Variable-wall-thickness bent pipe for butt joint of large-wall-thickness-difference steel pipes and production method of variable-wall-thickness bent pipe

Abstract

The invention discloses a variable-wall-thickness bent pipe for butt joint of large-wall-thickness-difference steel pipes and a production method of the variable-wall-thickness bent pipe. The variable-wall-thickness bent pipe comprises a thin-wall straight pipe section, a first wall thickness transition section, a middle bent section, a second wall thickness transition section and a thick-wall straight pipe section which are sequentially connected. The thin-wall straight pipe section is connected with the thin-wall steel pipe, the thick-wall straight pipe section is connected with the thick-wall steel pipe, the outer diameter of the variable-wall-thickness bent pipe is equal to the outer diameter of the thin-wall steel pipe and the outer diameter of the thick-wall steel pipe, and the thin-wall straight pipe section, the first wall thickness transition section, the middle bent section, the second wall thickness transition section and the thick-wall straight pipe section are different in wall thickness. According to the method, the wall thickness sudden change position is transferred from the butt joint circumferential weld to the transition area from the straight pipe section to the middle bent section in the bent pipe, unequal-wall-thickness butt joint of the two ends of the bent pipe is converted into equal-wall-thickness butt joint, the welding process is simplified, the welding quality of the butt joint circumferential weld is improved, stress concentration is reduced, and the welding quality of the butt joint circumferential weld is improved. And positive effects of improving the construction quality of the oil and gas pipeline and guaranteeing the operation safety of the oil and gas pipeline can be achieved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of oil and gas pipelines, in particular to a variable wall thickness elbow pipe for butt joint of steel pipes with large wall thickness difference and a production method thereof. BACKGROUND

[0002] Long-distance oil and gas pipelines are the main mode of transporting oil and natural gas in the world, which are connected by a large number of steel pipes and pipe fittings through welded joints, so the girth weld becomes an indispensable important component of long-distance oil and gas pipelines. Due to the limitations of welding technology and the influence of construction environment, some welding defects such as cracks, incomplete fusion, slag inclusion, and pores are prone to occur in the girth weld, which is particularly prominent in the girth weld between steel pipes and pipe fittings of different wall thickness specifications.

[0003] In the construction process of oil and gas pipelines, according to the design standard requirements, different strength design coefficients need to be used in different grade areas or crossing sections during pipeline design, which leads to the selection of steel pipes with different wall thickness specifications for different pipe sections; in addition, when the pipeline needs to be diverted or connected to different direction pipelines, hot bending elbow pipes are inevitably used. Considering the wall thickness reduction on the outer arc side of the bending section during the production process of the hot bending elbow pipe, the design wall thickness of the hot bending elbow pipe is usually not less than the wall thickness of the straight pipe connected thereto. Due to the change of the wall thickness of the steel pipes and pipe fittings along the pipeline, welding between steel pipes and elbow pipes with different wall thickness specifications becomes very common during on-site welding of the pipeline, especially in complex mountainous areas.

[0004] At present, land oil and gas pipelines adopt equal diameter design, and when butt joint is performed between steel pipes with different wall thicknesses or between steel pipes and elbow pipes with different wall thicknesses, wall thickness transition treatment is often required on the inner wall side. In the commonly used domestic and foreign standard specifications for land oil and gas pipelines, such as GB 50251-2015 "Design Specification for Gas Pipeline Engineering", GB 50253-2014 "Design Specification for Oil Pipeline Engineering", ASME B31.8-2022 "Gas and Gas Distribution Piping Systems", the groove forms for welding of steel pipes with different wall thicknesses are roughly the same. When the wall thickness difference is less than a certain value (2.5 mm as specified in the national standard), the end of the thick-walled pipe can be treated without treatment, and welding can be directly performed; when the wall thickness difference exceeds the specified value (2.5 mm as specified in the national standard), the inner end of the thick-walled pipe needs to be treated with a chamfered groove, that is, the inner wall of the pipe with a larger wall thickness is processed into a slope, and then welded with the side of the pipe with a smaller wall thickness, so that the thick-walled pipe is transitioned to the thin-walled pipe, as shown in Figure 1 .

