CN116254475A

CN116254475A - Thick-wall straight-seam steel pipe for deep-sea pipeline and processing method thereof

Info

Publication number: CN116254475A
Application number: CN202111495974.8A
Authority: CN
Inventors: 牛爱军; 毕宗岳; 刘云; 牛辉; 韦奉; 黄晓辉; 赵红波; 席敏敏; 刘斌; 田磊; 郭克星; 刘海璋; 张鹏; 张君; 王磊
Original assignee: Cnpc National Petroleum And Natural Gas Pipe Engineering Technology Research Center Co ltd; China National Petroleum Corp; Baoji Petroleum Steel Pipe Co Ltd
Current assignee: Cnpc National Petroleum And Natural Gas Pipe Engineering Technology Research Center Co ltd; China National Petroleum Corp; Baoji Petroleum Steel Pipe Co Ltd
Priority date: 2021-12-09
Filing date: 2021-12-09
Publication date: 2023-06-13

Abstract

The invention relates to the technical field of marine oil and gas conveying pipelines, in particular to a thick-wall straight-seam steel pipe for a deep-sea pipeline and a processing method thereof. The thick-wall straight-seam steel pipe for the deep sea pipeline comprises the following chemical element components in percentage by weight: c:0.03 to 0.07 percent, mn:1.50 to 1.75 percent of Si:0.15 to 0.35 percent, P: less than or equal to 0.012 percent, S: less than or equal to 0.004%, nb:0.04 to 0.08 percent, V: less than or equal to 0.03 percent, ti:0.008% -0.03%, al:0.01 to 0.06 percent, N: less than or equal to 0.01 percent, cu: less than or equal to 0.30 percent, cr: less than or equal to 0.35 percent, mo:0.06 to 0.35 percent of Ni:0.08 to 0.40 percent, B: less than or equal to 0.0005 percent, and the balance of Fe and unavoidable impurities. The invention makes the pipe body transverse yield strength of the thick-wall straight-seam steel pipe be 485 MPa-605 MPa, the tensile strength be 570 MPa-760 MPa, the pipe body longitudinal yield strength be 485 MPa-585 MPa, the tensile strength be 570 MPa-700 MPa, the pipe body longitudinal yield ratio be less than or equal to 0.85, the uniform plastic deformation elongation be 8% -16%, and the use requirement of the deep sea pipeline be satisfied through the processes of the design of the pipeline steel plate components, the performance control, the forming, the welding, the whole pipe body expanding and the like of the thick-wall straight-seam steel pipe.

Description

Thick-wall straight-seam steel pipe for deep-sea pipeline and processing method thereof

Technical Field

The invention relates to the technical field of marine oil and gas conveying pipelines, in particular to a thick-wall straight-seam steel pipe for a deep-sea pipeline and a processing method thereof.

Background

The ocean has huge oil gas resources and has extremely wide development prospect. With the increase of international energy demands and the increase of land oil and gas resource exploration difficulty, the exploitation of offshore oil gradually progresses from offshore to deep sea, and the exploration and development of deep water and ultra-deep water oil and gas resources have become the key field of world oil and gas exploitation. The submarine pipeline has great difference from the land pipeline, and besides the working load born by the submarine pipeline in normal operation, the submarine pipeline needs to consider the tensile buckling stress born by the pipeline in the laying process and the residual stress after the laying is completed, and the influence of environmental load on the pipeline in the operation process, such as external water pressure, wind, sea wave, dark current, earthquake and the like, on the translation and vibration of the pipeline, so that the steel pipe is required to have excellent plastic deformation capability, namely lower yield ratio and larger elongation. Because the submarine pipeline is in a complex working environment, the submarine pipeline can be greatly deformed from laying to service so as to cause plastic deformation of the pipeline, serious and even local buckling, wrinkling and the like are generated, at the moment, the failure of the pipeline is not controlled by the stress all but is controlled by the strain or displacement partially or wholly, and the stress on the pipeline exceeds the yield strength.

With the gradual trend of energy development from land to sea and even deep sea, the laying depth and the conveying pressure of submarine pipelines are continuously improved, and the pipe for conveying marine oil and gas is tending to develop in the directions of high steel grade, large pipe diameter and large wall thickness. At present, a plurality of pipeline steel and steel pipe production enterprises in China master the production technology of high-strength and high-toughness pipeline steel, and the use grade of the pipeline steel of the submarine long-distance pipeline is also improved to the L485 steel grade. As the strength of the steel pipe material increases, the plasticity of the steel pipe material decreases, and the pipe diameter is increased continuously, so that the deformation control of the pipe body becomes a prominent problem under severe service conditions. The current pipeline steel materials are of typical low-pearlite or acicular ferrite structures, the properties of the pipe corresponding to the structure types have good strength and toughness matching, but the plasticity is insufficient, the uniform deformation elongation UEL is not more than 5%, the yield ratio is above 0.85, and some of the pipe types even reach 0.92. Pipeline steel produced by adopting the traditional manufacturing process cannot meet the use requirement of deep sea pipelines. Chinese patent 200880025476.3 describes a steel pipe for an oil well pipe for pipe expansion excellent in pipe expansion characteristics, a low yield ratio pipe, and a method for manufacturing the same without performing water cooling requiring a large-scale heat treatment equipment. Chinese patent 201010251848.3 mentions a manufacturing method of high-grade high-strain pipeline steel and steel pipes with strength grade reaching X70 and X80, wherein carbon content in the steel is 0.04% -0.08%, and X70 and X80 high-strain and low-strain aging sensitivity longitudinal submerged arc welded steel pipes with pipe diameter ranging from 760mm to 1219mm and wall thickness ranging from 16mm to 32mm are produced. The Chinese patent 20110160105. X and 201110160120.4 refer to steel for the steel grade pipelines of X70, X80 and above based on strain design and a manufacturing method thereof, wherein the carbon content in the steel is 0.06-0.10%, V, B and other elements are not added, and the total amount of Mo, cu, cr, ni is lower. Chinese patent 201110160120.4 mentions a steel X70 for pipeline based on strain design and a manufacturing method thereof, wherein carbon content in the steel is 0.04% -0.07% and Mn is 1.00% -1.60%. The product can meet the use requirement of a land petroleum pipeline, but can not meet the use requirement of a deep sea pipeline.

