JP2008232823A - Expanded pipe crack evaluation device of welded steel pipe, and expanded pipe crack evaluation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device and method for precisely evaluating the expanded pipe crack properties of a steel pipe, having welded parts parallel in its longitudinal direction. <P>SOLUTION: The expanded pipe crack evaluation device of the welded steel pipe comprises a jig 5 for a matrix and a jig 3 for a welded part both of which have the arcuate regions opposed to the interior of an annular test object 1 and a drive part 7 for linearly advancing the jig 5 for the matrix and the jig 3 for the welded part in mutually opposed directions and a welded part opposed groove 4 is provided to the top part of the jig 3 for the welded part. This expanded pipe crack evaluation device is characterized in that the radius Rc of curvature of the central parts 3c of the jig 3 for the welded part formed in adjacent relation to both sides of the welded part opposed groove 4 and the radius Rs of curvature of the end parts 3s of the jig 3 for the welded part formed in adjacent relation to the outsides of the central parts 3c of the jig 3 for the welded part satisfy the formula: 0.3Rc≤Rs≤0.8 Rc, and the central parts 3c of the jig 3 for the welded part are respectively formed within a range of 30-60° on both sides of the center of the welded part opposed groove 4 with the center of the radius Rc of curvature as a referance. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an apparatus and a method for evaluating the expansion cracking property of a steel pipe having a welded portion parallel to the longitudinal direction, which is manufactured by forming a steel plate into a tubular shape and welding butt portions.

  Among the steel pipes formed by forming a steel plate into a tubular shape and seam-welding the butt portion, in particular, a steel pipe formed by the UOE method is expanded in order to improve the roundness. When the pipe expansion shown in FIG. 1 is performed by the UOE pipe forming process, a crack from the seam welded portion, that is, a so-called pipe expansion crack may occur.

  The pipe expansion crack is a complex phenomenon governed not only by the mechanical characteristics of the steel pipe and the shape of the weld, but also by various factors such as the tool of the pipe expander, the so-called segment shape, the material and the friction coefficient with the steel pipe. Therefore, it has been difficult to predict the occurrence of pipe expansion cracks before performing pipe expansion on the production line.

  In recent years, a construction method has been proposed in which a steel pipe inserted into an oil well is expanded in the oil well, thereby reducing a drilling area and greatly shortening a drilling construction period. In order to evaluate the expansion cracking property of an ERW steel pipe applied to such a use, the end of the steel pipe is expanded with a conical jig, and the expansion ratio of the portion where the crack occurs is measured. However, in this method, since the amount of strain is continuously changed, the pipe expansion crackability cannot be accurately evaluated.

  The mechanical properties of steel pipes are difficult to evaluate. Usually, steel pipes are cut and flattened with a press or the like, and specimens are collected. For this reason, the mechanical characteristics cannot be evaluated properly due to the influence of the introduced strain. For such a problem, a tensile test apparatus that cuts a steel pipe into a ring shape and applies a tensile force in the circumferential direction from the inside has been proposed (for example, Patent Document 1).

According to this tensile test apparatus, it is possible to measure the tensile strength of the base material of the steel pipe. However, it does not describe the evaluation of the strength of the welded portion, particularly the pipe cracking property.
JP-A-63-182545

  The present invention provides an apparatus and method for accurately evaluating the expansion cracking property of a steel pipe having a welded portion parallel to the longitudinal direction by improving the testing machine for measuring the tensile properties of the base material.

The gist of the present invention is as follows.
(1) A base material jig and a welding part jig that are arcuate in the part facing the inside of the annular test body, and a drive that linearly moves the base material jig and the welding part jig in opposite directions. A welded portion facing groove on the top of the welded portion jig, and a radius of curvature Rc of the welded portion jig central portion formed adjacent to both sides of the welded portion facing groove, and the welded portion The radius of curvature Rs of the welded jig end formed adjacent to the outside of the jig central part is:
0.3Rc ≦ Rs ≦ 0.8Rc
And the weld jig center part is formed in a range of 30 to 60 ° on both sides of the center of the weld-facing groove with respect to the center of the radius of curvature Rc. , Expansion crack evaluation equipment for welded steel pipes.
(2) With respect to the center of the radius of curvature Rc as a reference, facing the welded portion separable to the surface of the center portion of the welded jig in the range of 10 ° to 30 ° on both sides of the center of the welded portion facing groove. The apparatus for evaluating crack expansion of a welded steel pipe according to (1) above, wherein a jig is provided.
(3) In the tube cracking evaluation apparatus according to (1) or (2), the welded portion of the annular test body is installed facing the welded portion facing groove, and a welded portion jig and a base material jig are provided. A method for evaluating expansion cracking of a welded steel pipe, wherein a load and a displacement acting between the base material jig and the welding part jig are measured while moving in opposite directions.
(4) The method for evaluating crack expansion of a welded steel pipe according to (3) above, wherein a strain measuring means is provided at or near the welded portion of the annular specimen and the strain of the welded portion is measured.

