KR20150119764A - Joining Method for Polyethylene Pipes Using Butt Fusion - Google Patents

Abstract

The present invention relates to a method for connecting two polyethylene pipes with each other by using butt fusion, the method comprising: a cleaning step (S200) of cleaning inner and outer circumferential surfaces of ends of first and second pipes (10 and 20); a pipe clamping step (S300) of forming and fixing the first and second pipes (10 and 20) on a fusion device by clamping; a pipe finely arranging step (S500) of finely adjusting and arranging an installation position of ends of the first and second pipes (10 and 20); a pipe end dissolving step (S600) of dissolving both ends of the first and second pipes (10 and 20) by using an electric plate; and a pipe jointing step (S700) of contacting ends of the first and second pipes (10 and 20), applying pressure to the first and second pipes (10 and 20) until the contacting part is cooled to an appropriate temperature, making the first and second pipes (10 and 20) maintained while being pressed, and contacting with dissolved ends. Pressure applied to the second pipe (20) in the pipe jointing step (S700) is controlled to follow a change of a specific volume in a joint part of the first and second pipes (10 and 20). According to the configuration of the method of the present invention, polyethylene pipe fusion that is mechanically stronger and can block growth of cracks is performed.

Description

Technical Field [0001] The present invention relates to a method of joining a polyethylene pipe using butt joints,

The present invention relates to a polyethylene pipe connecting method, and more particularly, to a polyethylene pipe connecting method for connecting a large diameter polyethylene pipe such as a cooling water inlet pipe of a nuclear power plant, a city gas transfer pipe and the like by a butt joining heat sealing method .

When a large amount of cooling water or city gas is supplied from a nuclear power plant or a city gas reservoir to a required place, it is supplied through a pipe. At this time, a metal pipe is mainly used as a piping material.

However, for example, in a nuclear power plant, a large amount of cooling water is required to cool a primary coolant in a nuclear power plant. Accordingly, a large-diameter cooling water inlet pipe is buried in the sea, and seawater is taken out through it to be used as cooling water. When a metal pipe is used as a lead-in pipe, there is a problem that the lead pipe is easily corroded by seawater. Therefore, recently, a synthetic pipe such as a polyethylene pipe is used instead of a metal pipe as a coolant intake pipe.

In particular, polyethylene has excellent chemical resistance, hygienic properties, flexibility, light weight, and the like compared with other materials. Particularly, since polyethylene is semi-permanently usable without any corrosion or corrosion and has advantages such as easy maintenance and economical efficiency, It is also used for water, sewage and gas transportation.

When such a polyethylene pipe is used for piping, it is necessary to connect the polyethylene pipes to each other. In the method of connecting the polyethylene pipes, there are a mechanical connection method using a metal coupling and a method of connecting using a heat. Since the coupling and the connecting material used for it are made of metal, there is still a possibility of corrosion. In the case of connecting the polyethylene pipe, a method of connecting using mainly heat is used.

Heat fusion method and electro fusion method are also used for the connection of polyethylene pipe by using heat. Butfusion method, socket fusion method, And saddle fusion, and electric fusion is divided into electric socket fusion and electric saddle fusion. In this case, the heat fusion method is a method of melting a portion to be connected by using an external heat source, And electric fusion is a fusion method in which a part to be connected is melted and connected by inserting a heating coil into a joint pipe and applying a power source to the heat wire of the joint pipe to generate a connection, Since there is an inconvenience to use a separate connecting pipe (socket) for socket welding, when connecting the cooling water inlet pipe and the gas transfer pipe, The butt-welding method by heat fusion pipe does not need to be used.

When polyethylene pipes are connected to each other by the butt welding method, first, the two pipe ends to be connected are cleaned through the process of removing an oxide film formed on the outer surface of the pipe during the production of the pipe, and then the soil or dust is removed. After the polyethylene pipes are clamped by a fusing device and arranged in a line at regular intervals, the pipes are aligned so that the opposite cross sections of the pipes to be connected exactly match each other.

After the two pipes are accurately aligned on the fusing device by the above process, a plate-shaped heater is inserted between the two pipe ends to melt the end of the pipe, and then the two pipes are connected to each other The joint is completed by applying a suitable pressure until the molten part is cooled after it is left.

