JPH03243286A - Joining method for clad tube - Google Patents

Abstract

PURPOSE:To improve working efficiency by forming an U-groove on ends to be joined of the clad tubes, starting frictional contact between inside metal layers of the clad tubes and friction-welding both clad tubes. CONSTITUTION:The clad tubes 10 formed by cladding the inside metal layers 10b thinner than outside metal layers 10a on the inner peripheral sides thereof are subjected to butt welding together with the central axes thereof coincident with each other. When groove faces 10A and 10A' are then formed on the ends to be joined of the clad tubes 10 and 10 to be joined to abut the ends on each other, the U-groove 11 is formed. The frictional contact between the inside metal layers 10b and 10b of the clad tubes 10 and 10 to be joined is then started and both clad tubes 10 and 10 are subjected to friction welding. Consequently, outside metal layers are prevented from being exposed on the insides of the tubes when burrs on the insides of the tubes are removed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method of joining circumferential joints of clad pipes.

[Prior Art] In order to impart corrosion resistance to piping, clad pipes are used in which the inside is clad with a corrosion-resistant metal layer.

For example, in chemical plants, clad pipes are used in which stainless steel or nickel alloy steel is clad on the inside of carbon steel or chromium molybdenum steel. When such a rad tube is used, the cost can be reduced compared to the case where the entire tube is made of carbon steel or chromium molybdenum steel. Additionally, if the entire tube is made of carbon steel or chromium-molybdenum steel, cracks will easily penetrate through the wall thickness when stress corrosion cracking occurs from the inner surface of the tube, but if a clad tube is used, the cracks will penetrate through the wall. You can prevent it from happening.

Conventionally, clad pipes were mostly joined together by arc welding. Since most clad pipes have an outside diameter of 8 inches (216 mm) or less, arc welding must be performed from the outside of the pipe. Conventionally, therefore, welding was performed by filling the joints of clad pipes with molten metal in the groove so that they faced each other across the groove, thereby forming a weld metal layer sequentially from the inside to the outside.

Figure 8 shows 1. clad pipes joined by arc welding.
1- is a schematic cross-section of the joint portion of No. 1-, in which la and la- are outer metal layers made of carbon steel or chromium-molybdenum steel, and lb.

lb- is an inner metal layer made of stainless steel or nickel alloy steel.

When welding such a rad tube, it is necessary to fill the first layer 2 with stainless steel or nickel alloy steel in order to ensure corrosion resistance. Here, it is possible to make all the layers of the joint part stainless steel or nickel alloy steel, but if all the layers are made of stainless steel or nickel alloy steel, cracks will easily penetrate when stress corrosion cracking occurs.

Therefore, the upper layer 4 must be made of carbon steel or chromium molybdenum steel. However, if carbon steel or chromium molybdenum steel is welded directly onto the first layer of stainless steel or nickel alloy steel, some of the stainless steel or nickel alloy steel will melt and mix into the layer of carbon steel or chromium molybdenum steel. A weak martensitic weld metal is formed in the boundary region, reducing the strength of the weld. In order to avoid this, conventionally, an intermediate layer 3 made of pure iron or ultra-low carbon steel was provided between the first layer 2 and the upper layer 4.

When clad pipes are joined by arc welding as shown in FIG. 8, there is a problem that the intermediate layer 3 is significantly hardened (Vickers hardness: 350-450), resulting in a decrease in ductility of the joint. Furthermore, when the inside of the pipe is in a high-temperature hydrogen environment, there is a problem in that the intermediate layer 3 tends to become brittle. Furthermore, arc welding has the problem that the welding work is complicated and requires skill to perform, resulting in high costs.

Therefore, it was considered to join the clad pipes by friction welding. The procedure for joining clad pipes according to the conventionally well-known friction welding method is as follows.

As shown in FIG. 9, clad pipe 1. 1- pressure contact surface A,
One clad pipe 1 is fixed to a stationary clamp with A- being a plane perpendicular to the respective axial directions, and the other clad pipe 1' is gripped by a chuck of a rotationally driven main shaft. Then, the cladding tube 1- on the rotating side is rotated while one cladding tube is brought into pressurized contact with the other cladding tube at a predetermined pressure (referred to as heating pressure) using a pressurizing device, and the contact area between the two cladding tubes is rotated. generates heat due to friction. When the temperature of the joint reaches a predetermined temperature, the rotating side cladding pipe ↓- is stopped, and the cladding pipe 1.1- is pressurized with a large upset pressure by a pressurizing device to be welded together.

FIG. 10 shows a state in which the pressure welding of the clad pipe is completed. As is clear from the figure, the outer metal layers la, la- and the inner metal layers 1b, 1b- are pushed out to the outside and inside of the tube, respectively, resulting in holes 5 and 6.

