JP2008057640A - Special screw fitting for oil well pipe, and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the dispersion of sealing performance due to the dispersion of the surface treatment, such as cutting, shot blasting, etc. in the finishing step, and to furthermore improve the sealing performance. <P>SOLUTION: When a screw connecting portion 3 is formed between a pin 1 and a box 2. a pin screw is screwed into a box screw, and then the fastening and loosening operations are carried out one or more times. After that, the final fastening is carried out. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a special threaded joint for oil well pipes and a method for manufacturing the same, and in particular, a special threaded joint for oil well pipes that reduces variation in sealing performance due to variations in surface treatment such as cutting or shot blasting and further improves sealing performance. And a manufacturing method thereof.

In recent years, oil wells and gas wells that are easy to develop have decreased, and wells with higher depth and higher temperature and pressure have increased. In addition, with the progress of drilling technology, wells with more complicated shapes such as inclined wells and horizontal wells are increasing. Along with this, requirements for threaded joints of oil well pipes, such as airtightness under complex loads such as tension, compression, internal / external pressure, and bending, are becoming increasingly sophisticated. (Non-Patent Document 1)
As shown in Fig. 1, a special threaded joint for oil well pipes is composed of a male pin 1 and a female box (or coupling) 2 to be screwed together, and both of them are screwed at locations corresponding to each other. This is a threaded joint having a portion 3 and a seal portion 4 connected to one side of the screw fastening portion 3 by metal-metal contact, or a shoulder portion 5 further connected thereto. The screw fastening portion 3 is provided with a taper screw. In addition, the taper screw of the screw fastening part on the pin side is called a pin screw, and that on the box side is called a box screw.

The seal portion is generally cut at a feed rate of about 0.1 mm / rotation with a diamond-shaped tool called a point cut tool having a tip of about R0.8 mm, and the surface roughness after processing is finished to Ra ≦ 1.6 μm. In addition, alloy steel oil well pipes containing 9% or more of Cr are prone to galling called goling when the joint is fastened. To prevent this, the pin side surface is usually made of glass, alumina, ceramic, stainless steel, etc. A blasting process using the shot grains is applied, and the box side surface is subjected to a plating process such as copper plating. In addition, the pin surface roughness after blasting rises to about Ra 1.0 to 3.0 μm.
JFE Technical Report No. 9 (August 2005) p.46-50

The surface after the above-mentioned finishing cutting or surface treatment is considered to be a kind of oil sump that is a kind of oil sump and prevents go-ring by its lubricating action. If it exists in the seal portion, it becomes a gas leak path, which causes a decrease in sealing performance.
Accordingly, the present invention provides a special threaded joint for oil well pipes and a method for manufacturing the same, in which the variation in sealing performance due to the variation in surface treatment such as cutting or shot blasting in the finishing process is reduced and the sealing performance is further improved. With the goal.

In the final stage of the manufacturing process of the special threaded joint for oil country tubular goods, in the work of fastening the pin screw and the box screw, this fastening work is usually performed only once. The inventor has found that by performing this twice or more, the variation in the sealing property is reduced and the sealing property is improved. That is, the present invention is as follows.
1. A special threaded joint for oil well pipes having a screw fastening part between a pin and a box and a seal part by metal-metal contact, wherein the screw fastening part is fastened by final tightening after one or more tightening-returning operations. Special threaded joint for oil well pipes.

  2. In the manufacturing method of a special threaded joint for oil well pipes having a screw fastening portion between a pin and a box and a seal portion by metal-metal contact, the pin screw and the box screw are screwed together at least once to form the screw fastening portion. A method for producing a special threaded joint for oil well pipes, characterized in that final tightening is performed after tightening and retightening.

  According to the present invention, it is possible to obtain a special threaded joint for oil country tubular goods that stably exhibits excellent sealing properties.

  In the present invention, preliminary tightening-rewinding is performed at least once before final tightening. Thereby, a kind of familiarity is obtained in a non-uniform manner on both the pin side and the box side generated by cutting, blasting, etc., and a more stable and superior sealing property is obtained. This familiar phenomenon occurs mainly for two reasons. One is the elimination of excessive local surface roughness, and the other is that fine dents on the surface are filled with a lubricant or the like. As the lubricant, a grease compound containing an appropriate amount of Cu, Pb or the like is usually used.

  Note that the number of preliminary tightening and retightening is preferably 5 or less. If it exceeds 5 times, galling is likely to occur, which is not preferable.

  About a limit investigation sample of a special threaded joint for 110 ksi grade oil well pipes made of 13% Cr steel with an outer diameter of 5.5 "and a wall thickness of 0.415" where the actual seal interference amount is 70% of the minimum tolerance. A seal test was performed. The sample of the invention example used for this test was the final tightening after three times tightening (maximum torque 24877 N · m) -screw tightening between the pin screw and the box screw, The sample of the comparative example has been tightened only once. As a result, in the comparative example, a leak occurred at the point LP2 (ISO load point '2') on the 95% VME (Von Mises equivalent stress) curve shown in FIG. Then, there was no leak and passed.

FIG. 3 is a partial cross-sectional schematic diagram showing an example of a special threaded joint for oil country tubular goods. It is a conceptual diagram of the load condition in a gas seal test.

Explanation of symbols

1 pin 2 box (coupling)
3 Screw fastening part 4 Seal part 5 Shoulder part

Claims (2)

  A special threaded joint for oil well pipes having a screw fastening part between a pin and a box and a seal part by metal-metal contact, wherein the screw fastening part is fastened by final tightening after one or more tightening-returning operations. Special threaded joint for oil well pipes.   In the manufacturing method of a special threaded joint for oil well pipes having a screw fastening portion between a pin and a box and a seal portion by metal-metal contact, the pin screw and the box screw are screwed together at least once to form the screw fastening portion. A method for producing a special threaded joint for oil well pipes, characterized in that final tightening is performed after tightening and retightening.

Images