Disclosure of Invention

Aiming at the problems, the invention aims to provide the thick-wall straight-seam steel pipe for the deep sea pipeline and the processing method thereof, and the thick-wall straight-seam steel pipe has the advantages of low yield ratio, high uniform plastic deformation elongation, high deformation strengthening index and special longitudinal performance of a pipe body based on strain design, and the pipeline has the capability of resisting large deformation.

The technical scheme of the invention is as follows: the thick-wall straight-seam steel pipe for the deep-sea pipeline comprises the following chemical element components in percentage by weight: c:0.03 to 0.07 percent of Mn:1.50 to 1.75 percent of Si:0.15% -0.35%, P: less than or equal to 0.012 percent, S: less than or equal to 0.004 percent, nb:0.04% -0.08%, V: less than or equal to 0.03 percent of Ti:0.008 to 0.03 percent of Al:0.01% -0.06%, N: less than or equal to 0.01 percent, cu: less than or equal to 0.30 percent, cr: less than or equal to 0.35 percent, mo:0.06% -0.35%, ni:0.08 to 0.40 percent, B: less than or equal to 0.0005 percent, and the balance of Fe and unavoidable impurities.

Since the chemical composition of the pipeline steel is one of the key factors affecting the mechanical properties of the pipe steel pipe, the chemical composition of the steel is limited in order to obtain the pipeline steel with excellent comprehensive properties for the thick-wall straight joint steel pipe for the deep sea pipeline, which is because:

c: is a main element affecting the mechanical properties of low alloy high strength pipeline steel, has obvious effect on improving the strength of the steel through solid solution strengthening and precipitation strengthening, but improves the C content to have negative effect on the ductility, toughness and weldability of the steel. Reducing the C content on the one hand contributes to improving the toughness of the steel and on the other hand improves the weldability of the steel. When the carbon content is lower than 0.03%, the strength is lower, when the C content is lower than 0.11%, the pipeline steel can have good weldability, and for pipeline steel with higher toughness, the design of ultralow C content with C less than 0.07% is adopted. In the present invention, C is limited to a range of 0.03% to 0.07%.

Mn: manganese is a solid solution strengthening element, and delays transformation of austenite to ferrite in the steel, and is beneficial to refinement of ferrite and improvement of strength and toughness. When the manganese content is less than 1.50%, the above effect is insignificant, making the strength and toughness lower. When the manganese content is higher than 1.75%, severe band segregation and band pearlite structure are easily formed in the rolled super-thick steel plate. Mn is limited to a range of 1.50% to 1.75% in the present invention.

Si: silicon is an essential element for steelmaking deoxidization and has a certain solid solution strengthening effect, so that when it is added in an amount of 0.15% or more, the in-situ weldability is deteriorated when it is added in an amount exceeding 0.35%. In the present invention, si is limited to a range of 0.15% to 0.35%.

P, S: impurity elements in steel, such as phosphorus, sulfur, etc., can severely impair the low temperature toughness of the steel and the welded near-joint region. Therefore, the P, S content should be limited to 0.012% or less and 0.004% or less, respectively, in the present invention.

Nb: the solute dragging action of trace niobium and the pinning action of Nb (C, N) on austenite grain boundaries inhibit recrystallization of deformed austenite, and ferrite grains can be refined by combining TMCP, but excessive niobium promotes surface cracking of a continuous casting billet. In the present invention, the Nb content is limited to a range of 0.04% to 0.08%.

V: vanadium contributes to the improvement of strength due to its precipitation strengthening. However, when the content is less than 0.01%, the above-mentioned effect is not obtained, and when the content is 0.03% or more, the in-situ weldability may be lowered. In the invention, the V content is limited to less than or equal to 0.03 percent.

Ti: titanium is used for fixing nitrogen element in steel, and under proper conditions, titanium/nitrogen forms titanium nitride, so that the growth of grains of a steel billet in the heating/rolling/welding process is prevented, and the toughness of a base metal and a welding heat affected zone is improved. When the titanium content is less than 0.008%, the nitrogen fixation effect is poor, and when the titanium content exceeds 0.03%, the nitrogen fixation effect is saturated, and the toughness of the steel is deteriorated by excessive titanium. In the present invention, the Ti content should be limited to a range of 0.008% to 0.03%.

A1: aluminum is an important deoxidizing element in the steelmaking process, and even if a trace amount of aluminum is added into molten steel, the inclusion content in the steel can be effectively reduced, and grains can be refined. However, excessive aluminum can promote the surface cracking of the continuous casting billet and reduce the continuous casting process performance. In the present invention, the A1 content should be limited to 0.01% to 0.06%.

