JPH0576378B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The disclosed technology belongs to the technical field of manufacturing outer wear-resistant double pipes used for piping in abrasive fluids in boilers.

<Summary of the gist> The invention of this application is a method of relatively overlapping a high-hardness outer pipe such as a chromium-molybdenum steel pipe with respect to an inner pipe such as a carbon steel pipe (extrapolating an outer pipe with respect to the inner pipe, or After the inner tube is inserted into the tube (meaning a combination of both), both tubes are self-tightened by mechanical means, hydraulic means, etc. through the fitting margin. This invention relates to a method for manufacturing double-layered pipes, and in particular, the invention relates to a method for manufacturing a double-walled pipe, in which an outer pipe such as a chromium-molybdenum steel pipe with a high yield point and high wear resistance is layered relative to an inner pipe with a low yield point such as the above-mentioned carbon steel pipe. , furthermore,
At that time, the outer tube is annealed, a load is applied from the inner surface to the outer surface of the tube to bring the inner and outer tubes into close contact, and from that state, or at least the outer tube is quenched in that state to achieve high strength and high strength. By adding hardness and increasing wear resistance, we expand the diameter of both the inner and outer tubes integrally within a range that exceeds the elastic limit of the inner tube and does not damage the outer tube, and utilize the difference in elastic return. This invention relates to a method of manufacturing a wear-resistant double pipe that has a large fitting allowance and is self-tightening.

<Prior art> As is well known, piping is used in many industrial fields.
It is used for a variety of purposes, but the most commonly used mode is to transport fluids, etc. using the inside of the pipe as a transportation path, but it is used in boilers, factory waste piping, and chemical plants. For piping used in heat exchangers, etc., the surrounding environment contains slurry or sludge with a considerably high viscosity, for example, the outside of the pipe has a high viscosity and also contains a considerable amount of solids such as fine particles. As a result, the outside of the piping is subject to severe wear and tear, not only on the vent section but also on the straight pipe section.To deal with this, it is generally necessary to replace the piping regularly. Therefore, from the point of view of cost, inexpensive steel pipes are used.

However, in modern power plants, frequent replacement of piping is considered undesirable from the viewpoint of improving operating efficiency and safety measures. From this point of view, it has become desirable to install piping with excellent wear resistance on the outside.

<Problem to be solved by the invention> In order to solve this problem, wear-resistant, high-hardness cast steel pipes and double-walled pipes with a wear-resistant outer surface made by centrifugal casting are being used. Of these, the former type of wear-resistant cast steel pipe is superior in terms of its hardness on the outside, but due to constraints in the manufacturing process, pipes of the set unit length are connected to the set length at the installation site via joints. There are various types of containers and multiple containers that can be combined and connected, and in such cases,
Flange joints are often used due to their advantages such as ease of machining the joint, ease of maintenance, inspection, maintenance, removal and replacement, etc. However, due to the high hardness of the material of high hardness cast steel pipes, face cutting of the flange part is required. The problem is that it is difficult to drill holes for bolts and bolts.
In addition, when a through-hole defect occurs, there is a disadvantage that cracking spreads throughout the entire pipe at an early stage, and high toughness of the entire pipe cannot be obtained.

Even when wear resistance and high hardness are satisfied, the disadvantage is that the cost is extremely high.

In addition, there is a disadvantage in that there is little room for material selection in terms of the performance of metals in terms of wear resistance, which results in a correspondingly low degree of freedom in design and, in some cases, the inability to meet the needs of each application.

In addition, for the production of the latter double pipe, hydraulic expansion methods, shrink fitting methods, and the so-called thermal expansion method disclosed in many of the applicant's earlier inventions have been developed. In the method, there is a restriction in selecting conditions that it is difficult to bond if the yield point of the inner tube is higher than that of the outer tube, and if the strength of the outer tube is too high,
There is a problem that it is practically impossible to expand the tube, and in the case of the shrinkage spring method, the alignment accuracy of the outer tube and the inner tube is extremely strict, so there is a disadvantage that it cannot be used for long tubes. Furthermore, according to the thermal tube expansion method, if the outer tube has a high strength and a large wall thickness, a considerably large pressure is required, and there is a problem that management and control are actually complicated.

<Object of the Invention> The object of the invention of this application is to solve the above-mentioned conventional problems that cannot meet the potentially great need for piping that is wear-resistant outside of the satisfying conditions. We considered technological problems to be technical issues to be solved, and while making the outer tube highly hard,
For the inner pipe, we manufacture an excellent wear-resistant double pipe that can firmly support the outer pipe and improve the high hardness and wear resistance of the outer pipe, thereby benefiting piping technology applications in various industries. The purpose is to provide a method.

<Means and actions for solving the problem> In order to solve the above-mentioned problem, the structure of the invention of this application, which is summarized in the above-mentioned claims, includes an inner tube made of a material with a low yield point. On the other hand, an outer tube made of a material with a high yield point and high abrasion resistance is layered relative to each other, and at that time, the outer tube is further annealed to lower its hardness and strength, and then the inner tube is The tube is expanded to reveal a state of close contact between the outer tube and the inner tube after relative layering, and then further, or at least the outer tube is quenched to increase hardness and strength, increase wear resistance, and at least improve the inner tube. By expanding the diameter of the inner and outer tubes beyond the elastic limit and within the breakage limit of the outer tube, theoretically speaking, they should fit together with just one diameter expansion process, but The reason for repeating the diameter expansion one more time is as follows.If the diameter expansion amount of the inner tube is large, the pullout load will be large, and it is judged that it is difficult to control the degree of fitting, so from industrial considerations, First close contact (inner tube diameter expansion only),
A technical means that makes it possible to more tightly fit both tubes through a large fitting margin by utilizing the difference in elastic return between the two when they are fitted for the second time (diameter expansion of the inner and outer tubes). This is what I learned.

