JPH11287364A - Joining method for stainless steel pipes - Google Patents

Abstract

PROBLEM TO BE SOLVED: To establish a joining method for stainless steel pipes with each other easily at the site in a short time into a strong condition free of risk of corrosion. SOLUTION: The ends 10 and 20 of two stainless steel pipes 1 and 2 are inserted into a cylindrical socket 3 from the sides so that their end faces are positioned facing each other, and the peripheral surfaces of the pipes 1 and 2 are adhered to the inner surface of the socket 3 by reaction type adhesives 6 and 7 of acrylic resin type, and thereby the end parts of the pipes 1 and 2 are joined together. The inside diameter of the socket 3 is narrowest in the socket central part 30 and widens as approaching the end parts 31 and 32 of the socket 3, and the distance between the peripheralsurfaces of the pipes 1 and 2 and the inner surface of the socket 3 becomes greater as going apart from the socket central part toward the end of the socket 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for joining ends of two stainless steel pipes when performing indoor piping or the like.

[0002]

2. Description of the Related Art Conventionally, galvanized steel pipes (SG) have been used as indoor piping for water supply and hot water supply in buildings such as hotels and condominiums.
P), PVC-lined steel pipes and copper pipes are used. However, with the contamination of raw water, the corrosion problem has become more serious due to the increase in chloride ions and the strengthening of residual chlorine addition for sterilization. In particular, copper pipes used for hot water supply have problems such as leakage due to pitting corrosion and blue water due to elution of copper ions accompanying the corrosion. To solve these problems, stainless steel tubes are used.

[0003] The joining of stainless steel pipes includes welding, flange joining, mechanical joining and the like. In flange joining, a stainless steel stub end and a pipe welded and joined are fastened with bolts using a flange. In mechanical joining, joining is performed by caulking a pipe using a special joint.

[0004]

However, even with stainless steel, corrosion may occur depending on the quality of the water used and the structure. In the case of welding, the formation state of the weld scale and the shape of the bead affect the corrosion resistance. If the weld oxide scale remains or the bead shape is poor, a Cr-depleted layer will be formed immediately below the weld scale, causing pitting corrosion and eventually leading to water leakage. Therefore, it is necessary to perform good welding with no bead shape without a weld oxide scale. For this purpose, improvement of weldability by an automatic welding machine is currently being studied, but there are various problems in the use of the automatic welding machine on site, such as limitations on the working space and pipe diameter. Therefore, the current situation is to rely on the skills of skilled welding technicians, and the cost is also high.

In a flange joint or a mechanical joint, a Teflon packing comes into contact with the stub end surface, so that a gap structure is formed between the stub end surface and the packing. Press joining and pipe expansion joining are typical examples of mechanical joining, and a gap structure is created between metals to caulk a pipe and a joint. In the case of stainless steel pipes, crevice corrosion may occur depending on the water quality and usage environment if there is a crevice structure. In addition, for a flange joint, time is required for operations such as bolting.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for easily joining stainless steel tubes to each other at a site or the like, and to join them in a short time in a strong and corrosion-free state.

[0007]

In order to achieve this object, according to the first aspect of the present invention, two stainless steel pipes are inserted into a cylindrical socket from both sides to form two stainless steel pipes. A method of joining the ends of two stainless steel pipes by facing the end faces of the stainless steel pipes and bonding the peripheral surface of the stainless steel pipes and the inner surface of the socket with an acrylic resin-based reactive adhesive. The diameter of the inner surface of the socket is narrowest at the center of the socket,
It is formed so as to spread closer to both ends of the socket,
The distance between the peripheral surface of the stainless steel pipe and the inner surface of the socket is gradually increased from the center of the socket toward the end of the socket.

In the method for joining stainless steel pipes according to the first aspect, as described in the second aspect, the length of the end of the stainless steel pipe inserted into the socket is 20 mm or more, and the circumference of the stainless steel pipe is The distance between the surface and the inner surface of the socket is preferably 2 mm or more at the end of the socket. As described in claim 3, it is preferable that an O-ring is provided in the socket so as to be in close contact with both the end surface of the stainless steel pipe and the inner surface of the socket.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view showing a state in which ends 10 and 20 of two stainless steel tubes 1 and 2 are inserted into a socket 3 and joined according to a method according to an embodiment of the present invention.