N: the nitrogen energy is partially used in steel, has the functions of solid solution strengthening and improving hardenability, combines with other elements in the steel, and has the function of precipitation hardening. In the present invention, the N content should be limited to 0.01% or less.

Cr: chromium is an element for improving hardenability of steel, and can inhibit formation of polygonal ferrite and pearlite, promote transformation of low-temperature structure bainite or martensite, and improve strength of steel. However, too high a Cr content will affect the toughness of the steel and cause temper embrittlement, and in the present invention, the Cr content should be limited to 0.35% or less.

Mo: molybdenum has the effect of improving hardenability and strength. In addition, mo and Nb coexist, which effectively suppresses recrystallization of austenite during controlled rolling, and refines the austenite structure, thereby improving low-temperature toughness. In the present invention, the molybdenum content should be limited to a range of 0.06% to 0.35%.

Cu, ni: copper and nickel can improve the strength of steel through solid solution strengthening effect, meanwhile, cu can improve the corrosion resistance of the steel, and the addition of Ni mainly improves the hot brittleness easily caused by Cu in the steel and is beneficial to toughness. The decrease in strength due to the increase in thickness can also be compensated for in thick gauge pipeline steel. In the present invention, cu is limited to 0.30% or less, and Ni is limited to 0.08% to 0.40%.

B: boron has the effect of improving hardenability and easily obtaining a continuously cooled phase transition structure. B has an effect of improving the hardenability of Mo and an effect of synergistically increasing the hardenability in the coexistence of Nb. Therefore, the addition is performed as needed. However, when the content is less than 0.0002%, the effect is insufficient, and when the content exceeds 0.003%, slab cracking occurs. Therefore, the amount of boron added is limited to a very narrow range. In the present invention, B is limited to 0.0005% or less.

The sum of the weight percentages of the chemical elements Nb, V and Ti is less than or equal to 0.12 percent.

Nb, V and Ti are the most important microalloying elements. The addition of trace Nb, V and Ti in steel can ensure that the steel has good weldability and usability by the dispersion and precipitation of carbon and nitride particles (the size is smaller than 5 nm) and the solid solution of Nb, V and Ti, refining grains and greatly improving the strength and toughness of the steel, especially the low-temperature toughness. Nb, V, ti are carbide and nitride forming elements that meet this requirement at relatively low concentrations. When the sum of the weight percentages of Nb, V and Ti is less than or equal to 0.12%, the refining effect on high-temperature austenite grains is strongest, not only can excellent toughness be obtained, but also large heat input welding with the speed of more than 30KJ/cm can be realized. The sum of the weight percentages of the chemical elements Nb, V and Ti is limited to less than or equal to 0.12 percent in the invention, so that the content of single element is allowed to be finely adjusted.

The carbon equivalent of the thick-wall straight-slit steel pipe is less than or equal to 0.43%, and the cold crack sensitivity coefficient is less than or equal to 0.21.

The factors determining strength and weldability in the pipeline steel are mainly carbon content. Alloy steels (mainly low alloy steels) also play an important role in strength and weldability of steel materials by various alloying elements other than carbon. When the carbon equivalent exceeds 0.43%, the cold crack sensitivity coefficient exceeds 0.21, the pipe steel material has a low tendency to be easily quenched and to easily generate cold cracks, and preheating is required before welding to prevent the cold cracks. In the invention, the carbon equivalent and the cold crack sensitivity coefficient are respectively less than or equal to 0.43 percent and less than or equal to 0.21.

The transverse yield strength of the pipe body of the thick-wall straight-slit steel pipe is 485-605 MPa, the tensile strength is 570-760 MPa, the longitudinal yield strength of the pipe body is 485-585 MPa, the tensile strength is 570-700 MPa, the longitudinal yield ratio of the pipe body is less than or equal to 0.85, and the uniform plastic deformation elongation is 8-16%.

The processing method of the thick-wall straight-seam steel pipe for the deep sea pipeline comprises the following steps of:

s1: and (3) designing the components of the pipeline steel plate of the thick-wall straight-seam steel pipe:

the chemical element components in the pipeline steel plate are as follows by weight percent: c:0.03 to 0.07 percent of Mn:1.50 to 1.75 percent of Si:0.15% -0.35%, P: less than or equal to 0.012 percent, S: less than or equal to 0.004 percent, nb:0.O4% -0.08%, V: less than or equal to 0.03 percent of Ti: 0.08 to 0.03 percent of O, al:0.01% -0.06%, N: less than or equal to 0.01 percent, cu: less than or equal to 0.30 percent, cr: less than or equal to 0.35 percent, mo:0.O6% -0.35%, ni:0.08 to 0.40 percent, B: less than or equal to 0.0005 percent, and the balance of Fe and unavoidable impurity elements;

s2: pipeline steel plate performance control of thick-wall straight-seam steel pipes:

adopting a delayed accelerated cooling process below the bainite transformation starting temperature to obtain a composite structure with acicular ferrite, bainite and massive ferrite, wherein the pipeline steel plate has the following properties: the yield strength of the longitudinal tensile property is 420-570 MPa, the tensile strength is 570-720 MPa, the yield ratio is less than or equal to 0.80, the elongation is more than or equal to 20%, and the uniform elongation UEL is more than or equal to 12%; the yield strength of the transverse tensile property is 450-600 MPa, the tensile strength is 570-760 MPa, the yield ratio is less than or equal to 0.85, and the elongation is more than or equal to 28%; the transverse Charpy impact energy of the steel plate at the temperature of minus 20 ℃ reaches more than 240J, and the transverse drop hammer DWTT shearing area of the steel plate at the temperature of minus 10 ℃ is more than or equal to 85 percent;

