Title of invention: Threaded joint for steel pipe
Technical field
[0001]
This disclosure relates to threaded joints for steel pipes used for connecting steel pipes.
Background technology
[0002]
For example, exploratory drilling or production of oil wells, natural gas wells (hereinafter collectively referred to as "oil wells"), development of non-conventional resources such as oil sands and shale gas, and recovery and storage of carbon dioxide (CCS:). In carbon dioxide capture and storage), geothermal power generation, hot springs, etc., steel pipes called oil well pipes are used. Threaded joints are used to connect the steel pipes.
[0003]
The types of threaded joints for steel pipes of this type are roughly divided into coupling type and integral type.
[0004]
In the case of the coupling type, the steel pipes are connected to each other via a tubular coupling. Specifically, female threaded portions are provided on the inner circumferences of both end portions of the coupling, and male threaded portions are provided on the outer circumferences of both end portions of the steel pipe. Then, one end of one steel pipe is screwed into one end of the coupling, and one end of the other steel pipe is screwed into the other end of the coupling, whereby the steel pipes are connected to each other. To. That is, in the coupling type, of the pair of directly connected pipe materials, one pipe material is a steel pipe and the other pipe material is a coupling.
[0005]
In the case of the integral type, the steel pipes are directly connected to each other and no separate coupling is used. Specifically, a female threaded portion is provided on the inner circumference of one end of the steel pipe, a male threaded portion is provided on the outer circumference of the other end, and a male threaded portion is provided on one end of one steel pipe provided with the female threaded portion. By screwing the other end of the other steel pipe, the steel pipes are connected to each other.
[0006]
Generally, the joint portion of the pipe end portion of the steel pipe in which the male screw portion is formed is referred to as a "pin" because it contains an element inserted into the female screw portion formed in the steel pipe or the coupling. The end of the steel pipe or coupling in which the female thread is formed is referred to as a "box" because it contains an element that accepts the male thread of the steel pipe. Since these pins and boxes are the ends of the pipe material, they are both tubular.
[0007]
In recent years, well development technologies such as DwC (Drilling with Casing) and horizontal drilling have become widespread, and the demand for high torque joints is rapidly increasing. The applicant of the present application has been referred to as a dovetail screw as a high torque joint for steel pipes having an outer diameter size of up to 9-5 / 8 ″ (244.5 mm), for example, as disclosed in Patent Document 1 below. We manufacture threaded joints that use tapered threads with a dovetail cross section. For wedge-shaped threads, the thread width of the male thread of the pin gradually narrows toward the tip along the spiral of the thread. The thread groove width of the female threaded portion of the opposite box is also gradually narrowed. Further, both the load surface and the insertion surface of the thread of the male threaded portion and the female threaded portion have a negative flank angle, and the pin and the pin When the fastening with the box is completed, the load surfaces and the insertion surfaces come into contact with each other, so that the threads of the male and female threads are firmly fitted to each other. With this configuration, a wedge-shaped screw is adopted. Threaded joints can exhibit high torque resistance.
Prior art literature
Patent documents
[0008]
Patent Document 1: International Publication No. 2015/194193
Outline of the invention
Problems to be solved by the invention
[0009]
The applicant of the present application is developing a high torque threaded joint for a steel pipe having a larger diameter. In the combined load load test of the prototype conforming to ISO 13679: 2011 Series A, there was a problem that the thread of the male thread of the pin was sheared and broken at the time of maximum tensile load.
[0010]
An object of the present disclosure is to provide a threaded joint for a large diameter steel pipe which can exhibit high torque resistance and high sealing performance and has shear resistance according to the size of the steel pipe to be connected.
Means to solve problems
[0011]
As a result of diligent studies to investigate the cause of thread breakage of the male thread portion in a high torque threaded joint for a large diameter steel pipe, the present inventors have conducted intensive studies to find out the tensile strength required for a large diameter steel pipe, in other words, the resistance. The thread width of the thread end on the tip side of the thread of the male thread is too small for the shear performance, and the thread for one round from this thread end (hereinafter, also referred to as "first thread"). First found that shear failure. When the first thread is sheared, the load is concentrated on the second thread located inside the second thread in the cross section, and the second thread is sheared. When the second thread is sheared, the thread is inside the second thread. It is considered that the load is concentrated on the third thread and shear failure occurs, and in this way, the thread of the male thread undergoes shear failure over a wide range one after another.