When the polyethylene pipe is connected by the above process, a straight joint surface is formed as shown in FIG. 1, and when the pipe joint surface is formed in a straight line, if the bending stress or shock When cracks are formed on the joint portion due to an external force, impact, or the like, cracks easily grow on the joint surface, and in this case, there is a fear that leakage occurs in the pipe or eventually breakage occurs.

On the other hand, unlike the steel material, the specific volume of polyethylene, which is a crystalline polymer, shows a rapid change based on the melting point (Tm). As described above, when the heater is removed, The temperature of the bonding surface is gradually lowered. When the temperature of the bonding surface reaches the melting point, a phase change occurs at the boundary of the melting point (Tm), and a sharp volume Change (reduction) occurs.

Generally, when a polyethylene pipe is butt-connected by a heat fusion bonding method, the surface temperature of the heater, the pressure and time to be applied to the pipe, and the like are controlled so as to follow the pressure profile as shown in the graph shown in FIG. 2. At this time, In the process (T4 and T5 in FIG. 2), the pressure is continuously increased. The inventors of the present invention have found that when the pressure applied to the pipe is continuously increased while the pressure is applied, the abrupt change of the specific volume around the melting point And it was found through researches and experiments that the bonding strength was not improved as much as the pressure was increased.

JP 2001-162898 A US 8128853 B2 US 2006-0032349 A1

Disclosure of Invention Technical Problem [8] The present invention has been made in order to solve the problems of the conventional polyethylene pipe connecting method as described above, and it is an object of the present invention to provide a polyethylene pipe capable of effectively preventing growth of cracks, The purpose of the connection method is to provide.

According to another aspect of the present invention, there is provided a method of connecting a polyethylene pipe, the method comprising: a cleaning step of cleaning the inner and outer peripheral surfaces of the first and second pipe ends; A pipe clamping step of fixing the first and second pipes to the fusing device by clamping; Aligning the mounting positions of the ends of the first and second pipes by fine adjustment; A pipe end melting step of melting both ends of the first and second pipes using a heat transfer plate; And the first and second pipes are kept in a pressurized state by applying pressure to the second pipe until the molten portions are turned back to each other until the butted portion is cooled to an appropriate temperature so that the molten ends are joined together And controlling the pressure applied to the second pipe in the pipe joining step to follow the change in volume at the joining portion of the first and second pipes.

According to the present invention, when the first and second pipes are joined together before the cleaning step is performed, grooves and vertical portions are formed at the end of the first pipe so that the shape of the joint surface is " The end portion of the pipe is subjected to a pipe end cutting step for cutting the end portion of the pipe so as to form the protruding portion and the vertical portion, and the heat transfer plate used in the pipe end melting step is used as a heat transfer plate .

Further, between the pipe clamping step and the pipe micro-aligning step, a surface finishing device is provided between the first and second pipes to add a pipe end surface machining step for machining the opposite end surfaces of the first and second pipes, respectively Another feature.

In addition, the present invention is characterized in that a slope of 5 to 20 degrees is formed on a horizontal line as a connecting portion between the groove portion and the vertical portion and between the protruding portion and the vertical portion.

According to the present invention, by controlling the fusing pressure in accordance with the physical properties (specific volume change) of the polyethylene material, the polyethylene pipe can be firmly fused and connected without using large pressure.

Further, according to the present invention, grooves and protrusions are formed at the end portions of two polyethylene pipes, and these are connected to each other so as to have a shape of "┌┘" by abutting fusion, thereby providing a connecting portion having excellent mechanical performance.

In the present invention, since the fused portion is formed not in a straight line but in a shape of "┌┘", even when a crack is generated on the joint portion, the growth of the generated crack is blocked by the pipe base material, can do.

FIG. 1 is a cross-sectional view showing an example in which a conventional polyethylene pipe is heat-
FIG. 2 is a view showing a pressure profile showing the pressure applied to the pipe when the polyethylene pipe is connected using the conventional butt joint,
FIG. 3 is a flowchart showing a method of connecting a polyethylene pipe using butt welding according to the present invention.
Fig. 4 is a process diagram showing an example of thermally fusing a polyethylene pipe according to the present invention.

Hereinafter, the structure and operation of the present invention will be described in more detail with reference to the accompanying drawings, which show preferred embodiments.

