JPS5887227A - Cooling method for post annealing part of electric welded steel pipe - Google Patents

Abstract

PURPOSE:To reduce the time required for allowing the weld zone of an electric welded steel pipe to cool and to provide a reduction in a cooling zone and an increase in pipe making speed by cooling the areas on both sides of the weld zone of said pipe forcibly after heating said zone. CONSTITUTION:Cooling water is injected from the nozzles of a pair of water feed pipes 2 located near the outside surface of an electric welded steel pipe 1 moving in a direction (a) on the outside surface in both side parts of the weld zone 1a of the pipe 1 along the longitudinal direction of the pipe 1 in said parts. The pipes 2 are supported movably in one circumferential direction and are provided in proximity to the end on the upper stream side of a (direct) water cooler for the weld zone 1a with respect to the moving direction of the pipe 1. Thus, as the pipe 1 moves, the weld zone 1a thereof is heated to a prescribed temp. with a local heater called a ''post annealer'', and is allowed to cool. Both side parts thereof are cooled with the water from the pipes 2, and the weld zone 1a is cooled with a cooler for the weld zone. The results of detection with temp. detectors 3a, 3b which are movable in the circumferential direction of the pipe 1 are treated with an arithmetic device 5, by which the opening of a valve 4 is regulated and the flow rate of the cooling water from the pipes 2 is regulated.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for cooling the boss annealed portion of an electric resistance welded steel pipe, which makes it possible to shorten the cooling zone length or improve the pipe manufacturing speed.

For example, in the case of electric resistance welded steel pipes used for lines and iso, the welded parts are subjected to local heat treatment called boss annealing treatment to improve the performance (toughness, etc.) of the hardened welded parts. That is, the boss door of the welded part of the electric resistance welded steel pipe,
Neil treatment is performed by keeping the welded part at a specified temperature (for example, A3 point or higher).
This process improves the toughness, ductility, etc. of the welded part by heating it to a temperature and then allowing it to cool (air-cooling). However, from the equipment standpoint, it is usually The welded part is water-cooled instead of air-cooled at a temperature (for example, about 500° C. is the upper limit) that does not impede improvements in toughness, ductility, etc. even if it is cooled at a high cooling rate.

However, the above-mentioned boss annealing method for welded parts of ERW welded steel pipes still has the problem of requiring a long cooling zone for a small number of units. ``This means that we have to increase the pipe-making speed even further with the existing equipment.

Therefore, the inventors of the present invention conducted research to solve the above-mentioned problems, and as a result, they obtained the following general knowledge. In other words, when cooling the boss annealed part of an ERW welded steel pipe, when the weld is heated and allowed to cool, most of the heat in the weld is distributed along the circumferential direction of the pipe on both sides of the weld. It diffuses into the tube wall and as a result the temperature of the weld zone decreases. That is, it is cooled. In addition, in the initial stage of cooling of the welded part, the temperature of the pipe walls on both sides of the welded part is sufficiently lower than that of the welded part, so the heat of the welded part diffuses to the pipe walls on both sides at a somewhat faster rate. As a result, the cooling rate of the weld is also somewhat faster. On the other hand, as the cooling of the welded area approaches the final stage, the heat of the welded area has sufficiently diffused into the tube walls on both sides of the welded area, so the cooling rate of the welded area slows down. For this reason, the cooling zone length of the cooling reservoir becomes long. Therefore, by forcibly cooling the pipe walls on both sides of the welded part after heating the welded part and before starting water cooling, the heat diffused into the pipe walls on both sides of the welded part can be forcibly removed. As a result, it is possible to prevent the cooling rate of the weld from slowing down even in the final stage of cooling the weld, and the time required for cooling the weld can be shortened, so by shortening the cooling zone, Alternatively, the pipe production speed can be increased.

The present invention has been made based on the above knowledge, and is based on the -j? In the cooling method of the tasto-neel part, after the heating,
The present invention is characterized in that both side portions of the welded portion of the electric resistance welded steel pipe are forcibly cooled.

The present invention will be described below with reference to embodiments and drawings.

FIG. 1 is a schematic perspective view of a water cooling device for both sides of a welded portion of an electric resistance welded steel pipe according to the present invention.

As shown in the figure, 1 is an ERW welded steel pipe that moves in the direction of arrow a, and 2 is an ERW welded steel pipe that moves along the length direction of the ERW welded steel pipe 1 on both sides of a welded part 1a of the ERW welded steel pipe 1. This is a pair of water supply pipes located close to the outer surface. The water supply pipe 2 has a nozzle along its length, and cooling water is injected from the nozzle toward the outer surface of both sides of the welded portion 1a of the electric resistance welded steel pipe 1. The water supply pipe 2 is supported by support means (not shown) so as to be movable along the circumferential direction of the electric resistance welded steel pipe 1. Further, the water supply pipe 2 is provided close to the upstream end of the (direct) water cooling device (not shown) of the welded portion 1a with respect to the moving direction of the electric resistance welded steel pipe 1.

