JPS6257715A - Production of metallic tube having wall thickness difference - Google Patents

Abstract

PURPOSE:To easily form the tube having the wall thickness difference to show an excellent strength and fatigue characteristics for repeating load by forming the rectangular metallic sheet having large wall thickness of the peripheral edge part in tubular shape and by performing the vertical welding of the butt thick wall part. CONSTITUTION:The metallic sheet making the width W1 of the front and rear edge end parts of a plate stock and the width W2 of the side edge part at both sides the wall thickness is prepared. The wall thickness t2 thereof is equivalent to the thickness of the wall thickness part of a finished metal tube and the wall thickness t1 of the thin wall part is made the same as the thin wall part of the finished item, having the relation of 0.4t2<t1<0.85t2. The metallic tube is completed by forming the plate stock thereof in tubular shape and by subjecting the butt part to vertical welding. Said tube shows excellent strength and fatigue characteristics for the repeated load of the axial force and inner pressure and used properly for the metal tube of a pipe line and marine structure.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method of manufacturing a metal tube having a wall thickness difference in the longitudinal direction and the circumferential direction.

More specifically, the present invention relates to a method for producing a lightweight metal tube that has a wall thicker near the tube ends and longitudinal welds than other parts, has excellent strength and fatigue characteristics, and is lightweight.

Conventional technology Pipelines, live pipes, and other pipes that are manufactured by welding a steel plate formed by a press etc. have a weld bead in the vertical direction, and when the manufactured pipe is laid, the pipe end is circumferentially welded. used.

However, the strength of the weld bead part is lower than that of the base metal part, and depending on the usage environment, the pipe is subjected to loads due to axial force, bending, or internal pressure.

In conventional manufacturing methods, the wall thickness of metal tubes is uniform in the longitudinal and circumferential directions, but the overall strength of the metal tube is determined by the strength of the welded parts, so it is difficult to make the wall thicker than necessary. Metal pipes were manufactured using metal plate materials.

In order to deal with such problems, Japanese Patent Application Laid-Open No. 59-766
No. 17, JP-A No. 60-37219 to 37221 discloses that a rectangular metal plate material with thick walls at both ends in the longitudinal direction is prepared, formed into a tube shape, and welded to create a wall thickness difference in the longitudinal direction of the tube. A method for manufacturing a metal tube has been proposed.

Problems to be Solved by the Invention Although the above-mentioned prior art method guarantees the strength of the joints between metal pipes, the strength of the joints between the metal pipes is guaranteed, but due to repeated loads in the axial direction and repeated loads due to fluctuations in internal pressure when the pipes are laid, etc. No countermeasures can be taken to solve the problem of fatigue in the vertical welds of the metal tube itself. Particularly in line pipes for high-pressure transportation of natural gas, etc., fatigue strength due to repeated loads due to internal pressure is a major problem, and when cracks occur, they propagate at high speed and cause damage over long distances.

An object of the present invention is to provide a method for manufacturing a metal tube that has excellent strength and fatigue characteristics against repeated loads of axial force and internal pressure.

More specifically, the present invention has a wall thickness difference in the longitudinal direction of the pipe,
It is an object of the present invention to provide a method for manufacturing a metal tube that is particularly thick at the tube ends and also has a difference in wall thickness in the circumferential direction of the tube.

Means for Solving the Problems The inventors have studied various ways to effectively prevent the propagation of cracks in pipelines, and have found a method that has excellent mechanical strength, especially fatigue properties, against repeated loads of axial force and internal pressure. It is based on a metal tube.

Pipelines are usually constructed by forming metal plates into a tubular shape using the UO method and then seam-welding the pipes, which are then joined to each other by welding. However, if a crack occurs, it propagates at high speed and can cause serious damage. Damage occurs over a distance of Therefore, it is possible to effectively prevent the propagation of cracks by inserting and connecting metal pipes having thick walled portions in the longitudinal direction and circumferential direction into the pipeline at appropriate locations.