s3: and (3) forming a thick-wall straight-seam steel pipe:

the pipe forming of the thick-wall straight seam steel pipe is carried out by adopting a J-C-O pipe making process, and the concrete process comprises the following steps: after edge milling and pre-bending of the steel plate, pressing half of the pre-bent steel plate into a J shape by using a JCO forming machine in multiple steps, pressing the other half of the steel plate into a C shape by the same step number, and finally pressing the whole steel plate into an open O shape by one time; the number of pressing times is 15-21, the step length is 80-120 mm, and the pressing amount is 2.0-3.0 mm each time;

s4: welding of thick-wall straight-seam steel pipes:

adopting a submerged arc welding process, wherein a welding wire adopts a Mn-Ni-Ti-B alloy series fine grain acicular ferrite welding wire with low oxygen content, and a flux adopts an overbased sintered flux with the alkalinity range of 1.8-2.7 to weld a thick-wall straight joint steel pipe;

s5: full pipe body expanding of thick-wall straight joint steel pipe:

and (3) carrying out full-pipe body diameter expansion on the steel pipe in a mechanical diameter expansion mode, aligning the straight welding seam with a groove on a diameter expansion head die, then sending the steel pipe into the diameter expansion head in a step-by-step manner, and carrying out sectional diameter expansion until the full-pipe body diameter expansion is completed.

The step S1: in the design of the components of the pipeline steel plate of the thick-wall straight-seam steel pipe, the sum of the weight percentages of three chemical elements of Nb, V and Ti is less than or equal to 0.12 percent, the carbon equivalent is less than or equal to 0.43 percent, and the sensitivity coefficient of cold cracking is less than or equal to 0.21.

The step S2: in the performance control of the pipeline steel plate of the thick-wall straight-seam steel pipe, a delayed accelerated cooling process lower than the bainite transformation starting temperature is adopted, and the concrete process is as follows:

s21: preparing a steel-making material according to the pipeline steel plate component of the thick-wall straight-slit steel pipe designed in the step S1, smelting and continuously casting the steel-making material into a plate blank, wherein the heating temperature of the plate blank is 1160-1220 ℃, the accumulation of heating time and soaking time is not less than 120min, and the total in-furnace time of the plate blank is controlled to be 250-480 min;

s22: rolling slab

The slab rolling process comprises two stages of rough rolling and finish rolling, wherein the rough rolling stage is rolling in an austenite recrystallization region, the initial rolling temperature is 1080-1180 ℃, the final rolling temperature is 980-1160 ℃, and the tapping temperature is 1160-1220 ℃; in the finish rolling stage, namely rolling is carried out in an austenite non-recrystallization region, the initial rolling temperature is 800-860 ℃, and the final rolling temperature is 750-800 ℃;

s23: the rolled plate blank enters a water cooling system, is cooled to 250-350 ℃ at a cooling speed of 12-18 ℃/s, and is then air cooled to room temperature.

The step S4: in the welding of the thick-wall longitudinal steel pipe, a double-sided multi-wire submerged arc automatic welding process of internal welding three wires and external welding five wires is adopted to weld the thick-wall longitudinal steel pipe, and the specific parameters are as follows: the internal welding three-wire process parameters are as follows: the first wire current I=1050-1150A, the voltage 31-35V, the second wire current I=850-950A, the voltage 35-39V, the third wire current I=700-800A, the voltage 38-42V, the welding speed V=110-130 cm/min; the internal welding five-wire process parameters are as follows: first wire current i=1150-1250A, voltage 30-34V, second wire current i=950-1050A, voltage 34-38V, third wire current i=750-850A, voltage 36-40V, fourth wire current i=650-750A, voltage u=36-40V, fifth wire current i=550-650A, voltage u=38-42V; welding speed v=110 to 140cm/min.

The step S5: in the whole-pipe body expanding of the thick-wall straight-seam steel pipe, the length of the sectional expanding step section of the mechanical expanding of the whole pipe body is 0.6-1.0 m, and the expanding rate is 0.6-1.2 percent

The invention has the beneficial effects that:

1. the invention adopts lower C content (0.03-0.07%), carbon equivalent (less than or equal to 0.43%) and cold crack sensitivity coefficient (less than or equal to 0.21), and controls the sulfur and phosphorus content in a lower range (P less than or equal to 0.012%, S less than or equal to 0.004%), thereby ensuring the good low-temperature toughness and welding performance of thick-wall pipeline steel;

2. the invention adopts proper amount of Mn (1.50% -1.75%), and is matched with Cu, ni, mo and other alloy elements and proper amount of Nb, V and Ti microalloy elements, thereby fully playing the roles of solid solution strengthening, fine grain strengthening and phase change strengthening and ensuring that the thick-wall pipeline steel has higher strength and toughness;

3. the invention adopts a certain amount of Cr, and controls the total addition amount of Nb, V and Ti microalloy elements to be 0.03-0.12%, thereby ensuring that the plate has lower yield ratio and higher uniform elongation;