Therefore, as the electric resistance welded steel pipe 1 moves,
The weld zone 1a is heated to a predetermined temperature by a local heating device (not shown) called a boss annealer and then allowed to cool, - both sides of the weld zone 1a are cooled by cooling water from the water supply pipe 2, and the weld zone water cooling device (not shown), the welded portion 1a is cooled. Reference numeral 4 denotes a flow rate regulating valve for cooling water supplied to the water supply pipe 2.

As shown in FIG. 1, near both ends of the water supply pipe 2, welded parts 1 are placed close to the welded parts 1a of the ERW welded steel pipe 1.
Temperature detectors 3a and 3b each consisting of a linear array camera or the like are provided to detect the temperature of a.

The temperature detectors 3a and 3b are supported by support means (not shown) so as to be movable along the circumferential direction of the electric resistance welded steel pipe 1. The temperature detectors 3a and 3b are supported by support means (not shown) so as to be movable along the circumferential direction of the electric resistance welded steel pipe 1. The detection results of the welding part temperatures of the temperature detectors 3a and 3b are input to the arithmetic unit 5, and the following arithmetic is performed in the arithmetic unit 5 to control the flow rate regulating valve 4.

That is, the detected temperatures of the temperature detectors 3a and 3b are respectively t+
, t2, and both detectors 3a.

3b is the distance between L and the moving speed of the ERW welded steel pipe 1 is .
The amount of cooling water that can be sprayed from the nozzle of the water supply pipe 2 onto the outer surface of both sides of the welded portion 1a of the electric resistance welded steel pipe 1 is adjusted.

Next, examples will be explained.

Eight boss annealers were installed in series, and 38.5
It has a cooling zone with a length of m, followed by a water cooling device for the welded part with a length of 7.3m, and a welding part with a length of 16m in the rear end of the cooling zone, which is located close to the water cooling device for the welded part. A water cooling system was installed on both sides to cool both sides. A boss annealing treatment facility installed following a squeeze roll stand was used.

First, as a conventional example for comparison, eight boss annealers were used to weld the welded part of an ERW welded steel pipe with a squeeze roll stand to a size of 10.75 inches φ while moving at a speed of 23 m/wig. The welded portion of the ERW welded steel pipe was heated in stages, then passed through a cooling zone (without using the partial water cooling device on both sides), and the welded portion was water cooled by the welded portion water cooling device. Figure 2a
(External surface) and 3 (Internal surface) showed temperature changes as shown.

In the figure, the vertical axis shows the welding part temperature, and the horizontal axis shows the elapsed time from the time of welding in the squeeze roll stand, and the position and length of the cooling zone and the welding part water cooling device.

Next, as an example of the present invention, treatment was carried out under the same conditions as in the conventional example above, except that both sides of the welded part of an ERW welded steel pipe were completely cooled with water at a water flow rate of 60 T/H using a partial water cooling device on both sides. The welded portion of the seam-welded steel pipe showed a temperature change as shown in FIG. 2C. From Figure 2, the water cooling start temperature of the welded part of the ERW welded steel pipe is approximately 480°C1 in the conventional example.
In the embodiment of the present invention, the temperature is approximately 270°C. For example, in the embodiment of the present invention, the welding zone temperature reaches 480°C at approximately 10°C from the rear end of the cooling zone. ．． According to the present invention, the distance is at least 10.35 m.
It can be seen that the length of the cooling zone can be shortened.

According to the experiments conducted by the present inventors, if the cooling rate of both sides of the welded part of the ERW welded steel pipe after heating by the boss annealer is less than 20°C/see, the quality of the bath welding part can be improved. It turned out that there was no problem. For reference, the temperature change at a cooling rate of 20°C/sec is shown in Figure 2d. Furthermore, the cooling rate can be freely controlled by using heated water, steam, mist, blast, or the like as the refrigerant.

As explained above, in the present invention, it is possible to shorten the cooling zone or improve the pipe manufacturing speed in cooling an electric resistance welded steel pipe after boss annealing.

[Brief explanation of the drawing]

FIG. 1 is a schematic perspective view of a water cooling device for both sides of a welded portion of an ERW welded steel pipe according to the present invention, and FIG. 2 is a diagram showing an example of temperature change in the welded portion of an ERW welded steel pipe. 1...Erw welded steel pipe, 1-a...Welded part, 2...
Water supply pipe, 3a, 3b...Temperature detector, 4...Flow rate adjustment valve, 5...Arithmetic device. Applicant Nippon Kokan Co., Ltd. Agent Keitabe Tsutsumi (and 1 other person) Figure 2

Claims (1)

[Claims] A method for cooling the boss annealed portion of an ERW welded steel pipe, which comprises heating the welded portion of the ERW welded steel pipe to a predetermined temperature, allowing it to cool, and then cooling the welded portion with water.Forcibly cooling the portion of the ERW welded steel pipe. .