JPH0450129B2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The disclosed technology is a technical field of manufacturing multi-layer pipes with wear resistance, corrosion resistance, etc., in which an outer layer pipe and an inner layer pipe are tightly connected through an intermediate layer material between them. belongs to

<Summary of the gist> This invention aims to improve the abrasion resistance, corrosion resistance, etc. of piping used for corrosive fluid transportation, slurry transportation, powder and granular pneumatic transportation, etc. Layering the pipe and a highly wear-resistant inner layer pipe,
The multi-layered raw tube is moved in the axial direction relative to the outer annular heating of the outer layer tube and the peripheral cooling means before and after the axial direction, and the localized annular heating of the raw tube is performed continuously in the axial direction. This invention relates to a method for manufacturing a multilayer pipe in which the outer layer pipe is expanded in diameter and the outer layer pipe and the inner layer pipe are tightly connected. The middle layer material prevents the heating of the outer layer tube from reaching the inner layer tube, and the annular heating from the outside of the outer layer tube and the cooling at the front and rear of the axial direction are performed in the axial direction relative to the base tube. During the movement, while maintaining the cooled state of the inner layer tube, the expansion diameter of the annular heated portion of the outer layer tube is constrained by the surrounding cooling portion to yield, and in the subsequent cooling process, the heated portion is contracted. This invention relates to a method of manufacturing a multi-layer pipe in which the outer layer pipe is tightly connected to the inner layer pipe through the middle layer material with a sufficient fitting allowance by reducing the diameter.

<Prior art> As is well known, piping is widely used in various industrial fields to transport fluids. In pipes for transporting slurry in a mixed manner, or pipes for pneumatically transporting particulate materials such as dust and silica sand, the inner surface of the pipe is likely to wear significantly during transport.
Further, there is the disadvantage that corrosion is likely to occur.

Up until now, this type of piping has typically used inexpensive steel pipes such as gas pipes, and when they wear out or corrode, they are replaced with new pipes, or patch plates are welded to the worn or corroded parts. I was dealing with this by

<Problem to be solved by the invention> However, especially for piping applications that require wear resistance and corrosion resistance, pipes made of materials with excellent wear resistance and corrosion resistance, such as high chromium cast iron, are often used. There were times when it was done.

By the way, in general, the wear resistance and corrosion resistance of steel materials have a good correlation with the hardness.

And materials with excellent wear resistance are uniformly extremely hard and are often used as wear-resistant materials, e.g.
27Cr cast iron has a Shore hardness of 81 or higher.

However, on the other hand, as the hardness increases, the toughness of steel materials tends to decrease, and pipes made of wear-resistant materials such as the above-mentioned high chromium cast iron have the disadvantage of being easily damaged when subjected to impact force.

In addition, high-hardness wear-resistant materials have extremely poor weldability and workability, so firstly, it is impossible to attach the flange to the pipe body by welding, which is a disadvantage, and secondly, the flange cannot be attached to the pipe body by welding. Even when integrally formed, finishing and drilling are difficult, and thirdly, repair welding is difficult.

In addition, it also has the disadvantage of high manufacturing costs.

For this reason, so-called clad steel double-layer pipes, which have an outer layer of steel pipe and an inner layer of wear-resistant material tightly connected to the outer layer, have also come into use.

This type of clad steel multilayer pipe is usually made by centrifugal casting or overlay welding.
The inner tube is metallurgically bonded to the outer tube.

Since the inner surface of the outer layer of clad steel pipe is covered with an inner layer of wear-resistant material, clad steel pipes are much more resistant to wear than ordinary single-layer steel pipes made of materials that do not take wear resistance into account. Excellent quality.

And, unlike pipes made only of wear-resistant materials,
It has sufficient impact resistance, and it is also possible to form the flange separately and attach it by welding.

<Problems to be Solved by the Invention> However, with clad steel multi-layer pipes, tensile stress remains in the inner layer pipe regardless of the manufacturing method, so there is an inconvenience that cracks are likely to occur during manufacturing and operation. be.

Furthermore, once a crack occurs, since the inner layer tube and the outer layer tube are metallurgically joined, there is a disadvantage that the crack easily propagates to the outer layer tube, resulting in a through crack.

