm thick high strain pipeline steel plate, its chemical composition (mass percentage) is: C: 0.03% ~ 0.07%, Mn: 1.60% ~ 1.85%, Si: 0.10% ~ 0.30%, P: ≤ 0.010%, S: ≤ 0.004%, Cr: 0.15% ~ 0.30%, Mo: 0.10% ~ 0.30%, Ni: 0.10% ~ 0 0.30%, Nb: 0.03%-0.08%, V: 0.01%-0.05%, Ti: 0.008%-0.025%, Cu: 0.10%-0.30%, B: 0.0002%-0.001%, N: 0.003%-0.01%, the balance being Fe and unavoidable impurities. Nb+V+Ti≤0.12%, cold crack sensitivity coefficient 0.16-0.20. The chemical compositions of the pipeline steel plates from the four examples and four comparative examples are shown in Table 1.

[0076] Table 1 Chemical composition (wt.%) of pipeline steel plates of the embodiments of the present invention and comparative examples

[0077]

[0078] (2) According to the above pipeline steel plate composition design, a controlled rolling and controlled cooling process was used to complete the rolling of steel plates for X80M high-strain thick-walled straight seam steel pipe. The main process parameters for controlled rolling and controlled cooling of pipeline steel plates for the examples of the present invention and the comparative example are shown in Table 2. The transverse mechanical properties of the steel plates of the examples of the present invention are shown in Table 3. The longitudinal mechanical properties of the steel plates of the examples of the present invention are shown in Table 4.

[0079] Table 2 Main process parameters of controlled rolling and controlled cooling of pipeline steel plates in the embodiments of the present invention and the comparative examples

[0080]

[0081]

[0082] Table 3 Transverse tensile properties of pipeline steel plates in the embodiments of the present invention and the comparative examples

[0083] Example / Comparative Example <![CDATA[Yield strength R t0.5 (MPa)]]> <![CDATA[Tensile strength R m (MPa)]]> Elongation A(%) <![CDATA[Yield ratio R t0.5 / R m <!-- 7 -->]]> Example 1 480 692 43.5 0.69 Example 2 576 760 49.5 0.76 Example 3 600 760 37.0 0.79 Example 4 508 640 38.5 0.79 Comparative Example 1 468 638 50.7 0.73 Comparative Example 2 605 784 51.0 0.77 Comparative Example 3 477 701 44.5 0.68 Comparative Example 4 550 772 54.0 0.71

[0084] Table 4 Longitudinal tensile properties of pipeline steel plates in the embodiments of the present invention and the comparative examples

[0085]

[0086] (3) The JCO pipe making process is used to pre-bend the steel plates for the X80M high-strain thick-walled straight seam steel pipes produced above and form the steel pipes. After pre-bending, the straight edge width of the plate edge is less than 30 mm, the step length is 110 mm, and the pressing times are 22 to 26 times. The steel pipe is pressed to the ideal curvature by adjusting the pressing amount. After forming, the opening of the steel pipe is controlled at 130 mm to 150 mm, the difference between the two ends is ≤20 mm, the axial misalignment of the pipe end is ≤3 mm, and the ovality of the steel pipe after pre-welding is controlled within 10 mm. In actual production, appropriate adjustments can be made based on the actual mechanical properties of the steel plate and the specific conditions of the steel pipe forming quality.

[0087] (4) The welding groove design adopts X-type welding groove, and the groove design angle of internal welding and external welding is 60°. The welding material matching method of high strength and high toughness H08C welding wire and high basicity SJ102G inert sintered flux is selected. The steel pipe welding adopts the double-sided multi-wire submerged arc welding process of "four wires for internal welding + four wires for external welding". The specific welding process parameters are: the internal welding four-wire process parameters are: the first wire current I = 1120 ~ 1160A, the voltage 31 ~ 32V, the second wire current I = 820 ~ 860A, the voltage 35 ~ 36V, the third wire current I = 680 ~ 720A, the voltage 38 ~ 39V, the fourth wire current I = 580 ~ 620A, the voltage 40 ~ 41V, and the welding speed V = 110 ~ 130cm / min; the external welding four-wire process parameters are: the first wire current I = 1120 ~ 1160A, the voltage 31 ~ 32V, the second wire current I = 830 ~ 870A, the voltage 35 ~ 36V, the third wire current I = 730 ~ 770A, the voltage 38 ~ 40V, the fourth wire current I = 630 ~ 670A, the voltage U = 40 ~ 41V; the welding speed V = 120 ~ 140cm / min.