4. the invention adopts a strict slab heating system, the slab heating temperature is 1160-1220 ℃, and the total in-furnace time of the slab is controlled to be 250-480 min. In the rolling process, the slab is subjected to rough rolling in an austenite recrystallization region with an initial rolling temperature of 1080-1180 ℃ and a final rolling temperature of 980-1160 ℃ and finish rolling in an austenite non-recrystallization region with an initial rolling temperature of 800-860 ℃ and a final rolling temperature of 750-800 ℃, and is rapidly cooled to 250-350 ℃ at a speed of 12-18 ℃ per second, and then air-cooled to room temperature, so that a composite structure with acicular ferrite, bainite and massive ferrite is obtained, and the strength, toughness and plasticity of the slab are reasonably matched;

5. the invention adopts the pressing times of 15-21 times, the step length of 80-120 mm, the rolling reduction of 2.0-3.0 mm each time to control the J-C-O pipe making process of the thick-wall straight-seam steel pipe, adopts the welding wire with low oxygen content of the fine grain acicular ferrite of Mn-Ni-Ti-B alloy system to match with the high alkaline sintering welding flux with the alkalinity of 1.8-2.7, adopts the double-sided multi-wire submerged arc automatic welding process of internal welding three wires and external welding five wires to weld the thick-wall straight-seam steel pipe, adopts the mechanical expanding process with the sectional expanding step length of 0.6-1.0 m and the expanding rate of 0.6-1.2 percent to finish the whole pipe expanding of the thick-wall straight-seam steel pipe for the deep-sea pipeline, improves the distribution state of stress in the steel pipe and improves the dimensional precision of the steel pipe;

6. the thick-wall straight-slit steel pipe has the advantages that the transverse yield strength of the pipe body is 485-605 MPa, the tensile strength is 570-760 MPa, the longitudinal yield strength of the pipe body is 485-585 MPa, the tensile strength is 570-700 MPa, the longitudinal yield ratio of the pipe body is less than or equal to 0.85, the uniform plastic deformation elongation is 8-16%, the ovality of the pipe end and the pipe body is less than or equal to 4mm, the pipe end and the pipe body have higher strength and good low-temperature impact toughness, have higher deformation strengthening indexes, larger uniform elongation, lower yield ratio and stress-strain curve characteristics of a non-yield platform, can be suitable for the working condition characteristics of submarine pipelines, and meet the construction requirements of marine oil gas conveying pipelines.

Drawings

Fig. 1 is a microstructure chart of an L485 plate of a thick-wall straight-slit steel pipe for a deep sea pipeline according to an embodiment of the invention.

Fig. 2 is a microstructure morphology diagram of a welded seam of a thick-wall straight-seam steel pipe for a deep-sea pipeline according to an embodiment of the invention.

In the figure, the needles F are acicular ferrite, PF is polygonal ferrite, B grains are granular bainite, and P is pearlite.

Detailed Description

The invention is described in further detail below with reference to examples:

example 1

Example 2

A processing method of a thick-wall straight-seam steel pipe for a deep sea pipeline comprises the following steps:

adopting a delayed accelerated cooling process below the bainite transformation starting temperature to obtain a composite structure with acicular ferrite, bainite and massive ferrite, wherein a microstructure morphology chart is shown in figure 1, and the pipeline steel plate has the following properties: the yield strength of the longitudinal tensile property is 420-570 MPa, the tensile strength is 570-720 MPa, the yield ratio is less than or equal to 0.80, the elongation is more than or equal to 20%, and the uniform elongation UEL is more than or equal to 12%; the yield strength of the transverse tensile property is 450-600 MPa, the tensile strength is 570-760 MPa, the yield ratio is less than or equal to 0.85, and the elongation is more than or equal to 28%; the transverse Charpy impact energy of the steel plate at the temperature of minus 20 ℃ reaches more than 240J, and the transverse drop hammer DWTT shearing area of the steel plate at the temperature of minus 10 ℃ is more than or equal to 85 percent;

s3: and (3) forming a thick-wall straight-seam steel pipe:

s4: welding of thick-wall straight-seam steel pipes:

adopting a submerged arc welding process, wherein a welding wire adopts a Mn-Ni-Ti-B alloy series fine grain acicular ferrite welding wire with low oxygen content, a flux adopts an overbased sintered flux with the alkalinity range of 1.8-2.7, and a thick-wall straight joint steel pipe is welded, and the microstructure morphology of a welding seam is shown in figure 2;

s5: full pipe body expanding of thick-wall straight joint steel pipe:

s22: rolling slab

Example 3

The following processing method of the thick-wall straight-seam steel pipe for the deep sea pipeline is adopted to process the thick-wall straight-seam steel pipe for the deep sea pipeline with L485 phi 559 multiplied by 31.8mm, and the concrete process is as follows:

s1: and (3) designing the components of the pipeline steel plate of the thick-wall straight-seam steel pipe: the L485 thick-wall hot rolled steel plate with the thickness of 31.8mm is adopted, and the weight percentages of the chemical components are as follows: 0.05% of C, 0.20% of Si, 1.64% of Mn, 0.007% of P, 0.003% of S, 0.20% of Ni, 0.20% of Cr, 0.02% of Cu, 0.20% of Mo, 0.05% of Nb, 0.003% of V, 0.02% of Ti, 0.025% of Al, 0.0002% of B, 0.0051% of N, al/N=5, nb+V+Ti=0.07% of carbon equivalent Ceq of 0.41 and a cold crack coefficient Pcm of 0.17;