In the illustrated example, the stainless steel tubes 1 and 2 are both circular tubes having the same inner and outer diameters. The socket 3 has a substantially cylindrical shape having an inner diameter larger than the outer diameter of the stainless steel tubes 1 and 2.
The material is preferably the same stainless steel as the stainless steel tubes 1 and 2 from the viewpoint of imparting strength and avoiding galvanic corrosion. For example, if a copper tube or the like is used for the socket 3, if the stainless steel tubes 1 and 2 come into contact with the socket 3, galvanic corrosion may occur.

However, while the outer diameter of each of the stainless steel tubes 1 and 2 is constant, the diameter of the inner surface of the socket 3 is the narrowest at the central portion 30 of the socket 3, and is located at both ends 31 and 32 of the socket 3. The distance between the peripheral surface (outer surface) of the stainless steel tubes 1 and 2 and the inner surface of the socket 3 gradually increases from the central portion 30 of the socket 3 toward the ends 31 and 32 of the socket 3. It is configured as follows.

In the socket 3, O-rings 4 and 5 are disposed so as to be in close contact with both the end surfaces 11 and 21 of the stainless steel tubes 1 and 2 and the inner surface of the socket 3. These O-rings 4 and 5 are made of, for example, rubber.
The outer diameter of the O-rings 4 and 5 is
0 is larger than the inner diameter.

Further, between the inner surface of the socket 3 and the peripheral surfaces of the stainless steel tubes 1 and 2 inserted into the socket 3,
The adhesives 6 and 7 are filled and bonded. As the adhesives 6, 7, an acrylic resin-based reactive adhesive is used.

To join the stainless steel tubes 1 and 2 to each other, first, O-rings 4 and 5 are inserted into the socket 3 from both sides. Then, the ends 10 and 20 of the stainless steel tubes 1 and 2 with the adhesives 6 and 7 applied to the outer peripheral surfaces are inserted into the socket 3 from both sides. As a result, the O-rings 4 and 5 are pushed into the end surfaces 11 and 21 of the stainless steel tubes 1 and 2, and the O-rings are inserted into both the end surfaces 11 and 21 of the stainless steel tubes 1 and 2 and the inner surface of the socket 3 near the central portion 30 of the socket 3.
The rings 4 and 5 are brought into close contact. As described above, the diameter of the inner surface of the socket 3 is formed so as to be narrowest at the central portion 30 and widen toward the both end portions 31 and 32. When the ends 10 and 20 of the stainless steel tubes 1 and 2 are inserted into the socket 3, they can be easily inserted. Less worry about being scraped off by the end face.

Considering that the joint strength such as the earthquake resistance of the indoor piping is satisfied and that it can be bonded in a short time in the field, an acrylic resin-based adhesive is used for the adhesives 6 and 7. Good to do. For example, a water-soluble adhesive represented by an acetic acid resin emulsion type is
It is not suitable because it easily dissolves in water. In addition, a vinyl chloride solvent-based adhesive does not provide satisfactory strength and has a long time to cure. In order to obtain sufficient strength, a reactive adhesive is most suitable. Reactive adhesives include epoxy and acrylic resin adhesives. A reactive adhesive is the best in terms of adhesive strength, but in the case of an epoxy resin, chlorine may be generated from epichlorohydrin contained as an impurity in the adhesive, which may induce corrosion. For this reason,
Acrylic resin-based reactive adhesives are most suitable. In addition, by using an acrylic resin-based reactive adhesive, it is possible to prevent contamination such as water flowing in the stainless steel pipes 1 and 2, and the Ministry of Health and Welfare has specified water used for sanitary piping such as water supply and hot water supply. Satisfies the criteria.

As described above, the end portions 1 of the stainless steel tubes 1 and 2
When inserting 0 and 20 into the socket 3 and joining them, the lengths L1 and L2 of the ends 10 and 20 of the stainless steel pipe 12 inserted into the socket 3 are all set to 20 mm or more. If the lengths L1 and L2 are shorter than 20 mm, a necessary bonding strength cannot be obtained because a sufficient bonding area cannot be obtained.