<Example> Next, an example of the invention of this application will be described below with reference to the drawings.

Using an outer tube 2 made of, for example, chromium-molybdenum steel, which has a high yield point and high wear resistance, and an inner tube 1 made of carbon steel, which is a material with a low yield point, the outer tube 2 and the inner tube 1 are It is also possible to relatively stack the outer tube 2 on the inner tube 1 with an initial diameter difference of _R1 , and in this case, the outer tube 2 can be annealed, as shown in FIG. When the inner tube 1 is expanded by the mandrel 3 from inside the tube 1 and the mandrel 3 is pulled out relatively in the direction of the arrow, the horizontal axis represents the diameter R, and the vertical axis represents the stress F. As shown in the figure, the inner tube 1 follows the curves A, B, and C shown by the dotted lines, expands in diameter, yields, comes into close contact with the outer tube 2, and then both tubes 1 and 2
are integrally enlarged in diameter, and the outer tube 2 is also expanded in diameter.
It follows the path c' and expands in diameter.

At this time, the outer tube 2 may be appropriately quenched to increase its hardness and strength and improve its wear resistance.

In this case, if the diameter is expanded beyond the elastic limit of the inner tube 1 and within the limit of breakage of the outer tube 2, as shown in FIG. Yes,
Following b' and c', after passing mandrel 3,
The diameter expansion action is released and both tubes 1 and 2 contract (inner tube 1
Then, trace C and D, and C' and D' for the outer tube 2), but in the meantime, due to the difference in elastic return of both tubes 1 and 2, both tubes 1 and 2 are tightly connected with a large fitting margin of ΔR, Therefore, the tightening effect of the inner tube 1 on the outer tube 1 increases dramatically.

Note that R ₂ is the diameter expansion allowance for both tubes 1 and 2 as a unit, and R ₃ is the total diameter expansion allowance due to the mandrel 3.

It goes without saying that the embodiments of the invention of this application are not limited to the above-mentioned embodiments; for example,
When expanding the tube, various methods can be adopted, including means other than the diameter expanding operation using a mandrel in the above-described embodiment.

<Effects of the Invention> As described above, according to the invention of this application, in manufacturing a double-walled pipe whose outer pipe is basically wear-resistant, it is possible to manufacture a double-walled pipe whose outer pipe is basically wear-resistant, without using expensive manufacturing methods such as the conventional cast steel method or centrifugal casting method. A double-walled tube with a highly wear-resistant outer tube can be created at low cost, and the strong support of the outer tube by the inner tube results in high wear-resistance for the double-walled tube as a whole. This has the excellent effect of providing high toughness, and a large degree of freedom is obtained in the selection of materials for the outer and inner tubes.This allows for example The connecting flange can be welded together, and the workability of the bolt holes and surfaces of the flange is not hindered in any way, and therefore, the excellent effect of facilitating the manufacture of the unit pipe is achieved.

In addition, in order to ensure that the outer tube and the inner tube are in a self-tight state, even if a penetration defect occurs in the outer tube, the outer tube as a whole has high toughness, so the penetration defect is unlikely to occur. An excellent effect is achieved in that the function of the heavy pipe is easily maintained from beginning to end.

Therefore, by using a tube made of a material with a low yield point for the inner tube and a tube with a high yield point for the outer tube,
At that time, by simply annealing the outer tube and expanding the inner tube using a mandrel, etc., it is possible to make the two tubes come into close contact with each other. By increasing the strength and expanding the diameter of the inner tube to allow it to expand beyond the elastic limit of the inner tube while remaining within the breakage limit of the outer tube, the difference in elastic return during diameter contraction can be used more effectively. This provides an excellent effect of increasing the fitting allowance and making it possible to tighten the fittings strongly.

In addition, by using high hardness material for the outer tube,
This has the effect of imparting extremely high wear resistance to the piping itself.

By using a high-toughness material for the inner tube, the tightening effect of supporting the outer tube is fully demonstrated, and even if a penetration defect occurs unexpectedly in the outer tube, it will not reach the inner tube. An excellent effect is achieved in that the function of the entire pipe can be maintained from beginning to end.

[Brief explanation of the drawing]

The drawings are explanatory diagrams of one embodiment of the invention of this application, and FIG. 1 is a graph showing the characteristics of fitting allowance between the outer tube and the inner tube when expanding the diameter, and FIG. 2 is a diagram showing the diameter expanding means when expanding the diameter. FIG. 2...outer tube, 1...inner tube.

Claims (1)

[Claims] 1. A method for manufacturing a wear-resistant double tube in which an inner tube is layered relative to a highly wear-resistant outer tube and then both tubes are self-tightening, which is made of a material with a low yield point. After expanding the diameter of the inner tube by layering an outer tube made of a material with a high yield point and high wear resistance on the inner tube, and bringing the two tubes into close contact with each other, A method for manufacturing a wear-resistant double tube, characterized by expanding the diameter of both tubes within the damage limit of the outer tube so as to self-tighten the tubes. 2. In a method for manufacturing a wear-resistant double tube in which an inner tube is layered relative to a highly wear-resistant outer tube and then both tubes are self-tightened, the inner tube is made of a material with low hardenability and a low yield point. The outer tube, which is made of a material with high hardenability, high yield point in the hardened state, and high wear resistance, is annealed and layered relative to each other, the inner tube is expanded in diameter, and the two tubes are brought into close contact. Manufacture of an externally wear-resistant double-pipe tube characterized in that, after the tubes are quenched, the diameters of both tubes are expanded to at least exceed the elastic limit of the inner tube and within the breakage limit of the outer tube so that they self-tighten. Method.