s2: pipeline steel plate performance control of thick-wall straight-seam steel pipes: the composite structure of acicular ferrite + bainite + massive ferrite is obtained by adopting a delayed accelerated cooling process below the bainite transformation starting temperature, so that the strength, toughness and plasticity of the plate are reasonably matched, and the concrete process is as follows: smelting and continuously casting the steel into a slab according to the chemical components; the heating temperature of the slab is 1190 ℃, the heating time and the soaking time are 160min, the total furnace time of the slab is 280min, the rolling process is divided into two stages of rough rolling and finish rolling, the rough rolling stage is rolling in an austenite recrystallization zone, the initial rolling temperature is 1130 ℃, and the final rolling temperature is 1070 ℃; in the finish rolling stage, rolling is carried out in an austenite non-recrystallization zone, the initial rolling temperature is 800-850 ℃, the final rolling temperature is 770 ℃, the rolling is carried out in a water cooling system, the rolling is carried out at a speed of 15 ℃/s until the rolling temperature reaches 300 ℃, and then the rolling is carried out in air until the rolling temperature reaches room temperature;

the microstructure of the L485 hot rolled steel plate is a composite structure of acicular ferrite, bainite and massive ferrite with good strength and toughness matching, the yield strength of the longitudinal tensile property of the steel plate is 450-550 MPa, the tensile strength is 605-695 MPa, the yield ratio is less than or equal to 0.72, the elongation is more than or equal to 30%, and the uniform elongation UEL is more than or equal to 12%; the yield strength of the transverse tensile property is 485-585 MPa, the tensile strength is 615-705 MPa, the yield ratio is less than or equal to 0.75, the elongation is more than or equal to 30%, the transverse Charpy impact energy of the steel plate at minus 20 ℃ is more than 360J, and the transverse Drop Weight (DWTT) shearing area of the steel plate at minus 10 ℃ is more than 90%;

s3: and (3) forming a thick-wall straight-seam steel pipe: after edge milling and pre-bending of a steel plate, performing pipe manufacturing molding of the steel pipe by adopting a J-C-O pipe manufacturing process, firstly, performing 8-pass stepping pressing on half of the pre-bent steel plate on a JCO molding machine, then, bending the other half of the steel plate in the same way, pressing into a C shape, and finally, performing one-time pressing on the middle of the steel plate to form an open O shape, wherein the whole pressing process adopts 17-pass pressing molding, the step length is 115mm, and the reduction of each pass is 2.5-3.0 mm;

s4: welding of thick-wall straight-seam steel pipes: after the formed thick-wall straight-seam steel pipe is subjected to joint and pre-welding, inner welding four-wire and outer welding five-wire submerged arc automatic welding is adopted to weld inner side and outer side welding grooves of the thick-wall straight-seam steel pipe, the submerged arc welding material adopts an alloy-series fine-grain acicular ferrite welding wire with low oxygen content of 1.9% Mn-1.0% Ni-0.005% Ti-0.001% B to match with an overbased sintering flux with the alkalinity of 2.6, and the thick-wall straight-seam steel pipe is welded by adopting an inner welding three-wire and outer welding five-wire double-sided multi-wire submerged arc automatic welding process, wherein the inner welding three-wire process parameters are as follows: first wire current i=1100a, voltage 33V, second wire current i=900a, voltage 37V, third wire current i=750a, voltage 40V, welding speed v=120 cm/min; the internal welding five-wire process parameters are as follows: first wire current i=1200a, voltage 32V, second wire current i=1000a, voltage 36V, third wire current i=800a, voltage 38V, fourth wire current i=700A, voltage u=38v, fifth wire current i=600a, voltage u=40v; the welding speed V=125 cm/min, the welding seam composite structure with acicular ferrite as main material and small amount of granular bainite precipitated in the welding seam is obtained, the submerged arc welding seam has high toughness and excellent low temperature toughness, the strength of the tensile strength of the welding seam is not lower than 690MPa, the Charpy impact power single value of the welding seam reaches more than 150J at-20 ℃, and the average value is not lower than 180J;

s5: full pipe body expanding of thick-wall straight joint steel pipe: after the welded steel pipe is subjected to ultrasonic detection and X-ray inspection, the whole pipe body diameter expansion is carried out on the steel pipe in a mechanical diameter expansion mode, a straight welding seam is aligned to a groove on a diameter expansion head die, then the steel pipe is sent into the diameter expansion head in a step-by-step mode, the diameter is expanded in a step-by-step mode until the whole pipe body diameter expansion is completed, the thick-wall straight-slit steel pipe for the deep sea pipeline is obtained through a whole pipe body mechanical diameter expansion process with the step-by-step length of 0.8m and the diameter expansion rate of 1.0%, the stress distribution state in the steel pipe is improved, the appearance size precision of the steel pipe is improved, the transverse yield strength of the steel pipe body is 485-605 MPa, the tensile strength is 570-760 MPa, the longitudinal yield strength of the pipe body is 485-585 MPa, the tensile strength is 570-700 MPa, the longitudinal yield ratio of the pipe body is less than or equal to 0.85%, the uniform plastic deformation elongation is 8-16%, the deformation strengthening index is more than or equal to 0.1, the pipe end and pipe ovality is less than or equal to 3.5mm, and the mechanical performance of the steel pipe meets the design requirement for the submarine pipeline based on strain design, and has higher size precision.

