JPH06248412A - Tube joining method - Google Patents

Abstract

PURPOSE:To provide a tube joining method in which the operating environment can be improved by preventing the generation of a zinc gas or the like in the welding connection of metallic tubs with each other and the tube edges are properly connectable with each other. CONSTITUTION:The tube edge parts 1 and 11 of a metallic tube B and a tube joint A are coated with nonplating coating materials consisting essentially of inorganic coating materials to form nonplated parts separately, and the metallic tube B and tube joint A are applied with galvanizing treatment. Then, the nonplating coating materials of each nonplated part are removed away, and the tube edge 11 of the metallic tube B and the tube edge 1 of the tube joint A are connected by welding. In this way, the generation of welding defects can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pipe joining method for connecting metal pipes whose inner and outer peripheral surfaces are plated.

[0002]

2. Description of the Related Art Metal pipes, which are steel products, and pipe joints used for connecting pipes to each other, are plated on the inner and outer peripheral surfaces mainly for the purpose of rust prevention. Generally, hot dip galvanizing is often used for this type of plating. This hot-dip galvanizing forms a zinc film on the surface of iron, and has the advantage that it can reliably prevent rust over a long period of time and is economical. In other words, this hot dip galvanizing process prevents corrosive steel products placed in the atmosphere, seawater, soil and concrete from rusting due to the dense protective film formed on the coating surface and the electrochemical anticorrosion action. It has a protective function. In particular, hot-dip galvanizing has a long-term anticorrosion effect, and therefore has the advantage that no additional anticorrosion means is required.

Further, since this hot-dip galvanizing is bonded by the alloy reaction between the iron material and zinc, it has excellent adhesiveness and does not peel off due to impact or friction.
Further, the invisible portion such as the inner peripheral surface of the metal tube can be plated. In addition, chemical conversion treatment can be performed on the hot dip galvanized film, and coating on the film is also possible.

[0004]

By the way, in the case of connecting a metal pipe using the above-mentioned hot dip galvanized pipe joint, the end faces of the metal pipe and the pipe joint are brought into contact with each other and welded. Although they are connected, there is a problem that zinc gas is generated due to high heat during welding, which deteriorates the working environment. Furthermore, the zinc melted by the welding heat was also melted into the welded spots, resulting in welding defects. For this reason, the end face, which is the welded portion, is usually ground with a grinder before the welding, and then the welding work is started, but this work is very troublesome and inefficient. In addition, since the workability of the polished surface is lowered due to manual labor, a gap is generated when the end faces of the metal pipe and the pipe joint are brought into contact with each other, which is a main cause of welding defects. The present invention aims to solve the above problems.

[0005]

In order to achieve the above object, the present invention applies a non-plating coating material containing an inorganic coating material as a main component to pipe end portions of metal pipes and pipe joints to form non-plating portions respectively. Forming step, hot-dip galvanizing the metal pipe and pipe joint, removing the unplated coating material of each unplated portion, and connecting the pipe end of the metal pipe and the pipe end of the pipe joint by welding And a process.

[0006]

According to the present invention, since the non-plated portion is formed at the pipe end portion of the metal pipe and the pipe joint, zinc gas and the like are not generated when the two are welded and connected. In addition, since the non-plated part is chemically treated, each pipe end surface is maintained in the state of production accurately, unlike when welding is performed after the pipe end surface, which is the welding location, is polished with a grinder. Appropriate welding can be performed without forming a gap in the contact portion.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In this pipe joining method, a case where an elbow-type steel pipe fitting A and a steel metal pipe B (see FIG. 4) are connected will be described. First, an unplated portion is formed on the pipe ends 1 and 1 of the pipe joint A shown in FIG. This non-plated portion has an inner peripheral surface 3 and an outer peripheral surface 4 of a predetermined width a extending from 5 to 20 mm, preferably 5 to 10 mm from the tube end 1 including each tube end surface 2.
Then, the inorganic coating material is applied thereto. Of course, the non-plated portion can be set to have an appropriate width for both the inner and outer peripheral surfaces 3 and 4 depending on the pipe diameter.

As the coating material, degreasing, water washing, pickling,
An inorganic material is used in which the coating material itself does not drop off or swell in each of the steps of washing with water, flux treatment, and drying, and in which organic gas is not generated when immersed in a hot dip galvanizing bath. This coating material is a thermoplastic acrylic resin, an inorganic material, chlorinated rubber, zinc stearate, a thermosetting acrylic resin, a melamine resin, an epoxy resin, a solvent and the like, and those prepared by distributing these in an appropriate ratio are prepared.