[0005] For the welding of pipes with unequal wall thickness under actual working conditions, the following problems exist: (1) the inner groove is difficult to process, and the quality of the groove is low; (2) the welding quality of the girth weld of the pipe with unequal wall thickness is not ideal, and welding defects such as incomplete penetration, incomplete fusion and cracks are prone to occur; (3) due to the limitation of existing non-destructive testing technology, defects in the girth weld of the pipe with unequal wall thickness are missed or misjudged; (4) the forming quality of the girth weld of the pipe with unequal wall thickness is poor, and there is usually a large stress concentration, which further causes cracks. In recent years, the statistical results of oil and gas pipeline girth weld failure accidents also confirm that more than 50% of the oil and gas pipeline girth weld failure accidents occur at the girth weld of the pipe with unequal wall thickness. The stress concentration caused by the welding of the pipe with unequal wall thickness and the poor quality of the girth weld are important factors causing the failure of the oil and gas pipeline girth weld. When the welded joint with unequal wall thickness bears excessive axial stress and bending moment, the stress concentration caused by the change of the stress state due to the sudden change of the wall thickness and the shape of the inner wall root weld toe of the pipe, and the welding defects generated in the welding process of the girth weld will increase the possibility of crack initiation and propagation, and greatly reduce the carrying capacity of the welded joint. SUMMARY

[0006] The purpose of the present application is to provide a variable wall thickness elbow for butt joint of large wall thickness difference steel pipes and a production method thereof, which solves the problem of reduced carrying capacity of the welded joint caused by the sudden change of the wall thickness of the welded joint when connecting steel pipes with unequal wall thickness.

[0007] To achieve the above-mentioned purpose, the following technical solutions are adopted in the present application:

[0008] A variable wall thickness elbow for butt joint of large wall thickness difference steel pipes, comprising a thin-wall straight pipe section, a first wall thickness transition section, an intermediate bending section, a second wall thickness transition section and a thick-wall straight pipe section connected in sequence.

[0009] The thin-wall straight pipe section is connected to a thin-wall steel pipe, the thick-wall straight pipe section is connected to a thick-wall steel pipe, the outer diameter of the variable wall thickness elbow is equal to the outer diameters of the thin-wall steel pipe and the thick-wall steel pipe, the wall thickness of the thin-wall straight pipe section is determined by the wall thickness of the thin-wall steel pipe, the wall thickness of the thick-wall straight pipe section is determined by the wall thickness of the thick-wall steel pipe, the neutral zone wall thickness of the intermediate bending section is determined by the wall thickness of the thin-wall straight pipe section and the wall thickness of the thick-wall straight pipe section, the wall thickness of the outer arc side of the intermediate bending section is greater than or equal to the wall thickness of the thin-wall straight pipe section, the wall thickness of the inner arc side of the intermediate bending section is determined by the wall thickness of the thin-wall straight pipe section, the outer diameter of the variable wall thickness elbow and the bending radius of the variable wall thickness elbow, the maximum wall thickness difference of the first wall thickness transition section is the difference between the wall thickness of the inner arc side of the intermediate bending section and the wall thickness of the thin-wall straight pipe section, and the maximum wall thickness difference of the second wall thickness transition section is the difference between the wall thickness of the thick-wall straight pipe section and the wall thickness of the outer arc side of the intermediate bending section.

[0010] Further, the length of the thick-wall straight pipe section is equal to the length of the thin-wall straight pipe section.

[0011] Further, the length of the intermediate bending section is determined by the bending radius and the bending angle of the variable-wall-thickness elbow.

[0012] Further, the first wall thickness transition section and the second wall thickness transition section are both slowly transitioned using a circular arc profile.

[0013] Further, the length of the first wall thickness transition section and the length of the second wall thickness transition section are both determined by the maximum wall thickness difference.

[0014] A production method of the variable-wall-thickness elbow for butt joint of steel pipes with large wall thickness difference, comprising:

[0015] Selecting a steel plate of the same material type as the steel pipes to be connected, and processing according to the size of the steel plate;

[0016] Processing the steel plate with the processed size into a variable-wall-thickness steel plate;

[0017] Producing a straight-seam submerged-arc welded pipe from the variable-wall-thickness steel plate through pipe rolling;

[0018] Processing the straight-seam submerged-arc welded pipe into an elbow through hot bending to obtain the variable-wall-thickness elbow for butt joint of steel pipes with large wall thickness difference.