Further, according to the thick-walled straight-seamed steel pipe for deep-sea pipes of the above-mentioned embodiment 1, the thick-walled straight-seamed steel pipe for deep-sea pipes is processed by the processing method of the thick-walled straight-seamed steel pipe for deep-sea pipes of the embodiment 2, specifically, as in the embodiments 4, 5, 6 and 7, the comparative examples are comparative examples 1, 2, 3 and 4. The chemical element compositions of the thick-wall straight-seam steel pipe plates for deep-sea pipelines in examples 4 to 7 and comparative examples 1 to 4 are shown in the weight percentage of Table 1.

TABLE 1 chemical element components of thick-walled straight slit steel pipes of examples 4 to 7 and comparative examples 1 to 4 are represented by weight percent (wt%)

Sequence number	C	Si	Mn	Cr	Mo	Ni	Nb	V	Ti	B	S	P
													Example 4	0.05	0.20	1.50	0.20	0.18	0.20	0.05	0.02	0.02	0.0002	0.002	0.008
Example 5	0.06	0.24	1.75	0.18	0.24	0.15	0.05	0.02	0.02	0.0001	0.002	0.010
													Example 6	0.05	0.32	1.65	0.21	0.06	0.22	0.06	0.02	0.02	0.0001	0.003	0.010
Example 7	0.07	0.26	1.70	0.25	0.35	0.24	0.07	0.02	0.02	0.0002	0.003	0.007
													Comparative example 1	0.04	0.28	1.40	0.50	0.15	0.05	0.05	0.03	0.03	0.0001	0.001	0.0009
Comparative example 2	0.05	0.24	1.80	0.15	0.22	0.18	0.04	0.02	0.04	0.0002	0.002	0.0012
													Comparative example 3	0.06	0.25	1.65	0.25	0.05	0.20	0.04	0.10	0.02	0.0001	0.002	0.0008
Comparative example 4	0.05	0.30	1.70	0.24	0.40	0.24	0.05	-	0.03	0.0001	0.002	0.0015

The processing parameters of the thick-wall straight seam steel pipes in examples 4 to 7 and comparative examples 1 to 4 are shown in Table 2.

Table 2 processing parameters of the thick-wall straight-seam steel pipes of examples 4 to 7 and comparative examples 1 to 4

Sequence number	Example 4	Example 5	Example 6	Example 7	Comparative example 1	Comparative example 2	Comparative example 3	Comparative example 4
									Heating temperature/DEGC of continuous casting slab	1160	1220	1190	1200	1100	1250	1220	1200
Roughing start temperature/°c	1130	1130	1150	1180	1120	1120	1100	1000
									Rough rolling finishing temperature/°c	1070	1080	1070	1070	1050	1020	1050	1060
Finish rolling start temperature/DEGC	820	830	830	850	830	800	820	850
									Finish rolling finishing temperature/°c	770	770	780	780	780	750	770	780
Cooling-on temperature/°c	730	750	720	730	850	870	860	880
									Cooling final cooling temperature/°c	250	280	350	320	200	350	400	280
Cooling speed ℃/s	15	12	15	18	3	15	10	20

The mechanical properties of the thick-wall straight joint steel pipes of examples 4 to 7 and comparative examples 1 to 4 are shown in Table 3.

Table 3 mechanical Property results of the thick wall straight seam Steel pipes of examples 4 to 7 and comparative examples 1 to 4

Sequence number	Lateral yield of pipe body strength/MPa	Transverse tensile strength of pipe body strength/MPa	Longitudinal yield of pipe body strength/MPa	Longitudinal tensile strength of pipe body strength/MPa	The pipe body is longitudinal Yield ratio	Longitudinal uniform plasticity of pipe body Elongation at deformation/%	Pipe end and pipe body Ovality of
								Implementation of the embodiments Example 4	524	684	545	682	0.80	16	4.0
Implementation of the embodiments Example 5	555	684	572	675	0.85	8	2.0
								Implementation of the embodiments Example 6	539	689	575	685	0.84	10	3.4
Implementation of the embodiments Example 7	521	675	555	675	0.82	12	1.0
								Comparison Example 1	553	704	582	675	0.86	7.0	4.5
Comparison Example 2	550	706	580	672	0.86	4.5	6.5
								Comparison Example 3	540	675	575	661	0.87	6.0	3.5
Comparison Example 4	520	675	550	645	0.86	5.0	4.0

In table 1, the weight percentage of Mn element in comparative example 1 is lower than the range according to the technical scheme of the present invention, and the weight percentage of Mn element in comparative example 2 is higher than the range according to the technical scheme of the present invention, in combination with tables 1 and 2; in comparative example 3, the weight percentage of Mo element is lower than the range of the technical scheme, and in comparative example 4, the weight percentage of Mo element is higher than the range of the technical scheme; in table 2, certain processing parameters of the plates in comparative examples 1 to 4 are beyond the range of the technical scheme of the present invention, for example, the final cooling temperature and cooling speed of the plates in comparative example 1 are lower than the final cooling temperature and cooling speed of the plates in the technical scheme of the present invention, and the final cooling temperature and cooling speed of the plates in comparative example 3 are higher than the final cooling temperature and cooling speed of the plates in the technical scheme of the present invention; from table 3, it can be seen that at least one of the performance indexes of the thick-wall straight seam steel pipes in comparative examples 1 to 4 is lower than the standard design requirement, for example: the longitudinal uniform plastic deformation elongation of the pipe body, the pipe ends and the ovality of the pipe body in comparative example 2 do not meet the standard design requirements, and the longitudinal uniform plastic deformation elongation of the pipe body in comparative example 3 does not meet the standard design requirements; therefore, the performance of the thick-wall straight joint steel pipe in comparative examples 1-4 is not suitable for the characteristics of the working condition of the submarine pipeline, and cannot meet the construction requirements of the marine oil and gas conveying pipeline.

