JPH0159332B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The disclosed technology belongs to the field of manufacturing technology for corrosion-resistant metal pipes used in chemical plants, oil country tubular goods, oil transmission pipes, heat exchangers, and the like.

<Summary of the gist> This invention relates to a method for manufacturing metal pipes that can prevent stress corrosion cracking, etc. by applying a rolling force to the wall surface of a corroded pipe such as an oil country tubular pipe to cause it to self-tighten and to apply compressive stress. In particular, by applying local mechanical pressure to the surface of the metal tube wall using rollers, and pressing the tube wall surface, the rollers are rotated in the same direction and moved continuously in the tube axis direction, thereby damaging the tube wall skin. It spreads and expands, and compressive stress is built into the skin of the pipe wall through the self-tightening effect generated by the spread and expansion, thereby preventing the metal pipe wall from being corroded by the corrosive fluid that comes into contact with the metal pipe wall. This invention relates to a method of manufacturing a corrosion-resistant metal pipe that prevents corrosion.

<Prior art> As is well known, chemical plants, oil country tubular goods, oil transmission pipes,
For piping used in heat exchangers and the like, carbon steel pipes, stainless steel pipes, etc. are used depending on the purpose, such as high and low temperature resistance, increased strength, and corrosion resistance.

Recently, there has been a demand for even higher performance improvements in corrosion resistance and other aspects of these pipes. Alternatively, high-temperature, high-pressure steam and salt water have been injected into so-called secondary redevelopment oil wells, and serious corrosion damage has come to light that is incomparable to what was seen before. There are problems with corrosion cracks caused by chlorine ions in a high-pressure environment and corrosion cracks caused by a relatively low-temperature hydrogen sulfide atmosphere in the middle and upper layers of oil wells, but there are still no clear solutions to these problems. The current situation is that there is no solution.

These corrosion cracking problems are occurring not only in oil country tubular goods, but also in chemical plants, heat exchanger pipes, nuclear equipment piping, etc. Currently, the first solution to these problems is the development of corrosion-resistant paints. Second, new developments in corrosion-resistant metal materials themselves are underway.

<Problems to be Solved by the Invention> Regarding the development of the first paint mentioned above, there are methods such as mixing a corrosion inhibitor called INHIBITER into a corrosive medium and coating the pipe wall surface with a corrosion-resistant resin. Although they are being developed, they require cumbersome measures and efforts for maintenance, and none of them have reached perfection in terms of corrosion resistance.

On the other hand, with regard to the development of a second corrosion-resistant metal material, new developments are being aggressively advanced by material manufacturers and metal research institutes around the world.

By the way, as a general material characteristic of steel, as its strength increases, its corrosion resistance usually decreases, and when used for oil country tubular goods, as the oil well gets deeper, the oil country tubularity becomes more difficult to support its own weight. Therefore, when oil country tubular goods are carbon steel pipes, the corrosion resistance deteriorates as the strength increases.

Therefore, for use in deep oil wells, high-strength, rust-free metal pipes that have high strength and high corrosion resistance are required.

Corrosion resistance increases as the content of nickel, chromium, etc., which have strong corrosion resistance, increases in the material of so-called stainless steel, which is a typical non-corrosion metal, but on the other hand, strength increases beyond a certain limit. Therefore, the strength required for oil country tubular goods for deep oil wells cannot be satisfied.

On the other hand, although high-priced high-nickel alloys such as Incoloy 825 and Inconel 625 have extremely high corrosion resistance, their strength is not as high as that of high-strength carbon steel. However, in the worst corrosive environment where hydrogen sulfide, salt water, carbon dioxide gas, etc. are mixed, it cannot completely withstand various types of corrosion including corrosion cracks.

In other words, even highly corrosion-resistant nickel alloys can withstand carbon dioxide corrosion in certain corrosive environments but cannot withstand hydrogen sulfide corrosion, or may withstand hydrogen sulfide corrosion but withstand chloride ion corrosion. There is a selective resistance to corrosion that cannot be tolerated.

