JPS62185830A - Method for preventing longitudinal bend of small-diameter pipe material - Google Patents

Abstract

PURPOSE:To prevent the generation of a bend in the longitudinal direction of a small-diameter pipe material in the stage of a hardening treatment by subjecting the small-diameter pipe material to a normalizing treatment after rolling then to cold leveling prior to hardening in the stage of producing the small-diameter pipe material of a component system having low hardenability. CONSTITUTION:After the small-diameter pipe material consisting of the component system having the low hardenability is rolled, the material is heated to an adequate temp. above the transformation point such as Ac3 point or Acm point and is held for about >=5min. The heated material is cooled in air to form the finer and more uniform crystal grain sizes. The pipe material is then subjected to leveling in a cold leveling stage prior to hardening to strip and remove the scale generated in the normalizing treatment. The generation of the bend in the longitudinal direction of the pipe is thereby prevented in the stage of hardening the pipe material having a small diametral size.

Description

[Detailed description of the invention]

The present invention relates to a method for preventing longitudinal bending of small-diameter pipe materials, and in particular, when manufacturing small-diameter steel pipes by rolling and quenching using materials with low hardenability. B. Suitable for preventing bending occurring in the longitudinal direction of a tube material; relates to a method for preventing bending of a small diameter tube material in the longitudinal direction.

[Conventional technology]

In recent years, with the tightening of energy supply and demand, gas wells,
Many oil wells are being developed. In general, the connection of pipelines laid to such gas wells, oil wells (
(Pipe Connect) is all done by hand welding by a welding operator (worker). Since workability is an important consideration when performing manual welding, from the viewpoint of preventing weld cracking, the pipe material used in the vibrate line is required to be a product with low hardenability. Reflecting this situation, the high-quality line pipes used in the above-mentioned vibration lines are tempered using materials with component specifications that have as low hardenability as possible to improve their strength and toughness. It was necessary to ensure sex. However, among line pipes, small-diameter seamless line pipes have a problem in that they are easily bent during quenching due to their J quality in quenching and tempering equipment. As a technique for solving these problems, there is a rotary hardening method for pipe materials, which the applicant has already proposed in Japanese Patent Application Laid-Open No. 125327/1983. In this method, the high-temperature pipe material is rotated around its axis and brought into contact with a cooling liquid to rapidly cool the pipe material.
This is a technology that dramatically reduces the occurrence of bends in, for example, oil country tubular goods, by setting the speed at m/sec or more. 1. Problems to be Solved by the Invention] However, when quenching a pipe material such as a line pipe that has a component system with low hardenability and has a small diameter size, the pipe material is hardened using rotary quenching equipment based on the above technology. Even if the number of rotations in the circumferential direction is increased, it is difficult to eliminate the non-uniformity of the hardening depth that occurs in the longitudinal direction of the pipe. In addition, due to the unevenness, bends occur in the longitudinal direction of the line pipe. Especially in the case of small diameter line pipes, it is difficult to supply cooling water to the inner surface of the pipe, so it is difficult to supply cooling water to the inner surface of the pipe. The bending cliff in the longitudinal direction of the pipe tends to increase compared to the pipe material of Generally, if the number of bends in the pipe exceeds 150 mm, it will be difficult to transport the pipe to the next process, so it is necessary to prevent the increase in the bend R of the pipe as described above. It is a good idea to straighten the bent pipe immediately afterward! 1. It is unfavorable from the above point. As a result, pipe materials that are bent in the longitudinal direction during quenching have to be scrapped, which is a major factor in reducing yield.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to provide a method for preventing longitudinal bending of a small-diameter tube material, which can prevent longitudinal bending of a small-diameter tube material that occurs when a small-diameter tube is hardened. With the goal.

[Means to solve the problem]

In the present invention, when manufacturing a tube material with a component system with low hardenability and a small diameter by rolling and quenching, the tube material is normalized after rolling to homogenize its crystal grains. The above object is achieved by cold straightening the treated pipe material before quenching it to peel off the scale attached to the pipe surface.