[0012]
In addition, in the case of a conventional tapered screw with a trapezoidal cross section, the pin and box may be deformed and the male and female threads may jump out when an excessive tensile load is applied, but the thread may break over a wide area. There was no. On the other hand, in the above-mentioned high torque thread joint, since the threads of the male and female threads having a dovetail cross section are firmly meshed with each other, the mesh between the male thread and the female thread is not disengaged.
[0013]
Therefore, in a high torque thread joint in which a male thread and a female thread are composed of wedge-shaped threads having a dovetail cross section, the rigidity of the first thread where shear failure first occurs is important for ensuring tensile strength. As an index for evaluating the shear resistance performance of the first thread, the present inventors set the minimum thread width W min at the thread bottom of the portion having the smallest thread width at the end on the tip side of the male thread as the axial length. , The screw bottom diameter D W of that part is the inner diameter of the cylinder, and the thread height TH is the wall thickness. I paid attention to it.
[0014]
In addition, the shear resistance required for the thread differs depending on the magnitude of the tensile load at which the main body of the steel pipe yields.
[0015]
As a result of these studies, the present inventors have provided shear resistance according to the size of the steel pipe at the end of the thread of the male thread, so that the thread can be used even in a threaded joint for a large diameter steel pipe. It has been found that high torque resistance and high sealing performance can be exhibited without causing shear failure.
[0016]
The threaded joint for steel pipes according to the present disclosure includes a tubular pin provided at the tip of a steel pipe having an outer diameter OD larger than 240 mm, and a tubular box into which the pin is screwed and fastened to the pin. The pin has a male screw formed on the outer periphery of the pin and composed of a taper screw having a dovetail shape in cross section. The box has a female screw formed on the inner circumference of the box and composed of a tapered screw having a dovetail shape in cross section. This female thread has a thread profile corresponding to the male thread. Further, the insertion surface pitch of the male screw and the female screw is smaller than the load surface pitch of the male screw and the female screw.
[0017]
The male screw satisfies the following equations (1) and (2).
[0018]
[Number 1]

W min ≧ 3.0 mm ・ ・ ・ (2)
[0019]
In the formulas (1) and (2), OD is the outer diameter of the steel pipe, ID is the inner diameter of the steel pipe, D W is the bottom diameter of the end portion on the tip side of the male screw on the load surface side, and TH is the inner diameter of the male screw. The thread height and W min are the thread widths of the thread bottoms at the end of the male thread on the tip end side.
The invention's effect
[0020]
According to the present disclosure, a threaded joint for a large diameter steel pipe, which can impart shear resistance according to the size of a large diameter steel pipe to a male thread of a pin and also has high torque resistance and high sealing performance, is provided. Can be provided.
A brief description of the drawing
[0021]
FIG. 1 is a vertical cross-sectional view of a threaded joint for steel pipe according to an embodiment along a pipe axis direction.
FIG. 2 is an enlarged vertical sectional view of a male screw and a female screw in FIG. 1.
FIG. 3 is an enlarged vertical sectional view of a screw end portion on the tip end side of a male screw in FIG. 1.
FIG. 4 is a graph showing the evaluation result of torque withstand performance by FEM analysis.
FIG. 5 is a diagram showing a path of load conditions in the evaluation of sealing performance by FEM analysis.
FIG. 6 is a graph showing the evaluation result of sealing performance by FEM analysis.
FIG. 7 is a graph showing the evaluation results of shear resistance performance by FEM analysis.
Embodiment for carrying out the invention
[0022]
The threaded joint for steel pipes according to the present embodiment includes a tubular pin provided at the tip of a steel pipe having an outer diameter OD larger than 240 mm, and a tubular box into which the pin is screwed and fastened to the pin. The pin has a male screw formed on the outer periphery of the pin and composed of a taper screw having a dovetail shape in cross section. The box has a female screw formed on the inner circumference of the box and composed of a tapered screw having a dovetail shape in cross section. This female thread has a thread profile corresponding to the male thread.