Therefore, there is no existing metal material that has corrosion resistance against all types of corrosive media in various corrosive environments, and there is very little hope that new metal materials will be developed in the future.

For example, even if something similar to this were developed, it is certain that it would probably be uneconomically expensive.

By the way, the forms of corrosion that generally occur in oil country tubular goods are hydrogen-induced cracking, wear corrosion, crevice corrosion,
There are general corrosion, pitting corrosion, blister corrosion, annular corrosion, etc. In addition to these, corrosion cracks caused by hydrogen sulfide and chlorine ions are the most dangerous for piping.

According to recent theories of metallurgy, when a certain type of processing deformation is applied to a corrosion-resistant metal material at a certain temperature range,
It has been shown that the corrosion resistance of a deformed part increases. For example, when austenitic stainless steel is subjected to processing at a relatively low temperature, a structural transformation called so-called processing-induced transformation occurs.
It has been clarified that martensite is generated in the structure, and dislocations in the structure multiply due to plastic deformation of the structure, leading to cell formation of dislocations, which increases the stress corrosion cracking resistance of the material. ing.

Regarding corrosion cracks, regardless of whether the corrosive medium is hydrogen sulfide or chlorine ions, if tensile stress is built into the surface of a non-corrosive metal material that is in contact with the corrosive medium, the material No matter how strong the corrosion-resistant metal material is, it is exposed to an extremely dangerous condition due to corrosion cracking.On the other hand, when the metal material surface has built-in compressive stress, the higher the degree of built-in compressive stress, the more likely it will be corroded. It has also been shown to be safer against cracks.

Nickel chrome-based stainless steel pipes, which are generally known as corrosion-resistant metal materials, have a large coefficient of linear expansion, and because of their shape characteristics, it is difficult to make them after hot forming or to improve the quality of the pipe material. Because the pipe material is not uniformly cooled during the heat dissipation cooling period after heat treatment, it is common for tensile stress to remain in the skin of the inner wall of the pipe, especially for clad steel pipes made of carbon steel and stainless steel. In this case, a large tensile stress is built into the stainless steel side, which has a large coefficient of linear expansion.

As mentioned above, no matter how strong the corrosion-resistant metal material is, once it is subjected to tensile stress,
It has been found that resistance to corrosion cracking, not to mention general corrosion, deteriorates rapidly.

<Objective of the invention> The object of the invention is to solve the problems of corrosion-resistant fluid piping based on the above-mentioned conventional technology, and
The corrosion-resistant effect of the material is obtained by improving the combination of metal material components, the corrosion-resistant effect of the material is obtained by heat treatment using conventional metallurgical means, or the surface of the metal material is painted, This method is completely different from the method of mixing corrosion inhibitors into corrosive media to protect metal materials from the outside, and is based on a mechanical philosophy that imparts corrosion resistance to metal materials by introducing compressive stress inside them. Based on this method, we have developed superior corrosion-resistant metal pipes that are technologically innovative and economically extremely low-cost compared to conventional methods, which can benefit piping applications in various industries. The purpose is to provide a manufacturing method.

<Means and operations for solving the problems> In order to solve the above-mentioned problems, the structure of the present invention, which is based on the above-mentioned claims and in accordance with the above-mentioned object, is to solve the above-mentioned problems. Mechanical expansion pressure is locally applied to the skin using rollers, etc., and the expansion pressure is applied continuously to the entire skin, thereby causing self-stretching. Also, compressive stress is built into the skin, resulting in corrosion resistance. It takes technical measures to improve the performance.

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

Fig. 1 is a diagram showing the principle of the pipe 1 as carbon steel.
The inner wall of the tube is 3, and the thickness of the tube wall is _T1 .

Therefore, when the roller 4 is set in a predetermined position on a part of the inner wall 3 and a force F is applied to the skin of the inner wall 3 using appropriate means to compress it, the wall thickness T ₁ of the tube wall 3 becomes the thickness ΔT ₂ is recessed and reduced to a thickness of T ₂ , where it is
When the roller 4 is rotated in a predetermined manner in the circumferential direction along the inner wall 3 of the tube 1, a groove 5 in the tube wall 3 having a depression of ΔT ₂ is formed in the inner wall surface of the tube.