Then, the coating material is sprayed onto the pipe ends 1 and 1 by a spray 6 to apply. At this time, if both pipe ends 1, 1 of the pipe joint A are placed on the pedestal 5 so as to face upward, the coating material does not drip from the pipe end face 2 and the inner peripheral face 4 as well as the outer peripheral face 3 is prevented. It can be applied well to the inside. When forming the non-plated portions having the same width on the inner peripheral surface 3 and the outer peripheral surface 4, the coating is performed by immersing in the container 8 filled with the coating material 7 as shown in FIG. Here, the pipe end 1 may be immersed with the pipe end surface 2 of the pipe joint A facing downward.

Next, the pipe joint A is plated. This plating treatment is a conventionally known method, and the hot dip galvanizing filled in a plating bath (not shown) is heated to a high temperature of about 460 ° C. and the pipe joint A is immersed. Then, the non-plated coating material in the non-plated portion is removed. For example, the coating material of the non-plated portion is peeled off by a method of jetting sandblast or water jet from the nozzle 10. As a result, the background of the non-plated portion provided on both pipe ends 1, 1 of the pipe joint A is exposed. When removing the coating material, masking 9 as shown in FIG. 3 may be performed in advance to protect other portions. This masking 9
The tape is attached to the boundary between the non-plated portion and the plated portion using tape or urethane rubber, and the plated portion is covered.

The steps up to this point are the same for the metal tube B, and the background of a required width can be exposed by going through the steps described above. Then, the pipe joint A and the metal pipe B are connected. In this connection, as shown in FIG. 4, the pipe end face 2 of the one side pipe end 1 of the pipe joint A and the pipe end face 12 of the one side pipe end 11 of the metal pipe B are brought into contact with each other, and the joint portion is joined. It is done by welding. At this time, since the hot-dip galvanizing does not exist at the connection site, zinc gas is not generated by high heat and the working environment is not deteriorated.

Further, since the non-plated portion is chemically treated, the accuracy of the machined surface is deteriorated, unlike the conventional method in which the pipe end surfaces 2 and 12, which are the welding points, are ground with a grinder and then the welding operation is started. The problem that proper welding connection is not possible due to a gap occurring at the contact portion is avoided. Table 1 shows the accuracy test results of the pipe joint A thus connected.

[0013]

[Table 1]

As is clear from Table 1, the component constitutions excellent in the comprehensive evaluation are the type symbols D and H, both of which will be briefly described below. (1) Component composition of non-plating coating material D The ratio is 30% of thermoplastic acrylic resin, 10% of inorganic material, 15% of thermosetting acrylic resin and 45% of solvent. (2) Evaluation of unplated coating material D In this evaluation, a symbol (◎ ○ △
When x) was used, it was as follows. The unplated state is good, and almost complete unplated can be formed. The coating material does not remain on the non-plated portion, and therefore it does not take time to remove the remaining meal. There is no problem that smoke or odor is generated during the plating process. Since the boundary between the non-plated part and the plated part becomes clear,
Good plating finish. As a comprehensive evaluation, since the above points are excellent,
It can be said to be the most practical. (3) Component composition of the non-plating coating material H The ratio is 30% of thermoplastic acrylic resin, 15% of inorganic material, 15% of melamine resin, 7% of epoxy resin and 33% of solvent. (4) Evaluation of non-plated coating material H This coating material H has a content according to the above-mentioned D and can withstand practical use. In the above embodiment, the case where the elbow type pipe joint and the metal pipe are connected has been described. However, as shown in FIG. 5, a different diameter elbow (A in the same figure), a tee (B in the same figure), a reducer (C in the same figure) and caps (D in the same figure) and the like may be connected to the metal tube by forming an unplated portion at each tube end portion.

[0015]

As described above, according to the present invention, since the non-plated portion is formed at the pipe end portion of the metal pipe and the pipe joint and the pipe ends are welded and connected, generation of zinc gas or the like due to high heat is prevented. The working environment is improved. Also, because the non-plated part is formed by chemical treatment, unlike the conventional method in which the pipe end surface, which is the welded part, is ground with a grinder and then the welding work is started, each pipe end surface can be kept in the state of manufacture with good precision. Since the welding process can be appropriately performed without forming a gap at the contact portion, there is an effect that problems such as welding defects are prevented.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a coating operation of a non-plating coating material according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing another coating operation of the non-plating coating material.

FIG. 3 is an explanatory diagram showing a removing operation for removing an unplated coating material after a plating process.

FIG. 4 is an explanatory view showing a work of connecting a metal pipe and a pipe joint.

FIG. 5 is a front view showing four types of pipe joints to which the pipe joining method of the present invention is applied.

[Explanation of symbols]

 1 Pipe end portion 11 Pipe end portion A Pipe joint B Metal pipe

Claims (1)

[Claims] 1. A step of applying an unplated coating material containing an inorganic coating material as a main component to form unplated portions on the pipe end portions of the metal pipe and the pipe joint, and a hot dip galvanizing treatment for the metal pipe and the pipe joint. And a step of removing the unplated coating material of each unplated portion, and a step of connecting the pipe end of the metal pipe and the pipe end of the pipe joint by welding.