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Screw joint for oil pipe or casing

A technology of threaded joints and casings, which is applied in the field of threaded joints, casing threaded joints, and oil fields. It can solve the problems of low API thread connection strength, reduce thread peak stress, and poor stress corrosion resistance, so as to improve connection strength and anti-corrosion. Capability of stress corrosion, reduction of peak stress, effects of low processing cost

Inactive Publication Date: 2004-12-29
SHANGHAI JIAO TONG UNIV
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

According to the API standard, the oil pipe joint should be able to withstand at least 4 times of topping and unloading, and the casing joint at least 3 times without damage. buckle, damage the thread tooth surface, and sticking mainly occurs at both ends of the joint connection thread
(2) Low connection strength
The connection strength of the API thread is low, especially the API round thread, the connection strength is only about 70% of the pipe body
(3) Poor stress corrosion resistance
If the gaps between the threaded threads at both ends are increased and the increase is the same as in this design, the peak stress of the thread can be reduced only in a few cases, and the purpose will not be achieved in most cases, and the stress distribution will even be worsened.

Method used

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  • Screw joint for oil pipe or casing
  • Screw joint for oil pipe or casing

Examples

Experimental program
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Effect test

Embodiment 1

[0019] The present invention is used in the case of partial trapezoidal thread, which consists of pipe body 1, 3 and pipe coupling 2 screwed together by partial trapezoidal thread 4. The taper of the thread is 1:16, the thread height is 1.575mm, and the pitch is ( 25.4mm) 5 teeth, that is 5.08mm. The size of the pipe body is Φ139.7×7.72mm, the outer diameter of the coupling W=153.7mm, and the thickness of the big end face=5.21mm. The length of the engaging thread is 97.155mm, and there are 19 teeth in total. Material properties σs=552Mpa, E=2.1×10 5 MPa. After calculation, choose the variable pitch of 3 threads at both ends of the external thread, m x =0.014mm, m y=0.016mm, the pitch of the middle part of the external thread is 5.08mm, the pitch of the three teeth at the far right is 5.08-0.016=5.064mm, and the pitch of the three teeth at the leftmost end is 5.08+0.014=5.094mm, the axial clearance t3'= formed at this time 0.048mm, t3=0.042mm, t2'=0.032mm, t2=0.028mm, t1'=...

Embodiment 2

[0021] When the present invention is used for round threads, the thread taper is 1:16, the height is 1.810mm, and the thread pitch is 8 teeth per inch (25.4mm), that is, 3.175mm. The size of the pipe body is Φ139.7×7.72mm, the outer diameter of the coupling W=153.7mm, and the thickness of the big end face=5.79mm. Engaging thread length is 81.661mm, 26 teeth in total. Material properties σs=552Mpa, E=2.1×10 5 MPa. After calculation choose P 前 =P 后 =3.175+0.015=3.190mm, 3 threads at both ends of the external thread and then turned. After this treatment, the peak stress at both ends of the thread dropped by more than 1 / 3.

Embodiment 3

[0023] The present invention is used in the case of a cylindrical thread, the thread is a cylindrical thread, the tooth height is 1.575mm, and the pitch is 5.08mm. The outer diameter of the pipe is 140mm, the wall thickness is 10mm, the outer diameter of the coupling is 160.3mm, the wall thickness is 8.565mm, the length of the engaging thread is 45.72mm, and there are 9 teeth in total. Material properties σs=552Mpa, E=2.1×10 5 MPa. After calculation, choose 2 thread variable pitches at both ends of the external thread, m x = m y = 0.009mm, the pitch of the middle part of the external thread is 5.08mm, the pitch of the 2 threads at the far right is 5.08-0.009 = 5.071mm, the pitch of the 2 threads at the far left is 5.08+0.009=5.089mm, the axial gap formed at this time is at the extreme ends The second tooth is t1=0.018mm and the second inner tooth t2=0.009mm. After this treatment, the peak stress at both ends of the thread dropped by nearly 1 times.

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Abstract

A screw joint for oil pipe or casing is composed of pipe bodies and pipe collar, and is characterized by that said pipe collar has spiral thread whose pitch is segmentally changed. After the pipe collar is jointed with pipe, the axial gaps between internal and external threads are sequentially decreased from outside to inside. Its advantages are uniformly distributed load to spiral thread, high joint strength, and high power to resist stress corrosion.

Description

technical field [0001] The invention relates to a threaded joint, in particular to an oil and casing threaded joint, which belongs to the technical field of oil well pipe threaded connection. Background technique [0002] API (American Petroleum Institute) standard oil and casing round thread joints and partial trapezoidal thread joints are the most commonly used oil and casing thread joints in my country's oil fields, and are also the leading products of various oil and casing manufacturers in my country. The main advantage of this product is its mature technology and easy processing. However, due to its structural design itself, this thread also has some inherent disadvantages. For example: (1) prone to sticking. According to the API standard, the oil pipe joint should be able to withstand at least 4 times of topping and unloading, and the casing joint at least 3 times without damage. The buckle will damage the thread tooth surface, and the sticking mainly occurs at bot...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): E21B17/02
Inventor 高连新金烨
Owner SHANGHAI JIAO TONG UNIV
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