JPH10119135A - Joint inspection method and joint inspection electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for simply detecting a joint failure in piping for ultrapure water. SOLUTION: A method for inspecting a joint portion comprises steps of butt contacting end faces of pipe bodies 10, 11 to be connected which are made from a thermoplastic resin, placing a conductor 12 on the outer circumference of the butt contacted portion and generating resistance heat by energizing the conductor for thermowelding the pipe bodies. The method further comprises steps of (a) inserting an electrode 14 in the joint portion in such a manner that it is brought into contact with or close to the inner surface thereof before or after the pipe bodies 10, 11 are thermowelded, (b) impressing a high voltage between the contractor 12 and the electrode 14, (c) detecting the generation of electric discharge between the conductor 12 and the electrode 14, and (d) withdrawing the electrode 14 from the pipe bodies. When there is found any minute joint failure in the joint portion such as one in which the inner surface of the pipe bodies and the conductor 12 get continuous, it can be detected by existence of an electric discharge when a high voltage is impressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pipe joint inspection method and a pipe joint inspection part, and more particularly to a pipe joint inspection method and a pipe joint inspection part for inspecting the joint of a pipe for ultra-high purity liquid.

[0002]

2. Description of the Related Art The inner surface of a joint portion of a pipe for high-purity liquid such as ultrapure water is required to have smoothness in order to reduce the adhesion of microorganisms and impurities. On the other hand, various pipe joining methods have been proposed.

[0003] In a joining method for solving the demand for beadless, a conductor is arranged around a joint where a pipe is abutted, and a support for maintaining the smoothness of the joint is inserted into the pipe to form an inner surface of the pipe. In this state, a current is passed through the conductor to generate heat, thereby welding the tube. In this joining method, since the inner surface of the tube is supported by the support, the inner surface of the joint can be smoothed.

[0004] As a similar pipe joining method, there is a method in which a conductor disposed around a joint where the tubes are joined to each other is induction-heated to heat and weld the tubes, and even with this method, the joints can be smoothed. .

A problem with such a joining method is that when a joining defect such as a pinhole or a crevice occurs due to a defect in welding, there is a possibility that a conductor disposed around the joining portion may come into contact with the fluid in the pipe. It is. In piping of extremely high-purity fluid such as ultrapure water, the contact of the conductor with the fluid in the pipe is a serious problem that directly leads to contamination of the fluid in the pipe.

[0006] Unlike such a joint failure that causes a liquid leak, such a joint failure cannot be found by a visual inspection or an airtightness inspection using soapy water or the like because the pipe itself is completely sealed. For this reason, for example, fill the pipe with pure water,
After the elapse of a predetermined time, the connection failure was detected by an elution test or the like in which the water was analyzed to examine the elution of the conductor. This joining inspection method has a problem that it is extremely complicated and time-consuming, and cannot be inspected on-site.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem. That is, an object of the present invention is to provide a method capable of easily detecting a poor joint of a pipe. It is another object of the present invention to provide a method capable of detecting a joint failure of a pipe on-site during construction. A further object of the present invention is to provide an electrode for detecting a poor joint of a pipe at the time of construction.

[0008] The present invention can also be used to easily determine the poor connection of piping,
An object is to provide an electrode for detecting at the time of construction.

[0009]

According to a joint inspection method of the present invention, in the method for inspecting a joint, (a) an electrode is inserted so as to be in contact with or close to the inner surface of the joint before or after welding of the tubular body. And (b) applying a high voltage between the conductor and the electrode; and (c) detecting presence or absence of discharge between the conductor and the electrode. Further, the joint inspection method of the present invention is a method of inspecting, comprising: (a) inserting an electrode so as to be in contact with or close to the inner surface of the joint before or after welding of the tube; Applying a high voltage between the electrode and the electrode; (c) detecting the presence or absence of discharge between the conductor and the electrode; and (d) extracting the electrode from the tube. It is characterized by the following.

The bonding inspection electrode according to the present invention is characterized in that a wire is suspended between the electrode mounting portion and the base in an elastic bag having an electrode mounting portion at a front end and a gas inlet base at a rear end. A conductive wire brush is fixed to the mounting portion, and a vent pipe is attached to the base portion.

