JPH04123871A - Butt welding method utilizing backing ring for tubes - Google Patents

Abstract

PURPOSE:To perform circumferential welding from the tube outside and to secure good joint performance by enlarging the diameters of both pipe ends abutted and abutting the backing ring having the inside diameter larger than the inside diameter of the tubes on the tube end insides to be abutted. CONSTITUTION:The diameters of the tube ends 2 and 2a of both tube 1 and 1a to be butt-welded are enlarged extending over the specified length. The backing ring 4 having the inside diameter D2 larger than the inside diameter D1 of the tubes 1 and 1a and having a cross-sectional shape corresponding to a diameter enlarged shape by cutting off obliquely both side ends 5 and 5 of the periphery is set to the pipe end 2 whose diameter is enlarged and the other pipe end 2a whose diameter is enlarged in the same way is abutted thereon. When setting of the tubes is completed, circumferential welding is performed from the outside. At this time, since the backing ring reacts toward the pipe outside due to angular deformation generated by welding heat input, it is not projected on the tube inside.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of welding pipes together, mainly when laying small-diameter piping.

(Conventional technology) Manual welding,
Uranami welding is conventionally performed by semi-automatic or automatic welding. This is done by creating an appropriate gap at the butt part of the tubes as shown in Figure 8, and creating a height of 2 to 30 degrees on the inner surface of the tube in the first layer welding.
The entire circumference is welded from the outside while forming a 3 mm weld bead called Uranami 6a.

In Uranami welding, in order to obtain a good welded joint, it is necessary to maintain the gap of the butt part, groove shape, welding conditions, etc. with high accuracy, and manual welding requires a high degree of skill in addition.

On the other hand, instead of Uranami welding, a ninth
As shown in the figure, there is a method in which a backing ring 4 is installed and welding is performed from the outside. In this case, since the backing ring 4 is welded together with the pipe, welding defects are less likely to occur even if the gap accuracy is rougher than in Uranami welding, and good joint performance can be easily obtained.

(Problem to be solved by the invention) In Uranami welding, it is necessary to maintain the gap of the butt part, the groove shape, the welding conditions, etc. with high accuracy in order to obtain a good joint without defects, Welding management requires a great deal of effort and construction efficiency is low, and it is becoming difficult to secure highly skilled welders for manual welding.

On the other hand, in the welding method that uses a backing ring, there are fewer defects than in Urana welding, even if the gap accuracy is rougher.
Good joint performance can be easily obtained.

However, since the backing ring protrudes from the inner surface of the tube, it becomes an obstacle to the fluid flowing inside the tube, posing problems in terms of piping function.

Furthermore, in cutting and joining, which is performed to adjust the course of pipes, the pipes are cut and joined diagonally as shown in Figure 10, so the cut cross section of the pipes becomes elliptical as shown in Figure 11. , a special backing ring is required depending on the cutting angle. For this reason, there is a problem that butt welding using a backing ring is virtually impossible in on-site construction where the cutting angle cannot be determined in advance.

In order to solve the above-mentioned problems, the present invention is capable of ensuring good joint performance even if the accuracy of the gap, groove shape, welding conditions, etc. is rough, and the backing ring protrudes from the inner surface of the pipe to prevent fluid flow. The purpose is to provide a welding method that does not pose any obstacles.

(Means for Solving the Problems) A first aspect of the present invention is to expand the diameter of both pipe ends to be butted together in circumferential butt welding between pipes, so that the inner diameter is larger than the inner diameter of the pipes. A second invention is a pipe butt welding method using a backing ring, characterized in that the backing ring is brought into contact with the inner surface of the end of the pipe to be butted, and circumferential welding is performed from the outer surface of the pipe. In circumferential butt welding between a pipe and a pipe, the ends of both pipes to be butted are expanded into a spherical shape with the same diameter with the center point inside the pipe end or the pipe end, and the spherical end is aligned with the center axis of the pipe. On the other hand, it is recommended to cut at a predetermined angle and along a plane that passes through the center of the sphere, and then a backing ring with an inner diameter larger than the inner diameter of the tube is brought into contact with the inner surface of the tube end to be butted, and circumferential welding is performed from the outer surface of the tube. This is a pipe butt welding method that uses a distinctive backing ring.

