JPH0473486A - Internally protected steel tube and joint therefor - Google Patents

Abstract

PURPOSE:To solve a problem related to corrosion, heat, secular change or nailing resistance, almost eliminate the reduction of inner diameter, and obtain a less expensive pipe line with a screw joint by extending and expanding the end of an aluminum tube for adhesion to the edge of a steel tube, and forming a screw section for a joint on the end external surface of the steel tube. CONSTITUTION:An aluminum tube 2 is adhered to the internal surface of a steel tube 1. The end of such a tube material is so cut as to obtain the projection of the aluminum tube 2 by the length of delta, and this projected portion is expanded to a taper, and then adhered to the edge of the steel tube 1. In addition, a screw section 1A is formed on the end external surface of the steel tube 1, thereby obtaining an internally protected steel tube. Tube materials are connected to each other with a joint J for application. According to the aforesaid construction, piping can be easily laid with enough and proper internal protection at the end thereof. Consequently, the pipe line of long-term high reliability is obtained with a less expensive tube material and joint. In addition, the workability thereof can be simplified.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an internally protected steel pipe and a pipe joint thereof, which have high corrosion resistance and are intended for use, for example, in water supply/hot water supply or cold/hot water piping for air conditioning.

[Conventional technology]

As measures to prevent water quality deterioration in water supplies progress, the use of galvanized steel pipes, which are prone to rust, is being restricted, and instead, steel pipes with polyethylene powder lining on the inside or steel pipes with vinyl chloride lining on the inside have become popular. Ta. On the other hand, galvanized steel pipes are not suitable for hot water supply piping because zinc rapidly dissolves in hot water of 60 to 85°C, so heat-resistant vinyl chloride-lined steel pipes, copper pipes, or stainless steel pipes are used for hot water supply. In addition to metal piping materials, resin piping materials such as heat-resistant vinyl chloride or polybutene are used. Furthermore, similar pipe fittings are also used.

[Problem to be solved by the invention]

However, all of the conventional piping materials and joints described above have the following problems.

First, the disadvantage of steel pipes whose inner surfaces are lined with hard vinyl chloride or polyethylene powder is that rotary cutters are prohibited when cutting to a predetermined length because they deform the ends of the pipes and cause cracking or peeling of the vinyl chloride. Furthermore, the use of grindstone cutting machines that cause deterioration, deformation, and peeling due to heat generation during cutting is also prohibited. In addition, with respect to pipe joints, unless an extremely expensive dedicated core joint is used, it is not possible to isolate the exposed end surface of the pipe end by cutting the steel pipe from the fluid. In other words, it is essential to use a special joint with a built-in core for preventing corrosion at the pipe end. When performing piping work using fittings, it is mandatory to apply a special anti-corrosion agent to the pipe end surface and about three threaded threads on the pipe end before tightening. Therefore, it is prohibited to unscrew the joints or to reuse the joints that have been removed.

In addition, since the thickness of the vinyl chloride pipe is 2.5 mm, taking 20A as an example, the inner diameter is 51n [11 mm smaller,
In addition, the fitting also has a built-in stainless steel core, which further reduces the diameter and reduces the flow rate. therefore,
- There is a disadvantage that it is often necessary to use pipes with progressively larger diameters.

In heat-resistant PVC-lined pipes, aging due to heat is unavoidable, and the adhesion with the steel pipe is generally lost, and the steel pipe becomes nothing more than a sheath. The same goes for joints, as the resin is only several hundred micrometers thick, so it peels off from the malleable cast iron or steel surface more quickly than straight pipes.

■ The disadvantage of copper pipes is that erosion caused by foreign matter such as sand, rust, mud, etc. contained in the flowing water causes local wear in areas such as elbows where the direction of the flowing water changes, so it is limited to the flow conditions. There is. Therefore, it cannot be used for anything other than household use where pressure and flow rate are low. Furthermore, since joints are generally soldered with silver, it is essential to use a torch lamp, that is, use fire. In addition, due to their low strength, there is always a risk of nail-driving accidents at construction sites, so pressure tests are essential.

