JP5423122B2 - Heat treatment method and heat treatment equipment for ERW steel pipe made of dual phase steel for pipe expansion used as oil well pipe - Google Patents

Description

The present invention relates to a steel pipe heat treatment method and heat treatment equipment for continuously heat treating an entire ERW steel pipe made of dual phase steel for expansion used as an oil well pipe .

  As an apparatus for performing a continuous heat treatment on a steel pipe cut to a predetermined length, as shown in Patent Document 1, the steel pipe is horizontally conveyed while being rotated by a number of horizontally arranged rollers, and induction heating and cooling are performed. Devices that perform quenching with water are known. However, when induction heating is performed from the outer periphery, only the outer surface of the steel pipe is heated intensively due to the skin effect of the current, and the inner surface side only rises in temperature due to heat conduction, so that the heating tends to be delayed. And if it cools in this state, uniform heat processing will not be performed in the circumferential direction or thickness direction, but it will cause deformation, such as curvature, or a difference in material strength. In order to avoid this problem, it is necessary to devise such as arranging the induction heating devices in multiple stages to make the temperature distribution uniform, and there is a problem that a lot of equipment costs and a large installation space are required.

  In addition, in conventional heat treatment equipment, cooling water may infiltrate from the end face of the steel pipe, causing the inside of the steel pipe to cool down and causing the steel pipe to warp. There was also a risk of leading to a major accident. In order to avoid this problem, the distance between the heating device and the cooling device may be sufficiently increased, but there is a problem that a temperature drop occurs between them and a large installation space is required.

JP 2000-17339 A

Therefore, the object of the present invention is to solve the above-mentioned conventional problems and uniformly heat treat the entire ERW steel pipe made of dual phase steel for expansion used as an oil well pipe without causing deformation such as warpage. It is possible to provide a heat treatment method and a heat treatment facility for a steel pipe that can be produced and that does not cause a trouble due to intrusion of cooling water into the inside of the steel pipe.

In order to solve the above-described problems, the heat treatment method for an ERW steel pipe made of dual-phase steel for pipe expansion used as the oil well pipe of the present invention is arranged with a downward gradient of 3 to 6 ° in the conveyance path. and while rotating the steel pipe by a roller, sequentially moves inside the induction heater and the holding furnace and the cooling device, Atsushi Nobori, holding, characterized in that the heat treatment of cooling water 2m 3 ^/ min or more quench There is . In addition, it is preferable to move the inside of the heat treatment equipment in a state in which the rear end face of the preceding steel pipe and the front end face of the subsequent steel pipe are in contact with each other and continuously heat treat.

In addition, the heat treatment equipment for electric resistance welded steel pipe made of dual-phase steel for expansion used as the oil well pipe of the present invention has a roller having a rotation axis inclined to the traveling direction of the steel pipe with a downward slope of 3 to 6 °. The transfer path is configured by arranging an induction heater for heating the steel pipe from the outer periphery, a holding furnace, and a cooling device for injecting cooling water of 2 m ³ / min or more on the transfer path. It is what. In the present invention, the roller is preferably a thin drum roller.

  According to the present invention, since the heat treatment is performed while rotating the steel pipe by a large number of rollers arranged with a downward slope, even if cooling water enters the inside of the steel pipe, it does not flow back to the depth, and quickly. Discharged. For this reason, there is no possibility of trouble occurring due to intrusion of cooling water into the steel pipe. Further, since the heat treatment is performed while rotating the steel pipe, the end of the steel pipe is prevented from warping in one direction. In addition, if the inside of the heat treatment equipment is moved in a state where the rear end face of the preceding steel pipe and the front end face of the succeeding steel pipe are in contact with each other, productivity can be improved and cooling water can enter from the end face. Furthermore, it is reliably prevented.

  Further, according to the present invention, since the steel pipe is heated by the combination of the induction heater and the holding furnace, the temperature of the inner surface of the steel pipe is also raised while passing through the holding furnace, and the uneven temperature distribution is eliminated. For this reason, heat treatment is uniformly performed over the entire steel pipe, and warpage or strength difference due to uneven heat treatment does not occur.