[0019] Further, the size of the steel plate includes length, width and thickness; the length is:

[0020] L=L1+L2+L3+L A +L B

[0021] Wherein, L represents the length of the steel plate, L1 represents the length of the thin-wall straight pipe section, L2 represents the length of the thick-wall straight pipe section, L3 represents the length of the intermediate bending section, L A represents the length of the first wall thickness transition section, L B represents the length of the second wall thickness transition section;

[0022] The width is:

[0023] B=π×D 薄钢管 =π×D 厚钢管

[0024] Wherein, B represents the width of the steel plate, D 薄钢管 represents the outer diameter of the thin-wall steel pipe, D 厚钢管 represents the outer diameter of the thick-wall steel pipe;

[0025] The thickness is:

[0026] δ=δ2=δ 厚钢管

[0027] Wherein, δ represents the thickness of the steel plate, δ2 represents the wall thickness of the thick-wall straight pipe section, δ 厚钢管 represents the wall thickness of the thick-wall steel pipe.

[0028] Further, the wall thickness and length of the thin-wall straight pipe section of the elbow pipe are respectively:

[0029] δ1=δ 薄钢管

[0030] L1≥500mm

[0031] Wherein, δ1 represents the wall thickness of the thin-wall straight pipe section of the elbow pipe, δ 薄钢管 represents the wall thickness of the thin-wall steel pipe, and L1 represents the length of the thin-wall straight pipe section of the elbow pipe;

[0032] The wall thickness and length of the thick-wall straight pipe section of the elbow pipe are respectively:

[0033] δ2=δ 厚钢管

[0034] L2=L1≥500mm

[0035] Wherein, δ2 represents the wall thickness of the thick-wall straight pipe section of the elbow pipe, δ 厚钢管 represents the wall thickness of the thick-wall steel pipe, L1 represents the length of the thin-wall straight pipe section of the elbow pipe, and L2 represents the length of the thick-wall straight pipe section of the elbow pipe.

[0036] Further, the outer arc side wall thickness of the intermediate bending section of the elbow pipe is:

[0037] δ wh ≥δ1

[0038] Wherein, δ wh represents the outer arc side wall thickness of the intermediate bending section of the elbow pipe, and δ1 represents the wall thickness of the thin-wall straight pipe section of the elbow pipe.

[0039] The neutral zone wall thickness of the intermediate bending section of the elbow pipe is:

[0040]

[0041] Wherein, δ zx represents the neutral zone wall thickness of the intermediate bending section of the elbow pipe, and δ2 represents the wall thickness of the thick-wall straight pipe section of the elbow pipe.

[0042] The inner arc side wall thickness of the intermediate bending section of the elbow pipe is:

[0043]

[0044] Wherein, δ nh represents the inner arc side wall thickness of the intermediate bending section of the elbow pipe, D 弯 represents the outer diameter of the elbow pipe, and R represents the bending radius of the elbow pipe.

[0045] The length of the intermediate bending section of the elbow pipe is:

[0046]

[0047] Wherein, L3 represents the length of the intermediate bending section of the elbow pipe, and a represents the bending angle of the elbow pipe.

[0048] Further, the maximum wall thickness difference and the length of the first wall thickness transition section of the elbow pipe satisfy the following formula:

[0049]

[0050] Wherein, Δδ Amax represents the maximum wall thickness difference of the first wall thickness transition section of the elbow pipe, δ1 represents the wall thickness of the thin-wall straight pipe section of the elbow pipe, and δ nh represents the wall thickness of the inner arc side of the intermediate bending section of the elbow pipe, L A represents the length of the first wall thickness transition section of the elbow pipe.

[0051] The maximum wall thickness difference and the length of the second wall thickness transition section of the elbow pipe satisfy the following formula:

[0052]

[0053] Wherein, Δδ Bmax represents the maximum wall thickness difference of the second wall thickness transition section of the elbow pipe, δ2 represents the wall thickness of the thick-wall straight pipe section of the elbow pipe, and δ wh represents the wall thickness of the outer arc side of the intermediate bending section of the elbow pipe, L B represents the length of the second wall thickness transition section of the elbow pipe.