Then, if the rotation of the roller 4 is moved in the tube axis direction, the groove 5 having a depression of ΔT ₂ is formed continuously in the tube axis direction, and eventually the wall thickness T ₁ of the tube wall 3 becomes ΔT ₂ . The wall thickness is reduced by T ₂ , and the skin portion of the inner wall 3 of the tube 1 has an extension in the circumferential direction and the axial direction corresponding to the reduced wall thickness depression ΔT ₂ .

However, the spreading of the pipe wall 3 is actually restrained by the external pipe wall beyond which the spreading effect is applied, causing a self-tightening phenomenon in the spreading part itself, and as a result, the pipe wall 3 is spread by the rollers 4. Compressive stress is built into the skin of the inner wall 3 of the tube 1.

On the other hand, a roller 4 is appropriately set on the outer wall 2 of the tube 1, a spreading force F' is applied to the skin of the outer wall 2 of the tube 1 to compress it, and the same operation as that for the inner wall 3 is performed. When applied to the outer wall 2, compressive stress is similarly built into the skin of the outer wall 2 of the tube 1.

When the above-mentioned process is carried out on the outer wall 2 and inner wall 3 of the pipe 1, the stress distribution within the pipe wall is shown in FIG.
Compressive stress (-) is built into the skin of the inner wall 3,
A tensile stress (+) corresponding to this pressure stress is built inside the wall.

The tube 1, which has compressive stress (-) built into the skin of both the inner and outer walls 2 and 3, has corrosion resistance against corrosive media even if there is a corrosive medium inside and outside the tube 1. It is something.

Moreover, the embodiment shown in FIG. 3 is a stress distribution mode diagram in which only the outer wall 2 of the tube 1 is subjected to the spreading action by the roller 4, and compressive stress (-) is built in the skin of the outer wall 2 of the tube 1. In this case, the pipe 1 is resistant to corrosion from corrosive media outside the pipe 1.

On the other hand, the embodiment shown in FIG. 4 is designed to be resistant only to the corrosive medium inside the pipe, and compressive stress (-) is applied only to the skin of the inner wall 3 of the pipe 1.
It has a built-in function.

The embodiment shown in FIGS. 5 and 6 is an example in which the manufacturing method of the present invention is applied to the inner wall of a clad steel pipe 9 having a metallurgical joint surface 8 by cladding a stainless steel inner pipe 7 to a carbon steel outer pipe 6. Generally, carbon steel and stainless steel clad steel pipes are hot formed and
Immediately after the stainless steel pipe 7 is manufactured through the heat treatment process, tensile stress (+) is generated in the material of the stainless steel pipe 7, as shown in FIG.
However, there is compressive stress (-) in the material of the carbon steel pipe 6.
is built-in.

The tensile stress (+) built into the material of the stainless steel pipe 7 has very negative effects on corrosion as described above.

Therefore, in the clad steel pipe 9 made of carbon steel 6 and stainless steel 7, attempts have been made to convert the tensile stress (+) built into the material of the stainless steel pipe 7 into compressive stress by some method. However, it was considered extremely difficult to use metallurgical techniques such as pipe forming methods and heat treatment methods, but the roller 4 was developed by taking advantage of the fact that the hardness of the stainless steel inner pipe 7 material is lower than the hardness of the carbon steel outer pipe 6 material. In the embodiment shown in FIG. 5, a compression stress is applied to the inner wall of the stainless steel inner tube 7, and compressive stress is built into the skin of the inner tube 7.

In addition, as in the embodiment shown in FIG. 6, the stress distribution in FIG. 5 is fundamentally changed by applying the expansion force to the cladding surface 8 deeper than the inner wall surface of the inner tube 7, and the stress distribution in FIG. The entire wall of the steel inner tube 7 is expanded, and compressive stress is applied to the entire wall of the inner tube 7 due to the self-tensioning effect caused by the expansion, and the corresponding tensile stress (+) is applied to the wall of the carbon steel outer tube 6. ) can be incorporated to provide corrosion resistance.