[0088] (5) The mechanical cold expansion process is used to expand the entire steel pipe. Taking into account the influence of the expansion rate on the transverse and longitudinal mechanical properties of the pipe body and the influence of the expansion rate on the ovality of the steel pipe, an expansion rate of 0.6% to 1.0% is used to complete the expansion of the entire steel pipe body, eliminate the residual stress of the steel pipe forming and welding, and effectively improve the dimensional accuracy of the steel pipe.

[0089] (6) The X80 thick-walled, high-strain straight seam steel pipe manufactured using the above process has the characteristics of low yield strength ratio, high uniform elongation, high low-temperature toughness, and stable performance. The transverse mechanical properties of the steel pipes of the present invention and the comparative example are shown in Table 5. The longitudinal tensile properties of the steel pipes of the present invention and the comparative example are shown in Table 6.

[0090] Table 5 Transverse mechanical properties of pipeline steel pipes in the embodiments of the present invention and the comparative examples

[0091]

[0092] Table 6 Longitudinal tensile properties of pipeline steel pipes in the embodiments of the present invention and the comparative examples

[0093]

[0094]

[0095] The above examples and comparative examples demonstrate that the X80 thick-walled, high-strain straight seam steel pipe manufactured using the steel plate with the aforementioned composition, microstructure, controlled rolling and controlled cooling process, and properties exhibits low yield ratio, high uniform elongation, high low-temperature toughness, and stable performance. Key performance requirements meet the following: transverse yield strength of 575MPa-675MPa, tensile strength of 685MPa-765MPa, and yield ratio ≤0.90; longitudinal yield strength of 530MPa-610MPa, tensile strength of 675MPa-765MPa, yield ratio ≤0.85, and uniform elongation ≥7%; single impact energy of ≥285J at -60°C, single impact energy of ≥120J at the weld, and impact energy of ≥100J at the heat-affected zone; and DWTT shear area of ​​≥85% at -20°C. The performance of the steel pipe meets the performance index requirements of steel pipes used in pipeline construction in areas based on strain design. The manufacturing process is suitable for the production of X80 thick-walled high-strain straight seam submerged arc welded pipes used in areas based on strain design. The steel pipe can be used in areas with complex and harsh geographical environments such as earthquake fault zones, landslide zones, and subsidence zones.

[0096] In the absence of conflicts, those skilled in the art may combine the relevant technical features in the above examples according to actual circumstances to achieve corresponding technical effects. Specific descriptions of various combinations are omitted here.

[0097] It should be noted that all directional indications in the embodiments of the present invention (such as up, down, left, right, front, back, etc.) are only used to explain the relative position relationship, movement status, etc. between the various components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0098] In addition, the terms "first," "second," and so on, used in this disclosure are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, features specified as "first" or "second" may explicitly or implicitly include at least one of these features.

[0099] The above descriptions are merely preferred embodiments of the present invention. The present invention is not limited to these embodiments, but is intended to conform to the broadest scope consistent with the principles and novel features disclosed herein. Any simple modifications, equivalent variations, and modifications made to the above embodiments based on the technical essence of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. An X80 thick-walled high-strain straight seam steel pipe, characterized by: The chemical composition of the pipeline steel plate used is as follows in terms of mass percentage: C: 0.03%~0.07%, Mn: 1.60~1.85%, Si: 0.10%~0.30%, P: ≤0.010%, S: ≤0.004%, Cr: 0.15%~0.30%, Mo: 0.10%~0.30%, Ni: 0.10%~0.30%, Nb: 0.03%~0.08%, V: 0.01%~0.05%, Ti: 0.008%~0.025%, Cu: 0.10%~0.30%, B: 0.0002%~0.001%, N: 0.003%~0.01%, the balance is Fe and unavoidable impurity elements, Nb+V+Ti≤0.12%, cold crack sensitivity coefficient 0.16~0.

20.

2. The X80 thick-walled high-strain straight seam steel pipe according to claim 1, characterized in that: The pipeline steel plate adopts a "ferrite + bainite" dual-phase structure design, with a ferrite content of 30% to 60%, a grain size of more than 10 levels, a grain size of less than 10μm, and a banded structure of less than 2 levels.