Piping at construction sites will become unusable unless special care is taken to prevent deformation and damage.

■ The disadvantage of stainless steel pipes is that in the case of welded joints, extremely precise values are required for the butt accuracy before welding, which results in extremely high costs. Therefore, welded joints are used for vertically drawn pipes with a large diameter, and for smaller items, swaged joints (insert a straight pipe into the joint and then swage the inserted part with a special tool) are used.

The biggest drawback of this joint is that it is not possible to check later whether the pipe has been inserted into the joint for the specified length.
There is no way to 100% confirm whether the caulked parts of joints, which are found in thousands of places in buildings, etc., have actually been caulked (especially in the corners of ceilings), and the backing built into the joints is not in the specified position. There is no way to later check whether the pipe is in place, and the stainless steel pipe itself is thin and has low strength, so if you put your foot on the horizontal pipe or hit it with construction materials, it will deform and cause the pipe to become damaged. There is a high possibility of water leaking out of the joint, and there are countless examples of water leakage accidents, not only during pressure tests, but also after the start of use.

■ All resin-based pipes lack strength and rigidity, so the pipes are not self-sustaining, and water supply and hot water taps must be stopped with saddles. Horizontal draw pipes also require close support. In the case of hot water supply, it must be taken into consideration that vinyl chloride has a coefficient of linear expansion seven times that of steel. The decisive drawback is that there is always the risk of damage caused by nail punching, carpentry work requires extreme care, and pressure testing after completion is the most important item. It is necessary to take into consideration that there is a probability that the tip of the nail may stop halfway through the wall thickness of the pipe.

Since it is inevitable that resins undergo aging in response to high temperatures, their performance generally deteriorates rapidly after reaching adulthood, leading to breakage.

The present invention solves the problems of resin-lined steel pipes, copper pipes, thin-walled stainless steel pipes, resin pipes, etc., and uses the combined effects of pure aluminum, a highly corrosion-resistant metal, and strong steel pipes to provide corrosion and heat resistance. , it solves aging and nail punching resistance, almost eliminates the shrinkage of the inner diameter which is a drawback of resin-lined steel pipes, and creates inexpensive threaded joints using the most reliable steel pipes without using expensive core joints. The object of the present invention is to provide a steel pipe with inner surface protection for forming a conduit, and a pipe joint therefor.

(Means for Solving the Problems) According to the present invention, the above object is to provide an inner surface protection steel pipe having an aluminum pipe over the entire length on the inner surface of the steel pipe, the end of the aluminum pipe being extended and expanded in diameter so that the end face of the steel pipe is This is achieved by: closely fitting the steel pipe, and forming a threaded portion for a pipe joint on the outer circumferential surface of the end of the steel pipe.

In addition, regarding the above-mentioned steel pipe fitting, it is a pipe fitting made of cast iron or steel, and an aluminum plating layer is formed on at least the inner surface, and the surface layer of the aluminum plating layer at the threaded part is removed by thread cutting. achieved.

[Function] In the inner protective tube of the present invention, only a portion of the steel tube is cut at the end so that the aluminum tube protrudes, and the protruding portion is expanded and diameter-enlarged using an appropriate tool so as to come into close contact with the end surface of the steel tube, Thereafter, a threaded portion is formed on the outer surface of 5. In this way, the end faces of the steel pipe are also protected by aluminum.

At that time, if the length of the protruding portion of the aluminum tube is made even slightly larger than the thickness of the steel tube, a portion of the neck portion will be covered by the aluminum tube during thread cutting, and protection will be more reliable.

In the manufacture of pipe joints, when aluminum plating is applied, the base layer is formed of an aluminum alloy layer and the surface layer is formed of an extra aluminum layer. So 1. Thread cutting is performed to remove the surface layer of the threaded portion. As a result, an aluminum alloy layer with good corrosion resistance remains, and the threaded portion forms a highly accurate helical surface.