The object of the joining inspection method of the present invention is as follows.
The end face of a tubular body made of a thermoplastic resin to be connected is abutted, a conductor is arranged on the outer periphery of the abutted portion, and a resistance is generated by welding or energizing or inductively applied to the conductor. If a bonding defect such as a pinhole or a crevice occurs due to a welding defect, there is a possibility that the conductor disposed around the bonding portion and the liquid inside the pipe come into contact with each other. In order to detect such a joint failure, it is sufficient to check whether or not the inner surface of the tube body joined by heat welding and the conductor arranged around the joint are insulated. Basically, such a joint failure is determined by a pinhole test in which an electrode is inserted into the joint of the tube and a high voltage is applied between the inserted conductor and the conductor arranged around the joint of the tube. Can be detected. If there is a passage through which the fluid in the tube can communicate with the conductor, a discharge occurs, so that a defective connection can be detected.

On the other hand, as a support to be inserted into the tube at the time of welding to keep the inner surface of the tube smooth, a balloon-shaped elastic bag made of a material having low conductivity such as silicon rubber is generally used. . If conductive rubber is used as the material of the balloon-shaped elastic sac, the elastic sac can also be used as an electrode, and the joining and inspection of the tube can be performed continuously, which is complicated and time-consuming. In addition, it is possible to easily detect defective bonding without using such a dissolution test.

If the elastic sac inserted into the tube at the time of welding does not have conductivity and cannot be used as an electrode, the electrode is inserted into the joint portion of the tube after the elastic sac is pulled out and the connection is poor. May be detected. Further, even when the support is not inserted into the tube at the time of welding, the electrode may be similarly inserted into the joint of the tube to detect a poor connection.

A conductive brush may be used as an electrode to be inserted into the tube. The conductive brush is generally made of metal, but if there is a risk of damaging the piping, a carbon brush may be used.

When the support to be inserted into the tube at the time of heat welding is a balloon-shaped elastic sac having no conductivity, a conductive wire brush is attached to the tip of the support, and the balloon made of conductive rubber is used. As in the case of the elastic sac, it may be possible to detect a joint failure when joining the pipes.

Such an electrode is inserted into the joint of the tube before or after the heat welding and connected to the high voltage applying means.
It is preferable to connect to the high voltage applying means in advance and then insert it into the tube.

On the other hand, a conductor arranged on the outer periphery of the tube joint is connected to the high voltage applying means as the other electrode.

After connection, a pinhole test is performed using the conductor inserted into the tube and the conductor arranged on the outer periphery of the tube joint as electrodes. At this time, a defective bonding portion that connects to the copper wire from inside the pipe can be detected by the presence or absence of discharge. The discharge may be checked using a commercially available pinhole detector, or the occurrence of noise generated in the circuit may be checked. The applied voltage is preferably lower than the withstand voltage of the pipe material. For example, in the case of polyvinylidene fluoride, it is 40 KV or less, in the case of polyethylene, it is 70 KV or less, and in the case of polypropylene, it is 75 KV.
It is preferable to set KV or less.

If there is no joint failure, the fluid in the balloon-shaped elastic capsule is discharged and pulled out of the pipe to complete the inspection. If a bonding failure is found, the above-described inspection may be performed again after energizing and welding the copper wire again.

Also, when a wire brush is used as an electrode to be inserted into the tubular body, a joint failure can be similarly detected. When a wire brush is attached to the tip of the balloon-shaped elastic sac, if it is connected to a wire for a pinhole test after heating and welding, a joint failure can be detected at the same time as the removal.

As described above, according to the joining inspection method of the present invention, a conductor is arranged on the outer periphery of the end face where the tubular body made of thermoplastic resin to be connected abuts, and a current is applied to the conductor to heat and weld the tubular body. A defective joint at which the surrounding conductor and the liquid inside the pipe come into contact with each other can be detected by examining the insulation between the conductor and the inner surface of the pipe.

Further, according to the joint inspection method of the present invention, a joint failure of the pipe can be detected at the time of construction by performing a pinhole test using the support inserted at the time of heat welding of the tube as an electrode. Further, according to the joint inspection electrode of the present invention, a joint failure of the pipe can be detected at the time of construction.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An example in which the joint inspection method of the present invention is applied to an inspection of a joint of a pipe for ultrapure water will be described with reference to the drawings.

