阅读说明：本技术 钢管用螺纹接头 (Threaded joint for steel pipe ) 是由 奥洋介 于 2018-04-09 设计创作，主要内容包括：提供一种能够兼顾耐扭矩性能的确保和制造成本的降低的钢管用螺纹接头。钢管用螺纹接头(1)包括：公扣(10),其在外周具有外螺纹部(11)；以及母扣(20),其在内周具有内螺纹部(21),与公扣(10)紧固。外螺纹部(11)具有主外螺纹(111)和副外螺纹(112)。主外螺纹(111)由具有恒定的螺纹牙宽度和螺纹槽宽度的梯形螺纹构成。副外螺纹(112)配置于主外螺纹(111)的螺纹槽,螺纹牙宽度和螺纹牙高度比主外螺纹(111)的螺纹牙宽度和螺纹牙高度小。在公扣(10)的管轴线方向的截面中,相邻的主外螺纹(111)的插入牙侧面(111c)的牙型半角和副外螺纹(112)的载荷牙侧面(112d)的牙型半角比0度大。(Provided is a threaded joint for steel pipes, which can ensure torque resistance and reduce manufacturing costs at the same time. A threaded joint (1) for steel pipes comprises: a male buckle (10) having an external thread part (11) on the outer periphery; and a female buckle (20) having an internal thread portion (21) on the inner periphery and fastened to the male buckle (10). The male screw portion (11) has a main male screw (111) and a sub male screw (112). The main male thread (111) is formed of a trapezoidal thread having a constant thread ridge width and thread groove width. The sub male screw (112) is disposed in the thread groove of the main male screw (111), and the thread width and the thread height are smaller than those of the main male screw (111). In the cross section of the pin (10) in the pipe axis direction, the profile half angle of the insertion flank surface (111c) of the adjacent main male thread (111) and the profile half angle of the load flank surface (112d) of the sub male thread (112) are greater than 0 degree.)

1. A threaded joint for steel pipes, wherein,

this threaded joint for steel pipe includes:

a male buckle having a tubular shape and an external thread portion on an outer periphery thereof; and

a female buckle having a tubular shape, an inner thread part corresponding to the outer thread part on an inner circumference, and fastened to the male buckle,

the external thread portion includes:

a main external thread composed of a trapezoidal thread having a constant thread ridge width and thread groove width; and

a sub male screw disposed in a thread groove of the main male screw and having a thread width and a thread height smaller than those of the main male screw,

the primary male thread and the secondary male thread each have an stabbing flank and a load flank disposed on a side opposite to the stabbing flank,

in a cross section of the pin in a pipe axis direction, a thread form half angle of an insertion thread side surface of the main male thread and a thread form half angle of a load thread side surface of the sub male thread adjacent to each other are larger than 0 degree.

2. A threaded joint for steel pipes according to claim 1,

the thread ridge of the auxiliary external thread has a longitudinal sectional area which is 15-40% of the longitudinal sectional area of the thread ridge of the main external thread adjacent to the auxiliary external thread.

Technical Field

The present disclosure relates to a threaded joint for joining steel pipes.

Background

Oil well pipes such as casings and pipes are used in oil wells, gas wells, and the like (hereinafter, also referred to as "oil wells" collectively) to extract underground resources. The oil country tubular goods are formed by connecting steel pipes in sequence, and threaded joints are used for the connection.

The form of such a threaded joint for steel pipes is roughly classified into a combination type and an integral type. In the combined type, one of the pair of pipes to be connected is a steel pipe, and the other pipe is a short pipe called a pipe joint. In this case, male screw portions are formed on the outer peripheries of both end portions of the steel pipe, and female screw portions are formed on the inner peripheries of both end portions of the pipe joint. Then, the male screw portion of the steel pipe is screwed into the female screw portion of the pipe joint to fasten and connect the two. In the integral type, both of the pair of pipes to be connected are steel pipes, and no additional pipe joint is used. In this case, an external thread portion is formed on the outer periphery of one end portion of the steel pipe, and an internal thread portion is formed on the inner periphery of the other end portion. Then, the male screw portion of one steel pipe is screwed into the female screw portion of the other steel pipe, whereby the two are fastened and coupled.

In general, a joint portion of a pipe end portion formed with an external thread portion includes an element to be inserted into an internal thread portion, and is therefore called a pin. On the other hand, the joint portion of the pipe end portion formed with the female screw portion includes an element for receiving the male screw portion, and is therefore called a box. The male buckle and the female buckle are end parts of the pipe, and are tubular.

In recent years, with the development of new technologies such as horizontal excavation and inclined excavation, high torque resistance and sealing performance are required for threaded joints. In order to achieve both torque resistance and sealing performance, a method of applying, for example, a dovetail-shaped tapered thread, also called a wedge thread, to a threaded portion is effective. In a threaded joint having a wedge thread, the thread width of the male thread portion (pin) becomes narrower toward the tip in the advancing direction of the right-hand thread along the helix of the thread, and the thread groove width of the opposite female thread portion (box) also becomes narrower toward the tip in the advancing direction of the right-hand thread along the helix of the thread. In a wedge thread, both the load flanks (hereinafter also referred to as "load faces") and the stab flanks (hereinafter also referred to as "stab faces") are at negative angles, and the load faces and the stab faces contact each other. This allows the entire screw portion to be firmly fitted, thereby exhibiting high torque resistance. In addition, in the fastened state, the thread crest surface of the screw portion and the thread groove bottom surface contact each other, and therefore, the sealing performance can be ensured.

On the other hand, patent documents 1 and 2 disclose a threaded joint in which torque resistance is improved without using a wedge thread.

In the threaded joint of patent document 1, the load surface and the insertion surface of the threaded portion are each formed in a Z-shape in cross section. In this threaded joint, the load surfaces and the insertion surfaces of such shapes are brought into contact with each other, thereby controlling the tightening of the threaded portion in the pipe axial direction and the radial direction.

In the threaded joint of patent document 2, each load surface of the threaded portion is formed in a hook-like shape in cross section. Therefore, the hook-shaped load bearing surfaces are fitted to each other at the time of fastening. This allows the threaded portion to receive a part of the torque received by the torque shoulder, thereby suppressing plastic deformation of the torque shoulder and achieving high torque resistance.

The present specification refers to the following prior art documents.

Patent document 1: specification of U.S. patent application publication No. 2008/0073909

Patent document 2: japanese laid-open patent publication No. 2002-

Disclosure of Invention

However, in a threaded joint in which a wedge thread is applied to a threaded portion, the ridge width of the male thread portion and the groove width of the female thread portion corresponding thereto vary. This makes it difficult to cut the threaded portion and takes a cutting time, which increases the manufacturing cost. From the viewpoint of reducing the manufacturing cost, it is also conceivable to apply an API (American petroleum institute) standard buttress thread (trapezoidal thread) to the threaded portion. However, in the case of a threaded joint to which a buttress thread is applied, a torque amplification mechanism such as a torque shoulder is not provided, and high torque resistance performance cannot be exhibited.

An object of the present disclosure is to provide a threaded joint for a steel pipe that can ensure torque resistance and reduce manufacturing cost at the same time.

The threaded joint for a steel pipe of the present disclosure includes a tubular pin and a tubular box. The male buckle has an external thread portion at an outer periphery. The female buckle has an internal thread portion corresponding to the external thread portion on an inner periphery thereof, and is fastened to the male buckle. The external thread portion includes a primary external thread and a secondary external thread. The main external thread is formed by a trapezoidal thread having a constant thread ridge width and thread groove width. The sub male screw is disposed in a thread groove of the main male screw, and has a thread width and a thread height smaller than those of the main male screw. The main male thread and the sub male thread each have an stabbing flank surface and a load flank surface disposed on the opposite side of the stabbing flank surface. In a cross section of the pin in the pipe axis direction, a thread form half angle of an insertion thread side surface of adjacent main male threads and a thread form half angle of a load thread side surface of the sub male thread are larger than 0 degree.

According to the threaded joint for a steel pipe of the present disclosure, the manufacturing cost can be reduced while torque resistance performance is ensured.

Drawings

Fig. 1 is a longitudinal sectional view of a threaded joint for steel pipes according to an embodiment.

Fig. 2 is a vertical cross-sectional view of the threaded portion of the threaded joint for steel pipes shown in fig. 1.

Fig. 3 is a longitudinal sectional view of a threaded joint for steel pipes according to the prior art (comparative example).

Fig. 4 is a graph showing the yield torques of the threaded joints for steel pipes of the examples and comparative examples.

Fig. 5 is a graph showing the minimum sealing contact force of the threaded joints for steel pipes of the examples and comparative examples.

Detailed Description