Therefore, we developed a double-layered pipe in which an outer-layer pipe with sufficient toughness for practical use and an inner-layer pipe with excellent wear resistance are layered, and the two pipes are not metallurgically joined, yet they contact each other with a certain surface pressure. Therefore, it is desired to develop multi-layer pipes such as self-consolidating double pipes in which the inner layer pipe is in a state of compressive stress.

This is because multilayer pipes such as self-consolidated double pipes with lids have the same advantages as clad steel pipes, and moreover, the above-mentioned disadvantages of clad steel pipes are eliminated.

By the way, conventional self-tightening double pipe manufacturing techniques include firstly the shrink fitting method, secondly the pipe expanding method, and thirdly the heat expanding method developed by the applicant and which is the subject of many prior inventions.

However, each of these methods has disadvantages that are undesirable as a method for manufacturing a self-stressing multi-layer pipe whose inner layer pipe has wear resistance and corrosion resistance.

First, the first method requires strict machining accuracy on the inner diameter of the outer layer tube and the outer diameter of the inner layer tube, but in the case of a double tube with a wear-resistant inner layer, the inner layer tube is made of a wear-resistant material with poor workability. Therefore, although the required processing is performed, it is extremely difficult.

In addition, it is no exaggeration to say that this method generally makes it impossible to fit long tubes.

In addition, in both the second and third methods, the inner layer pipe is expanded plastically, but in this case, the strength (yield point) of the inner layer pipe is extremely high, and the inner layer pipe is Because of the increased thickness, extremely high tube expansion pressure is required, which has the disadvantage of being impractical.

In particular, in the second method, the strength (yield point) of the outer layer pipe is higher than the strength (yield point) of the inner layer pipe, and in the case of this type of double pipe, even if the inner layer pipe is expanded plastically, the inner layer There is a problem where a gap occurs between the pipe and the outer layer pipe.

As described above, although there is a strong need for a wear-resistant double pipe, the conventional techniques have not been able to provide a wear-resistant double pipe that satisfies the requirements.

<Basic Background of the Invention> Generally, the pipe diameter is changed by subjecting the pipe to local heating and cooling treatment in an annular manner.

This phenomenon is due to thermo-elasto-plastic behavior.

In other words, when a local part of the tube is heated, the heated part tends to expand in diameter due to thermal expansion, but at this time, if the area around the heated part is forcibly cooled, the expanded diameter is restrained by the cooled part, and the yield stress is reduced at high temperatures. Coupled with the fact that the height is lower, the heated portion easily undergoes plastic deformation, and the amount of expansion becomes significantly smaller than that during free expansion.

During subsequent cooling, the tube undergoes thermal contraction relatively freely, so the tube diameter of the portion that has undergone this thermal history becomes smaller than the initial diameter.

By continuously applying this heat treatment in the longitudinal direction of the tube, the tube diameter can be uniformly reduced, and
By applying it locally, it is also possible to locally reduce the tube diameter.

Figure 6 shows a simulation of the basic phenomenon in which the diameter of a pipe changes by the ring thermal reduction method (a method of reducing the diameter by applying annular heating and cooling to the pipe) using thermoelastic-plastic analysis. In this case, the analysis model is a mild steel pipe (outer diameter 165.2mmφ x wall thickness 5.5mm)
The analysis conditions were to provide a continuous thermal history in the longitudinal direction of the tube, in which the tube was locally and annularly heated up to 800°C rapidly and then cooled down.

In the figure, the vertical axis represents the amount of plastic strain that occurs in response to a given thermal history and the corresponding transient change in the pipe diameter (both values at the center of the plate thickness), and the coordinates in the longitudinal direction of the pipe are plotted. Shown on the horizontal axis.

During heating, the amount of apparent expansion is small and large compressive plastic strain occurs in the circumferential direction, and while during cooling, tensile plastic strain occurs, but the amount is smaller than during heating, so after cooling It can be seen that compressive plastic strain remains in the pipe and the pipe diameter decreases.

Furthermore, changing the shape of the heat source (heating gradient, cooling gradient, maximum heating temperature, etc.) changes the amount of plastic strain that occurs, which changes the amount of change in pipe diameter, so depending on the material and cross-sectional shape of the pipe, This shows that the amount of change in tube diameter can be controlled by providing a predetermined thermal history.