As shown in FIG. 3, the method for connecting a polyethylene pipe according to the present invention includes a pipe end cutting step S100, a cleaning step S200, a pipe clamping step S300, A surface finishing step S400, a pipe fine aligning step S500, a pipe end melting step S600, and a pipe joining step S700. Hereinafter, each step will be described in detail.

(1) Pipe end cutting step (S100)

This step is a step of cutting the end portions of both pipes as shown in Fig. 4 so that the shape of the joint surface becomes "┌┘" when both pipes are joined by a pipe joining step (S700) Since the pipe connection method of the invention is mainly applied to large diameter polyethylene pipes having a diameter of 300 mm or more, this step is usually performed at a cutting plant, but it may be performed at a work site depending on the situation.

As described above, if a polyethylene pipe is connected by a butt joint fusion method so as to form a straight joint surface, there is a problem that it is weak against a hardening stress or an impact and a crack easily grows. Accordingly, in the present invention, To achieve this, a cutout is formed in the pipe end of one of the two pipes to form a groove, and a protrusion having a length equal to the depth of the groove is formed at the end of the other pipe So that when the two pipes are brought into contact with each other, the shape of the joining surface is made to be an overall shape, and the thickness of the groove and the protrusion is formed to be equal to the thickness of the vertical portion desirable.

Further, when forming the groove portion and the projection portion, it is preferable that the surface of the surface constituting the vertical portion continuing to each of the groove portion and the projection portion is also finely cut so that the surface of the vertical portion is smooth.

When the ends of the pipe are cut so that the shape of the joining surface is shaped like the above and then the pipes are pressed together by the pipe joining step (S700) to be described later, portions where the grooves and the projections come into contact with each other Since appropriate pressure is applied to the vertical portions, appropriate strength is ensured for the joined surfaces. However, since the surfaces connecting the groove portion and the vertical portion and the portions connecting the projecting portion and the vertical portion are parallel to each other as horizontal, But the strength at this part can be lower than that of the other part because it is connected only by the bonding of the melted polyethylene.

Accordingly, it is preferable to form the groove portion, the vertical portion, and the portion connecting the projecting portion and the vertical portion so as to be inclined at 5 to 20 degrees with respect to the horizontal line without horizontally cutting. Sufficient joining strength can be ensured, and when the inclined surface is formed at an angle larger than this range, the effect of inhibiting the progress of the crack is not so large.

When the grooves and protrusions are formed on the ends of the first and second pipes 10 and 20 by the above process, the processed polyethylene pipe is transported to a work site. At this time, .

(2) Cleaning step (S200)

When producing a polyethylene pipe, an oxide film is usually formed on the outer surface of the pipe. When the pipe is stored or transported, the outer surface of the pipe adheres to the inner surface of the pipe with foreign matter such as soil or dust. The inner and outer peripheral surfaces of the ends of the pipes (the first pipe 10 and the second pipe 20) are cleaned.

(3) Pipe Clamping Step (S300)

In this step, after the ends of the first and second pipes 10 and 20 to be connected are cleaned by the cleaning step S200, the first and second pipes 10 and 20 are installed in the fusing device Wherein the fusing device comprises four clamping jaws, one pair of left and right clamping jaws, a pair of right and left clamping jaws, a pair of right and left clamping jaws, And a controller for controlling the movement of the driving means and the operation of the heat transfer plate, and the like, which are installed between the pair of clamping tanks and are rotatable by the hinge.

The four clamping jaws are composed of a lower jaw located at the lower side and a upper jaw located at the upper side of the lower jaw and rotatable by the hinge. When these upper and lower jaws are coupled to each other, a circular shape is formed like a pipe, An adjusting bolt for joining the upper and lower tanks is provided, and an insert of an appropriate size is provided, if necessary, depending on the size of the pipe provided inside the clamping tank.

The driving means for moving the pair of clamping jaws in the left and right direction is constituted by a hydraulic device having a hydraulic cylinder and a hydraulic pump, and the pair of clamping jaws are coupled to one hydraulic cylinder, At the same time, it is moved in the left and right direction.