3. The X80 thick-walled high-strain straight seam steel pipe according to claim 1, characterized in that: The transverse yield strength of the steel plate is controlled in the range of 480MPa to 600MPa, the tensile strength is controlled in the range of 640MPa to 760MPa, the yield strength ratio is ≤0.88, and the elongation is ≥28%; the longitudinal yield strength is controlled in the range of 430MPa to 550MPa, the tensile strength is controlled in the range of 630MPa to 765MPa, the yield strength ratio is ≤0.80, the elongation is ≥28%, the uniform elongation is ≥10%, and the tensile curve is "vault-shaped".

4. The method for manufacturing an X80 thick-walled, high-strain straight seam steel pipe according to any one of claims 1 to 3, wherein: The following steps are included: Step 1: Prepare steelmaking materials according to the proportion of pipeline steel plates; Step 2: mixing the steelmaking materials prepared in step 1 and then melting them; Step 3: Ca treatment; Step 4: refining outside the furnace; Step 5: vacuum degassing; Step 6: Continuously casting into thick slabs; Step 7: Steel pipe manufacturing Steel pipe manufacturing is completed through forming, welding and pipe expansion processes.

5. The method for manufacturing an X80 thick-walled high-strain straight seam steel pipe according to claim 4, characterized in that: The steel pipe is formed in step seven by using the JCO forming process, double-sided submerged arc welding of "four internal welding wires + four external welding wires" and mechanical cold expansion of the entire steel pipe body.

6. The method for manufacturing an X80 thick-walled, high-strain straight seam steel pipe according to claim 5, characterized in that: The transverse yield strength of the steel pipe body is 575MPa~675MPa, the tensile strength is 685MPa~765MPa, and the yield strength ratio is ≤0.90; the longitudinal yield strength of the pipe body is 530MPa~610MPa, the tensile strength is 675MPa~765MPa, the yield strength ratio is ≤0.85, and the uniform elongation is ≥7%; at -60°C, the single value of the impact energy of the pipe body is ≥285J, the single value of the impact energy of the weld is ≥120J, and the impact energy of the heat-affected zone is ≥100J; at -20°C, the DWTT shear area of ​​the pipe body is ≥85%.

7. The method for manufacturing an X80 thick-walled high-strain straight seam steel pipe according to claim 5, characterized in that: The steel pipe forming process adopts small-step multi-pass pressing, with a step length of ≤150 mm and a pressing number of ≥21 times. The steel pipe is pressed to a preset curvature by adjusting the pressing amount. After forming, the opening of the steel pipe is controlled at 130 mm to 180 mm, the difference between the two ends is ≤30 mm, the axial misalignment of the pipe end is ≤6 mm, and the ovality of the steel pipe after pre-welding is controlled within 15 mm.

8. The method for manufacturing an X80 thick-walled, high-strain straight seam steel pipe according to claim 5, wherein: The welding adopts an X-shaped welding groove design, the groove design angle of the internal welding and the external welding is 60°, and the welding wire adopts a welding material matching method of H08C welding wire and high basicity CHF102GX flux; The process parameters for internal welding of four wires are: current I = 1120 ~ 1180A, voltage 30 ~ 33V, current I = 820 ~ 880A, voltage 34 ~ 37V, current I = 670 ~ 730A, voltage 37 ~ 40V, current I = 580 ~ 640A, voltage 39 ~ 42V, welding speed V = 110 ~ 140cm / min; the process parameters for external welding of four wires are: current I = 1120 ~ 1180A, voltage 30 ~ 33V, current I = 820 ~ 880A, voltage 34 ~ 37V, current I = 720 ~ 780A, voltage 38 ~ 40V, current I = 620 ~ 680A, voltage U = 39 ~ 42V, welding speed V = 120 ~ 150cm / min.

9. The method for manufacturing an X80 thick-walled, high-strain straight seam steel pipe according to claim 5, wherein: The expansion rate of the entire steel pipe is 0.6% to 1.0%.

10. The method for manufacturing an X80 thick-walled high-strain straight seam steel pipe as described in any one of claims 4 to 9 is applied to the manufacture of X80 steel grade high-strain pipeline steel pipes with a wall thickness of 30 mm or more for strain-based pipeline design in areas with complex and harsh geographical environments such as earthquake fault zones, landslide zones, and subsidence zones.

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