<Objective of the Invention> The object of the present invention is to solve the problems of manufacturing multi-layer pipes such as double pipes based on the prior art described above, and to solve the problems of manufacturing multi-layer pipes such as double-layer pipes based on the above-mentioned prior art. An annular heating action in the circumferential direction and a cooling action in the axial direction from the outside are simultaneously applied to the outer layer pipe of the base pipe, for example, continuously while moving relative to the axial direction, and the outer layer pipe of the middle layer material is The outer layer pipe is reduced in diameter by maintaining the inner layer pipe in a cooled state due to the heating suppressing effect on the inner layer pipe, and the inner layer pipe is tightened via the middle layer pipe, making it possible to use piping technology in various industries. It is an object of this invention to provide an excellent method for manufacturing multilayer pipes that will benefit the field.

<Means/effects for solving the problem> In order to solve the above-mentioned object and the scope of the above-mentioned claims as a gist, the structure of the present invention is to In order to provide corrosion resistance by reducing the diameter of a wear-resistant material and applying compressive residual stress, we use an inner layer with excellent wear resistance through a middle layer material that is a heat suppressing material with high insulation and heat insulation properties. The pipe and the outer layer pipe are relatively layered to form a base pipe, and the annular heating means in the circumferential direction for the outer layer pipe, the annular cooling means before and after the axial direction, and the base pipe are relatively moved in the axial direction, and at this time, By providing cooling means at the rear of the annular heating means, or at the front and rear of the annular heating means, a radial bending moment can be suppressed in the center direction at the rear of the heated portion, or at the front and rear of the heated portion, in terms of the axial length. make it work,
Moreover, the annular heating of the outer layer tube is prevented from reaching the inner layer tube by the heat suppression function of the middle layer material, and the base tube attempts to expand in diameter at the heating section, but the cooling section on one or both sides of the heating section in the axial direction The outer layer tube, middle layer material, and inner layer tube are bonded together so that the outer layer tube, the middle layer material, and the inner layer tube are bonded together so that the inner layer tube is constrained and yields, and the diameter is reduced from the initial diameter by cooling immediately after heating, and strong compressive residual stress is imparted to the inner layer tube, which improves wear resistance. Technical measures have been taken to improve corrosion resistance.

<Example> Next, an example of the present invention will be described below with reference to the drawings of FIGS. 1 to 5.

The illustrated embodiment is a manufacturing mode of a triple-layered pipe having wear resistance and corrosion resistance such as a slurry transport pipe as a multi-layered pipe.
Using high toughness material such as low carbon steel of about 0.25%,
In addition, the inner layer tube 2 is made of wear-resistant material, such as high carbon steel with a carbon content of about 0.55%, which has been quenched and hardened. A middle-layer pipe 3 with a thin wall thickness as a middle-layer material made of aluminum is wrapped, and the three parts are loosely inserted into each other to form a triple-pipe base pipe 4.

The triple-pipe tube 4 is set to move at a predetermined speed in the axial direction as shown by the arrow, and further, as shown in FIGS. As a heating means, for example, a high-frequency induction heating device 5 is set, and cooling devices 6, 6 for an annular shower device, such as tap water, are set in the front and back in the axial direction close to the high-frequency induction heating device 5 at a predetermined distance apart. By moving the raw tube 4 in the direction of the arrow, the annular heating device 5 and the annular cooling devices 6, 6 can be changed to the triple tube blank tube 4.
It is made to move relative to.

Therefore, when the triple tube blank tube 4 is moved in the axial direction at a predetermined speed, the annular heating device 5 applies an expansion effect by induction heating to the cooling of the outer layer tube 1 by the annular cooling devices 6, 6 before and after it. However, in this process, if both ends of the heating part are free ends with respect to the cooling part, as schematically shown by the dotted line A in Fig. 2, the diameter will expand freely as shown in Fig. 2. However, in reality, both axial ends of the heating portion are restrained by the cooling portion, so that the heating portion protrudes in the circumferential direction, as shown in the schematic diagram of Fig. 4. A radial pressing bending moment F acts toward the center, and as a result, a circumferential ring-shaped curved plastically deformed portion is formed.