When the two pipes (first and second pipes 10 and 20) to be connected to the fusing apparatus having the above structure are installed and fixed, the heat transfer plate is first rotated to lift the heat transfer plate, and the adjustment in the four clamping tanks The pair of left clamping jaws are placed in the first pipe 10 and the pair of right clamping jaws are provided with the second pipe 20 in the pair of right clamping jaws So that the first and second pipes 10 and 20 are arranged linearly along the axial direction on the fusing device at an appropriate interval do. At this time, by adjusting the coupling force of the adjusting nut, the two clamping jaws located outside the pair of right and left clamping jaws are fixed relatively firmly, and the two clamping jaws located inside are relatively loosely fixed.

In addition, if necessary, a support roller capable of adjusting the installation height can be provided on the outside of the fusing device, and a pipe is provided on these support rollers whose installation height is appropriately adjusted to thereby maintain the two pipes in a straight line, Make sure that the left and right movement is smooth.

(4) Step of machining the pipe end surface (S400)

In this step, if the first and second pipes 10 and 20 are fixed on the fusing device at appropriate intervals by the pipe clamping step (S300), a face machining device is installed between the pipes, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, However, since the cross-sectional state of the pipe significantly affects the quality of the joint, foreign substances or the like may be adhered to the end of the pipe during the transportation process or the pipe installation process, In the end cutting step S100, if the vertical section of each of the first and second pipes 10 and 20 is not cut, this step is performed, so that this step is performed in an optional step to be.

When processing the end surface of the pipe in this step, the controller of the fusing device is controlled in a state in which the surface machining device is installed between the first and second pipes 10 and 20 so that the amount of the first and second pipes 10 and 20 The end face of the pipe is finely cut or ground by operating the face machining device so that the end face of the face end faces the side face of the face finishing machine so that the vertical portions of the pipe end become smooth and perpendicular to the center line of the pipe respectively.

The processing of the pipe end surface may be performed by one surface processing apparatus, but may also be performed by two surface processing apparatuses, in which processing of the pipe end surface is performed for the entire projections, grooves and vertical portions.

(5) Pipe fine alignment step S500

In this step, the two pipes are arranged in a straight line by the above-mentioned process, or after the end surfaces of the pipes are processed, the positional deviation of the end faces when the first and second pipes 10, The position of the end of the pipe facing each other is finely adjusted and aligned so that the position of the end of the pipe facing each other can be minimized. Such positioning is achieved by adjusting the coupling force of the position adjusting bolts respectively provided in the four clamping jaws. This is accomplished by repeating the tightening process of the adjusting bolt while moving the pipe (second pipe 20) connected by using the driving means to the left and right, And can be done accurately.

(6) Melting step of pipe end (S600)

This step is performed so that both end portions of the first and second pipes 10 and 20 are precisely matched by the pipe fine alignment step S500 and the heat transfer plate of the fusing device is interposed between the first and second pipes 10 and 20 The second pipe 20 is moved so that the ends of the first and second pipes 10 and 20 are brought into contact with the side surface of the heat transfer plate. Then, power is supplied to the heat transfer plate, Wherein the cross-sectional shape of the heat transfer plate is formed so as to have a shape suitable for the shape when the both ends are joined, that is, the shape of "shape ".

When the ends of the first and second pipes 10 and 20 are melted by applying power to the heat transfer plate, the driving device is operated to move the second pipe 20 as the length of the pipe becomes shorter as the melting progresses, At this time, if an excessive force is applied to the pipe axis direction, fusion defects such as formation of a concave of a "V " shape on the end face of the welded surface may occur. In order to achieve this, the fusing device is provided with a pressure measuring device for measuring the pressure applied to the end of the pipe. The result of the measurement is inputted to the controller, So that the pipe is not pressurized. The structure and control method of such a fusing device are already known And thus a further detailed description thereof will be omitted.

The length of the portion melted by the heat transfer plate can be confirmed by the size of the bead protruding to the side of the heat transfer plate. The size of the bead differs depending on the diameter and thickness of the pipe, A suitable look-up table is prepared in advance to form a bead having an appropriate size according to the thickness of the pipe.