The present invention provides a method for economically and easily manufacturing a metal tube having thick wall portions in the longitudinal direction and the circumferential direction. A metal tube having a wall thickness difference in the longitudinal direction and the circumferential direction, which is characterized by preparing a large rectangular metal plate, forming the metal plate material into a tube shape, and welding the butted thick parts in the longitudinal direction. A manufacturing method is provided.

The attached FIG. 1(a) is a perspective view of an example of a metal tube manufactured by the method of the present invention, and FIG. It is a perspective view of a metal plate material.

As shown in FIG. 1(a), the metal tube manufactured according to the present invention has a uniformly thick wall at both ends, and also a uniformly thick wall at the seam weld in the tube axis direction. The metal tube shown in FIG. 1(a) has a smooth inner surface and a uniform inner diameter in the axial direction, and the tube ends and seam welds protrude outward and are thick. However, the thick wall portion may be formed to protrude evenly on the inside and outside of the tube, or the outside surface of the tube may be smooth and have a uniform outside diameter, and the tube end and seam weld may be formed on the inside. It may be protruding and thick.

Furthermore, as shown in FIG. 1(a), it is preferable that the thickness of the thick portion and the thin portion not change abruptly, but change gradually.

On the other hand, as shown in Fig. 1 et al., the metal plate material used in the method of the present invention is thickened by a predetermined width W1 at the front and rear edge portions of the plate material, and the side edge portions on both sides are also thickened by a predetermined width W1. The thickness is increased by the width W2. The wall thickness t2 of these front and rear edge portions and both side edge portions are shown in Figure 1 (
It is equal to the wall thickness of the thick inner portion of the finished metal tube shown in a). The thickness t1 of the thin portion of the metal plate material is the same as that of the thin portion of the finished metal tube.

According to a preferred embodiment of the present invention, the thickness t2 of the thick portion and the thickness t1 of the thin portion preferably have the following relationship.

0.4 t2< t + <0.85 t2 As mentioned above last month, line pipes are subjected to repeated loads of axial force and internal pressure in the usage environment. The line pipe itself is installed by butt welding the pipe ends of vertical seam welded metal pipes, so the fatigue strength of the base metal, butt weld, and vertical bead is calculated to determine their wall thickness. There must be.

First, the strength grades of each N-LO6 cycle time strength are as shown in Table 1.

Table 1 Fatigue Strength Grade Generally, the thickness of a material is determined in inverse proportion to the fatigue strength, so the ratio of the required thickness of each part is as shown in Table 2.

Furthermore, according to other reports regarding fatigue strength, N=2X
The 106 cycle time intensities are shown in Table 3.

Table 3 Fatigue Strength (M N / m') The thickness ratio of each part to guarantee the fatigue strength shown in Table 3 is as shown in Table 4.

In view of the required wall thickness ratios shown in Tables 2 and 4, in a preferred embodiment of the present invention, the wall thickness t2 of the thick wall portion and the wall thickness t1 of the thin wall portion
was defined as follows.

0.4t2<t+<0.85t2 By manufacturing the metal tube to have such a wall thickness ratio, the fatigue strength balance against repeated loads of axial force and internal pressure is maintained as a whole for the tube.

In addition, metal pipes with normal thickness in the base material and thick walls in the butt and vertical bead parts have excellent fatigue strength against repeated loads of axial force and internal pressure, and when inserted into a pipeline, Since the strength of that part is significantly improved, it is extremely effective as a member for preventing crack propagation.

Example A rectangular metal plate material was manufactured on the rolling line shown in FIG.

The rolling line is composed of two reversible rolling mills 12, a universal roughing mill 13, an edger mill 14, and a saw 15 connected by a roller table from the slab discharge side of the heating furnace 11.

First, the cross section as shown in Figure 3(a) is 250 mm
A continuous casting slab of 1500mm is rolled by rolling mill 11.
40 mm x 1674 as shown in Figure 3 et al.
It was rolled down to a cross section of mm. Next, the material is sent to the universal roughing mill 13, and the material is stopped when the leading edge of the material is 100 mm or more downstream from the universal roughing mill center, and the gap between the horizontal rolls is widened as shown in Fig. 3 (C). reduce a part of the material to 25 mm, and then move the material to reduce the thickness to 25 mm by a certain length.
It was pushed down. At this time, the opening degree of the vertical rolls of the universal rough mill is maintained at 16741 Tl to regulate the spread of the material width due to the reduction by the horizontal rolls.