(Function) The first invention uses a backing ring that can easily provide good joint performance even if the precision of the pipe end gap is rough in butt welding. In order to use a tube with an inner diameter D2 that is larger than the inner diameter of the tube 7 so as not to become an obstruction, the tube end is expanded in diameter and brought into contact.

The second invention is a butt welding method that can be further applied to butted pipes, in which both ends of the pipes to be butted are expanded into a spherical shape with the same diameter, and then cut along a plane passing through the center point of the spherical shape. Taking advantage of the fact that the pipe always forms a perfect circle no matter what the angle, the two pipe ends are butt-welded together with the pipe ends completely aligned.

(Example) Figures 1 to 3 are diagrams showing an example of the first invention, which is mainly used for linear joining.

Tube ends 2 of both tubes 1.1a to be butt welded
．． 2a is expanded over a predetermined length using a tube end expander. In this case, the cross-sectional shape of the enlarged diameter portion in the longitudinal direction of the tube may be a linear taper shape as shown in FIG. 1, or a circular arc shape as shown in FIG. 3, and the tube end may be beveled if necessary. The amount of diameter expansion varies depending on the thickness and shape of the backing ring used, but normally a backing ring with a thickness of about 1 to 3 mm should be used, so the diameter of the tube end should be expanded by about 4 to 8 mm. Good (exaggerated in the diagram for illustrative purposes).

Next, as shown in FIG. 2, a backing ring 4 with a cross-sectional shape corresponding to the enlarged diameter shape is set on the diameter-expanded tube end 2 by obliquely cutting off both ends 5.5 of the outer periphery. The other tube end 2a which has been subjected to diameter expansion processing is butted together. in this case,
Although the gap between the tube ends 2.2a is preferably around 2 mm, it does not need to be strictly controlled.

Once the tube is set, perform circumferential welding from the outside. Welding can be manual welding, semi-automatic or automatic welding;
Four-layer welding is performed depending on the wall thickness of the pipe.

At this time, the backing ring 4 tends to warp toward the outside of the tube due to the angular deformation caused by the welding heat input, so it does not protrude from the inner surface of the tube.

4 to 7 are diagrams showing embodiments of the second invention, and show examples of cutting and joining.

In this invention, first, as shown in FIG. 4, both tube ends to be butt-welded are expanded into a spherical shape having the same diameter with the center point 0 located inside the tube ends.

As a means for expanding the tube into a spherical shape, a spherical expander or the like can be used, which can be inserted into and taken out from the tube end 3 and has a mechanism for pressing the inner surface of the tube into a spherical shape and a mechanism for shaping/supporting the outer periphery of the tube into a spherical shape. The inner diameter of the expanding spherical shape must be determined so that the inner surface of the backing ring that contacts the abutting portion does not protrude inward from the inner surface of the tube, and the inner diameter of the spherical shape must be increased as the cutting angle increases. Also, the center point O of the sphere
is inside the tube end, and the distance l from the tube end to the center point of the sphere is the cutting angle θ, and the cutting position is within the range of the spherical tube end 7 when cutting with a plane passing through the center point. As the cut angle increases, it must be located farther from the pipe end. In addition, when the cut angle is 0 degrees, the center point position can be set to the pipe end position.

Next, the end of the spherical tube 7 is cut at a predetermined cutting angle θ1 and along a plane passing through the center point 0 of the sphere, as shown in FIG. 6th
As shown in the figure, when cutting both pipe ends that are butted together, the cutting angles θ7 and θ2 of both pipes are determined so that the sum of 01+02 becomes the cutting angle θ. In addition, it is also possible to set the cutting angle θ1 of one pipe to zero (orthogonal to the pipe axis) and cut only the other pipe end. In this case, the cutting angle θ1 of the other pipe end
2 is the same as the cutting angle θ. The cut tube end is processed into a predetermined groove shape suitable for the welding method.

