JPS58184073A - Manufacture of welded tube - Google Patents

Abstract

PURPOSE:To enable sure manufacture of an excellent thin-walled tube, by giving compressive stress by heating to the general part other than both ends of a sheet material and giving tensile stress to both ends and welding both ends. CONSTITUTION:When delivering a coiled sheet material 1 and manufacturing a welded tube by roller forming, necessary number of stages of high frequency heating devices 7, 7 are provided on the whole periphery except edge parts 2, 2 between the bending stage of edges 2, 2 and the welding stage 4, and heated. Accordingly, tensile stress is applied to the edges 2, 2 in a pulling and bending stage. However, the temperature of the general part is raised by temperature distributions 8, 8 and compressive stress acts on the meeting section 3, and tensile stress acts on the edges 2, 2, and no buckling takes place. When welding 4 is performed at the seam part in smooth conditions, tensile residual stress due to welding acts on the edges 2. However, it is made very small by cooling to room temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION The disclosed technology belongs to the field of heat treatment technology for preventing buckling deformation that occurs at the seam during the manufacture of thin-walled seam welded pipes.

The present invention relates to a welded pipe manufacturing method in which a coiled plate material is fed out, passed onto a roller forming means, and both edges are bent and curved to meet, and the joining seam is welded to form a perfect circular cross section. In particular, the bending process of both grades is 4.4!
I'! In the subsequent assembling process or the wafer, all or a part of the general part, excluding both edges, is heated to apply compressive stress,
This invention relates to a method for manufacturing a welded pipe in which tensile stress is applied to both edges to prevent buckling of the seam portion and to reduce residual stress in the entire pipe.

As is well known, pipe materials are widely used in various fields such as transportation pipes and wiring pipe bodies, and there are many types. Because of its advantages, seam bath tubing is widely used.

To manufacture the seam bath connecting pipe, as shown schematically in Fig. 1, a coil-shaped raw material steel plate l is rolled out, and the edge 2.2 is bent inward by a forming roller (not shown), and then curved and brought together at different times. The joint 3 is made into a perfect circle, and welding 4 is performed to form a pipe.

Therefore, during the bending process of the edge 2.2, the edge 2.
Tensile stress acts strongly in the length direction (axial direction).

However, when the bending process is completed and both edges 2.2 meet, a tensile stress is applied to the general portion 6, and a compressive stress is applied to the ring *2.

Therefore, in the welding process after assembly, buckling occurs between the rollers as they roll in the direction of the weld line, resulting in a so-called seaweed-like deformation.

Although this phenomenon is unlikely to occur in thick-walled tubes, it is more likely to occur in thin-walled tubes.Therefore, manufacturing thin-walled tubes by seam welding is difficult.

The purpose of this invention is to solve the technical problem of manufacturing seam welded pipes based on the above-mentioned prior art, and to apply heat to general parts other than the inner edge between the process of bending both edges together and the welding process. The purpose of the present invention is to provide an excellent welded pipe manufacturing method that applies compressive stress to the welded pipe and applies tensile stress to both edges to prevent buckling, which is useful for thin seam welding applications in the pipe manufacturing industry. .

The structure of this invention, which is full of the above-mentioned objects, is that in the process of bending a coil-wound plate material into a circular cross-section with a feeding roller, heating is applied to the general area other than the inner edge to impart compressive stress to both edges. We have developed technical means to apply tensile stress to prevent buckling deformation between the forming rollers, reduce residual stress due to the preheating effect during welding, and ensure the production of thin-walled welded pipes. The gist is the same.

Next, an embodiment of the present invention will be described below with reference to the drawings from FIG. 2 onwards.

Note that the same parts as in FIG. 1.2 will be explained using the same reference numerals.

The raw material steel plate l is rolled out into a coil shape, and the excise and mechanical forming itself is exactly the same as the conventional method, with both edges 2.
2 is passed through a forming roller (not shown) and bent to form a perfect circular cross section.

In the embodiment shown in FIG. 2, a predetermined number of stages (two stages in the embodiment) of high-frequency heating devices 7 are installed between the bending process of the edge 2.2 and the welding process. .7 Heat the entire circumference except for the edge 2.2 by placing it between rollers.

Therefore, in the bending process, tensile stress is applied to the edge 2.2, but in the meeting part 3, the temperature rises in the general part due to the temperature distribution 8.8, and compressive stress acts on the edge 2.2. Tensile stress acts on .

Therefore, originally, at the meeting part, tensile stress acts on the general part and compressive stress is applied to the edge 2.2, and buckling occurs between the rollers, resulting in so-called wakame-shaped deformation, as shown in Figure 3a. Since compression is applied in the general area and tension is applied to the edges, no buckling occurs at the edges 2.2.

Therefore, if welding 4 is performed at the seam part in a smooth state, tensile residual stress due to the welding is applied to the edge 2, but the tensile residual stress that would normally reach the yield stress is also reduced when cooled to room temperature as shown in Figure 3b. As shown in Figure 2, the amount is extremely small and is effective against stress corrosion cracking, etc.

The tube 6 made in this way has no buckling deformation at the seam and has reduced residual stress.
The tube surface is also smooth.

Next, in the embodiment shown in FIG. 4, a high frequency heating device 7',
7' is provided at a partial position in the circumferential direction of the general portion other than both edge portions 2.2, and is essentially the same as the embodiment described above.

It goes without saying that the embodiments of the present invention are not limited to the above-mentioned embodiments. For example, a heating device may be provided in the general part during the bending process of both edges and the joining process, or,
Various modes can be adopted as the heating device, such as using a strip heater.

As described above, according to the present invention, heating is applied to the general part excluding both edges in at least one of the both edge process and the meeting process in which a coil-wound plate material is fed out and formed into a circular cross section by a forming roller. Compressive stress is applied and tensile stress is actively applied to the edge as a reflection condition, so no compressive stress is applied to the edge during the process from joining to welding, and therefore buckling occurs at the joining edge. First, deformation such as so-called wakame seaweed does not occur, and as a result, an excellent effect can be achieved in that even thin-walled pipes can be manufactured.

Also, - the compressive stress applied to the crotch decreases when the temperature drops to equal to the room temperature after welding, and the tensile stress applied to the edge also decreases, so the preheating effect applied prior to welding Even if the tensile residual stress due to welding is large enough to be equal to the yield stress, the residual stress will be reduced to a small amount after cooling.
It also has the effect of preventing stress corrosion cracking, etc.

In this way, the inherent advantages of seam welded pipes can be utilized, so there is also the advantage of being able to meet the needs of welded pipes.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the forming plane of a welded pipe, Fig. 2 is a schematic explanatory diagram of one embodiment of the present invention, Figs. 3a and 3b are explanatory diagrams of stress distribution and residual stress distribution, and Fig. 4 is an explanatory diagram of the same stress distribution. Fig. 5a and 5b are explanatory drawings of another embodiment, and Figs. 5a and 5b are explanatory drawings corresponding to Fig. 38.3b. 1...Coil plate material, 2...Both edges, 3...Meeting (
), 4...Welding, 7.7'...Heating (equipment), "11 211 Figure 3a Figure 3b Figure 50

Claims (1)

[Claims] In a welded pipe manufacturing method in which a coil plate material is fed out and roller-formed to asymptotically bring together both edges of the plate material and welded together,
During at least one of the bending process of the plate material and the assembly process before welding, the general part excluding the edges is heated to apply compressive stress to the part and tensile stress is applied to both edges. A welded pipe manufacturing method characterized in that both edges are welded in such a manner that both edges are welded.