When used in chemical plant piping, etc., it is necessary to remove paris so as not to impair the flow of fluid within the pipe. The removal of paris is performed by a paris cutting blade. FIG. 11 shows the state of the clad pipe after the paris was removed by the paris cutting blade.

[Problems to be Solved by the Invention] When clad pipes are joined together according to the conventionally well-known friction welding method, the outer metal layer is largely pushed outward and inward as shown in FIG. 10.

Therefore, when the splints are removed from the joined cladding pipes, the outer metal layer is exposed at the location B where the inner splints are removed, and there is a problem in that the characteristics of the cladding pipes are lost in this area.

An object of the present invention is to provide a method for joining clad pipes that allows clad pipes to be joined without exposing the outer metal layer on the inside of the pipes and without causing cracks or a brittle hardened alloy layer. It's about making suggestions.

[Means for Solving the Problems] The present invention provides a plurality of clad pipes each having a plurality of clad pipes each having an inner metal layer clad on the inner circumferential side of an outer metal layer with an inner metal layer thinner than the outer metal layer, the center axes of which are made to coincide with each other. This relates to a method of butting and joining.

In the method of the present invention, a U-shaped groove is formed at the ends of the cladding pipes to be joined, and frictional contact is started between the inner metal layers of the cladding pipes to be joined, so that both cladding pipes are friction welded. do.

Preferably, the U-shaped groove has a groove angle of 15 degrees or more and 45 degrees or less.

The above U-shaped groove has a groove surface 10 as shown in FIG. 7(A).
A, 10A- and the root face IO8゜10B- may have no curvature at the boundary, or as shown in Fig. 7(B).
or D), the groove face 10A, IOA'' and the root face 10B.

A curvature may be provided at the boundary portions 10C and 10C- with respect to 10B-. Also root face IOB.

The radial dimension F of 10B'' may correspond to the thickness C of the inner metal layer as shown in FIGS. 7(A) and (B),
As shown in FIG. 7(C), the radial dimension F of the root face may be smaller than the thickness C of the inner metal layer. Furthermore, the seventh
As shown in Figure (D), the radial dimension F of the root face may be set larger than the thickness C of the inner metal layer.

The outer metal layer is made of carbon steel or chromium molybdenum steel, for example, and the inner metal layer is made of stainless steel or nickel alloy steel.

[Function] As mentioned above, the U is attached to the end of the clad pipe to be joined.
When a shaped groove is provided to initiate frictional contact between the inner metal layers of the clad pipes to be joined and friction weld the clad pipes, a portion of the inner metal layer initially moves toward the groove side and inside the pipe. Since the pressure welding progresses in this manner, the inner metal layers can be reliably joined to each other, and the outer metal layer can be prevented from being exposed on the inner surface of the tube when the debris inside the tube is removed. Therefore, according to the present invention, clad pipes can be joined to each other without losing the characteristics of the clad pipes, by taking advantage of the characteristics of friction welding, and without creating a fragile hardened metal layer at the connection portion.

Further, since it requires less effort than arc welding, the number of man-hours required for joining can be reduced, and work efficiency can be improved.

[Embodiments] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Figure 1 shows a clad pipe 10.1 joined in an embodiment of the present invention.
This figure shows a half cross section near the end to be joined of 0-, and clad pipes 10 and 10 are outer metal layers 10a and 10, respectively.
a- and inner metal layers 10b, 10b" clad on the inside of the outer metal layer. In this embodiment, the end of the outer metal layer is on the side of the to-be-joined end of the clad pipe 10°10-. Diagonally cut all around, groove surface 10A, IOA
” is formed, and as shown in Figure 2, the cladding pipe is 10° (
A U-shaped groove 11 is formed at the joint portion of both cladding pipes when the ends to be joined 0' are butted against each other.

Inner metal layer 10b of cladding tube 10.10-.

The end faces of 10b' are root faces (pressing surfaces) IOB and 10B-, which are perpendicular to the axes of both cladding pipes.
Bevel 11 between the ends to be joined of clad pipe 10.10-
Only these root faces come into surface contact when they are butted together through the .

When joining the clad pipes 10 and 10-, for example, one clad pipe 10 is fixed to a stationary clamp provided on a friction welding device, and the other clad pipe 10' is fixed to a chuck of a rotationally driven main shaft. hold it. Then, the cladding tube 10- on the rotating side is rotated with one cladding tube brought into pressurized contact with the other cladding tube at a predetermined pressure (referred to as heating pressure) using a pressurizing device, and the contact portion of both tubes is rotated. generates heat due to friction.

Although the pressurizing device may be provided on either the rotating side or the stationary side, in the embodiment, the pressurizing device was provided on the rotating side.

In the friction welding device used in the example, the main shaft for rotating the cladding pipe IO- and the pedestal supporting the drive mechanism for rotating the main shaft were movable in the axial direction of the main shaft, and the pedestal was moved using a hydraulic cylinder. A necessary pressing force was applied between the clad pipe 10°↓0' by applying force using a pressurizing device.

Inner metal layer 10b of cladding tube 10.10-.

10 b, - When brought into contact with each other and relative rotation is caused between the two, the temperature of the joint increases due to frictional heat. This softens the inner metal layers 10b, 10b-, so that the inner metal layers 10b, 10b-
The vicinity of the abutting portion of is pushed out to the groove 1 side and inside the tube, and at the same time, the clad tube 10.10- approaches.

As time passes further, the U-shaped groove 11 is formed as shown in Fig. 4.
The outer metal layers 10a, 10a' come into contact with each other from the trough side, and as the outer metal layers 10a, 10a- move outward within the groove, the Clasod pipes 10.10- move closer together. .

When the temperature of the joint reaches a predetermined value, the rotating side cladding pipe 10- is stopped, and the cladding pipe 10.
1CI is pressurized with a large upset pressure and welded together.

The total approach distance δ from the start of rotation to the end of upsetting is finally determined by the end 1 on the opening side of the groove surface, as shown in FIG.
0A1. 10A2 the farthest point of the joint)
set large enough to fully join.

When the bonding is completed in this manner, holes 13 and 14 are formed on the outer and inner circumferential sides of the bonded portion, respectively, as shown in FIG. Finally, these particles are removed to obtain the state shown in FIG.

When carrying out the method of the present invention, it is preferable to set the groove angle θ of the U-shaped groove 11 in the range of 15 degrees to 45 degrees. If the groove angle θ is smaller than 15 degrees, the amount of debris protruding into the inside of the tube will increase, which is undesirable. Moreover, if the groove angle is larger than 45 degrees, the offset margin becomes too large, the time required for pressure welding increases, and the work efficiency decreases.

Experiments conducted to confirm the effects of the present invention will be described below.

[Experiment 1] Clad pipe 10.10- (US Asume Standard 4B) with outer metal layers 10a, 10a- made of carbon steel and inner metal layers 10b, 10b- made of stainless steel (SUS 304).
Those that satisfy xSch80. ) was used as the clad pipe to be joined. In this experiment, no beveling was performed, the rotation speed N during heating and pressing was 750 [rpm], and the heating pressure Pi was 2 (
kgf/mm2], upset pressure P2 to 8 [k
g [/mm2], and the total offset δ was set to 10 [mm]. After pressure welding, the inner and outer blades of the tube were removed, the joint was cut, and the cross section was observed under a microscope, and it was confirmed that the outer metal layer of carbon steel was exposed on the inner surface of the tube. .

[Experiment 2] Clad pipe 10.10" (US Asume Standard 3BxSc
Something that satisfies h80. ) was used as the clad pipe to be joined. In this experiment, no beveling was performed, the rotation speed N during heating and pressing was 750 [rpm], and the heating pressure P1 was 3 (kg[
/mm2], the upset pressure P2 is 12 [4217
mm2], and the total offset δ was set to 10 [mm]. After removing the internal and external debris from the pressure-welded tubes, the joint was cut and the cross section was observed under a microscope, and it was confirmed that the outer metal layer of carbon steel was exposed on the inner surface of the tube.

[Experiment 3] The outer metal layers 10a and 10a- were made of 21/4Cr-IMo steel, and the inner metal layers 10b and 10b- were made of stainless steel (S
A 10° 10' clad pipe made of US316 (which satisfies the American Asme Standard 4BxSch80) was used as the clad pipe to be joined. The groove angle θ is 60 degrees, the rotation speed N during heating and pressing is 750 [rpm], the heating pressure Pi is 3 [kgf/mm2], and the upset pressure P2 is 1.
After pressure welding was carried out at a pressure of 0 [kg[/mm2] and a total approach distance δ of 14 [mm], pars from the inside and outside of the tube were removed, the joint was cut, and its cross section was observed under a microscope. As a result, it was confirmed that the inner metal layer was completely joined at the joint, and the characteristics of the clad pipe were not lost. Furthermore, when a non-destructive test was conducted on the joint using ultrasonic waves, no defects such as cracks, blowholes, or poor fusion were found in the joint.

The groove employed in the method of the present invention may be a so-called U-shaped groove. FIGS. 7(A) to 7(D) illustrate examples of U-narrow groove shapes that can be employed in the method of the present invention.

The example shown in FIG. 7(A) is the groove surfaces 10A, 10A- and the root face (groove tip surface) IOB.

In the case where there is no curvature (no radius) at the boundary between 10B and 10B-, the U narrow groove shown in Figure 7 (A) is adopted in the examples shown in Figures 1 to 6. ing.

In addition, the example shown in FIG. 7(B) or D) is the groove surface 10.
A, l0A- and root face 10B.

This is a case where the boundary portions 10C and 10C- between the line 10B- and the line 10B- are given a curvature.

The radial dimension F of root face IOB, IOB” is the seventh
As shown in FIGS. (A) and (B), the inner metal layer 10b,
It may be equal to the thickness C of 10b-, or may be smaller than the thickness C of inner metal layers lOb and 10b-, as shown in FIG. 7(C). Further, as shown in FIG. 7(D), the radial dimension F of the root faces 10B and 10B- is set to the inner metal layer 10b.

It may be larger than the thickness C of 10b-.

Generally, the wall thickness t of this type of metal tube is in the range of 5 to 3 Qmm, and the thickness C of the inner metal layer is 2 to 3 mm (however, t>C)
within the range of

The radial dimension F of the root faces IOB, 10B- depends on the thickness C of the inner metal layers 10b, 10b-, but is usually preferably set to 1 to 1Q mm. Further, when rounding the boundary between the groove face and the root face, the radius of curvature is preferably set to 1 to 5 mm.

In the above embodiment, after the cladding tubes 10.10'' are butted together and heated and rotated, the rotation of the cladding tubes is stopped when the joint reaches a predetermined temperature, and then the upset is performed. Alternatively, the pressure may be increased temporarily during heating rotation, and finally the pressure may be increased rapidly.

In the above explanation, one of the clad tubes 10, 10- is kept stationary and the other is rotated, but the rotation during heating rotation is arbitrary, and various methods already proposed for friction welding can be used. A method of rotation can be adopted.

For example, the cladding tubes 10, 10- may be rotated in opposite directions.

In the above embodiment, the case where two clad pipes 10 and 10' are joined is taken as an example, but three clad pipes are butted one after another, and there is a gap between the central clad pipe and the clad pipes on both sides. The method of the present invention can also be applied to the case where friction welding is performed by causing rotation.

[Effects of the Invention] As described above, according to the present invention, a U narrow groove is provided in the outer metal layer portion of the ends to be joined of the cladding pipes to be joined, and a narrow gap is provided between the inner metal layers of the cladding pipes to be joined. By starting frictional contact and friction welding the clad tube, the inner metal layers can be reliably joined together, and when the inner surface of the tube is removed, the outer metal layer is exposed on the inner surface of the tube. can be prevented. Therefore, there is an advantage in that clad pipes can be joined together without losing the properties of the clad pipes, by taking advantage of the characteristics of friction welding, and without creating a fragile hardened metal layer at the connection portion.

In addition, since it requires less effort than arc welding, the number of man-hours required for joining can be reduced and work efficiency can be improved.

[Brief explanation of drawings]

Fig. 1 is a half sectional view showing the cross-sectional shape of the vicinity of the joined end of a clad pipe to be joined by the method of the present invention, and Figs. 2 to 6 show cases in which clad pipes are joined by the method of the present invention. 7(A) to D) are sectional views illustrating various groove shapes suitable for the method of the present invention. FIG. 8 is a sectional view schematically showing changes in the cross-sectional shape of the joint. A cross-sectional view schematically showing the cross-sectional shape of the joint when clad pipes are joined by arc welding, and Figures 9 to 11 are cross-sections of the joint when clad pipes are friction welded without a groove. FIG. 3 is a cross-sectional view showing a change in shape. 10.1CI... clad pipe, 10a, 10a...
Outer metal layer, IQb, 10b--inner metal layer, 11
...U narrow groove, 13.14... Paris, θ... groove angle. Figure Figure Figure Figure

Claims (3)

[Claims] (1) In a method of joining clad pipes in which the inner circumferential side of an outer metal layer is clad with an inner metal layer thinner than the outer metal layer, by butting each other with their central axes aligned, the cladding to be joined is A method for joining clad pipes, characterized in that a U-shaped groove is formed at the ends of the pipes to be joined, and frictional contact is initiated between the inner metal layers of the clad pipes to be joined, thereby friction welding both clad pipes. . (2) The method for joining clad pipes according to claim 1, wherein the U-shaped groove has a groove angle of 15 degrees or more and 45 degrees or less. (3) The method for joining clad pipes according to claim 1 or 2, wherein the outer metal layer is made of carbon steel or chromium molybdenum steel, and the inner metal layer is made of stainless steel or nickel alloy steel.