It is a front view which shows embodiment of this invention. It is a side view which shows embodiment of this invention. It is an enlarged view of a roller. It is a graph which shows heat processing temperature conditions.

Hereinafter, preferred embodiments of the present invention will be described.
1 and 2, reference numeral 1 denotes a conveyance path formed by arranging a large number of rollers 2 on a straight line. As shown in FIG. 1, a steel pipe P to be heat-treated is disposed on the conveyance path 1 on the right side of the drawing. It is conveyed in the direction. An induction heater 3, a holding furnace 4, and a cooling device 5 using cooling water are provided at an intermediate position of the transport path 1, and the steel pipe P is heat-treated while passing through these. Each roller 2 is driven at a predetermined speed and conveys the steel pipe P at a low speed of about 0.2 to 3.0 m / min.

The type of the steel pipe P is an electric resistance welded steel pipe used as an oil well pipe for expansion. This steel pipe is, for example, as an essential element, C: 0.03 to 0.20% (mass%, the same shall apply hereinafter), Si: 0.01 to 1.20%, Mn: 0.30 to 2.50%, P: 0.03% or less, S: 0.01% or less, AL: 0.001-0.01%, N: 0.01% or less, Ti: 0.005% -0.05%, Ca: 10-40 ppm , And Nb: 0.01 to 0.1%, V: 0.01 to 0.1 as a selection element, and a composition composed of the remaining Fe. The ERW steel pipe having such a composition is heated to a temperature of Ac ₁ point or more and Ac ₃ point or less to form a two-phase structure composed of ferrite and austenite, and then rapidly cooled to precipitate martensite in the ferrite. By using dual phase steel, the steel pipe has both workability (pipe expandability) and strength.

  As shown in FIG. 3, each roller 2 is a medium and thin drum roller made of metal having a small diameter at the center and a large diameter at both ends. By adopting such a shape, the outer diameter of the steel pipe P is obtained. It can be transported without hindrance even when it is large or small. In this embodiment, the minimum diameter is 110 mm and the maximum diameter is 340 mm. Needless to say, the central portion of the roller 2 may have an arc shape.

  As shown in FIG. 1, each roller 2 is disposed with a downward gradient, and constitutes a transport path 1 having a downward gradient of 3 to 6 °. The reason will be described later. Further, as shown in FIG. 2, each roller 2 is arranged such that its rotating shaft 6 is not inclined at right angles to the traveling direction of the steel pipe P, that is, the direction of the transport path 1 on the horizontal plane. By tilting the rotating shaft 6 of the roller 2 in this way, the steel pipe P receives a force in a direction perpendicular to the traveling direction at the contact point between the roller 2 and the steel pipe P, and proceeds while rotating in a certain direction. It will be.

  The induction heater 3 is a well-known heating means that causes a high-frequency current to flow through a coil disposed on the outer periphery of the steel pipe P and generates an induction current in the steel pipe P that passes through the coil to heat it. In this embodiment, the one having an output of 600 kW is used, and the steel pipe P at room temperature is rapidly heated to a necessary high temperature region. In this embodiment, the temperature is raised to a temperature range of 760 to 845 ° C. in a short time of about 7 to 50 seconds. As described above, the heating by the induction heater 3 intensively heats the outer surface due to the skin effect, but the tendency for the temperature rise to be delayed inside cannot be avoided.

  Therefore, in the present invention, the holding furnace 4 is provided immediately after the induction heater 3, the steel pipe P is held at a heated temperature, and the inside of the steel pipe P is heated to substantially the same temperature as the outer surface. In the case of the above-described embodiment, this holding temperature is preferably 1 minute or more, and this makes the structure a two-phase structure composed of ferrite and austenite. If the holding time is less than 1 minute, the cementite in the tissue cannot be completely dissolved. In this embodiment, the holding furnace 4 is an electric furnace.