First, the joint of the pipe to be inspected will be described. FIG. 1 is a diagram showing an example of a pipe. Polyvinylidene fluoride (PVDF) pipe (piping) to be joined 10,
A socket 13 having a coiled copper wire 12 inside
Into the socket and butt the end faces in the socket. FIG. 2 is a diagram showing an example of a state at the time of pipe joining. A balloon-like elastic sac 14 made of, for example, a conductive rubber material is inserted into the pipe joint as a support for maintaining the smoothness of the inner surface. The balloon-shaped elastic sac 14 has a fluid introducing means. In this case, nitrogen gas is introduced and closely adheres to the inner surface of the pipe.
The gas to be introduced is not limited to nitrogen, but may be a rare gas or air, or may be a liquid in some cases. In this state, the terminals 15 and 16 connected to the coiled copper wire and the power supply 17 are connected, and an electric current is applied to heat and weld the pipe and the socket. Reference numeral 18 denotes a welded portion, and in this case, a poor connection portion 19 that connects to the copper wire 12 from inside the pipe occurs.

In addition to such a joining method, as shown in FIG. 3, instead of using a socket having a coiled copper wire inside, as shown in FIG. There is also a method in which the end faces are butted, dielectric heating is performed from the outside, and the pipe is heated and welded. In this case, a high-frequency current flows through the coil 23 to induce an eddy current in the conductive ring 20. Next, the joints of the pipes heated and welded as described above are inspected.

FIG. 4 is a diagram schematically showing an example of a state at the time of a bonding inspection. A pinhole inspection is performed using the balloon-shaped elastic sac 14 made of conductive rubber material inserted into the pipe at the time of joining as an electrode.

First, one of the terminals 15 and 16 is connected to the high voltage applying means 31. This terminal is connected to the copper wire 12 in the socket even after welding. In addition, the balloon-shaped elastic sac 1
4 and the high voltage applying means 31 are connected. The balloon-shaped elastic sac 14 is preferably inserted into a pipe while being connected to the high voltage applying means 17.

Once connected, a high voltage is applied between the copper wire 12 and the balloon-like elastic sac 14 by the high voltage applying means 31. At this time, the poor connection portion 19 that connects to the copper wire 12 from inside the pipe can be detected by the presence or absence of discharge. The discharge may be checked using a commercially available pinhole detector, or the occurrence of noise generated in the circuit may be checked. The applied voltage is preferably equal to or lower than the dielectric strength of the piping material. In the case of polyvinylidene fluoride, the pressure is preferably 40 KV or less, in the case of polyethylene, 70 KV or less, and in the case of polypropylene, it is preferably 75 KV or less. In this case, since the piping material was polyvinylidene fluoride, the detection voltage was set to 20 KV.

If there is no connection failure, the fluid in the balloon-shaped elastic capsule is discharged and pulled out of the piping to complete the inspection.

If a bonding failure is found, the copper wire 12
After the current is applied and welding is performed, the above inspection may be performed again.

Next, a description will be given of an embodiment in which a balloon-like elastic sac used at the time of pipe joining is pulled out, a wire brush is inserted, and a joining failure is detected by a pinhole test.

FIG. 5 is a diagram schematically showing an example of a state at the time of a bonding inspection. The piping to be inspected was joined in the same manner as in the first embodiment. First, the balloon-shaped elastic sac inserted in order to keep the inner surface of the joint smooth during pipe joining is pulled out, and the wire brush 41 is inserted.

Next, the terminal 15 used as a heating means,
16 is connected to the high voltage applying means 31 and changed. Further, the wire brush 41 is connected to the high voltage applying means 31. It is preferable that the wire brush is inserted into the pipe while being connected to the high voltage applying means.

A high voltage is applied between the copper wire and the wire brush, and a defective connection is detected based on the presence or absence of discharge. The applied voltage is preferably equal to or lower than the dielectric strength of the piping material. The withstand voltage of polyvinylidene fluoride is 40 KV / mm,
In this case, the detection voltage was set to 20 KV.

If there is no joint failure, the wire brush is pulled out of the pipe to complete the inspection. If a defective joint is found, the above-described inspection may be performed again after welding again.