[0023]
Further, the insertion surface pitch of the male screw and the female screw is smaller than the load surface pitch of the male screw and the female screw. That is, the male screw and the female screw are wedge-shaped screws whose thread width gradually narrows toward the tip side.
[0024]
The male screw satisfies the following equations (1) and (2).
[0025]
[Number 2]

W min ≧ 3.0 mm ・ ・ ・ (2)
[0026]
In the formulas (1) and (2), OD is the outer diameter of the steel pipe, ID is the inner diameter of the steel pipe, D W is the bottom diameter of the end portion on the tip side of the male screw on the load surface side, and TH is the inner diameter of the male screw. The thread height and W min are the thread widths of the thread bottoms at the end of the male thread on the tip end side. The thread heights of the male and female threads are approximately equal. The thread height of the male thread and the thread height of the female thread are uniform over the entire length of the spiral complete thread portion.
[0027]
More preferably, the male screw satisfies the following formula (3).
[0028]
[Number 3]

[0029]
In the threaded joint for steel pipe according to the present disclosure, the thread height TH of the male thread is preferably 1.8 mm or more in order to obtain sufficient torque resistance performance. On the other hand, if the thread height TH of the male screw is too high, a deep thread groove is formed on the inner circumference of the box and the tensile strength of the box is lowered. Therefore, the thread height TH of the male screw is 2.3 mm. The following is preferable.
[0030]
The cross-sectional shape of the thread top of the male and female threads and the cross-sectional shape of the valley of the male and female threads may be line segments parallel to the axis of the steel pipe, and the male and female threads may be line segments. It may be a line segment inclined along the entire taper angle of.
[0031]
The "male thread" and "female thread" defined in the claims may be a complete threaded portion, and the range in which the fully threaded portion of the male thread and the fully threaded portion of the female thread are fitted in the fastened state of the pin and the box is 40. It may have an axial length of ~ 60 mm. An incomplete threaded portion may be continuously provided on the tip end side of the complete threaded portion constituting the male and female threads. An incomplete threaded portion or another complete threaded portion having a constant thread width is continuously provided on the base end side (pipe body side of the steel pipe) of the complete threaded portion constituting the male and female threads defined in the claims. It may have been done. In the present disclosure, the completely threaded portion may be a portion where the thread height is uniformly continuous, and the incomplete threaded portion may be a portion where the thread height gradually decreases. In the fastened state, both the load surface and the insertion surface of the thread of the complete thread and the incomplete thread of the male thread may be in contact with the load surface and the insertion surface of the thread of the female thread, respectively. In the fastened state, both the load surface and the insertion surface of the thread of the female thread and the incomplete thread may be in contact with the load surface and the insertion surface of the thread of the male thread, respectively.
[0032]
Both the load surface and the insertion surface of the thread having a dovetail cross section have a negative flank angle. For example, the flank angles of the load surface and the insertion surface may be −10 ° to -1 °. The flank angle of the load surface is the angle formed by the load surface and the straight line orthogonal to the pipe axis CL (see FIG. 1) in the vertical cross section. The flank angle of the insertion surface is orthogonal to the insertion surface and the tube axis CL in the vertical cross section.It is the angle formed by the straight line. When the load surface or the insertion surface is parallel to a straight line orthogonal to the tube axis CL, the flank angle is 0 °. When the load surface or insertion surface of the male screw is tilted outward in the radial direction, their flank angles are positive values. On the contrary, when the load surface or the insertion surface of the male screw is tilted inward in the radial direction, their flank angles are negative values. Further, when the load surface or the insertion surface of the female screw is tilted inward in the radial direction, their flank angles are positive values. Conversely, if the loading or insertion surfaces of the female threads are tilted outward in the radial direction, their flank angles are negative.