  According to the present invention, in particular, it is possible to easily and inexpensively quantify the generation factor of pipe expansion cracks, which is a factor that significantly hinders the productivity of welded steel pipes manufactured by the UOE method. The above contribution is very remarkable.

  FIG. 1 shows a schematic view of a pipe expander employed in a normal UOE pipe making process. When the pipe expansion is performed, the pipe expansion segments 21 that are divided and arranged in the circumferential direction inside the steel pipe 20 are radially expanded at the same time.

  In the present invention, the pipe expansion performed in the UOE pipe making process is accurately reproduced. In the present invention, in order to simplify the mechanism, the steel pipe is expanded by two segments (a welding part jig 3 and a base material jig 5).

  2A and 2B are schematic views showing a testing machine according to an embodiment of the present invention, in which FIG. 2A is a plan view of the welded portion 2 of the annular test body 1 as viewed from above, and FIG. The front view which looked at the testing machine attached inside from the front, (C) is the elements on larger scale of the jig 3 for welding parts, and the cyclic | annular test body 1. FIG. As shown in FIG. 2, the welded portion 2 of the annular test body 1 corresponds to a welded portion facing groove 4 provided on the top of the welded portion jig 3 so as not to contact the welded portion jig 3. Installed. The annular test body 1 is obtained by cutting a steel pipe manufactured by the UOE pipe making process into an appropriate length. Inside the annular test body 1, a base material jig 5 is arranged on the opposite side of the welded part jig 3. The welded part jig 3 and the base material jig 5 are formed in an arc shape so that a portion facing the inside of the annular test body 1 follows the internal shape (circular shape) of the annular test body 1. The welding part jig 3 and the base material jig 5 are moved in opposite directions by the drive part 7. That is, in the example of FIG. 2, the welding portion jig 3 is pushed upward relatively by the driving portion 7, and the base material jig 5 is pushed downward relatively. Both the welding part jig 3 and the base material jig 5 may be moved by the driving part 7, or one of them may be fixed and the other may be moved. The drive unit 7 is a loading device such as a hydraulic cylinder.

  Moreover, if the curvature radius of the site | part which opposes the inside of the cyclic | annular test body 1 of the jig | tool 3 for welding parts is made the same in all the ranges, stress will concentrate on other than the weld part 2 of the cyclic | annular test body 1, and the weld part 2 will be concentrated. May not crack. Therefore, in order to cause the welded portion 2 to break, the curvature of the central portion 3c of the welded portion jig 3 corresponding to the vicinity of the welded portion 2 of the annular specimen 1 is made smaller than the curvature of the end portion 3s. It is necessary to concentrate stress on 2.

Specifically, as shown in FIG. 3, 30-60 respectively on both sides of the center of the top of the welding portion jig 3 (welded portion facing groove 4) with the center of the top portion of the welding portion jig 3 as a reference. The radius of curvature Rc of the welded part jig center part 3c in the range of ° and the curvature radius Rs of the welded part jig end part 3s formed adjacent to the outside of the welded part jig center part 3c are:
0.3Rc ≦ Rs ≦ 0.8Rc
It is necessary to satisfy In addition, the jig 3 for welding parts has comprised the left-right symmetric shape with respect to the center line L shown with the dashed line. Therefore, in FIG. 3, only the left half part of the jig 3 for welding parts is shown.

  In addition, as shown in FIG. 3, the range of the angle of the welding part jig | tool center part 3c is a center angle on the basis of the curvature center of the curvature radius Rc of the jig | tool center part 3c for welding parts. The position where this angle is 0 ° is the top of the welded part jig 3 provided with the welded part facing groove 4 as indicated by the alternate long and short dash line. The boundary between the welded jig center portion 3c and the welded jig end portion 3s is indicated by a broken line M. The center of curvature of the radius of curvature Rs of the welded jig end 3s is Rs on the boundary (dashed line M) between the welded jig center 3c and the welded jig end 3s, as indicated by x. The position where / Rc is 0.3 to 0.8.

