JPH0437941B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for detecting coating failure points of underground coated metal pipes having an electrically insulating coating layer.

Conventional technology Conventionally, in order to detect damaged parts of a coated metal pipe, the underground pipe is partially exposed through a plurality of vertical holes, and the electrically insulating coating layer of the coated metal pipe is partially peeled off. In each case, the potential difference between the metal pipe and the ground was measured to detect the corrosion protection effect area, and the area was estimated based on the areas where there was a large difference. Such prior art techniques require a great deal of effort and have poor measurement accuracy.

Problems to be Solved by the Invention An object of the present invention is to provide a method for detecting a damaged part of a coated metal tube with improved workability and measurement accuracy.

Means for Solving the Problems The present invention provides a method for inserting a plurality of pipe wire passing tools made of conductive material into a coated metal pipe having an electrically insulating coating layer buried underground at different positions in the pipe axis direction. death,
While intermittently connecting and cutting off the coated metal pipe and the underground current anode or the other terminal of the DC power supply with one terminal connected to the ground, This is a method for detecting a damaged part of the coating of a coated metal pipe, which is characterized by detecting the voltage between the ground and the ground in the vicinity of the contact position with the coated metal pipe.

Effect According to the present invention, a plurality of in-pipe wiring tools are inserted into the underground coated metal pipe at different positions, and the connection between the underground galvanic anode and the underground coated metal pipe is intermittently established. The voltage between each pipe fitting and the ground in its vicinity is measured, and the location of damage to the sheathing of the coated metal pipe can be detected from the change in the voltage.

Embodiment FIG. 2 is a sectional view of an embodiment of the present invention. A covered metal pipe 52 is buried in the ground 51.
The coated metal tube 52 has an electrically insulating coating layer formed on the outer peripheral surface of the steel tube. In order to protect the steel pipe of the coated metal pipe 52 from corrosion, a galvanic anode 53 made of magnesium or the like is connected to the steel pipe via a switch 65. This causes an anti-corrosion current to flow through the steel pipe,
Corrosion protection of steel pipes is carried out. For example, gas fuel is transported to the coated metal tube 52. Coated metal tube 52
From there, gas fuel is introduced into the house via a supply pipe 54 and a standpipe 55, from a valve 56 to a gas meter 57, as shown in FIG. There are a plurality of supply pipes 54 and standpipes 55 at intervals along the tube axis direction of the coated metal pipe 52, and these are 54a, 54.
b, 54c, 54d, 54e and 55a, 55
b, 55c, 55d, and 55e. Further, these and the coated metal tube 52 may be electrically insulated.

In order to detect a damaged part of the coated metal tube 52, a U-shaped tube 58 is connected to the upper part of the standpipe 55 and sealed with water 59. This prevents the gas fuel from being spouted to the outside via the valve 56 which is in the open state. The tube wire passing tool 60 is inserted into the coated metal tube 52 from the U-shaped tube 58 through the open valve 56, the standpipe 55, and the supply tube 54. This intraductal wire passing tool 60 is made of a flexible wire, and at least its tip 70 is exposed. This in-pipe wire passing tool 60 contacts the inner circumferential surface of the steel pipe of the coated metal pipe 52 to establish electrical continuity. In-pipe wire passing devices 60a to 60e, which are similarly inserted through each of the standpipes 55a to 55e, are made of a conductive material, and their external ends are connected to one terminal of voltmeters 61a to 61e, respectively. Voltmeter 61a-61
The other terminal e is grounded in the vicinity of the position directly above the position where the tip of each of the intra-tube wire passing tools 60a to 60e comes into contact with the coated metal tube 52 and is electrically conductive.

The electrically insulating coating layer of the coated metal tube 52 is indicated by reference numeral 6.
Assume that the steel pipe is damaged at the position shown in 6 and is in contact with the ground. This damaged part 66
In order to detect
The reading of 61e is detected. Voltmeters 61a to 61e
The voltage values detected by are shown individually in FIGS. 3a to 3e. During period W1, switch 65 is turned on, and during period W2, switch 65 is turned off. The voltage measurements read by voltmeters 61a-61e when switch 65 is conducting are the values V shown in FIG.
2a to V2e. The voltage values V1a to V1e measured by the voltmeters 61a to 61e when the switch 65 is cut off are the voltage values V1a to V1e measured by the voltmeters 61a to 61e when the
This is the natural potential of the steel pipe covered with the second electrically insulating coating layer. The corrosion protection potentials V0a to V0e are expressed by the first equation. In addition, V0a to V0e, V1
A to V1e, V2a to V2e are collectively referred to as V
0, V1, and V2, respectively.

V0=V2-V1...(1) When the damaged part 66 does not exist, the voltage measurement values of all the voltmeters 61a to 61e are the same value.

When there is a damaged part 66, the voltmeter 61
The measured voltage values of a to 61e are the value V1 when the switch 65 is cut off, and the value V1 becomes smaller as the distance from the damage point 66 increases, and the value V1 increases as the voltage value approaches the damage point 66. Also, corrosion protection potential V0
increases as it moves away from the damaged location 66, and decreases as it approaches the damaged location 66. That is, V1a<V1b<V1c...(2) V1e<V1d<V1c...(3) V0a>V0b>V0c...(4) V0e>V0d>V0c...(5) In this way, the voltmeters 61a to 61e measure By comparing and looking at the voltage values, damage location 6 can be determined.
You can know 6.

FIG. 4 shows the value of the corrosion protection potential V0 along the tube axis direction of the coated metal tube 52. When there is a damaged part 66, the corrosion protection potential V0 has the lowest value at the damaged part 66. When the broken point 66 does not exist, the voltage value V2 when the switch 65 is conductive is constant regardless of the position of the coated metal tube 52 in the tube axis direction.