[0054] Compared with the prior art, the present application has the following beneficial effects:

[0055] The application provides a variable wall thickness elbow pipe for butt joint of steel pipes with large wall thickness difference, which connects a thin-wall straight pipe section, a first wall thickness transition section, an intermediate bending section, a second wall thickness transition section and a thick-wall straight pipe section in sequence, connects the thin-wall straight pipe section with a thin-wall steel pipe, connects the thick-wall straight pipe section with a thick-wall steel pipe, determines the outer diameter of the variable wall thickness elbow pipe to be equal to the outer diameters of the thin-wall steel pipe and the thick-wall steel pipe, and determines the different wall thicknesses of the thin-wall straight pipe section, the first wall thickness transition section, the intermediate bending section, the second wall thickness transition section and the thick-wall straight pipe section respectively, so that the wall thickness mutation problem existing in the welding joint of the traditional hot bending elbow pipe when connecting steel pipes with different wall thicknesses is solved. The wall thickness mutation position is transferred from the butt joint fillet weld to the area of the transition from the straight pipe section to the intermediate bending section in the elbow pipe, and the butt joint with different wall thicknesses at the two ends of the elbow pipe is converted into the butt joint with equal wall thicknesses, so that the thick-wall side pipe inner end part no longer needs to be treated with chamfered groove, the welding process is simplified, the welding quality of the butt joint fillet weld is improved, the stress concentration is reduced, and the oil and gas pipeline construction quality and the oil and gas pipeline operation safety can be positively improved. BRIEF DESCRIPTION OF DRAWINGS

[0056] In order to more clearly illustrate the technical solutions of the embodiments of the application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some of the embodiments of the application, and therefore should not be regarded as a limitation to the scope. For those skilled in the art, other related drawings can also be obtained without creative labor.

[0057] Figure 1 It is a schematic diagram of traditional equal wall thickness and unequal wall thickness welding joint, wherein (a) is a schematic diagram of equal wall thickness or wall thickness difference less than 2.5mm welding joint, and (b) is a schematic diagram of wall thickness difference greater than 2.5mm welding joint.

[0058] Figure 2 It is a schematic diagram of variable wall thickness steel plate structure of the application.

[0059] Figure 3 It is a schematic diagram of straight seam submerged arc welding pipe structure of the application.

[0060] Figure 4 It is a schematic diagram of variable wall thickness elbow pipe structure of the application.

[0061] Figure 5 It is a schematic diagram of variable wall thickness elbow pipe butt joint of steel pipes with large wall thickness difference of the application. DETAILED DESCRIPTION

[0062] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some but not all of the embodiments of the present application. The components of the embodiments of the present application described and shown in the drawings can be arranged and designed in various different configurations.

[0063] Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the claimed application, but only represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of protection of the present application.

[0064] It should be noted that: similar reference numbers and letters represent similar items in the following drawings, therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0065] In the description of the embodiments of the present application, it should be noted that, if the orientation or position relationship indicated by the terms "upper", "lower", "horizontal", "inner" and the like is based on the orientation or position relationship shown in the drawings, or is the orientation or position relationship when the product of the present application is usually placed, and is only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the indicated device or element must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application. In addition, the terms "first", "second" and the like are only used for differentiation in description, and cannot be understood as indicating or implying relative importance.

[0066] In addition, if the term "horizontal" appears, it does not mean that the component must be absolutely horizontal, but can be slightly inclined. For example, "horizontal" only means that its direction is relatively more horizontal than "vertical", and does not mean that the structure must be completely horizontal, but can be slightly inclined.

[0067] In the description of the embodiments of the present application, it should also be noted that, unless otherwise explicitly specified and limited, if the terms "arrangement", "installation", "connection", "connection" appear, they should be understood in a broad sense, for example, can be fixedly connected, can be detachably connected, or integrally connected; can be mechanically connected, can be electrically connected; can be directly connected, can be indirectly connected through an intermediate medium, or can be the communication inside two elements. For those of ordinary skill in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0068] The present application will be described in further detail below with reference to the drawings:

[0069] Referring toFigure 1 The present application provides a variable wall thickness elbow for butt joint of steel pipes with large wall thickness difference, which comprises thin-wall straight pipe section, first wall thickness transition section, intermediate bending section, second wall thickness transition section and thick-wall straight pipe section connected in sequence. 弯 The outer diameter D 薄钢管 of the thin-wall steel pipe to be connected and the outer diameter D 厚钢管 of the thick-wall steel pipe are equal, i.e. D 弯 =D 薄钢管 =D 厚钢管 .