(7) Pipe joining step (S700)

In this step, after the ends of the first and second pipes 10 and 20 are melted to an appropriate length by the pipe end melting step S600, the second pipe 20 is retracted by using the driving device, If the molten end of the pipe 10 or 20 is removed and the end of the molten end is checked for flatness or defect, then if the molten state of the end portion is judged to be good, The first pipe 10 is advanced to the pipe 10 so that the end of the second pipe 20 is brought into contact with the end of the first pipe 10 and the proper pressure is applied to the second pipe 20 in a state where the first and second pipes 10 and 20 are fixed So that the welded portion of the pipe continues to be maintained in a pressurized state so that the pipe integrally joins by the engagement of the molten portion. This pressurized state continues until the welded portion is cooled to an appropriate temperature, Once the pipe The fusion welding operation is terminated. At this time, the cooling time (pressurization holding time) has a considerable influence on the operation of the pipe fusion part, so that the cooling time usually takes a minimum of 11 minutes per inch of pipe thickness.

If it is judged that the melted end is bad in the above inspection process, cut off the melted part and then repeat the above procedure.

As described above, when the temperature of the joining portion becomes the melting point portion when the pipe is joined, the bulkiness is sharply reduced. Even if the pressure is continuously increased in this state, the strength of the joining portion is not greatly improved. On the contrary, In the present invention, the pressure applied to the pipe is controlled according to the physical properties of the polyethylene material. To this end, the fusing device includes a pressure sensor for detecting the pressure applied to the pipe, A temperature sensor for measuring the temperature of the pipe, and an encoder for measuring the feed amount of the pipe in accordance with the pressure of the pipe, and is connected to the controller, and the controller of the fusing apparatus is provided with means for inputting a melting point and a timer.

According to the above-described configuration, when joining is performed, the joining is performed while the pressure applied to the pipe is continuously increased while the melting point is inputted to the controller. At the same time, the temperature of the joining portion is detected by the temperature sensor, The pipe moving speed is controlled by controlling the moving speed of the pipe by controlling the pressure applied to the piston of the driving means so that the pipe moving speed is calculated by the pipe diameter and thickness, The calculated moving speed of the pipe is input to the controller as a control program in advance. Whether the pipe is actually moved in accordance with the inputted pipe moving speed can be confirmed by the timer and the moving distance detected by the encoder. The feed distance can be used as a feedback value for accurate feed of the pipe. The.

As described above, according to the present invention, the grooves and the projections are formed at both ends of the polyethylene pipe, and the fusion process is controlled according to the physical properties of the polyethylene material. Thus, / RTI >

10: first pipe 20: second pipe

Claims (4)

A pipe connecting method for connecting two polyethylene pipes made up of first and second pipes (10, 20) by butt welding,
A cleaning step (S200) of cleaning inner and outer peripheral surfaces of the ends of the first and second pipes (10, 20);
A pipe clamping step (S300) of fixing the first and second pipes (10, 20) to the fusing device by clamping;
(S500) for finely adjusting and aligning the installation positions of the ends of the first and second pipes (10, 20);
A pipe end melting step (S600) for melting both ends of the first and second pipes (10, 20) using a heat transfer plate;
After the end portions of the first and second pipes 10 and 20 are turned back to each other, a pressure is applied to the second pipe 20 until the butted portion is cooled to an appropriate temperature, (S700) for allowing the molten ends to be joined to each other,
Wherein the pressure applied to the second pipe (20) in the pipe joining step (S700) is controlled so as to follow a change in specific volume in the butted portion of the first and second pipes (10, 20) Connection method of polyethylene pipe using thermal welding.

The method according to claim 1,
When the first and second pipes 10 and 20 are joined before the cleaning step S200, the groove and the vertical portion are formed on the end of the first pipe 10 such that the shape of the joint surface is " A pipe end cutting step S100 is performed in which an end portion of the pipe is machined so as to form a protrusion and a vertical portion at the end of the second pipe 20,
Wherein the heat transfer plate used in the pipe end melting step (S600) is a heat transfer plate manufactured to have a shape suitable for the shape of a cross section.
The method of claim 2,
A surface machining device is installed between the first and second pipes 10 and 20 between the pipe clamping step S300 and the pipe fine aligning step S500, And a pipe end surface machining step (S400) for machining the facing end surfaces, respectively, is added to the pipe end surface machining step (S400).
The method of claim 2,
Wherein the groove and the vertical portion, and the portion connecting the projecting portion and the vertical portion, respectively, have inclined surfaces of 5 to 20 degrees with respect to a horizontal line.

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