FIG. 5 is a side view of the pipe wire passing device 60 used in the present invention. The main wire 1 has relatively high bending rigidity and is made of piano wire, etc., and is constructed by winding the piano wire in a spiral shape.
It may have a length of m or more. The end of the auxiliary wire 2 is fixed to the end of the main wire 1. A guiding member 3 is fixed to the other end of the auxiliary wire 2 . The auxiliary wire rod 2 can be bent by the weight of the guide member 3 and has a bending rigidity smaller than that of the main wire rod 1. The auxiliary material 2 is also made of piano wire or the like and is wound spirally. The length of this auxiliary wire 2 may be, for example, about 10 cm.

FIG. 6 is a perspective view of the vicinity of the guide member 3. The guiding member 3 has a free end (left side in FIG. 6), that is, a square surface 4 when viewed from the front, and is partially formed into a prismatic shape. The proximal end of the guide member 3 is tapered and is fixed to the auxiliary member 2 as described above. This guide member 3 is made of a material such as steel. By applying a rotational force to the main wire 1, torsional stress is accumulated in the pipe, and when the load falls below a certain level, it can rotate and vibrate due to reaction, and can withstand reuse.

Referring to FIG. 7, in the upper part of the underground pipe 5,
Chi 6 is connected. An above-ground standpipe 8 is connected to this chi 6 from a service pipe 7, and gas is supplied to a house 9. A pipe joint 10, an elbow 11, a valve 12, and the like are interposed between the lead-in pipe 7 and the standpipe 8. In-pipe wire passing tool 6 according to the present invention
0, the guiding member 3 can enter the pipe 5 from these standpipes 8 via the lead-in pipe 7.

FIG. 8 shows the state in which the pipe wire passing tool enters the chi 6 from the lead-in pipe 7. The auxiliary wire 2 is deflected by the gravity of the guide member 3, so that the guide member 3 is easily allowed to advance from the chi 6 into the tube 5. When the auxiliary wire 2 hangs down due to the gravity of the guide member 3, by pushing the main wire 1 while rotating the main wire 1 around its axis, the guide member 3 rotates and vibrates. can enter into the tube 5.

Further, as shown in FIG. 9, the end of the tube 14 is closed with a plug 15.
Even when the branched pipe 16 is connected to the vicinity of the pipe 5, the intra-pipe wire passing device 60 according to the present invention can be introduced from the pipe 14 to the pipe 16 as shown by the arrow 17, and vice versa. From tube 16, tube 14 can be entered as indicated by arrow 18.

The free end surface 4 of the guiding member 3 is square, and therefore, the corner portion 4a of the free end surface 4 is likely to get caught in a step at an elbow, a tee, a pipe joint, etc. When this corner portion 4a hits a step inside the pipe, it jumps due to the bending rigidity of the auxiliary wire 2 and the main wire 1. This allows the guide member 3 to enter the pipe while overcoming the step.

According to experiments conducted by the inventor of the present invention, when wires were threaded through various gas pipes using the pipe wire threading device 60 of the illustrated embodiment, wire threading could be carried out with a probability of approximately 92 to 93%, and the wire threading was successful. It was confirmed that the rate was extremely high, and the time required to run the line was relatively short.

The in-pipe wiring device 60 according to the present invention is capable of passing not only underground gas pipes, but also pipes disposed inside the walls of other buildings, other sealed parts, or exposed pipes. It's okay.

As another embodiment of the present invention, the main wire 1 may be constituted by a coil spring having an inner and outer double structure wound in opposite directions. Further, the pipe wire passing tool 60 may have another configuration, and the tip 70 of the guide member 3 or the like may electrically contact the inner circumferential surface of the steel pipe of the coated metal pipe. This means that the pipe wire passing tools 60a to 60e
The same is true.

Effects of the Invention According to the present invention, voltages at different positions along the axial direction of the coated metal tube are measured while intermittently interrupting conduction between the coated metal tube and the galvanic anode or the DC power supply. Therefore, it is possible to detect damaged parts of the coated metal pipe.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view for explaining the method of inserting a wire passing through a U-shaped tube according to the present invention, FIG. 2 is a cross-sectional view of an embodiment of the present invention, and FIG. FIG. 4 is a diagram showing the measured voltage values of the voltmeters 61a to 61e along the tube axis direction of the coated metal tube 52, and FIG. FIG. 6 is a front view of the pipe wire threading tool 20 used, FIG. 6 is a perspective view of the vicinity of the guide member 3 of the wire threading tool used in the present invention, FIG. 7 is a piping diagram for explaining the insertion work of the pipe wire threading tool, and FIG. FIG. 8 is a piping diagram for explaining the wire running operation near the tee 6, and FIG. 9 is a sectional view for explaining the wire running operation to the pipes 14 and 16. 51...Ground, 52...Coated metal pipe, 53...
Galvanic anode, 60, 60a to 60e... In-pipe wiring fitting, 61, 61a to 61e... Voltmeter, 66...
Damaged area.

Claims (1)

[Claims] 1. A plurality of in-pipe wire fittings made of conductive material are inserted into a covered metal pipe having an electrically insulating coating layer buried underground at different positions in the tube axis direction, and the covered metal pipe and the underground flow are connected. While intermittently conducting and cutting off the electrode anode or one terminal of the DC power supply connected to the ground, the conductor is connected to each pipe fitting and near the contact position between the pipe fitting and the coated metal pipe. A method for detecting a damaged location of a coated metal pipe, the method comprising detecting each voltage between the ground and the ground.