[0070] The thin-wall straight pipe section is used to connect the thin-wall steel pipe with thinner wall thickness, and the wall thickness of the thin-wall straight pipe section is determined by the wall thickness of the thin-wall steel pipe to be connected. The length of the thin-wall straight pipe section should be determined according to the engineering construction requirements, but the length is generally not less than 500 mm.

[0071] The thick-wall straight pipe section is used to connect the thick-wall steel pipe with thicker wall thickness, and the wall thickness of the thick-wall straight pipe section is determined by the wall thickness of the thick-wall steel pipe to be connected. The length of the thick-wall straight pipe section should also be determined according to the engineering construction requirements, and in general, the length of the thick-wall straight pipe section is equal to the length of the thin-wall straight pipe section, and the length of the thick-wall straight pipe section is generally not less than 500 mm.

[0072] The intermediate bending section is located between the first wall thickness transition section and the second wall thickness transition section, and the neutral zone wall thickness of the intermediate bending section can be selected between the wall thickness of the thin-wall straight pipe section and the wall thickness of the thick-wall straight pipe section, but the value thereof should ensure that the wall thickness of the outer arc side of the intermediate bending section is not less than the wall thickness of the thin-wall straight pipe section. Under this premise, the neutral zone wall thickness of the intermediate bending section can generally be determined by the wall thickness of the thin-wall straight pipe section and the wall thickness of the thick-wall straight pipe section. In addition, the wall thickness of the inner arc side of the intermediate bending section is determined by the wall thickness of the thin-wall straight pipe section, the outer diameter of the variable wall thickness elbow and the bending radius of the variable wall thickness elbow. The length of the intermediate bending section is determined by the bending radius and the bending angle of the variable wall thickness elbow.

[0073] The first wall thickness transition section is located between the thin-wall straight pipe section and the intermediate bending section, and serves to slowly transition the wall thickness of the thin-wall straight pipe section to the wall thickness of the intermediate bending section. Considering that wall thickness thinning occurs on the outer arc side and wall thickness thickening occurs on the inner arc side during bending of the elbow, the maximum wall thickness difference of the first wall thickness transition section is the difference between the wall thickness of the inner arc side of the intermediate bending section and the wall thickness of the thin-wall straight pipe section. In order to avoid stress concentration of the first wall thickness transition section, the first wall thickness transition section is slowly transitioned using a circular arc profile, and the length of the first wall thickness transition section is determined by the maximum wall thickness difference.

[0074] The second wall thickness transition section is located between the intermediate bending section and the thick wall straight pipe section, and serves to slowly transition the wall thickness of the intermediate bending section to the wall thickness of the thick wall straight pipe section. In view of the fact that wall thickness thinning occurs on the outer arc side and wall thickness thickening occurs on the inner arc side during bending pipe bending, the maximum wall thickness difference of the second wall thickness transition section is the difference between the wall thickness of the thick wall straight pipe section and the wall thickness of the outer arc side of the intermediate bending section. In order to avoid stress concentration of the second wall thickness transition section, the second wall thickness transition section is slowly transitioned using a circular arc profile, and the length of the second wall thickness transition section is determined by the maximum wall thickness difference.

[0075] The application also provides a production method of the variable wall thickness bending pipe for butt joint of steel pipes with large wall thickness difference, specifically comprising the following steps:

[0076] Step one: select a steel plate of the same material type as the steel pipe to be connected, and the length, width and thickness of the steel plate are determined by the following formulas, and the steel plate is processed according to the length, width and thickness:

[0077] L=L1+L2+L3+L A +L B

[0078] B=π×D 薄钢管 =π×D 厚钢管

[0079] δ=δ2=δ 厚钢管

[0080] Wherein, L represents the length of the steel plate, L1 represents the length of the thin wall straight pipe section, L2 represents the length of the thick wall straight pipe section, L3 represents the length of the intermediate bending section, L A represents the length of the first wall thickness transition section, L B represents the length of the second wall thickness transition section, B represents the width of the steel plate, D 薄钢管 represents the outer diameter of the thin wall steel pipe, D 厚钢管 represents the outer diameter of the thick wall steel pipe, δ represents the thickness of the steel plate, δ2 represents the wall thickness of the thick wall straight pipe section, δ 厚钢管 represents the wall thickness of the thick wall steel pipe.

