JPH08276282A - Joining method of steel boiler tube - Google Patents

Abstract

PURPOSE: To attain such simple and easy joining method of steel boiler tube that dispenses with a skilled technique and that reduces time required for manufacturing a joint by thermally spraying on the joining surface a low melting point down element with a prescribed amount of B to Fe. CONSTITUTION: The face for butt welding of a boiler tube 3 is smoothed, and thermally sprayed on one or both faces with a mixed particles of Fe and B whose amount is 2-4% to Fe. An argon shield chamber 6 is filled with oxidation preventing argon while allowing it to flow constantly. The end part 4, a joining part, coated by the thermal spraying is heated for example at a heating temperature of 1,250 deg.C and a holding time of 120 seconds with a high frequency heating coil 5 using a temperature controller 10 for such coil. In addition, it is constantly pressurized for example at a pressurizing force of 0.5kgf/mm<2> with an upper and lower chuck 8 of a loading device 7 using a load controller 9, with the pressurizing released at the holding time of 120 seconds. In preventing oxidation in the proximity of the joining part, it is cooled in the argon chamber 6 until reaching 300 deg.C, and afterwards cooled down to room temperature in the air.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a new method for producing a butt joint of a ferritic steel pipe used as a steel pipe for a boiler.

[0002]

2. Description of the Related Art Conventionally, a butt joint of a steel ferrite-based steel pipe for a boiler has generally been manufactured by using a weld metal (welded metal) having a component equivalent to that of a base metal and by manual welding or automatic welding.

[0003]

In the conventional butt-welded joint manufacturing, first of all, the groove processing of the material (usually X, V, Y) is carried out.
Complex groove), groove alignment, welding (welding rod and wire, etc.). In addition, welding requires a lot of pass layers depending on the pipe thickness, and it takes time to manufacture the joints. Further, if the welding technique is not skilled, there is a great possibility that welding defects will occur even if the joint is manufactured.

In view of the above-mentioned state of the art, the present invention provides a method for joining steel pipes for boilers, which simplifies the groove processing (I-groove), groove alignment, and joining of the butt joints described above, thereby reducing the time and skill. It is the one we are trying to provide.

[0005]

According to the present invention, when butt-joining a steel pipe for a boiler, the butt-joint surface is made smooth, and the amount of B is 2 to 4% with respect to Fe on one or both surfaces of the butt-joint surface. Mixed particles of Fe particles and B particles or Fe
On the other hand, a method for joining steel pipes for boilers is characterized in that single particles containing 2 to 4% of B are sprayed, and the sprayed surfaces are butted and pressure-bonded while heating with high frequency.

That is, the present invention comprises the following means. (1) The groove shape of the steel pipe for a boiler, which is a butt joint surface, is set to the simplest I groove, and three peaks are finished (# 180 to 240).
Surface roughness). (2) On one side or both sides of the I-groove surface of the above three finish,
It is composed of mixed particles of Fe particles and B particles in which the amount of B is 2 to 4% with respect to Fe, or single particles (obtained by mechanical alloying) containing 2 to 4% of B in Fe. Sprays low melting point depressing elements. (3) Next, the groove surfaces sprayed with the low melting point depressing element are put together and subjected to high-frequency heating and pressure bonding.

[0007]

According to the present invention, when manufacturing a butt joint, the steel pipe for a boiler is I-grooved, so that it can be carried out without requiring a skilled technique, and the amount of B relative to Fe in the joint surface can be reduced. Since 2 to 4% of the low melting point depressing element is sprayed, the butt joining and the diffusion joining can be performed without melting the boiler steel pipe itself by only melting the low melting point depressing element, and the joining time is shortened. Moreover, a joint with excellent quality can be obtained.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 1 to 3 to clarify the effect of the present invention. FIG. 1 is a situation in which the end portion of the boiler tube material is sprayed, and FIG. 2 is a situation in which both ends of the end portion of the tube sprayed are combined to produce a butt joint using a high frequency heating device and a load application device, and FIG.
Shows the appearance of the obtained tube joints, respectively.

First, as shown in FIG. 1, a single particle or Fe obtained by a mechanical alloy containing B in an amount of 2 to 4 wt% with respect to Fe by using plasma spraying, that is, a plasma jet generated by a so-called plasma spray gun 1. On the other hand, the composite thermal spray material 2 obtained by heating and accelerating the composite particles of Fe particles and B particles containing 2 to 4 wt% of B is sprayed onto the end portion of the boiler tube material, for example, the carbon steel pipe (STB340) 3 The end 4 is formed. Next, as shown in FIG. 2, the sprayed coating end 4 of the carbon steel pipe 3 and the sprayed coating end 4 of the carbon steel pipe 3 are butted against each other without any misalignment, and the periphery thereof is covered with a high-frequency heating coil 5. In addition, the joint is shielded by the argon seal chamber 6 to prevent the joint from being oxidized. Further, the non-sprayed end of the carbon steel pipe 3 is fixed by the upper and lower chucks 8 of the load applying device 7. The load application device 7 can be controlled by the load control device 9, and the high frequency heating coil 5 can be controlled by the high frequency heating coil temperature control device 10 by the heating temperature. With the above, the preparation for joining is completed.

The bonding conditions will be described below. First, the argon shield chamber 6 is filled while constantly flowing argon for oxidation prevention. Next, using the high-frequency heating coil 5, the temperature control device 10 for the high-frequency heating coil is used to heat the sprayed coating end portion 4 which is the joint, at a heating temperature of 1250 ° C. and a holding time of 12
It is heated for 0 seconds, and the load is applied by the load chuck 7 and the upper and lower chucks 8 using the load controller 9: 0.5 kgf / m.
The pressure is constantly applied to m ² and the pressure is released after a holding time of 120 seconds. After that, cooling is performed. At this time, cooling is performed in the argon chamber 6 until the temperature reaches 300 ° C. to prevent oxidation in the vicinity of the bonded portion, and then cooled to room temperature in the atmosphere.

By the above steps, the liquid phase diffusion bonding joint of the plasma spray coating portion of the boiler tube material, for example, the carbon steel pipe (STB340) 3 is completed. In addition, as shown in FIG. 3, the outer appearance of the joint has a bulged shape 11 under the optimum conditions. Therefore, compared to the conventional welded joint manufacturing, less skillful techniques are required, and the welding can be performed easily and easily.

[0012]

As described above, by using the joining method of the present invention, compared with the joining method (welded joint) which has been conventionally used, no skilled technique is required, and it can be easily and easily performed. In addition, the time required to manufacture the joint can be shortened.

[Brief description of drawings]

FIG. 1 is an explanatory view of a thermal spraying state of an end portion of a boiler tube material.

FIG. 2 is an explanatory view of a situation in which both ends of a tube sprayed end face are aligned and a butt joint is manufactured using a high frequency heating device and a load applying device.

FIG. 3 is an explanatory view of the appearance of a tube joint obtained by the method of the present invention.

Claims (1)

[Claims] 1. When butt-joining a steel pipe for a boiler, the butt-joint surface is smoothed, and one or both surfaces of the joint surface are mixed with Fe particles and B particles in which the amount of B is 2 to 4% with respect to Fe. The amount of B is 2 to 4 with respect to the particles or Fe.
% Of a single particle is sprayed, and the sprayed surfaces are butted against each other and pressure-bonded while high-frequency heating is performed.