JP2006281217A - Connecting tube and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a connecting tube excellent in buckling resistance and also to provide its manufacturing method. <P>SOLUTION: This connecting tube is equipped with steel tubes 10, 20 and a butt-welded zone 30. The steel tube 20 is installed coaxially with the steel tube 10 and provided with the same nominal outside diameter DA (mm) as the steel tube 10. The butt-welded zone 30 is between the tubes 10, 20 and formed by butt-welding of these tubes 10, 20. The outside diameter DO1 (mm) and the inner diameter DI1 (mm) of the end 11 of the steel tube 10 and those DO2 (mm) and DI2 (mm) of the end 21 of the steel tube 20 satisfy following expressions (1), (2). The yield stress Y1 (MPa) of the steel tube 10 and that Y2 (MPa) of the steel tube 20 satisfy expression (3) below. Expressions (1), (2) and (3) are: ¾DO1-DO2¾≤1.5×¾DI1-DI2¾ (1); ¾DI1-DI2¾≤0.01×DA+2 (2); and ¾Y1-Y2¾≤120 (3), respectively. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a connecting pipe and a manufacturing method thereof, and more particularly to a connecting pipe in which a plurality of steel pipes are butt welded and a manufacturing method thereof.

  Submarine pipelines for transporting oil, natural gas, etc. are laid on the seabed after steel pipes are transported by ship to the ocean where they are laid, and the ends of the steel pipes are butt welded on board. Such a laying method is called S-ray or J-ray. In laying methods such as S-ray and J-ray, the local weldability of the steel pipe is important. There are a plurality of reports on improvement of on-site weldability, such as JP-A-2001-198678 (Patent Document 1).

  By the way, there is a reel barge as a method of laying a submarine pipeline other than S-ray and J-ray. In the reel barge, the pipe ends of the steel pipes are joined in advance by butt welding on land. Further, the connecting pipe is wound (reeled) on a large drum, and the drum is transported to the ocean on the laying site. Lay the pipes wound around the drums offshore at the laying site while laying them on the seabed.

As described above, in the reel barge, not only a steel pipe is welded to form a connecting pipe, but the connecting pipe is bent and wound around a drum. Since bending stress is generated in the connecting pipe when the drum is wound, a part of the connecting pipe may be buckled. For this reason, the improvement of buckling resistance is particularly required for a connecting pipe laid as a submarine pipeline by a reel barge.
JP 2001-198678 A

  The objective of this invention is providing the connecting pipe excellent in buckling resistance, and its manufacturing method.

Means for Solving the Problems and Effects of the Invention

  In order to investigate the buckling phenomenon of the connecting pipe at the time of reeling, the present inventors performed a bending test using the connecting pipe and a simulation by a finite element method. As a result, it has been found that buckling does not occur at the toe portion of the butt welded portion of the connecting pipe, but occurs at a steel pipe base material portion that is separated from the toe portion by a predetermined distance in the axial direction.

  Therefore, as a result of further investigation on the buckling phenomenon in the steel pipe base material part, the following knowledge was obtained.

  (A) Buckling occurs due to a difference between the shapes of the ends of the steel pipes to be butt welded.

  As shown in FIG. 1, when the steel pipes 10 and 20 are butt welded, due to the difference in shape between the end portion 11 of the steel pipe 10 and the end portion 21 of the steel pipe 20, the misalignment UO on the outer surface and the inner surface A difference UI occurs. Specifically, the outer surface misalignment UO is caused by the outer diameter difference ΔDO = | DO1-DO2 | between the outer diameter DO1 (mm) of the end portion 11 and the outer diameter DO2 (mm) of the end portion 21. Further, the inner surface misalignment UI is caused by the inner diameter difference ΔDI = | DI1-DI2 | between the inner diameter DI1 (mm) of the end portion 11 and the inner diameter DI2 (mm) of the end portion 21.

  Therefore, the outer diameter difference ΔDO and the inner diameter difference ΔDI of the connecting pipe where buckling occurred was investigated. As a result, it has been found that buckling occurs when the local stress generated by the outer surface misalignment UO becomes excessively larger than the local stress generated by the inner surface misalignment UI. Specifically, when the outer diameter difference ΔDO is 1.5 times or more of the inner diameter difference ΔDI, the local stress due to the outer surface misalignment UO becomes excessively larger than the local stress due to the inner surface misalignment UI, and the buckling is reduced. Occurred.