[0081] Step two: the steel plate processed in step one is processed into a variable wall thickness steel plate as shown in Figure 2 by die forging or the like. The specific processing requirements are as follows: from one end of the steel plate to the L1 length range, the wall thickness of the steel plate is processed to δ1, so that it is equal to the wall thickness δ 薄钢管 of the thin wall steel pipe to be connected; from the L1 length of the steel plate to the L1+L A length range, the wall thickness of the steel plate is gradually transitioned from δ1 to δ3 through a circular arc profile, so that δ3 is equal to the neutral zone wall thickness δ zx of the intermediate bending section of the bending pipe, i.e. δ3=δ zx ; from the L1+L Alength range L1+L A +L3, the wall thickness of the steel plate is processed to δ3; from the length L1+L A +L3 to L1+L A +L3+L B length range, the wall thickness of the steel plate is gradually transitioned from δ3 to the wall thickness δ2 of the thick wall straight pipe section of the elbow pipe through a circular arc profile.

[0082] Step three: the steel plate processed in step two is rolled into a pipe to produce a straight seam submerged arc welded pipe with the following characteristics: as shown in Figure 3 , the wall thickness of the welded pipe in the length range L1 of one end is δ1 (δ1=δ 薄钢管 ), the wall thickness of the welded pipe in the length range L2 of the other end is δ2 (δ2=δ 厚钢管 ), and the wall thickness of the two ends is gradually and smoothly transitioned to the wall thickness δ3 (δ3=δ zx ) of the middle section through the first wall thickness transition section and the second wall thickness transition section respectively.

[0083] Step four: the straight seam submerged arc welded pipe produced in step three is processed into an elbow pipe through hot bending, as shown in Figure 4 , the wall thickness and length of the thin wall straight pipe section of the elbow pipe meet the following formulas respectively:

[0084] δ1=δ 薄钢管

[0085] L1≥500mm

[0086] Wherein, δ1 represents the wall thickness of the thin wall straight pipe section of the elbow pipe, δ 薄钢管 represents the wall thickness of the thin wall steel pipe, and L1 represents the length of the thin wall straight pipe section of the elbow pipe.

[0087] The wall thickness and length of the thick wall straight pipe section of the elbow pipe meet the following formulas respectively:

[0088] δ2=δ 厚钢管

[0089] L2=L1≥500mm

[0090] Wherein, δ2 represents the wall thickness of the thick wall straight pipe section of the elbow pipe, δ 厚钢管 represents the wall thickness of the thick wall steel pipe, L1 represents the length of the thin wall straight pipe section of the elbow pipe, and L2 represents the length of the thick wall straight pipe section of the elbow pipe.

[0091] The outer arc side wall thickness of the middle bending section of the elbow pipe meets the following formula:

[0092] δ wh ≥δ1

[0093] Wherein, δ wh represents the outer arc side wall thickness of the middle bending section of the elbow pipe, and δ1 represents the wall thickness of the thin wall straight pipe section of the elbow pipe.

[0094] The wall thickness of the neutral zone of the intermediate bending section of the elbow pipe satisfies the following formula:

[0095]

[0096] wherein δ zx represents the wall thickness of the neutral zone of the intermediate bending section of the elbow pipe, and δ2 represents the wall thickness of the thick-walled straight pipe section of the elbow pipe.

[0097] The wall thickness of the inner arc side of the intermediate bending section of the elbow pipe satisfies the following formula:

[0098]

[0099] wherein δ nh represents the wall thickness of the inner arc side of the intermediate bending section of the elbow pipe, D 弯 represents the outer diameter of the elbow pipe, and R represents the bending radius of the elbow pipe.

[0100] The length of the intermediate bending section of the elbow pipe satisfies the following formula:

[0101]

[0102] wherein L3 represents the length of the intermediate bending section of the elbow pipe, and α represents the bending angle of the elbow pipe.

[0103] The first wall thickness transition section of the elbow pipe is a circular arc transition, and the maximum wall thickness difference and the length thereof satisfy the following formula:

[0104]

[0105] wherein Δδ Amax represents the maximum wall thickness difference of the first wall thickness transition section of the elbow pipe, δ1 represents the wall thickness of the thin-walled straight pipe section of the elbow pipe, δ nh represents the wall thickness of the inner arc side of the intermediate bending section of the elbow pipe, and L A represents the length of the first wall thickness transition section of the elbow pipe.