  The steel pipe P held at a predetermined temperature in this way is rapidly cooled in the cooling device 5 arranged at the outlet of the holding furnace 4. The cooling device 5 includes a large number of water cooling nozzles, cools the steel pipe P by injecting a large amount of cooling water, and precipitates martensite in the ferrite. In the case of this embodiment, it is preferable to rapidly cool a temperature range from 700 ° C. to 300 ° C. at a cooling rate of 20 ° C./second or more. The steel pipe P after passing through the cooling device 5 is finally cooled to room temperature by cooling. The heat treatment conditions in the embodiment are shown in FIG.

In order to perform such rapid cooling, for example, it is necessary to inject a large amount of cooling water of 2 m ³ / min or more, and as a result, a part of the cooling water may enter the inside of the steel pipe from the end face of the steel pipe P. It is as described above. In order to solve this problem, in the present invention, a downward gradient is given to the transport path 1. As a result, the steel pipe P is in a forward-downward posture, so that even if cooling water enters the inside from the front end face of the steel pipe P, it does not flow back deeply and is quickly discharged. The problem is the backflow to the holding furnace 4 side (high temperature side), and there is no problem because the downstream steel pipe P has already been cooled.

  In order to obtain the above effect, the descending slope of the transport path 1 may be increased. However, it is necessary to increase the building for storing the transport path 1, increasing the equipment cost, and the steel pipe P on the roller 2. Therefore, it is preferable to set the angle to about 3 to 6 °. 6 ° is a value calculated from the friction coefficient of the surface of the steel pipe P. Also, if the angle is less than 3 °, the effect of preventing the backflow is reduced, so 3 to 6 ° is optimal in this embodiment.

  In this embodiment, in order to prevent intrusion of cooling water from the end face of the steel pipe P, the heat treatment is continuously performed in a state where the rear end face of the preceding steel pipe P and the front end face of the subsequent steel pipe P are in contact with each other. Is going. By keeping the end surfaces in contact with each other in this way, the gap into which the cooling water enters can be reduced, and the intrusion of the cooling water can be prevented more reliably. Moreover, by bringing the end faces of the steel pipes P into contact with each other, useless space is eliminated and productivity is improved.

  Even during the heat treatment, the steel pipe P advances in a spiral shape while continuously rotating. Therefore, even if warping due to non-uniformity of the circumferential structure transformation during the heat treatment occurs, correction by gravity is performed. The action works and warpage is prevented. Therefore, according to the present invention, the entire steel pipe P can be uniformly heat-treated without causing deformation such as warpage. Moreover, since the penetration of the cooling water into the inside of the steel pipe P is suppressed, there is an advantage that there is no possibility of trouble occurring due to the inside being cooled. Further, the present invention has an advantage that the equipment cost is low.

DESCRIPTION OF SYMBOLS 1 Transfer route 2 Roller 3 Induction heater 4 Holding furnace 5 Cooling device 6 Rotating shaft

Claims (4)

While the steel pipe is rotated by a roller arranged with a downward gradient of 3 to 6 ° in the conveyance path , the inside of the induction heater, the holding furnace, and the cooling device is sequentially moved to raise the temperature, hold the cooling water amount 2 m ³ Heat treatment method for ERW steel pipe made of dual-phase steel for expansion used as an oil well pipe , characterized by performing rapid heat treatment of at least 1 min / min .   2. The heat treatment method for a steel pipe according to claim 1, wherein the heat treatment equipment is continuously heat treated by moving the inside of the heat treatment equipment in a state where the rear end face of the preceding steel pipe and the front end face of the succeeding steel pipe are in contact with each other. An induction heater for heating the steel pipe from the outer periphery on the conveying path is configured by arranging a roller having a rotation axis inclined with respect to the traveling direction of the steel pipe so as to have a downward gradient of 3 to 6 °. A heat treatment facility for ERW steel pipe made of dual-phase steel for pipe expansion used as an oil well pipe , wherein a holding furnace and a cooling device for injecting cooling water of 2 m ³ / min or more are arranged.   4. The heat treatment equipment for steel pipes according to claim 3, wherein the rollers are thin drum rollers.

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