  The radius of curvature Rc of the welded part jig 3 in the range of at least ± 30 ° (both sides 30 °) (the welded part jig central part 3c) is made constant with the top of the welded part jig 5 as the center. This is because the pipe expansion by the segment of the production line is accurately reproduced. On the other hand, the radius of curvature Rs of the welded jig 3 in a range (weld jig end 3s) exceeding ± 60 ° (60 ° on both sides) with the top of the welded jig 5 as the center is the radius of curvature Rc. If the same, the crack may not occur in the welded portion 2 of the annular test body 1.

  The curvature radius Rc of the welding portion jig central portion 3c within 30 to 60 ° on both sides with the top portion of the welding portion jig 3 as the center and the curvature radius of the base material jig 5 are the product (annular specimen). It is preferable to be equivalent to the radius of 1). Thereby, the deformation state of the steel pipe at the time of pipe expansion by the segment of the pipe expander on the production line can be reproduced with extremely high accuracy.

  Further, in order to cause the welded portion 2 to break, it is preferable to process the vicinity of the welded portion 2 of the annular specimen 1 with a narrow width as shown in FIG. In FIG. 2 (A), the welded part 2 by seam welding is provided in the reduced width processed part of the annular test body 1.

  Further, the welded part jig 3 may be integrated, but as shown in FIG. 4, the welded part facing jig 3a including the welded part facing groove 4 and the other welded part base jig 3b are divided. It is preferable that The welded part facing jig 3a and the welded part base jig 3b are joined by bolts 6 as illustrated in FIG.

  In the welded part jig 3, the vicinity of the welded part facing groove 4, specifically, the range within 10 to 30 ° on both sides from the center of the welded part facing groove 4 is a portion with the highest load and may be damaged. Is higher than other parts. Therefore, maintenance costs can be reduced by making this part separable. In addition, the center angle within a range of 10 to 30 ° on both sides from the center of the weld-facing groove 4 is based on the center of curvature of the radius of curvature Rc as in FIG.

  Further, by making the welded part facing jig 3a separable, it becomes possible to investigate the influence of the coefficient of friction of the pipe expander segment on the spread cracking property. Specifically, a plurality of welded portion facing jigs 3a having different friction coefficients from the welded portion base jig 3b are prepared, and the friction of the welded portion facing jig 3a contacting the vicinity of the welded portion 2 of the annular specimen 1 is prepared. The expansion crack is evaluated by changing the coefficient. If a lubricant is used in combination, the friction coefficient can be changed from 0.04 to 0.4.

  The load of the drive unit 7 is measured by a load meter 8, and the displacement generated between the base material jig 5 and the welded part jig 3 is measured by a displacement meter 9. It is preferable to attach a strain gauge 11 as a strain measuring means near the welded portion 2 of the test body 1 and measure the strain in the circumferential direction with the strain gauge 10. The strain gauge 11 can be affixed to a portion of the inner surface side around the welded portion 2 where the welded jig 3 and the annular test body 1 do not contact each other by providing the welded portion facing groove 4. Thereby, the drive part 7 can be stopped when distortion reaches a predetermined value. Note that the strain gauge 11 may be attached to the welded portion 2.

  The outer diameter × wall thickness is φ914 × 16t, φ1016 × 19t, φ1219 × 20t, and the tensile strength is 840 to 1040 MPa before UBE steel pipe expansion. The pipe was expanded by the pipe expansion tester of the invention.

  FIG. 5 is a graph comparing the pipe expansion ratio in the actual machine and the displacement of the test machine when a crack occurs in the weld. FIG. 5 shows that there is a good correlation between the limit pipe expansion rate at which pipe expansion cracks occur in the actual machine and the limit displacement at which cracks occur in the test machine of the present invention.

  FIG. 6 is a comparison of the amount of circumferential strain around the welded part when a crack occurs in the welded part of the same steel pipe, using an actual machine and a test machine. The amount of circumferential strain was measured with a strain gauge. The strains at the time of occurrence of pipe expansion cracks agree well on both the outer surface and the inner surface of the steel pipe, indicating that the deformation state around the seam weld in the actual pipe expansion machine can be reproduced with the test machine of the present invention.

The effect by implementation of this invention is demonstrated below by an Example and a comparative example.
Table 1 shows the UOE steel pipe before expansion with product dimensions φ914 × 16t, φ1016 × 19t, φ1219 × 20t, steel pipe strength 840 to 1040 MPa and different peaking values. As an example, a weld joint tensile test in which a test piece is taken after flattening a seam weld according to API Spec 5L was performed, and the strains were compared when cracks occurred in each seam weld. When compared with the actual machine expansion, the weld joint test was flattened once, so the distortion at the time of cracking could not be evaluated accurately, but the distortion of the test machine was confirmed to match the actual machine well.

  Table 2 shows the range in which the segment radius of curvature differs from the product radius and the value of the radius of curvature of the welded steel pipe before product expansion with product dimensions of φ1219 × 20t, strength of 870MPa and φ1016 × 19t, strength of 930MPa. It is a result. In Comparative Examples 1, 2, 5, and 6, the segment curvature radius is 80% or more or 30% or less compared to the product radius. In Comparative Examples 3, 4, 7, and 8, the range in which the segment curvature radius differs from the product radius is within 30 ° or 60 ° or more on the left and right sides of the seam weld. do not do.

  According to the present invention, the tensile properties of the base metal and the welded part during the expansion of the steel pipe, such as the pipe expansion process for increasing the roundness, the oil well pipe expanded in the oil well, the line pipe breaking due to the internal pressure, in particular, -The intensity curve can be measured with high accuracy. Therefore, it is possible to easily identify the cause of the occurrence of cracks associated with tube expansion.

It is a schematic diagram of a pipe expander. BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram which shows the testing machine concerning embodiment of this invention, (A) is the top view which looked at the welding part 2 of the cyclic | annular test body 1 from the top, (A) is attached inside the cyclic | annular test body 1. FIG. FIG. 2C is a partially enlarged view of the welding part jig 3 and the annular specimen 1. It is a schematic diagram of the jig for welding parts of the testing machine of this invention, and has shown only the left half part of the jig for welding parts which makes a left-right symmetric shape. It is a schematic diagram of the separable welding part opposing jig | tool of this invention. It is a figure which shows the pipe expansion rate by a pipe expander, and the displacement of the testing machine of this invention. It is a figure which shows the distortion distribution after the pipe expansion by the pipe expander and the testing machine of this invention.

Explanation of symbols

1: Annular specimen 2: Welded portion 3: Welded portion jig 3a: Welded portion facing jig 3b: Welded portion base jig 4: Welded portion facing groove 5: Base material jig 6: Bolt 7: Drive Part 8: Load meter 9: Displacement meter 10: Strain meter 11: Strain gauge

Claims (4)

A base material jig and a welding part jig that are arc-shaped in a portion facing the inside of the annular test body, and a drive part that linearly moves the base material jig and the welding part jig in opposite directions. A welding portion facing groove on the top of the welding portion jig, and a radius of curvature Rc at the center of the welding portion jig formed adjacent to both sides of the welding portion facing groove, and the welding portion jig. The curvature radius Rs of the jig end portion for welding formed adjacent to the outside of the center portion is
0.3Rc ≦ Rs ≦ 0.8Rc
And the weld jig center part is formed in a range of 30 to 60 ° on both sides of the center of the weld-facing groove with respect to the center of the radius of curvature Rc. , Expansion crack evaluation equipment for welded steel pipes.   With reference to the center of the curvature radius Rc, a welding part facing jig that can be separated on the surface of the center part of the welding part jig in a range of 10 ° to 30 ° on both sides of the center of the welding part facing groove. The expansion crack evaluation apparatus for welded steel pipes according to claim 1, wherein the apparatus is provided.   In the pipe expansion crack evaluation apparatus according to claim 1 or 2, the welded portion of the annular test body is installed facing the groove facing the welded portion, and the welded portion jig and the base material jig are moved in opposite directions. However, a method for evaluating the expansion crack of a welded steel pipe, comprising measuring a load and a displacement acting between the base material jig and the welding part jig.   The method for evaluating expansion cracks in a welded steel pipe according to claim 3, wherein a strain measuring means is provided at or near the welded portion of the annular test body to measure the strain at the welded portion.

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