The embodiment shown in FIGS. 5 and 6 is an embodiment in which the manufacturing method of the present invention is applied to a clad steel having a metallurgical joint surface 8 in which a stainless steel inner tube 7 is clad to a carbon steel outer tube 6. Yes, but carbon steel outer tube 6
By applying the manufacturing method of the present invention to a double pipe having a clad surface with a contact surface 8 that is not metallurgically bonded to a stainless steel inner pipe 7, the compressive stress can be applied to the entire inner pipe wall or to the inner pipe. By incorporating it into the skin of the tube wall, the inner surface of the inner tube can be provided with corrosion resistance.

In addition, contrary to the above embodiment, a rolling force is applied to the outer wall surface of a clad steel pipe in which the outer pipe is a stainless steel pipe and the inner pipe is a carbon steel pipe, so that the stainless steel outer pipe has corrosion resistance against corrosive media outside the pipe. It is possible to make it equipped.

Next, the embodiment shown in FIG. 7 will be explained.
The carbon steel outer tube 1 is set as described above on the stands 11, 11 provided on the base 10, and the rotary motor 13 having the roller 4 via the arm 12 is installed so as to be able to freely slide in the axial direction. A stand 15 installed in the steel pipe 1 and a winding device 16
The cable 20 is stretched between the reel 18 and the core 19 of the motor 13.

Therefore, the motor 13 is rotated on one end side of the carbon steel pipe 1, and the roller 4 is pressed against the inner wall surface 3 of the pipe 1 to rotate and rotate, and the cable 2 is rotated at a set speed.
By pulling 0, the rollers 4 press and spread the entire inner wall surface 3 of the tube 1.

Then, as described above, the inner wall skin of the tube 1 is self-tensioned by stretching, and compressive stress is built-in.

In addition, although the explanation in the figure describes the case where the roller rotates in a direction perpendicular to the tube axis, it also applies when the roller rotates in the direction of the tube axis or diagonally to the tube axis. There is no difference in the effect of tube wall expansion, which is the basic principle of this invention.

Further, in the present invention, the target pipe is not subject to any restrictions, regardless of whether it is a single-material pipe or a multi-material pipe, as long as the material to be rolled is capable of being rolled.

<Effects of the Invention> As described above, according to the present invention, a spreading force is applied to the skin of the wall surface of the pipe which is in contact with a corrosive medium and may suffer corrosion thereby, giving an expanding action and thereby causing residual compressive stress. It has the excellent effect of being able to provide a high degree of corrosion resistance easily, reliably, and at low cost.

Therefore, it is only necessary to apply a spreading pressure using a roller or the like to the surface of the set steel through which the corrosive medium flows, and the work is simple and the number of man-hours is small, which has the effect of making manufacturing easier.

Moreover, according to the present invention, there is an advantage that construction can be performed even on ready-made thin-walled pipes.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention; FIG. 1 is a partial cutaway diagram explaining the principle, FIG. 2 is a perspective view of the stress distribution in FIG. 1, and FIGS. FIGS. 5 and 6 are perspective views illustrating the stress distribution of a double pipe before and after applying a spreading force to a wall surface, and FIG. 7 is a longitudinal sectional view of a specific example. 1, 9...metal tube, F, F'...expansion pressure.

Claims (1)

[Claims] 1. A method for manufacturing a corrosion-resistant metal tube in which compressive stress is applied by applying a rolling force to the wall surface of the metal tube, in which a local mechanical rolling force is continuously applied to the wall surface of the metal tube by a rolling roller. The surface skin of the metal tube wall surface is expanded and expanded, and a self-tensioning effect is generated through the expansion and expansion, so that compressive stress is built into the surface layer of the metal pipe wall surface, thereby providing corrosion resistance. A manufacturing method for corrosion-resistant metal pipes.