[0033]
The outer diameter of the pipe body of the steel pipe is more preferably 245 mm or more, and further preferably 270 mm or more. The outer diameter of the main body of the steel pipe is preferably 400 mm or less, more preferably 350 mm or less, and further preferably 310 mm or less. The pipe body of the steel pipe preferably has a substantially uniform wall thickness over the entire length in the axial direction. Further, it is preferable that the pipe body of the steel pipe has a substantially uniform outer diameter and inner diameter over the entire length in the axial direction. The pin is provided at the end of the pipe body of the steel pipe.
[0034]
When making a steel pipe, the inner and outer surfaces are rolled while rotating with a tool. However, because it is affected by various factors such as the tool position during rolling, tool wear, and rolling temperature, the cross-sectional shape of the steel pipe is not necessarily a perfect circle, but may be deformed into a non-round shape such as an ellipse. Regardless of the shape of a perfect circle or non-round, the outer diameter of the manufactured steel pipe is measured at multiple points in the circumferential direction, and the maximum value is the value specified by API (American Petroleum Institute) (the current standard is steel pipe). If it is within 101% of the nominal value of the outer diameter), it is shipped as a accepted product. The outer diameter OD of the steel pipe in the present disclosure may be a nominal value of the outer diameter of the steel pipe.
[0035]
Regarding the inner diameter, as disclosed in Japanese Patent Application Laid-Open No. 2016-130668, the inner diameter and inner surface of the manufactured steel pipe are inspected using a drift gauge. The diameter of this drift gauge is also defined by the API standard, and in the case of a steel pipe of 10-3 / 4 "65.7 # (pipe body outer diameter: 273.05 mm, pipe body inner diameter: 242.82 mm), the drift diameter is (steel pipe). Since the nominal inner diameter is -5/32) inches, if the minimum inner diameter of the manufactured steel pipe is 242.82-5 / 32 x 25.4 = 238.851 mm or more, it can be shipped as a accepted product. The inner diameter ID of the steel pipe may be a nominal value of the inner diameter of the steel pipe.
[0036]
Further, the thread height TH may be the nominal value of the thread height of the steel pipe. Regarding the D W and W min of the above formula (1), various parameters that define the profile of the tapered screw, such as the screw length, the thread taper angle, the thread height, the load surface pitch, and the insertion surface pitch, respectively. It may be a value calculated based on a nominal value.
[0037]
Note that the above nominal value conforms to the API standard in the case of oil country tubular goods, and the dimensions of each part can be assumed to be the nominal value as long as it is within the tolerance specified in the API standard. The outer diameter OD, inner diameter ID, thread height TH, D W, and W min may be measured values ​​thereof. When the cross-sectional shape of the steel pipe is not a perfect circle, it is preferable to use the respective values ​​when the steel pipe is actually or simulated so that the cross-section becomes a perfect circle.
[0038]
Hereinafter, the threaded joint for steel pipes according to this embodiment will be described with reference to the drawings. In the figure, the same and corresponding configurations are designated by the same reference numerals, and the same description is not repeated.
[0039]
With reference to FIG. 1, the steel pipe threaded joint 1 according to the present embodiment includes a tubular pin 10 and a tubular box 20. The pin 10 is formed at the end of the steel pipe 2. The box 20 is formed at the end of the coupling 3 and the pin 10 is inserted and fastened to the pin 10. In the present specification, a portion other than the end portion of the steel pipe 2 may be referred to as a “pipe body”. FIG. 1 shows the axial center CL of the steel pipe 2, the outer diameter OD of the pipe body of the steel pipe 2, that is, the diameter of the outer peripheral surface, and the inner diameter ID of the pipe body, that is, the diameter of the inner peripheral surface. The steel pipe 2 of the present embodiment is a large diameter steel pipe having an outer diameter OD of a pipe body larger than 240 mm.
[0040]
The pin 10 has a male screw 11 and a lip 12. The male screw 11 is composed of a thread formed spirally on the outer peripheral surface of the pin 10. The male screw 11 is composed of a wedge-shaped screw whose thread width gradually narrows toward the tip end side of the pin 10. The thread of the male screw 11 has a dovetail-shaped cross-sectional shape. The lip 12 extends toward the tip end side of the screw end portion on the tip end side of the male screw 11. A pin seal 13 is provided on the outer peripheral surface of the lip 12. In the illustrated example, the pin seal 13 is composed of a cylindrical sealing surface having an arcuate cross section, but the cross-sectional shape of the pin seal 13 may be a straight line or a combination of a straight line and an arc. ..
[0041]
The box 20 has an open end for receiving the pin 10. The box 20 includes a female screw 21 provided on its inner peripheral surface and a box seal 22. The female screw 21 is composed of a thread formed spirally on the inner peripheral surface of the box 20 corresponding to the male screw 11. The female screw 21 is composed of a wedge-shaped screw whose thread width gradually widens from the open end of the box 20 to the inner side. The thread of the female thread 21 has a dovetail-shaped cross-sectional shape. The box seal 22 is formed of a tapered surface provided on the inner side of the box 20 with respect to the female screw 21. The box seal 22 may be formed of a cylindrical seal surface having an arc-shaped cross section, or may have a shape in which a straight line and an arc are combined in a cross section.
[0042]
As shown in FIGS. 1 and 2, the male screw 11 of the present embodiment has a pin complete thread portion and a pin incomplete thread portion. The pin completely threaded portion has a predetermined thread height TH, and is a portion in which a thread is formed by a predetermined load surface pitch LP and an insertion surface pitch SP. In the pin incomplete threaded portion, the virtual tapered surface that defines the tapered shape of the tapered thread intersects the outer surface of the steel pipe 2, so that the cutting depth of the outer surface of the steel pipe 2 is insufficient and a predetermined thread height is formed. It is a part that has not been done. Further, the female screw 21 has a box complete screw portion and a box incomplete screw portion. The box complete threaded portion is provided from the vicinity of the open end of the box 20 to the vicinity of the second thread of the male thread 11 of the pin 10. The thread of the box incomplete thread portion engages with the first thread 11A of the male thread 11 of the pin 10 in the fastened state of the pin 10 and the box 20. In the fastened state, as shown in FIG. 2, a slight gap (for example, about 0.1 mm) is formed between the thread top surface of the male thread 11 and the thread bottom surface of the female thread 21, and the thread top surface of the female thread 21 and the male thread 21 are formed. The thread height of the fully threaded portion of the male thread 11 is smaller than the thread height of the fully threaded portion of the female thread 21 so as to be in contact with the bottom surface of the thread of 11. The range in which the fully threaded portion of the male screw 11 and the fully threaded portion of the female screw 21 fit in the fastened state preferably has an axial length of 40 to 60 mm.
[0043]
As shown in FIGS. 1 and 2, the load surfaces 11L and 21L and the insertion surfaces 11S and 21S of the threads of the male screw 11 and the female screw 21 each have a negative flank angle θ. The flank angles θ of the load surfaces 11L and 21L and the insertion surfaces 11S and 21S may be the same, or different flank angles may be set.
[0044]
In the state where the pin 10 and the box 20 are fastened, the insertion surface 11S and the load surface 11L of the thread of the male screw 11 come into contact with the insertion surface 21S and the load surface 21L of the thread of the female screw 21, respectively. Is locked to the box 20, thereby exhibiting high torque resistance, and the pin seal 13 is fitted to the box seal 22 in a tightly fitted state to exhibit high sealing performance.
[0045]
In the present embodiment, as shown in FIGS. 1 and 3, the male thread 11A of the thread end portion on the tip end side of the complete thread portion of the male thread 11 satisfies the following equations (1) and (2). Eleven profiles have been designed.
[0046]
[Number 4]

W min ≧ 3.0 mm ・ ・ ・ (2)
[0047]
In the formulas (1) and (2), OD is the outer diameter of the steel pipe 2, ID is the inner diameter of the steel pipe, D W is the bottom diameter of the thread 11A on the load surface side, and TH is the thread on the load surface side of the thread 11A. The thread height with respect to the groove, W min, is the thread width of the thread bottom of the thread 11A.