As described above, since the diameter of the inner surface of the socket 3 is narrowest at the central portion 30 and widens toward the both ends 31, 32, the end portions 10 of the stainless steel tubes 1, 2 are formed. , 20 are inserted into the socket 3, a gap is formed between the peripheral surfaces of the stainless steel tubes 1, 2 and the inner surface of the socket 3 at the ends 31, 32 of the socket 3. The distances H1, H2 of this gap
Is 2 mm or more at the end of the socket 3. Thereby, the film thicknesses of the adhesives 6 and 7 necessary for joining the pipes can be obtained. If the distances H1 and H2 are smaller than 2 mm, sufficient adhesive strength cannot be obtained because the adhesives 6 and 7 are thin.

According to the joining method of this embodiment, the stainless steel tubes 1 and 2 are provided near the central portion 30 of the socket 3.
Since the O-rings 4 and 5 are in close contact with both the end surfaces 11 and 21 and the inner surface of the socket 3, the adhesive 6,
7 can be prevented from flowing out between the outer peripheral surfaces of the stainless steel tubes 1 and 2 and the inner surface of the socket 3, and the formation of a metal gap between the stainless steel tubes 1 and 2 and the socket 3 at the bonded portion can be prevented. Even if the adhesive is hardly soluble such as an acrylic resin-based reaction type, if the adhesives 6 and 7 are exposed in the stainless steel pipes 1 and 2, there is a possibility that water quality is contaminated. For this reason,
O-rings 4,5 so that adhesives 6,7 are not exposed inside
Should be placed. Further, by disposing the O-rings 4 and 5, it is possible to prevent the adhesive strength of the adhesives 6 and 7 from being lowered due to the absorption of water. O-rings 4 and 5 are made of soft EPD
Those made of M resin are preferred. This is because if it is hard, crevice corrosion may occur at the contact portions with the stainless steel tubes 1 and 2.

[0019]

The present invention will now be described by way of examples with reference to its effects. It will be described.

(Embodiment 1) In order to use an adhesive for joining pipes, a predetermined joining strength is required for indoor pipes. Therefore, the bonding strength after joining was measured using a commercially available adhesive. A commercially available SUS304TPD 20Su tube was adhesively bonded using the socket 3 according to the present invention described in FIG. 1 and the cylindrical socket 3 ′ having a constant inner diameter as shown in FIG. In the joining example shown in FIG. 2, no O-ring was used. In addition, the example shown in FIG.
Except that the ring was not used, the rest of the configuration is the same as that of the embodiment of the present invention described above with reference to FIG. 1, and therefore, in FIG. Are given the same reference numerals as in FIG.
A duplicate description will be omitted. In all of the sockets 3 and 3 ′, the adhesives 6 and 7 include, in addition to acrylic resin-based reactive adhesives, commercially available water-soluble vinyl acetate emulsion-based solvents and solvent-based vinyl chloride-based adhesives. Then, bonding was performed using a reactive epoxy adhesive. The bonding strength was measured 5 minutes and 30 minutes after bonding according to the tensile test of the joint standard (SAS32) determined by the Stainless Steel Association.
Table 1 shows the test results.

[0021]

[Table 1]

The standard of the tensile test is that the force for preventing the escape of the air sealed in the stainless steel tube is 1.9 KN or more.
The adhesive of vinyl acetate emulsion type and vinyl chloride type is 1.9KN regardless of socket shape and time after bonding.
Below, strength is not satisfied. In the case of an epoxy-based adhesive, a strength of 1.9 KN or more is obtained 30 minutes after bonding regardless of the shape of the socket, but no strength is obtained 5 minutes after bonding. Considering the actual work of joining pipes, it is not preferable because it takes time. On the other hand, in the case of the acrylic resin-based adhesive, the required strength was obtained even after 5 minutes of bonding when the socket 3 according to the present invention was used. However, no satisfactory strength was obtained with the socket 3 '5 minutes after bonding. This is because a uniform adhesive film thickness and area could not be obtained because the socket shape was flat.