〔Example〕

Hereinafter, the present invention will be described in detail based on the accompanying drawings.

FIG. 1 shows the manufacturing method of the inner surface protection steel pipe of this example according to its procedure.

In FIG. 1 (8), an aluminum tube is provided in close contact with the inner surface of the steel tube 1. This can be obtained by a known method, for example, by loosely fitting a small-diameter aluminum tube into a steel tube and pulling it out inside the aluminum tube using a die or the like to plastically deform the aluminum tube to expand its diameter.

Next, as shown in FIG. 1(B), the end of the tube material is cut so that the aluminum tube 2 protrudes from the steel tube by .delta..

Thereafter, as shown in FIGS. 1(C) and 1(D), the protruding portion of the aluminum tube 2 is expanded into a tapered shape using appropriate tools T, T2, and then brought into close contact with the end surface of the steel tube 1.

Finally, a threaded portion IA is provided on the outer peripheral surface of the end portion of the steel pipe 1 to obtain the inner surface protection steel pipe of this example. In use, the pipe fittings J connect the pipes to each other.

Regarding the protrusion amount δ of the aluminum pipe, in this embodiment, it is approximately equal to the thickness of the end face of the steel pipe after forming the threaded portion IA, but as shown in Fig. 2, it is larger than this. If the aluminum tube is made to protrude and is folded back, a surface layer will be formed on a part of the aluminum tube splash part IA, and protection will be more reliable.

Next, the pipe joint of this embodiment is obtained by aluminum-plating a known cast iron or steel pipe joint, and threading it at the threaded portion.

First, as shown in FIG. 3A, a pipe joint 3 made of, for example, cast iron is prepared and an aluminum plating layer 4 is applied thereto.The aluminum plating layer is applied to at least the inner surface of the pipe joint 3. The aluminum plating layer 4 reacts with iron to form a corrosion-resistant aluminum alloy layer on the base layer, and an extra aluminum layer is formed as a surface layer thereon.

Thereafter, as shown in FIG. 3(B), the threaded portion 4A is threaded to remove the surface layer. As a result, a highly accurate threaded surface is obtained, and an aluminum alloy layer with good corrosion resistance forms the threaded surface.

Note that it is effective to increase the effective diameter of the screw in advance by the thickness of the aluminum-iron alloy layer.

Piping is performed using such a pipe joint in conjunction with the inner protection pipe shown in FIG.

(Effects of the Invention) Since the present invention is configured as described above, it is possible to easily perform piping with sufficient and reliable internal protection, especially at the pipe ends, by taking advantage of the characteristics of high-strength steel pipes. As a result, pipes with high reliability over a long period of time can be obtained using inexpensive pipe materials and pipe joints.Moreover, the work is simplified.

[Brief explanation of drawings]

1(A) to 1(E) are partially broken pressure surface views showing an inner surface protection steel pipe according to an embodiment of the present invention according to its manufacturing procedure;
Part 3 is a partially cutaway front view showing a modified example of the steel pipe in Figure 1.
FIG. 3(A) is a cross-sectional view of the pipe joint of this embodiment before thread processing, and FIG. 3(B) is an enlarged schematic cross-sectional view of the threaded portion of the pipe joint of FIG. 3(A) after thread processing. 1... Steel pipe IA... Thread section 2... Aluminum pipe 3... Pipe fitting 4. ......Aluminum coating layer 4A...
...Threaded part 5 ...Alloy layer

Claims (2)

[Claims] (1) An aluminum pipe is provided on the inner surface of the steel pipe over its entire length, and the end of the aluminum pipe is expanded and expanded in diameter to fit closely against the end surface of the steel pipe, and a threaded portion for a pipe fitting is formed on the outer peripheral surface of the end of the steel pipe. The inner surface is protected by a steel pipe. (2) A pipe joint made of cast iron or steel, in which an aluminum plating layer is formed on at least the inner surface, and the surface layer of the aluminum plating layer at the threaded portion is removed by thread cutting.