[0048]
In the threaded joint 1 for steel pipes according to the present embodiment, the male thread 11 and the female thread 21 are composed of wedge-shaped threads, and the minimum thread width at the bottom of the first thread 11A of the male thread 11 is secured at 3 mm or more. By configuring the male screw 11 so as to satisfy the formula (1), high torque resistance, high sealing performance, and high shear resistance can be achieved in a well-balanced manner.
[0049]
This disclosure can be applied not only to coupling type but also to integral type threaded joints. In addition, the present disclosure is not limited to the above-described embodiment, and various changes can be made without departing from the spirit of the present disclosure.
Example
[0050]
In order to confirm the effect of the threaded joint for steel pipes according to this embodiment, the torque resistance, sealing performance and shear resistance were evaluated by numerical analysis simulation by the elasto-plastic finite element method.
[0051]

In FEM analysis, multiple specimens (analysis models) with different screw profiles were created, and elasto-plastic finite element method analysis was performed for each specimen to compare the differences in performance. Each specimen was a coupling type threaded joint having the basic structure shown in FIGS. 1 to 3, and the following steel pipes were used.
Steel pipe size: 10-3 / 4 "65.7 # (pipe body outer diameter: 273.05 mm, pipe body inner diameter: 242.82 mm)
Material: API standard oil country tubular goods Q125 (nominal yield strength YS = 862MPa (125ksi))
Frank angle of screw load surface and insertion surface: -5 °
[0052]
Table 1 shows the dimensions of the threaded joints used in the analysis.
[0053]
[table 1]

[0054]
In Table 1, the test piece # 1 was created according to the same design rules as the conventional threaded joint for medium and small diameter steel pipes, and the test pieces # 2 to # 7 were based on the design of the test piece # 1. , The load surface pitch LP and the insertion surface pitch SP are changed. The test piece # 8 has a screw profile based on the test piece # 1, having a load surface pitch LP of 11.00 mm, an insertion surface pitch SP of 10.50 mm, and a thread height TH increased. The test piece # 9 has a screw profile based on the test piece # 8 in which the screw length is increased by reducing the screw taper. When the value of the formula (1) and the value of W min were obtained for the specimens # 1 to # 9, the specimens # 1 to # 3 are comparative examples not within the scope of the present disclosure, and the specimens # 4 to # # 9 is within the scope of this disclosure. In Table 1, the "screw length" is the total length of the screw including the complete screw portion and the incomplete screw portion. The "thread taper" is an angle twice the angle between the straight line passing through the middle of the load surface of each thread in the cross section of the male thread in the height direction and the axis of the steel pipe.
[0055]
[Evaluation of torque resistance performance]
For torque performance, the value MTV (Maximum Torque Value) at which the fastening torque diagram begins to yield was defined as the yield torque and evaluated based on that value. The evaluation results are shown in Table 1 and FIG.
[0056]
[Evaluation of sealing performance]
For the sealing performance evaluation, as shown in FIG. 5, a compound load simulating a substantive test was applied, and the sealing contact force generated on the seals 13 and 22 was calculated. The value with the lowest contact force in the load path was defined as the minimum seal contact force Fs, and the sealing performance was evaluated based on the magnitude of the value. The evaluation results are shown in Table 1 and FIG.
[0057]
[Shear resistance]
Regarding the shear resistance performance, a load of 90% of the tensile load at which the pipe body of the steel pipe 2 yields is applied, and the surface near the screw bottom on the load surface side of the first thread 11A, which is the starting point of shear failure of the male screw 11. Calculate the shear plastic strain Ps of the surface near the R part that connects the load surface and the surface of the thread groove on the load surface side), and the smaller the absolute value of this value, the more the shear resistance It was evaluated as having excellent performance. The evaluation results are shown in Table 1 and FIG.
[0058]
[Evaluation results]
As shown in FIG. 4, for the specimens # 1 to # 7, although the MTV decreased slightly due to the increase in the load surface pitch LP of the thread, the torque resistance required for the product was secured. Can be evaluated. Further, in the specimens # 8 and # 9, the MTV increased slightly due to the improvement in the rigidity of the male screw and the slight increase in the screw length. From these results, it can be evaluated that the threaded joint according to the present disclosure exhibits the same torque resistance performance as the threaded joint according to the same design rule as the conventional threaded joint for medium and small diameter steel pipes.