[0106] The second wall thickness transition section of the elbow pipe is a circular arc transition, and the maximum wall thickness difference and the length thereof satisfy the following formula:

[0107]

[0108] wherein Δδ Bmax represents the maximum wall thickness difference of the second wall thickness transition section of the elbow pipe, δ2 represents the wall thickness of the thick-walled straight pipe section of the elbow pipe, δ wh represents the wall thickness of the outer arc side of the intermediate bending section of the elbow pipe, and L B represents the length of the second wall thickness transition section of the elbow pipe.

[0109] The present application fundamentally solves the problems of poor welding quality and stress concentration caused by the wall thickness mutation of the welding joint at both ends of the elbow pipe when connecting two pipe sections with large wall thickness difference. The wall thickness mutation position is transferred from the butt welding seam at both ends of the elbow pipe to the area where the two straight pipe sections of the elbow pipe transition to the bending section, and the butt welding of the elbow pipe with different wall thicknesses is converted to the butt welding with equal wall thickness, as shown in Figure 5 Therefore, the thick-walled pipe end does not need to be chamfered and beveled during welding, which not only simplifies the welding process, but also improves the welding quality of the butt welding seam, improves the oil and gas pipeline construction quality, and ensures the safe operation of the oil and gas pipeline.

[0110] The above is only a preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A variable wall thickness elbow for butt joining large wall thickness differential steel pipes, characterized in that, The variable-wall-thickness elbow pipe comprises, in sequence, a thin-wall straight pipe section, a first wall-thickness transition section, an intermediate bending section, a second wall-thickness transition section and a thick-wall straight pipe section. The thin-wall straight pipe section is connected with a thin-wall steel pipe, the thick-wall straight pipe section is connected with a thick-wall steel pipe, the outer diameter of the variable-wall-thickness elbow pipe is equal to the outer diameters of the thin-wall steel pipe and the thick-wall steel pipe, the wall thickness of the thin-wall straight pipe section is determined by the wall thickness of the thin-wall steel pipe, the wall thickness of the thick-wall straight pipe section is determined by the wall thickness of the thick-wall steel pipe, the wall thickness of the neutral zone of the intermediate bending section is determined by the wall thickness of the thin-wall straight pipe section and the wall thickness of the thick-wall straight pipe section, the wall thickness of the outer-arc side of the intermediate bending section is greater than or equal to the wall thickness of the thin-wall straight pipe section, the wall thickness of the inner-arc side of the intermediate bending section is determined by the wall thickness of the thin-wall straight pipe section, the outer diameter of the variable-wall-thickness elbow pipe and the bending radius of the variable-wall-thickness elbow pipe, the maximum wall thickness difference of the first wall-thickness transition section is the difference between the wall thickness of the inner-arc side of the intermediate bending section and the wall thickness of the thin-wall straight pipe section, and the maximum wall thickness difference of the second wall-thickness transition section is the difference between the wall thickness of the thick-wall straight pipe section and the wall thickness of the outer-arc side of the intermediate bending section.

2. A variable thickness bend pipe for butt joining of steel pipes having a large wall thickness difference according to claim 1, characterized in that, The length of the thick-wall straight pipe section is equal to the length of the thin-wall straight pipe section.

3. A variable thickness bend pipe for butt joining of steel pipes having large wall thickness difference according to claim 1, characterized in that, The length of the intermediate bending section is determined by the bending radius and the bending angle of the variable-wall-thickness elbow pipe.

4. The variable thickness bend pipe for butt joint of large wall thickness difference steel pipes according to claim 1, characterized in that, The first wall-thickness transition section and the second wall-thickness transition section are both slowly transitioned by a circular arc profile.

5. A variable thickness bend pipe for butt joining of steel pipes having large wall thickness difference according to claim 1, characterized in that, The length of the first wall-thickness transition section and the length of the second wall-thickness transition section are both determined by the maximum wall thickness difference.