(Example 2) The corrosion resistance of the adhesive joint was evaluated by a hot water loop test simulating the actual piping environment. Using the sample used in Example 1 as a comparative example, a T
A welded joint tube subjected to IG circumferential welding and a joint tube with a commercially available compression joint were used. The test solution is 2 in water at 60 ° C.
00 ppm of chloride ions were added. Flow velocity 1m / se
As c, the test was conducted for 6 months. Table 2 shows the observation results of the inner surface of the pipe at the joint after the test.

[0024]

[Table 2]

SUS304TPD for welded joints
Pitting corrosion was observed in the tube bead affected by the heat of the pipe. In the case of compression joints, crevice corrosion was observed at the metal contact area between the joint and the stainless steel pipe. In the case of the joint using an adhesive, when the socket 3 'was used, crevice corrosion was observed in the gap between the socket and the stainless steel pipe regardless of the type of the adhesive. On the other hand, when the socket 3 was used, pitting was observed on the stainless steel pipe only in the epoxy resin. This is probably due to the effect of chlorine eluted from the adhesive. In addition, when bonding was performed using a water-soluble vinyl acetate emulsion-based adhesive, the adhesive was almost eluted. No corrosion was observed in the samples bonded with other adhesives, indicating good corrosion resistance. In the socket 3 according to the present invention, the O-ring eliminates the gap structure between the socket and the stainless steel tube. It was also found that epoxy adhesives were not preferable from the viewpoint of corrosion resistance.

Example 3 A change in water quality after the hot water loop test was investigated using the samples used in Example 2. The test conditions are the same as in Example 2. Judgment of water quality is JISK635
The turbidity, chromaticity, potassium permanganate consumption, odor and taste were measured in accordance with the procedure of Example 3. Table 3 shows the results of water quality analysis of each adhesive bonding agent after the test. Turbidity, chromaticity, and odor / taste were within the standard values, but there was a difference in permanganate consumption. The welding and compression joining materials of the comparative examples were within the standard, but the permanganate consumption when joining with an adhesive was higher. In particular, the value when bonding was performed using a vinyl acetate emulsion-based adhesive was high. When the socket 3 was used, the permanganate consumption was within the reference value irrespective of the type of the adhesive, and when the socket 3 'was used, the value exceeded the reference value. This is because the adhesive easily dissolves in water if it has a shape like the socket 3 '. By using the socket 3 having the shape according to the embodiment of the present invention, contamination of the used water can be prevented.

[0027]

According to the present invention, when a stainless steel pipe is joined to an indoor pipe or the like, sufficient strength can be achieved without impairing the corrosion resistance of the joint and the water used is not contaminated. Simple joining becomes possible. According to the present invention, since the welding process is omitted, it is advantageous in terms of cost. Also, a skilled welder is not required.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a joining method according to an embodiment of the present invention.

FIG. 2 is an explanatory view of a joining method of a comparative example.

[Explanation of symbols]

 1,2 stainless steel pipe 3 socket 4,5 O-ring

[Table 3]

Claims (3)

[Claims] An end of two stainless steel pipes is inserted into a cylindrical socket from both sides so that end faces of the two stainless steel pipes face each other, and an acrylic space is formed between a peripheral surface of the stainless steel pipe and an inner surface of the socket. A method of joining the ends of two stainless steel pipes by bonding with a resin-based reactive adhesive, wherein the inner surface of the socket has the smallest diameter at the center of the socket, and the both ends of the socket. Characterized in that the distance between the peripheral surface of the stainless steel pipe and the inner surface of the socket gradually increases from the center of the socket toward both ends of the socket. How to join steel pipes. 2. The length of the end of the stainless steel pipe inserted into the socket is 20 mm or more, and the distance between the peripheral surface of the stainless steel pipe and the inside of the socket is 2 mm or more at the end of the socket. The method for joining stainless steel pipes according to claim 1, characterized in that: 3. The method for joining stainless steel pipes according to claim 1, wherein an O-ring is provided in the socket so as to be in close contact with both the end face of the stainless steel pipe and the inner face of the socket.