As can be seen from Table 3, compared with comparative examples 1-4, the longitudinal yield ratio of the pipe body of the thick-wall straight-slit steel pipe in examples 4-7 is less than or equal to 0.85, the uniform plastic deformation elongation is 8% -16%, and the ovality of the pipe end and the pipe body is less than or equal to 4mm, so that the thick-wall straight-slit steel pipe in examples 4-7 has the characteristics of higher deformation strengthening index, larger uniform elongation, lower yield ratio and stress strain curve without yield platform, and can be suitable for the working condition characteristics of submarine pipelines and meet the construction requirements of marine oil and gas conveying pipelines.

The present invention is not limited to the above-mentioned embodiments, and any changes or substitutions that can be easily understood by those skilled in the art within the technical scope of the present invention are intended to be included in the scope of the present invention.

Claims

1. A thick-wall straight-slit steel pipe for a deep sea pipeline is characterized in that: the thick-wall straight joint steel pipe comprises the following chemical element components in percentage by weight: c:0.03 to 0.07 percent of Mn:1.50 to 1.75 percent of Si:0.15% -0.35%, P: less than or equal to 0.012 percent, S: less than or equal to 0.004 percent, nb:0.04% -0.08%, V: less than or equal to 0.03 percent of Ti:0.008 to 0.03 percent of Al:0.01% -0.06%, N: less than or equal to 0.01 percent, cu: less than or equal to 0.30 percent, cr: less than or equal to 0.35 percent, mo:0.06% -0.35%, ni:0.08 to 0.40 percent, B: less than or equal to 0.0005 percent, and the balance of Fe and unavoidable impurities.

2. A thick-walled straight joint steel pipe for deep sea pipes according to claim 1, characterized in that: the sum of the weight percentages of the chemical elements Nb, V and Ti is less than or equal to 0.12 percent.

3. A thick-walled straight joint steel pipe for deep sea pipes according to claim 1, characterized in that: the carbon equivalent of the thick-wall straight-slit steel pipe is less than or equal to 0.43%, and the cold crack sensitivity coefficient is less than or equal to 0.21.

4. A thick-walled straight joint steel pipe for deep sea pipes according to claim 1, characterized in that: the transverse yield strength of the pipe body of the thick-wall straight-slit steel pipe is 485-605 MPa, the tensile strength is 570-760 MPa, the longitudinal yield strength of the pipe body is 485-585 MPa, the tensile strength is 570-700 MPa, the longitudinal yield ratio of the pipe body is less than or equal to 0.85, and the uniform plastic deformation elongation is 8-16%.

5. A method of processing the thick-walled straight-seamed steel pipe for deep-sea pipelines of claim 1, characterized by: the method comprises the following steps:

s3: and (3) forming a thick-wall straight-seam steel pipe:

s4: welding of thick-wall straight-seam steel pipes:

s5: full pipe body expanding of thick-wall straight joint steel pipe:

6. The method for processing the thick-wall straight joint steel pipe for the deep sea pipeline, which is characterized by comprising the following steps of: the step S1: in the design of the components of the pipeline steel plate of the thick-wall straight-seam steel pipe, the sum of the weight percentages of three chemical elements of Nb, V and Ti is less than or equal to 0.12 percent, the carbon equivalent is less than or equal to 0.43 percent, and the sensitivity coefficient of cold cracking is less than or equal to 0.21.

7. The method for processing the thick-wall straight joint steel pipe for the deep sea pipeline, which is characterized by comprising the following steps of: the step S2: in the performance control of the pipeline steel plate of the thick-wall straight-seam steel pipe, a delayed accelerated cooling process lower than the bainite transformation starting temperature is adopted, and the concrete process is as follows:

s22: rolling slab

8. The method for processing the thick-wall straight joint steel pipe for the deep sea pipeline, which is characterized by comprising the following steps of: the step S4: in the welding of the thick-wall longitudinal steel pipe, a double-sided multi-wire submerged arc automatic welding process of internal welding three wires and external welding five wires is adopted to weld the thick-wall longitudinal steel pipe, and the specific parameters are as follows: the internal welding three-wire process parameters are as follows: the first wire current I=1050-1150A, the voltage 31-35V, the second wire current I=850-950A, the voltage 35-39V, the third wire current I=700-800A, the voltage 38-42V, the welding speed V=110-130 cm/min; the internal welding five-wire process parameters are as follows: first wire current i=1150-1250A, voltage 30-34V, second wire current i=950-1050A, voltage 34-38V, third wire current i=750-850A, voltage 36-40V, fourth wire current i=650-750A, voltage u=36-40V, fifth wire current i=550-650A, voltage u=38-42V; welding speed v=110 to 140cm/min.

9. The method for processing the thick-wall straight joint steel pipe for the deep sea pipeline, which is characterized by comprising the following steps of: the step S5: in the whole-pipe body expanding of the thick-wall straight-seam steel pipe, the length of the segmental expanding step section of the whole-pipe body mechanical expanding is 0.6-1.0 m, and the expanding rate is 0.6-1.2%.