6. A method of producing a variable thickness bend pipe for butt joining of steel pipes having different wall thicknesses according to any one of claims 1 to 5, characterized in that, The method comprises the following steps: a steel plate with the same material type as the steel pipes to be connected is selected, and the steel plate is processed according to the size of the steel plate; the variable-wall-thickness steel plate is processed into a straight-seam submerged-arc welded pipe through pipe rolling; the straight-seam submerged-arc welded pipe is processed into an elbow pipe through hot bending, thereby obtaining the variable-wall-thickness elbow pipe for butt joint of steel pipes with large wall thickness difference. The size of the steel plate comprises length, width and thickness; the length is:

7. The method for producing a variable wall thickness elbow pipe for butt joining of steel pipes having a large wall thickness difference according to claim 6, characterized by, The width is: L = L1 + L2 + L3 + L A +L B wherein L represents the length of the steel sheet, L1 represents the length of the thin-walled straight pipe section, L2 represents the length of the thick-walled straight pipe section, L3 represents the length of the intermediate bending section, L A represents the length of the first wall thickness transition section, L B represents the length of the second wall thickness transition section; The thickness is: B = π x D 薄钢管 = π x D 厚钢管 where B represents the width of the steel sheet, D 薄钢管 represents the outer diameter of the thin-walled steel pipe, D 厚钢管 represents the outer diameter of the thick-walled steel pipe; The wall thickness and length of the thin-wall straight pipe section of the elbow pipe are respectively: δ = δ2= δ 厚钢管 wherein 6 denotes the thickness of the steel sheet, δ2 denotes the wall thickness of the thick-walled straight pipe section, and δ 厚钢管 denotes the wall thickness of the thick-walled steel pipe.

8. The method for producing a variable wall thickness elbow pipe for butt joining of steel pipes having a large wall thickness difference according to claim 6, characterized by, L1≥500mm δ1= δ 薄钢管 The wall thickness and length of the thick-wall straight pipe section of the elbow pipe are respectively: wherein δ1 represents the wall thickness of the thin-walled straight pipe section of the bend pipe, 6 薄钢管 δ1 represents the wall thickness of the thin-walled straight pipe section of the bend pipe, and L1 represents the length of the thin-walled straight pipe section of the bend pipe. L2=L1≥500mm δ2= δ 厚钢管 The wall thickness of the outer-arc side of the intermediate bending section of the elbow pipe is: wherein δ2 represents the wall thickness of the thick-walled straight pipe section of the bend, δ 厚钢管 wherein δ represents the wall thickness of the thick-walled steel pipe, Li represents the length of the thin-walled straight pipe section of the bend, and L2 represents the length of the thick-walled straight pipe section of the bend.

9. The method for producing a variable thickness bent pipe for butt joining of steel pipes having a large wall thickness difference according to claim 6, characterized by, The wall thickness of the neutral zone of the intermediate bending section of the elbow pipe is: δ wh ≥δ1 wherein δ wh represents the outer arc side wall thickness of the intermediate bending section of the elbow pipe, and δ1 represents the wall thickness of the thin-walled straight pipe section of the elbow pipe. The wall thickness of the inner-arc side of the intermediate bending section of the elbow pipe is: wherein δ zx represents the wall thickness of the neutral zone in the intermediate bending section of the bend, and δ2 represents the wall thickness of the thick-walled straight section of the bend. The length of the intermediate bending section of the elbow pipe is: wherein δ nh represents the inner arc side wall thickness of the intermediate bending section of the elbow pipe, D 弯 represents the outer diameter of the elbow pipe, and R represents the bending radius of the elbow pipe; Wherein, L3 represents the length of the intermediate bending section of the elbow pipe, and a represents the bending angle of the elbow pipe. The maximum wall thickness difference and the length of the first wall-thickness transition section of the elbow pipe satisfy the following formula:

10. The method for producing a variable thickness bent pipe for butt joining of steel pipes having a large wall thickness difference according to claim 6, characterized by, The maximum wall thickness difference and the length of the second wall-thickness transition section of the elbow pipe satisfy the following formula: wherein Δδ Amax represents the maximum wall thickness difference of the first wall thickness transition section of the bend pipe, δ1 represents the wall thickness of the thin-walled straight pipe section of the bend pipe, and δ nh represents the wall thickness of the inner arc side of the intermediate bending section of the bend pipe, L A represents the length of the first wall thickness transition section of the bend pipe; ​ wherein Δδ Bmax represents the maximum wall thickness difference of the second wall thickness transition section of the bend pipe, δ2 represents the wall thickness of the thick-walled straight pipe section of the bend pipe, and δ wh represents the wall thickness of the outer arc side of the intermediate bending section of the bend pipe, L B represents the length of the second wall thickness transition section of the bend pipe.

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