[Effect]

In the present invention, when manufacturing a pipe material having a component system with low hardenability and a small diameter, after the rolling step indicated by 100 in FIG. 1, and before the quenching and tempering step indicated by 130, Next, the tubing is subjected to a normalizing process indicated by the reference numeral 110. , this normalizing treatment step 11
0, for example, the tube material is heated to a suitable temperature above the transformation point such as the Ac3 point or the Acm point, and after being held at the temperature above the transformation point for 5 minutes or more in order to prevent uneven baking. , which is usually cooled in air. This reduces the coarse crystal grains that occur during pre-processing of the tube material, such as hot working, and minimizes the unevenness of the crystal grains in the material of the tube (e) to create fine and uniform crystal grains. By making the crystal grains fine and homogeneous in this way, the tube material is more likely to harden during quenching, and the quenched structure tends to be homogeneous.Therefore, insufficient quenching of the tube material can be prevented. In addition, by straightening the normalized pipe material in a cold straightening process indicated by the reference numeral 120 in FIG. 1, when the pipe material is rolled (for example, during hot working). And the scale generated during the normalizing treatment is peeled off and removed. This prevents uneven quenching that would occur when the pipe material is quenched with scale still attached, and prevents the bending of the pipe material caused by this. As described above, the present invention adds the above-mentioned treatment to the conventional [rolling-quenching-tempering treatment] process, so that it is possible to prevent damage in the longitudinal direction of the pipe caused by insufficient quenching in the longitudinal direction of the pipe during quenching. Bending can be minimized.

[Examples] Examples of the present invention will be described below. In order to put the method of the present invention into practice, the inventors used low-carbon steel with a composition system with low hardenability as shown in Table 1 below and a small-diameter size (outer diameter 88.9mm x wall thickness 7mm). 11I x length 135
1850 line pipes of No. 00a) were processed in a quenching and tempering line under the operating conditions shown in Table 2 below. Table 1 Table 2 Figure 2 shows the results of a sample inspection of the occurrence of bending when line pipes were treated as described above. In addition, the bend in the longitudinal direction of the line pipe measured at that time was measured at the maximum distance from the reference line A connecting both ends of the pipe 10, as shown in FIG. As is clear from FIG. 2, the bend in the longitudinal direction of the pipes was 1501 m or less in all the line pipes. From this result, it is understood that according to the present invention, bending in the longitudinal direction of the pipe can be minimized with a component system having low hardenability. In addition, in the above example, the case where the pipe material having the component system shown in Table 1 was processed under the operating conditions shown in Table 2 was exemplified, but the component system of the pipe material and its operating conditions under which the present invention can be carried out are It is clear that the present invention is not limited to this and can be implemented with other component systems and operating conditions. [Effects of the Invention] As explained above, according to the present invention, bending that occurs in the longitudinal direction of the pipe can be prevented and minimized when hardening a pipe material with a component system with low hardenability and a small diameter size. It can be suppressed. Therefore, the bending in the longitudinal direction of the tube can be reduced, so that the tube material can be transported to the next process. In addition, it is possible to demonstrate the decrease in yield of manufactured pipe materials caused by bending,
It has the excellent effect of being able to manufacture high-quality pipe materials, such as line pipes.

[Brief explanation of drawings]

Figure 1 is a flowchart showing the process from rolling to quenching to provide a detailed explanation of the present invention, and Figure 2 is a flow chart showing the occurrence of bending when a small-diameter line pipe is processed under the operating conditions of the present invention. A diagram showing the situation, FIG. 3 is a perspective view showing the measurement points of the line pipe bend. 10...Line pipe.

Claims (1)

[Claims] (1) When manufacturing a tube material with a component system with low hardenability and a small diameter by rolling and quenching, the tube material is normalized after rolling to homogenize its crystal grains. A method for preventing longitudinal bending of small-diameter pipe material, characterized by cold straightening the treated pipe material to peel off scale before quenching the pipe material.