Next, the horizontal roll cap of the universal coarse mill 13 is opened, the material alone is advanced by 200 m..., the gap between the horizontal rolls is narrowed again, the roll is rolled down to 25 mm, and a certain length is rolled to a thickness of 25 mm.

In this manner, the universal coarse mill 13 reduces only the central portion of the material to a thickness of 25 mm at regular intervals, but at this time, the edge portions of the material are free ends, so the thickness becomes uneven. Therefore, as shown in FIG. 3(d), both side edges of the material are rolled down to a predetermined size by an edger mill 14 in the latter stage to a depth of 37 mm.

The plate material thus obtained has a thickness of 25 mm at the center and 37 mm at both side edges, as shown in Figure 3(e).
m thickness, 200+r over the entire width with a period of every 10 m
The length is +m and the thickness is 37mm.

This plate material was cut at intervals of 10 m using a saw 15, formed into a tube shape using a press, and after cutting off both side edges where bending deformation was insufficient, seam welding was performed to obtain a metal tube. The obtained metal tube is
Outer diameter 508Lo [111 wall thickness 25mm at thin wall part.

The thick part had an outer diameter of 533 mm, a cross-sectional shape with a wall thickness of 37 holes, and a length of 10 m.

Plate-shaped test pieces were cut from the thin-walled portions of the obtained metal tubes, that is, the thick-walled portions including the base metal portion and the vertical bead portion, and subjected to a fatigue strength test. The axial force oscillation fatigue strength at cycle time of N=2 Xl06 is 282 MPa and 1, respectively.
It was 85 MPa. These values are inversely proportional to the wall thicknesses of the thin and thick parts, 25 mm and 37 mm, and it can be seen that the pipe has a shape in which the strength of the entire pipe is balanced under usage conditions in which axial force is applied repeatedly.

In other words, if a metal tube with a uniform wall thickness is used as a whole as in the conventional method, the wall thickness will be 37 mm under the same usage conditions.
Compared to this case, a material saving of about 30% can be achieved with the metal tube produced according to the above embodiment of the invention. Further, when the thickness of the thin wall portion is the same and the thickness of the thick wall portion is increased, a metal tube with excellent fatigue strength against repeated loads due to axial force and internal thickness can be obtained.

Effects As explained above, by the method of the present invention, a metal tube having a wall thickness difference in the longitudinal direction and the circumferential direction can be easily manufactured. The metal tube manufactured by the method of the present invention has great strength against fatigue caused by repeated loads of axial force and internal thickness, and is suitable as a metal tube for offshore structures and pipelines laid under the influence of these forces. used. In particular, interposing a metal tube manufactured by the method of the present invention in a pipeline is extremely effective in preventing cracks from propagating if they occur.

In addition, although the above-mentioned example showed the example which manufactures a metal plate material by rolling, it goes without saying that it may manufacture by other methods, for example, cutting a flat plate material.

[Brief explanation of drawings]

FIG. 1(a) is a perspective view of an example of a metal tube manufactured by the method of the present invention, and FIG. 1(b) is a perspective view of an example of a metal plate material used in the method of the present invention. , FIG. 2 is a flow diagram of a rolling line for producing metal sheet materials used in the method of the present invention, and FIGS. 3(a) to 3(d) show each step of the rolling line shown in FIG. FIG. 3(e) shows a plane of the metal plate after rolling. (Reference number) 11. Heating furnace, 12. Reversible rolling mill, 13Φ Universal rough mill

Claims (1)

[Claims] (1) A method in which a rectangular metal plate with a large wall thickness at the peripheral edge is prepared, the metal plate material is formed into a tube shape, and the butted thick portions are welded in the longitudinal direction and circumference. A method for manufacturing a metal tube having wall thickness differences in directions.