Based on the above investigation results, the present inventors have found that buckling resistance can be improved if the following expression (1) is satisfied.
| DO1-DO2 | ≦ 1.5 × | DI1-DI2 | (1)

  (B) Even if the outer diameter difference ΔDO and the inner diameter difference ΔDI satisfy the formula (1), if the inner surface misalignment UI is excessively large, buckling occurs due to local stress caused only by the inner surface misalignment UI. The present inventors considered that buckling due to only the inner surface misalignment UI occurs when the inner surface misalignment UI becomes excessively larger than the nominal outer diameter DA (mm) of the steel pipes 10 and 20.

Therefore, as a result of investigating the relationship between the nominal outer diameter DA and the inner diameter difference ΔDI and the buckling, the present inventors, if satisfying the formula (2), the occurrence of buckling caused only by the inner surface misalignment UI. I found out that it can be prevented.
| DI1-DI2 | ≦ 0.01 × DA + 2 (2)

  (C) If the expressions (1) and (2) are satisfied, buckling due to misunderstanding will not occur. However, buckling may occur not only due to the above-mentioned misunderstanding but also due to the strength of steel pipes butt welded to each other. Specifically, if the difference between the yield stress Y1 (MPa) of the steel pipe 10 and the yield stress Y2 (MPa) of the steel pipe 20 is too large, buckling occurs even if there is no mistake. Therefore, it is necessary to reduce the yield stress difference between the steel pipes 10 and 20 to be butt welded.

As a result of investigating the relationship between the yield stress difference and buckling, the present inventors have found that the occurrence of buckling due to the yield stress difference can be prevented if Expression (3) is satisfied.
| Y1-Y2 | ≦ 120 (3)

  Based on the above findings, the present inventors have completed the following invention.

The connecting pipe according to the present invention includes a first steel pipe, a second steel pipe, and a butt weld. The second steel pipe is provided coaxially with the first steel pipe, and has the same nominal outer diameter DA (mm) as the first steel pipe. The butt weld is between the first and second steel pipes and is formed by butt welding the first steel pipe and the second steel pipe. Of the first steel pipe, the outer diameter DO1 (mm) of the first end adjacent to the butt weld, the inner diameter DI1 (mm) of the first end, and the butt weld of the second steel pipe The outer diameter DO2 (mm) of the second end portion and the inner diameter DI2 (mm) of the second end portion satisfy the expressions (1) and (2). The yield stress Y1 (MPa) of the first steel pipe and the yield stress Y2 (MPa) of the second steel pipe satisfy Expression (3).
| DO1-DO2 | ≦ 1.5 × | DI1-DI2 | (1)
| DI1-DI2 | ≦ 0.01 × DA + 2 (2)
| Y1-Y2 | ≦ 120 (3)

The connecting pipe manufacturing method according to the present invention includes a step of preparing a first steel pipe having a yield stress of Y1 (MPa), a yield stress of Y2 (MPa), and the same nominal outer diameter DA ( mm) and satisfying the formulas (1) to (3), and a step of butt welding the end of the first steel tube and the end of the second steel tube Prepare.
| DO1-DO2 | ≦ 1.5 × | DI1-DI2 | (1)
| DI1-DI2 | ≦ 0.01 × DA + 2 (2)
| Y1-Y2 | ≦ 120 (3)

  Here, DO1 (mm) is the outer diameter of the first end of the first steel pipe to be butt welded, DI1 (mm) is the inner diameter of the first end, DO2 (mm) Is the outer diameter of the second end of the second steel pipe to be butt welded, and DI2 (mm) is the inner diameter of the second end.

  Here, the outer diameter DO1 and the inner diameter DI1 of the first end can be obtained, for example, by the following method. The outer diameter and the inner diameter were measured at 10 different locations in the range from 200 to 400 mm in the axial direction from the pipe end, and the average (mm) of the measured outer diameters was defined as the outer diameter DO1. The inner diameter is DI1. The outer diameter DO2 and the inner diameter DI2 of the second end can be obtained by the same method.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

  As shown in FIG. 2, the connecting pipe according to the present embodiment is manufactured by butt welding steel pipes 10 and 20 having the same nominal outer diameter DA (mm).

  First, a steel pipe 10 and a steel pipe 20 that satisfy the following requirements (A) to (C) are prepared.