If this wire brush 41 is attached to the tip of a balloon-shaped elastic sac 51 inserted to keep the inner surface of the joint smooth during pipe joining, the balloon-shaped elastic sac 51 is electrically conductive. Balloon-like elastic sac 5
When pulling out No. 1, it is possible to detect defective bonding. FIG. 6 is a diagram schematically showing one example of such a bonding inspection. In this case, for example, a conductive wire 52 is provided inside the balloon-shaped elastic sac to attach the conductive wire 52 to the wire brush.
May be secured. FIG. 7 is a view schematically showing an example of the structure of the bonding inspection electrode having such a structure. This bonding inspection electrode is configured such that a wire 54 is suspended between the electrode mounting portion 52 and the base 53 in an elastic sac 51 having an electrode mounting portion 52 at the front end and a gas inlet base 53 at the rear end. A conductive wire brush 41 is fixed to 52 and a vent tube 55 is attached to a base 53.

That is, the wire brush 41 is attached to the tip and inserted into the joint of the pipe, and nitrogen gas, air, etc. are introduced into the elastic bag body 51 through the ventilation pipe 55 to inflate it and adhere to the inner surface of the pipe joint. Let it. Then, as described above, the joint portion was heated and the pipe was welded.
Shrink the inside. In addition, a high-voltage power supply is connected to the electrode used at the time of pipe connection and the wire 54 connected to the wire brush.

Then, by slowly pulling out the inspection electrode, if there is a joint failure such that the inner surface of the pipe communicates with the heating conductor provided in advance at the joint, discharge is generated and detected. Can be.

[0039]

According to the joining inspection method of the present invention, a conductor is arranged on the outer periphery of the end face where two tubes made of a thermoplastic resin abut, and a current is applied to the conductor to heat and join the tubes. The joints that are in contact with the surrounding conductor and the liquid inside the pipe can be tested for pinholes by using a pinhole test with the support inserted as an electrode during heating and welding of the pipe. Can be detected by a simple method.

Further, according to the present invention, poor joint of the pipe
It can be detected on-site during the construction of pipe joints.

Further, when the pinhole inspection electrode of the present invention is used, it can be detected on-site by a simple method at the time of pipe joining.

[Brief description of the drawings]

FIG. 1 is a view schematically showing a state of a pipe to which a pipe joint inspection method of the present invention is applied.

FIG. 2 is a view schematically showing a state of joining pipes to which the pipe joining inspection method of the present invention is applied.

FIG. 3 is a diagram schematically showing a state of joining pipes to which the pipe joining inspection method of the present invention is applied.

FIG. 4 is a view schematically showing a state in which a defective joint portion is detected by applying the pipe joint inspection method of the present invention.

FIG. 5 is a view schematically showing a state in which a defective joint portion is detected by applying the pipe joint inspection method of the present invention.

FIG. 6 is a view schematically showing a state in which a defective joint portion is detected by applying the pipe joint inspection method of the present invention.

FIG. 7 is a sectional view showing a bonding inspection electrode of the present invention.

[Explanation of symbols]

10, 11 ... pipe (piping), 12 ... copper wire 13 ... socket, 14 ... balloon-like elastic sac 15, 16 ... terminal, 17 ... power supply 18 ... welded part, 19 ... poor connection Part 20: Conductive ring, 21, 22, Pipe (piping) 23: Coil, 31: High voltage applying means 41: Wire brush 51: Balloon-shaped elastic sac 52: Electrode mounting part, 53 …… Base 54 …… Wire, 55 …… Vent pipe

Claims (6)

[Claims] 1. An end face of a tubular body made of a thermoplastic resin to be connected is abutted, a conductor is arranged on the outer periphery of the abutting portion, and a resistance is generated by applying a current or induction to the conductor to inspect a joint where the tubular body is welded. And (b) applying a high voltage between the conductor and the electrode so as to contact or approach the inner surface of the joint before or after welding of the tube. And (c) detecting whether or not discharge has occurred between the conductor and the electrode. 2. The bonding inspection method according to claim 1, wherein said electrode is a conductive wire brush which is in contact with or close to an inner surface of said bonding portion. 3. The bonding inspection method according to claim 1, wherein said electrode is a conductive elastic sac having a means for introducing a fluid. 4. The bonding inspection method according to claim 1, wherein the electrode is a conductive wire brush attached to an elastic sac having a means for introducing a fluid into the electrode. 5. The bonding inspection method according to claim 1, wherein the conductive wire brush is a carbon brush. 6. A wire is suspended between the electrode mounting portion and the base portion in an elastic bag having an electrode mounting portion at a front end and a gas inlet base portion at a rear end, and a conductive wire brush is provided on the electrode mounting portion. A bonding test electrode comprising a base and a vent tube attached to the base.