[0059]
On the other hand, as shown in FIG. 6, for the specimens # 1 to # 7, the minimum seal contact force Fs remained almost unchanged even if the load surface pitch LP of the thread changed. In addition, the sealing performance of the specimens # 8 and # 9 was slightly lower than that of the specimens # 1 to # 7. However, the amount of decrease is suppressed to an acceptable range, and it can be evaluated that the sealing performance required for the product is ensured. In any of the specimens, the minimum seal contact force Fs was in the external pressure + compression load steps (9) and (17).
[0060]
Regarding the shear resistance performance, as shown in FIG. 7, in the specimens # 2 and # 3 which do not satisfy the conditions of the present disclosure, the shear plastic strain Ps was hardly reduced as compared with the specimen # 1. On the other hand, it can be seen that in all of the specimens # 4 to # 9 according to the present disclosure, the shear plastic strain Ps can be significantly reduced as compared with the specimen # 1.
[0061]
From the above, it was found that the specimens # 4 to # 9 according to the present disclosure have the same torque resistance and sealing performance as the specimen # 1, but the shear resistance is significantly improved.
[0062]
[Actual tube test]
Samples were manufactured for specimens # 1 and # 9, and shear resistance performance was evaluated by an actual tube test.
[0063]
As for the surface treatment of the test sample, the pin was not surface-treated after cutting, and the box was surface-treated with manganese phosphate. When fastening the pin and box, BOL4010NM, which is an environment-friendly lubricant, is applied to the joint, and after fastening with a predetermined torque, the tensile load and compression of 90% of the tensile compressive load in which the pipe body of the steel pipe yields. A tensile compression test was conducted in which loads were applied alternately, and the presence or absence of shear failure of the male thread of the pin was confirmed.
[0064]
As a result of such a test, in the specimen # 1, the male screw was shear-broken during the 15th tension, whereas in the specimen # 9, shear failure did not occur even by repeated loading of the tensile load and the compressive load 25 times. rice field. This demonstrated the excellent shear resistance of the threaded joint according to the present disclosure.
Code description
[0065]
1: Threaded joint for steel pipe, 10: Pin, 11: Male thread, 20: Box, 21: Female thread
2: Steel pipe
The scope of the claims
[Claim 1]
A tubular pin provided at the tip of a steel pipe having an outer diameter OD larger than 240 mm and a tubular box into which the pin is screwed and fastened to the pin are provided, and the pin is formed from a tapered screw formed on the outer periphery of the pin. The box has a female screw made of a tapered screw formed on the inner circumference of the box, and the thread cross-sectional shape of the male screw and the female screw is a dovetail shape, and the load surface of the male screw and the female screw is formed. In a threaded joint for steel pipes in which the insertion surface pitch of the male and female threads is smaller than the pitch.
The male thread is a threaded joint for steel pipes that satisfies the following formulas (1) and (2).
[Number 1]

W min ≧ 3.0 mm ・ ・ ・ (2)

In the formulas (1) and (2), OD is the outer diameter of the steel pipe, ID is the inner diameter of the steel pipe, D W is the bottom diameter of the end portion on the tip side of the male screw on the load surface side, and TH is the inner diameter of the male screw. The thread height and W min are the thread widths of the thread bottoms at the end of the male thread on the tip end side.
[Claim 2]
In the threaded joint for steel pipe according to claim 1, the male thread is a threaded joint for steel pipe that satisfies the following formula (3).
[Number 2]

[Claim 3]
The threaded joint for steel pipe according to claim 1 or 2, wherein the thread height (TH) of the male thread is 1.8 mm or more.
[Claim 4]
The threaded joint for steel pipe according to claim 1, 2, or 3, wherein the thread height (TH) of the male thread is 2.3 mm or less.
[Claim 5]
The threaded joint for steel pipe according to any one of claims 1 to 4, wherein the taper angle of the male thread is 5.72 ° or less.