Next, as shown in FIG. 6, a backing ring 4 is set on the end of the tube, and the other tube 1a, which has been similarly enlarged, cut, and beveled, is butted against it. In this case, since the diameter of the tube end is enlarged into a spherical shape and the tube is cut along a plane passing through the spherical center point, the cross-sectional shapes of the tubes to be abutted become completely identical perfect circles, and a highly accurate abutment state can be obtained. Furthermore, a backing ring with a constant shape can be used regardless of the cutting angle.

Once the tube is set, perform circumferential welding from the outside. Welding may be manual welding, semi-automatic or automatic welding, and lamination welding is performed depending on the wall thickness of the pipe.

In this invention, since the abutting portions are perfect circles with the same diameter, the seventh
As shown in the figure, the cutting and joining direction can be set arbitrarily.

(Effects of the Invention) According to the present invention, since a backing ring is used, there is a large margin of accuracy in the gap of the butt portion, the groove shape, the welding conditions, etc., and problems in construction management are reduced.

Furthermore, since a backing ring is used, welding can be performed at a faster welding speed than Uranami welding, and the amount of welding can also be increased, making it possible to improve welding efficiency.

Furthermore, since the diameter of the tube end is enlarged to prevent the backing ring from protruding into the inner surface of the tube, the backing ring does not become an obstacle to the fluid and no problems arise in the functionality of the piping.

In addition, even in cut-and-joint joints, the diameter of the tube end is enlarged into a spherical shape and cut along a plane that passes through the center point of the sphere, so the tube end can be processed (cutting, beveling) at any angle to the longitudinal axis of the tube. However, the ends of the pipes will be perfectly circular, resulting in a highly accurate butt-matched state, and a backing ring with a fixed shape can be used regardless of the cut angle, improving practicality in on-site construction. The following effects are obtained, and the problems of the prior art are solved.

[Brief explanation of the drawing]

1 to 3 show an embodiment of the first invention, in which FIG. 1 is an expanded diameter cross-sectional view of the tube end, FIG. 2 is a cross-sectional view of the expanded tube end joined by abutting a backing ring, and FIG. 3 is a sectional view showing an example in which the diameter of the tube end is expanded into an arc shape, FIGS. 4 to 7 are illustrative of an embodiment of the second invention, FIG. Figure 5 is a cross-sectional view of the pipe ends cut for cutting and joining, Figure 6 is a cross-sectional view of the jointed pipes, Figure 7 is a three-dimensional view of the joined state of the pipes, and Figures 8 to 11. 8 shows an example of conventional butt welding between pipes, FIG. 8 is a cross-sectional view of Uranami welding, FIG. 9 is a cross-sectional view of backing ring welding, FIG. 10 is a cross-sectional view of cut and join, and FIG. 11
This figure is an explanatory view of the state in which the tube ends are butted together in FIG. 10. 1.1a...Pipe, 2.2a...Pipe end, 3...Pipe end, 4...Backing ring, 5...Outer peripheral side end, 6...
Welding, 6a... Uranami, 7.7a... Spherical tube end, D
,...Pipe inner diameter, D2...Backing ring inner diameter, D,...
- Ball inner diameter, 0...Sphere center point, l...Distance from the tube end to the ball center point, θ...Cut angle, θ,...Cut angle, θ,...Cut angle.

Claims (2)

[Claims] (1) In circumferential butt welding between tubes, the diameters of both tube ends to be butted are expanded, and a backing ring with an inner diameter larger than the inner diameter of the tubes is placed on the inner surface of the tube ends to be butted. A method of butt welding pipes using a backing ring, which is characterized in that the circumferential welding is performed from the outside surface of the pipe. (2) In circumferential butt welding of pipes, both ends of the pipes to be butted are expanded into a spherical shape with the same diameter centered at the end or inside the end, and the spherical ends are The pipe is cut at a predetermined angle to the central axis of the pipe and along a plane that passes through the spherical center point, and a backing ring with an inner diameter larger than the inner diameter of the pipe is abutted against the inner surface of the pipe end, and circumferential welding is performed from the outer surface of the pipe. A method of butt welding pipes using a backing ring, which is characterized by performing the following steps: