JPH03204493A - Screw joint excellent in torsional characteristic for petroleum drilling pipe - Google Patents

Abstract

PURPOSE:To obtain a screw joint excellent in torsional characteristic and used for petroleum drilling apparatus by maintaining the width of the surface whose corners are chamfered at the tip part of a female screw and a male scrw at 10% and less of the difference between the inside diameter of the tip part of the female screw and the outside diameter of the male screw. CONSTITUTION:Corners for chamfering are provided on a female screw joint 1 and a male screw joint 2. The ratio S(%) of the width t of the C corners and (the joint outside diameter D-the inside diameter d of the tip part of the male screw) is set at 10% and less. As a result, torsional characteristic is en hanced, and the tip part of the female screw becomes hard to warp.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a threaded joint for pipes used in oil drilling equipment such as trill vibes and drill collars.

[Prior Art] Due to recent use and deterioration of the oil well environment, oil country tubular goods are required to have higher performance and quality than API standards, and steel pipes with sufficient fracture toughness and corrosion resistance, as well as their manufacturing methods, have been developed.
Drill vibes and drill collars, which are oil drilling equipment, are used as bits.

Drill pipes have the role of transmitting driving force from the ground to the bits that crush rock, and are joined one by one using threaded connection members called tool joints.

A drill collar is a vibrator that is connected between the bit and the drill pipe and provides downward thrust to the bit. Each vibrator used in such oil drilling equipment is connected with a tapered threaded joint.

However, due to excessive twisting of this thread fiber during excavation, a portion of the female thread shoulder expands into a bell shape, causing damage, which increases excavation costs. Therefore, recently, as shown in Figure 3, the tip of the female thread and the male thread are elongated and an auxiliary shoulder (second
Measures have been taken to improve the torsional properties, such as by providing a 5-holder) A. However, the degree of improvement was small, and further improvement was desired. There are also problems such as incompatibility with API standard products.

[Problems to be Solved by the Invention] Breakage of a part of the female threaded shoulder due to tube expansion occurs due to compressive stress generated at the tip of the female thread. Conventionally, this compressive stress is considered to be uniform in the radial direction as shown in FIG. 4(a), and therefore, torsion-resistant design has been carried out in accordance with this. However, it was confirmed that this compressive stress is not actually uniform. This is because the tip of the female thread is not only compressed in the axial direction, but is also bent as shown in FIG. 4(b). Therefore, as shown in Figure 4(b), a much higher compressive stress is generated at the tip of the female thread than if it were simply compressed in the axial direction, and the design value was made assuming that it is uniform in the radial direction. Destruction occurs at values much lower than . In other words, it has been found that the fundamental means for improving torsional properties is to minimize the bending that occurs at the tip of the female thread.

As a result of various studies regarding means for solving this problem, the inventors of the present invention focused on the chamfered portion provided at the tip of the screw, particularly from the viewpoint of shape strength. As a result, it has been found that there is a significant relationship between the shape of the chamfer and the torsion characteristics, and that the problem can be solved by making this an appropriate shape.

[Means for Solving the Problems] That is, the present invention aims to provide a threaded joint shape for a pipe used in oil drilling equipment that has excellent torsion characteristics and meets such requirements. The gist of this is to keep the width t of the C surface, which is chamfered at the tip of the female thread and male thread, within 10% of the difference between the inner diameter of the female thread tip and the outer diameter of the male thread in threaded joints for oil drilling pipes. A threaded joint for oil drilling pipes with excellent torsional properties characterized by: 1. [Function and Examples] The present invention will be described in detail below with reference to embodiment threaded joints shown in the drawings.

FIG. 1 shows a cross-sectional shape of a threaded joint for petroleum cutting pipe according to an embodiment of the present invention, and as shown, the female thread fiber 1 and the male thread joint 2 are each provided with a C surface for chamfering. The ratio s of the width t of this C surface and (1 hand outer diameter - male screw tip inner diameter d)
It is important that (t) be within 10%.

FIG. 2 shows the relationship between the ratio S (96) and the torsional strength T. It can be seen from the figure that the torsional strength improves as S decreases. This is because the tip of the female thread becomes difficult to bend as the C-plane becomes smaller. however,
When S is less than 10%, there is almost no room for improvement in torsional strength. Therefore, by keeping S within 10%, torsional strength can be significantly improved.

Originally, the chamfer on the tip of the threaded part was provided for basically the same purpose as that on the end face of the normal machined part, but the width t of the C surface is approximately the same as the dimension specified by the API standard etc. 20-25% (exceptions: 12.
(as much as 5%). Therefore, the width t of the conventional C-plane is excessive, and on the contrary, even if it is set within 10% as in the present invention, there is no substantial problem in view of the purpose.

[Effects of the Invention] Next, the effects of the invention will be explained based on an example using the threaded joint according to the embodiment of the invention.

A torsion test was conducted on the API standard threaded joint shown in Table 1 and the material of the present invention. For API standard Dever threaded joints,
The torsion strength of the material of the present invention was improved by approximately 1.3 times. The reason for this is that as the C-plane becomes smaller, the tip of the female thread becomes bent.

As described above, by using the joint of the present invention in a pipe joint, the torsional characteristics thereof can be greatly improved.

There is also no problem with compatibility with API standard products.

Table 1 API standard products and inventive materials Thread type and dimensions Table 2 Torsion test results

[Brief explanation of drawings]

FIG. 1 shows a cross-sectional shape of a threaded joint for an oil drilling pipe according to an embodiment of the present invention. Fig. 2 shows the relationship between the width t of the 0 surface and the ratio S (*) of (111 hand outer diameter - male thread tip inner diameter d) and torsional strength T. Figure 3 is a cross-sectional view of the female thread and male thread of a pipe joint, which are conventional improved products, and Figures 4 (a) and (b) show the stress distribution at the tip of the female thread, which was considered in the conventional design, and the actual stress. distribution.

Claims (1)

[Claims] 1. In threaded joints for oil drilling pipes, the width t of the C surface that is chamfered on the tips of the female and male threads must be kept within 10% of the difference between the inner diameter of the female thread tip and the outer diameter of the male thread. A threaded joint for oil drilling pipes with excellent torsional properties.