As the triple-pipe tube 4 moves relatively in the axial direction as shown by the arrows in FIGS. 2 and 5, the part that is heated and plastically deformed by the annular heating device 5 passes through the heated part and is cooled in an annular manner. When cooled by the device 6, as shown in FIG. 3, the diameter is greatly reduced, thereby providing a large fitting allowance, and a compressive force is applied to the inner layer tube 2, so that the outer layer tube 1 is inner layer pipe 2
The hoop is tightened and fastened via the middle layer pipe 3.

During this time, a thin-walled middle layer tube 3 made of austenitic stainless steel with low magnetic permeability and excellent magnetic shielding function is interposed between the outer layer tube 1 and the inner layer tube 2. The magnetic field generated by the induction coil is reliably blocked from the inner layer tube 2, and the inner layer tube 2
Therefore, the inner layer tube 2 is maintained in a cooled state, and the tightening is promoted by the diameter reduction action of the outer layer tube 1.

Note that, since the middle layer tube 3 is thin, the diameter reduction effect of the outer layer tube 1 on the inner layer tube 2 is hardly inhibited.

Since this action acts on all circumferential portions of the outer layer tube 1, by continuously moving the triple tube element tube 4 relatively in the axial direction, all portions of the outer layer tube 1 are reduced in diameter. A constrained fit state appears in all regions of the triple tube element tube 3, thereby creating a large compressive residual stress in the inner layer tube 2, and as a result, a large self-stressing triple tube 7 is formed.

The above-mentioned tightening process is carried out regardless of the wall thickness of the inner layer tube 2, and since it is formed in the entire triple tube element tube 4 regardless of the axial length, the outer layer tube 1 and the inner layer tube 2 are This process has almost no relation to the accuracy of each joining surface with the middle layer tube 3, and is difficult to manufacture a wear-resistant and corrosion-resistant triple layer tube where the inner layer tube 2 has a large wall thickness and is a long tube. is extremely effective.

This process may be performed once, but by repeating it not only once but twice or more, the amount of diameter reduction can be increased.

Next, an experimental example based on the above embodiment is as follows.

Figure 7 shows the amount of external diameter change (cumulative) of the outer layer tube 1 and the occurrence of fitting surface pressure between the inner and outer tubes of the middle layer material 3 for each ring thermal diameter reduction process in triple tube manufacturing using the ring thermal diameter reduction method. In this experimental example, both steel pipes (material:
STPG-38, shape: outer layer pipe 90A/Sch40, middle layer material
80A/Sch40).

In this case, the clearance (diameter difference) between the two is
The diameter is 1.5 mm, and the two are brought into contact with each other in four processes, and after the fifth process, they fit together.

Here, the clearance may be sufficient to overlap the two, and in practical terms, it is, for example, about 1 to 5 mm.

In addition, the amount of diameter reduction can be arbitrarily determined depending on the implementation conditions, but in reality, for example, the diameter of the outer tube
It is about 0.5%.

As can be seen from the data of the experimental example, the amount of diameter reduction of the outer layer tube 1 increases as the number of treatments increases until the two come into contact, and after the two come into contact, a fitting surface pressure is generated.

Furthermore, since the fitting surface pressure increases as the number of treatments increases, it is understood that the fitting surface pressure can be changed by controlling the number of treatments.

It goes without saying that the embodiments of the present invention are not limited to the above-mentioned embodiments, and the intermediate layer material is not limited to the intermediate layer pipe. For example, powder of austenitic stainless steel, non-magnetic cast iron, etc. can be used for the outer layer pipe and the inner layer pipe. Alternatively, if an annular heating device is used instead of an induction heating device, an asbestos strip may be wrapped around the inner tube as a middle layer material, or ceramics such as zirconia may be thermally sprayed on the outer surface of the inner tube. It is also possible to interpose a heat insulating material such that the inner layer tube is made of ceramics, or to manufacture a corrosion-resistant triple layer tube, that is, to use a corrosion-resistant material for the inner layer tube. can be adopted.

It is also possible to provide an appropriate amount of cooling means within the inner tube.

Moreover, it is applicable not only to straight pipes but also to curved pipes such as bent pipes.