(A) The outer diameter DO1 (mm) of the end portion 11, the inner diameter DI1 (mm) of the end portion 11, the outer diameter DO2 (mm) of the end portion 21, and the inner diameter DI2 (mm) of the end portion 21 are The following expression (1) is satisfied.
| DO1-DO2 | ≦ 1.5 × | DI1-DI2 | (1)

  In short, in order to prevent the occurrence of buckling, the outer diameter difference ΔDO = | DO1-DO2 | between the end portion 11 of the steel pipe 10 and the end portion 21 of the steel pipe 20 is set to 1. of the inner diameter difference ΔDI = | DI1-DI2 | 5 times or less. Thereby, it is possible to prevent the local stress caused by the misalignment on the outer surface from becoming excessively larger than the local stress caused by the misalignment on the inner surface, thereby improving the buckling resistance.

  The outer diameter DO1 and the inner diameter DI1 of the end portion 11 can be obtained, for example, as follows. The outer diameter and inner diameter are measured at 10 different locations within a range R1 from the pipe end to 200 to 400 mm in the axial direction. The average of the measured outer diameters is defined as the outer diameter DO1, and the average of the measured inner diameters is defined as the inner diameter DI1. The outer diameter DO2 and the inner diameter DI2 of the end portion 21 can be obtained similarly. Specifically, the outer diameter and inner diameter are measured at 10 different locations within a range R2 from the pipe end to 200 to 400 mm in the axial direction. The average of the measured outer diameters is defined as the outer diameter DO2, and the average of the measured inner diameters is defined as the inner diameter DI2.

(B) The inner diameter difference ΔDI = | DI1-DI2 | satisfies the expression (2).
| DI1-DI2 | ≦ 0.01 × DA + 2 (2)

  Even if the outer diameter difference ΔDO and the inner diameter difference ΔDI satisfy the equation (1), if the inner diameter difference ΔDI is large, buckling occurs due to local stress caused only by the difference in the inner surface. If the inner diameter difference ΔDI satisfies the formula (2), it is possible to prevent the occurrence of buckling due to only the difference in the inner surface and improve the buckling resistance.

(C) The yield stress Y1 (MPa) of the steel pipe 10 and the yield stress Y2 (MPa) of the steel pipe 20 satisfy Expression (3).
| Y1-Y2 | ≦ 120 (3)

  If the expressions (1) and (2) are satisfied, local stress due to misunderstanding will not occur. However, if the yield stress difference between the steel pipes 10 and 20 is large, stress concentration occurs in the steel pipe on the low strength side, and buckling occurs. Therefore, as shown in Formula (3), the yield stress difference between the steel pipe 10 and the steel pipe 20 is set to 120 MPa or less. A preferred yield stress difference is 100 MPa or less.

  After preparing the steel pipes 10 and 20 satisfying the above requirements (A) to (C), the end 11 of the steel pipe 10 and the end 21 of the steel pipe 20 are butt welded. First, before performing butt welding, the edge part 11 and the edge part 21 are grooved. After processing, the steel pipe 20 is arranged coaxially with the steel pipe 10, and the steel pipe 10 and the steel pipe 20 are butt welded by TIG welding using a welding material.

  The connecting pipe shown in FIG. 1 is manufactured by the above process. The butt welding between the steel pipe 10 and the steel pipe 20 may employ a welding method other than TIG welding. Examples of other welding methods include MIG welding, MAG welding, covering arc welding, and laser welding. The welding material preferably has the same strength as the steel pipes 10 and 20.

  As shown in FIG. 1, the manufactured connecting pipe has a butt weld 30 formed between the steel pipe 10 and the steel pipe 20. Although FIG. 1 shows two steel pipe portions 10 and 20 and a butt weld portion 30 therebetween, the connecting pipe is composed of two or more steel pipes and a plurality of butt weld portions between adjacent steel pipes. May be.

A steel pipe 1 having a nominal outer diameter DA of 60.3 mm, a nominal wall thickness of 5.3 mm, a length of 900 mm, and having the yield stress Y1 (MPa) shown in Table 1, and the same nominal outer diameter and nominal thickness as the steel pipe 1 A plurality of steel pipes 2 each having a thickness and a length and having a yield stress Y2 (MPa) were prepared.

  The steel pipes 1 and 2 were butt-joined and butt-welded by TIG welding using a welding wire corresponding to AWS A5.28 ER90S-G to produce a plurality of connecting pipes. At this time, after processing a groove with an angle of 30 ° at the ends of the steel pipes 1 and 2, TIG welding was performed.

After welding, the outer surface and the inner surface of the connection pipe of each test number shown in Table 2 were ground, and an outer diameter difference ΔDO (mm) and an inner diameter difference ΔDI (mm) were artificially produced.

  Specifically, as shown in FIG. 3, the outer peripheral surface of the steel pipe 1 was cut in a range R1 of 300 mm from the center of the butt weld portion 3 to the steel pipe 1 side to produce an outer diameter difference ΔDO. Further, in the range R2 of 300 mm from the center of the butt weld 3 to the steel pipe 2 side, the inner peripheral surface of the steel pipe 2 was cut to produce an inner diameter difference ΔDI. A lathe was used for cutting.

  The outer diameter difference ΔDO and the inner diameter difference ΔDI were determined as follows. The outer diameter and the inner diameter are measured at any 10 locations within the range R1, the average of the measured outer diameter is defined as the outer diameter DO1 (mm) of the steel pipe 1, and the average of the measured inner diameter is the inner diameter DI1 (mm) of the steel pipe 1. did. Also, the outer diameter and inner diameter were measured at any 10 locations within the range R2, the average of the measured outer diameters was the outer diameter DO2 (mm) of the steel pipe 2, and the average of the measured inner diameters was the inner diameter DI2 (mm ). A caliper was used for the measurement. An outer diameter difference ΔDO = | DO1-DO2 | and an inner diameter difference ΔDI = | DI1-DI2 | were determined from the determined outer diameters DO1 and DO2 and inner diameters DI1 and DI2.

Furthermore, F1 and F2 were calculated | required based on the following formula | equation (4) and (5) with respect to the connection pipe of each test number.
F1 = 1.5 × ΔDI (4)
F2 = 0.01 × DA + 2 (5)

  In short, F1 is the right side of equation (1), and F2 is the right side of equation (2). The obtained F1 and F2 are shown in Table 2.

  A bending test was carried out on the connecting pipe of each test number produced by the above process using a bending tester as shown in FIG.

  Referring to FIG. 4, the bending tester includes a chuck 101, a roller 102 that is driven horizontally by a hydraulic cylinder (not shown), and a bending jig 103. The longitudinal section of the surface 104 of the bending jig 103 was a convex arc having a radius of 1830 mm.

  The bending test was performed by the following method. First, the connecting tube 100 of each test number was fixed vertically by the chuck 101. Subsequently, the portion P1 of 300 mm was pushed in the horizontal direction by the roller 102 from the upper end to the lower end of the connecting pipe 100. When the connecting tube 100 was bent by the roller 102 and the connecting tube 100 contacted the upper side P2 of the surface 104, the roller 102 was stopped and the bending test was completed.

  After the bending test, it was investigated whether or not buckling occurred in the connecting pipe 100. Specifically, the shape profile of the connecting tube was measured with a contact-type shape measuring instrument. An example of the measurement result is shown in FIG. FIG. 5A is an external view of a part of the connecting pipe 100 after the bending test is completed, and the shape profile of the connecting pipe 100 in the region 200 in FIG. 5A is a curve L1 (FIG. 5B). Wavy line). As shown in FIG. 5B, when an inflection point occurred on the curve L1, it was determined that buckling occurred.

  Table 2 shows the results of investigation for the presence or absence of buckling. “O” in the buckling resistance column indicates that buckling did not occur, and “x” indicates that buckling occurred.

  With reference to Table 2, buckling did not occur in the connecting pipes of Test Nos. 1 to 5 and 8 that satisfied Expressions (1) to (3). On the other hand, the connecting pipes of test numbers 6 and 7 satisfied the expressions (2) and (3), but did not satisfy the expression (1), and therefore buckled.

  The shape profile of the connecting pipe after the bending test was obtained by simulation using the finite element method, and the presence or absence of buckling was investigated. For the simulation, general-purpose finite element method analysis software MARC Ver. 2003 was used. The shape of the connecting pipe, which is a condition for the simulation, was the same as in Example 1. Specifically, the nominal outer diameter of each of the steel pipe 1 and the steel pipe 2 was set to 60.3 mm, the nominal thickness was set to 5.3 mm, and the length was set to 900 mm.

  First, it was confirmed whether the simulation by the finite element method was consistent with the actual bending test result. Specifically, as the simulation conditions, the yield stresses of the steel pipes 1 and 2 are set to the same values as Y1 and Y2 shown in Table 1, and set to the same ΔDO and ΔDI as the test number 6 in Table 1. A simulation was performed. The simulation result is shown in FIG. A curve L2 (solid line) in FIG. 5 is a shape profile obtained by simulation, and a curve L1 is a shape profile obtained by test number 6 of Example 1. From FIG. 5B, the shape profile (curve L2) obtained by the simulation is almost the same as the shape profile (curve L1) obtained in Example 1, and it was confirmed that the simulation has reproducibility.

Subsequently, the nominal outer diameter DA, the nominal wall thickness, the yield stress Y1 of the steel pipe 1 and the yield stress Y2, ΔDO, ΔDI of the steel pipe 2 are set for each connection pipe having the simulation number shown in Table 3, and the equation (4) and F1 and F2 were determined based on (5). Furthermore, a simulation was performed on the connecting pipes with the respective simulation numbers shown in Table 3, and it was investigated whether or not buckling occurred in the shape profile obtained by the simulation.

  The simulation results are shown in Table 3. “O” in the buckling resistance column indicates that buckling did not occur, and “x” indicates that buckling occurred.

  With reference to Table 3, since simulation numbers 3-9, 12-16, and 19 all satisfied Formula (1)-(3) Formula, buckling did not generate | occur | produce.

  On the other hand, although simulation numbers 1 and 2 satisfied the expressions (1) and (2), buckling occurred because the yield stress difference between the steel pipe 1 and the steel pipe 2 exceeded 120 MPa. In addition, although simulation numbers 10, 11, 17, and 18 satisfied Expressions (2) and (3), buckling occurred because ΔDO and ΔDI did not satisfy Expression (1). Although simulation numbers 20 to 23 satisfied Expressions (1) and (3), buckling occurred because ΔDI did not satisfy Expression (2).

  While the embodiments of the present invention have been described above, the above-described embodiments are merely examples for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiment, and can be implemented by appropriately modifying the above-described embodiment without departing from the spirit thereof.

  The connecting pipe according to the present invention can be used as a pipeline, and is particularly useful as a pipeline laid by a reel barge.

It is a longitudinal cross-sectional view of the connecting pipe by embodiment of this invention. It is a figure which shows 1 process in the manufacturing method of the connecting pipe shown in FIG. It is a longitudinal cross-sectional view of the test piece of the bending test in an Example. It is the schematic of a bending test machine. It is a figure which shows the shape of the connection pipe after a bending test.

Explanation of symbols

10, 20 Steel pipe 11, 21 End 30 Butt weld

Claims (2)

A first steel pipe;
A second steel pipe provided coaxially with the first steel pipe and having the same nominal outer diameter DA (mm) as the first steel pipe;
A butt weld formed between the first and second steel pipes and formed by butt welding the first steel pipe and the second steel pipe;
Out of the first steel pipe, the outer diameter DO1 (mm) of the first end adjacent to the butt weld, the inner diameter DI1 (mm) of the first end, and the second steel pipe of the first steel pipe The outer diameter DO2 (mm) of the second end adjacent to the butt weld and the inner diameter DI2 (mm) of the second end satisfy Expression (1) and Expression (2),
The connecting pipe characterized in that the yield stress Y1 (MPa) of the first steel pipe and the yield stress Y2 (MPa) of the second steel pipe satisfy the formula (3).
| DO1-DO2 | ≦ 1.5 × | DI1-DI2 | (1)
| DI1-DI2 | ≦ 0.01 × DA + 2 (2)
| Y1-Y2 | ≦ 120 (3) Preparing a first steel pipe having a yield stress of Y1 (MPa);
Preparing a second steel pipe having a yield stress of Y2 (MPa), having the same nominal outer diameter DA (mm) as the first steel pipe, and satisfying the formulas (1) to (3);
A method of manufacturing a connecting pipe, comprising the step of butt welding the end of the first steel pipe and the end of the second steel pipe.
| DO1-DO2 | ≦ 1.5 × | DI1-DI2 | (1)
| DI1-DI2 | ≦ 0.01 × DA + 2 (2)
| Y1-Y2 | ≦ 120 (3)
Here, DO1 (mm) is the outer diameter of the first end of the first steel pipe to be butt welded, DI1 (mm) is the inner diameter of the first end, and DO2 ( mm) is the outer diameter of the second end of the second steel pipe to be butt welded, and DI2 (mm) is the inner diameter of the second end.

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