By repeating the above-mentioned process, it is also possible to manufacture quadruple-layered pipes or more.

Therefore, this invention differs from an embodiment using a circumferential diameter increasing/reducing means by means of adding a linear heating or cooling means to the moving method, in that the expanding diameter of the annular portion of the heated tube is adjacent to each other. It is restrained by the cooling part, and the heating part is reduced in diameter after cooling, so that, for example, when manufacturing triple pipes, the outer layer pipe is tightly connected to the inner layer pipe via the middle layer pipe. , the self-control mechanism is completely different.

<Effects of the Invention> As described above, according to the present invention, basically, when manufacturing a double-layered pipe such as a triple-layered pipe, it is possible to reduce the diameter of the outer layer pipe, thereby increasing the strength of the inner layer pipe compared to the outer layer pipe. There is no risk of clearance between the contraction of the outer layer tube and the expansion of the inner layer tube, such as a highly wear-resistant triple layer tube, and the excellent effect of obtaining extremely high accuracy as a self-tightening double layer tube is achieved. Ru.

In addition, when the outer layer tube is subjected to annular heating from the outside and annular cooling in the front and back of the axial direction, a middle layer material such as a middle layer tube with excellent magnetic shielding and heat insulation functions is interposed between the outer layer tube and the inner layer tube. By doing this, electric heat and heating from the outer layer tubes are not transmitted to the inner layer tubes, and the inner layer tubes are bonded while maintaining a cooled state, so a large fitting allowance can be made for tightening, and a stronger compressive residual stress is formed in the inner layer tubes. This has the advantage that stress corrosion cracking and the like of the piping does not occur when piping the product, and as a result, the excellent effect that wear resistance is guaranteed by corrosion resistance is achieved.

In addition, there is no need for the enormous pressure necessary for pipe expansion pressure, and the power cost for manufacturing is low, resulting in low-cost manufacturing.

In addition, unlike conventional shrink fitting methods, the accuracy of the joint surface between the outer layer pipe and the inner layer material for the middle layer material is not required to be so high, and therefore, it has the advantage of being able to freely manufacture long pipes, etc. effect is produced.

In addition, even if the inner layer pipe is wear-resistant and the outer layer pipe is high toughness, the diameter can be reduced without any restrictions on design freedom, and therefore the selection of materials for the outer layer pipe and inner layer pipe is also easy. It has the advantage of being free.

In this way, a multilayer pipe with excellent wear resistance and corrosion resistance can be obtained.

[Brief explanation of the drawing]

1 to 5 are schematic explanatory diagrams of one embodiment of the present invention, and FIG. 1 is a partial cross-sectional side view when the outer layer pipe and the inner layer pipe are stacked relative to each other via an intermediate layer material, and FIG. FIG. 3 is a sectional view of a mechanism for reducing the diameter of the presser foot by applying bending moment by annular heating; FIG. 4 is a schematic perspective view of the mechanism for applying presser foot bending moment; FIG. 5 is a perspective view of heating and cooling, FIG. 6 is a simulation graph of the basic phenomenon of the ring-thermal diameter reduction method, and FIG. 7 is a graph of an experimental example of ring-thermal diameter reduction. 1... Outer layer pipe, 2... Inner layer pipe, 3... Middle layer material,
5... Annular heating (means), 6... Annular cooling (means).

Claims (1)

[Claims] 1. In a method for manufacturing a multi-layer pipe in which an outer layer pipe and an inner layer pipe are bonded together by applying heating and cooling to the base pipe and the outer pipe through an intermediate layer material, The material pipe is used as a suppressor, and the heating means on the outside of the outer layer pipe of the material pipe is moved relative to the cooling means in the axial direction, and the outer layer pipe is annularly heated from the outside in the circumferential direction. At the same time, annular cooling is applied to both the front and rear sides of the tube in the axial direction, and the thermal expansion of the heating section is restrained by the low temperature sections on both sides to suppress the expansion diameter and the temperature rise of the inner layer tube is suppressed by the middle layer material. At the same time, the heating section is cooled through a cooling means to contract so that the diameter of that part becomes smaller than the initial diameter, and the pipe diameter after cooling is made smaller than the initial diameter over the entire length of the heating section. A method for manufacturing a multilayer pipe, characterized in that: