JPH0259950B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for non-destructively detecting a breakage condition of a parallel cable used when mooring a marine floating structure.

Mooring cables for offshore floating structures used for the development of offshore oil fields are required to have long-term durability of 20 to 30 years.

On the other hand, parallel wire cables used in suspension bridges and the like have high breaking strength, fatigue strength, and a large longitudinal coefficient, so they have the best performance as tensile structural members. Therefore, it is conceivable to use parallel wire cables as mooring lines for offshore floating structures.

However, during a long period of use, the anti-corrosion layer, such as plastic, coated on the outer layer of the parallel cable to prevent seawater from coming into contact with the parallel cable, breaks and seawater enters the parallel cable. There is a possibility that the cable will corrode and eventually break, or that excessive tension may be applied to the cable due to typhoons and the like, causing part of the cable to break.

In order to ensure that offshore floating structures can operate safely for a long period of time, the parallel cables are non-destructively inspected during the operation period to detect any breakage of the cable wires, and if necessary, It is necessary to take measures such as repair or replacement.

A method for detecting fractures is AE (Acoustic
There are methods such as the method of injecting sound waves into the material and determining the presence or absence of cracks in the material from the reflection or transmission of the sound waves. However, the AE method requires sensors to be placed in direct contact with the material because the sound generated is extremely weak, and for cables that are several hundred meters long, sensors must be installed at tens to hundreds of locations. Is required. Furthermore, even the latter method has not been put to practical use because of the problem of adhering the acoustic vibrator to the end face of each cable strand and the problem of acoustic insulation between each cable strand.

Furthermore, there is a method of magnetizing the material from the outside and detecting the leakage magnetic flux generated at the crack, but in a parallel cable made of several hundred strands, it is difficult to detect a break in the center, and it is difficult to detect the breakage in the center. However, it is structurally difficult to apply this method to parallel cables used for mooring floating structures in the ocean. It is also possible to know whether there is a break from the electrical resistance of each cable wire (at the time of break, the resistance is ∞), but in this case, it is necessary that each cable wire is electrically insulated. . However, in parallel wire cables, in order to equalize the tension applied to each strand, each strand is cast with a joining alloy in a branched state at both end sockets, so some of the strands are Even if it breaks, the change in resistance is extremely small.

For example, a cable with a diameter of 7 mm and a length of 500 m,
The electrical resistance between the sockets at both ends of a parallel cable consisting of 500 cables is approximately 3 when there is no breakage.
(mΩ), and if 10 out of 500 break, it is 3.06
(mΩ). Therefore, extremely high-precision measurements are required, and changes in the resistance of the lead wire from the bottom socket on the seabed to the measuring instrument, resistance changes due to changes in seawater temperature, and cable tension caused by wind and waves. Resistance changes due to changes become a problem.

The present invention solves these problems and provides a method that non-destructively detects the breakage of a parallel cable in use based on resistance changes and allows repair or replacement as necessary.

That is, the present invention provides a group of cable wires that are insulated from each other except for the conductive socket portions at both ends, and a plurality of measurement cable wires that are insulated from other wires except for the lower end socket portions. a constant current generation source between the upper end socket and the end of the measuring cable bare wire, and a constant current generating source between the upper end socket and the end of the measuring cable bare wire different from the measuring cable bare wire. The electrical resistance of the cable wire group is measured by connecting a voltage measuring device to each of the two cable wires, and a constant current source and a voltage measuring device are respectively connected between the two measurement cable wires. Measures the electrical resistance of the measurement cable wire, and uses the signal to correct changes in the electrical resistance of the cable wire group due to temperature and strain, making it possible to detect cable wire breakage non-destructively and with high detection accuracy. The present invention relates to a method for detecting breakage of parallel cables for mooring floating structures in the ocean, characterized by the following.

The details of the present invention will be explained below with reference to the drawings.

Fig. 1 shows a cross-sectional plan view of a parallel cable used in the present invention, in which 1 is a group of cable strands arranged in the center, 2 is a cable strand for measurement, and each cable strand 1 has sockets at both ends. They are insulated from each other by being covered with plastic or the like. Further, numeral 3 is an anti-corrosion layer in which the outer layer of the parallel cable is coated with plastic or the like to prevent the cable strands from coming into contact with seawater.

Fig. 2 is a longitudinal cross-sectional side view of a parallel cable, in which 1 to 3 indicate the same parts as 1 to 3 in Fig. 1, 4,
Reference numeral 4' denotes an upper end socket and a lower end socket connected to the upper and lower ends of the cable, whereby the cable is supported and fixed to the upper end socket support 5 and the lower end socket support 5'.

In order to equalize the tension applied to each wire, the cable wire group 1 is cast with a bonding alloy in a branched state within the sockets 4 and 4'. Each strand is in a conductive short-circuit state only at the socket portions at both ends. Furthermore, the measurement cable strand 2 is cast together with the cable strand group 1 in the lower end socket 4' with a bonding alloy, but in the upper socket 4, the cable strand 2 is molded with other strands. The measurement cable strand 2 is led to the outer surface of the socket through the hole 6 in an insulated state, so that the measurement cable strand 2 is short-circuited and electrically connected to other strands only in the lower socket.

The constant current generation source 7 generates a cable wire group 1 and a measurement cable wire group 2 depending on the state of the interlocking switch 10.
or between the measurement cable bare wire 2
and a measurement cable wire 2' different from the cable wire 2, and a voltage measuring device 8
Depending on the state of the interlocking switch 10', the connection between the measurement cable strand 2' and the cable strand group 1, or between the measurement cable strand 2' and the measurement cable strand 2' is separated. is connected to the end of the measurement cable strand 2. Further, the signal analysis section 9 receives the signals from the constant current source 7 and the voltage measuring device 8, and determines the electric resistance R ₁ between the lower end sockets of the cable wire group 1 and the measurement cable wires 2 and 2'. The electrical resistance R ₂ is calculated, and the change in the electrical resistance R ₁ due to temperature and strain is corrected based on the change in the electrical resistance R ₂ , and the disconnection status of the cable wire group 1 is detected.

FIG. 3 shows a constant current source 7 and a voltage measuring device 8.
This is an equivalent circuit showing the connection status between the cable wires and each cable wire, and in FIG. This is a case where one end of 7 is connected to the measurement cable wire 2, and one end of the voltage measuring device 8 is connected to the measurement cable wire 2'.

Figure 3a shows the case where the cable wire group 1 is composed of N cable wires, and r indicates the electrical resistance of one wire, and therefore the electrical resistance of the cable wire group 1. R ₁ is expressed by the following formula.

R ₁ = r/N (1) The current I ₁ from the constant current source 7 is
By using one with high input impedance, the current flowing through the circuit of the cable group 1 and the measurement cable element 2, and the current flowing through the circuit of the voltage measuring device 8 and the measurement cable element 2' can be ignored. can. Therefore, the voltage drop V ₁ at both ends of the cable wire group 1 can be measured by the voltage measuring device 8, and the resistance R ₁ of the cable wire group 1 is set as R ₁ =V ₁ /I ₁ for measurement. This can be accurately determined without being affected by the resistance of the cable wires 2, 2'.

The resistance R ₁ of cable wire group 1 changes to R ₁ = r/(N-n) (2) when n wires in the cable wire group break, and from the measurement of R ₁ Can detect the situation.
However, since R ₁ changes depending on the seawater temperature around the cable and fluctuations in the tension applied to the cable, these corrections are necessary to accurately determine the rupture situation.

Therefore _, if the switches 10 _and 10' are changed to the circuit configuration shown in FIG. If the output current of the current source 7 is I ₂ and the indication of the voltage measuring device is V ₂ , it is determined as V ₂ /I ₂ . Since the measurement cable wires 2 and 2' are made of the same material as the cable wire group 1 and are enclosed within the same cable, _R2 may vary from _R1 due to changes in seawater temperature or tension. If the ratio of R ₁ and R ₂ is calculated as K=R ₁ /R ₂ , if the cable is not broken, K will be a constant value K ₀ . Therefore, even if R ₁ changes, if K=K ₀ , then
It can be determined that this is not caused by a cable break.

Here, K ₀ is calculated from (1) and (3) as follows: K ₀ = (r//N)/(2r) = 1/2N (4) Also, when a break occurs in a group of cable wires, K is From equations (2) and (3), the value is K = {r/(N-n)}/(2r) = 1/{2(N-n)} (5), and from these equations, the cable bare wire The group failure rate P=n/N is expressed by the following equation.

P=1−K ₀ /K (6) Therefore, the signal analysis section 9 calculates the current of the constant current source 7.
From I ₁ , I ₂ and voltage measuring instrument indications V ₁ , V ₂ respectively
By determining R ₁ and R ₂ and performing calculations of equations (4) to (6), it is possible to quantitatively detect the state of breakage of the cable strand group.

Next, examples of the present invention will be shown.

In the cable with the structure shown in Figure 1, the diameter of the strands is 7 mmφ, the cable group 1 consists of 500 strands, the total length of the cable is 500 m, and the resistance r of each strand is 1.5Ω. , the resistance R ₂ of the cable wire group 1 before use is 3 mΩ, the combined resistance R ₂ of the measurement cable wires 2 and 2' is 3 Ω, and therefore K ₀ is 1×
It was 10 ^-3 . A crack appeared in a part of the anti-corrosion layer 3 of this cable, and seawater entered, corroding and breaking a part of the cable wire group, resulting in the value of K being approximately
The value of P was ^0.05 . So, when we collected the parallel cable and inspected it, we found that
It was verified that 25 strands, accounting for 5% of the cable strands, were broken at the above-mentioned cracks in the anti-corrosion layer.

Therefore, according to the method of the present invention, even if a part of the cable should break during use, the breakage situation can be detected quantitatively, so that measures such as repair or replacement can be taken quickly and accurately. It is possible to prevent accidents. Furthermore, it goes without saying that the present invention can be applied not only to underwater inspections but also to onshore inspections during manufacturing of mooring ropes, intermediate inspections after use, and the like.

By the way, we will calculate the resistance change due to changes in seawater temperature and tension. First, temperature fluctuation Δt of seawater temperature
is 10℃, the temperature coefficient of resistance α of the cable wire is
is 5×10 ^-3 , so the resistance change rate ΔR/R due to seawater temperature is ΔR/R=α・Δt=0.05. on the other hand,
If the tension fluctuation ΔT is 40Kg/mm ² , the elastic modulus of the cable wire E = 20000Kg/mm ² and the gauge factor β = 3, so the resistance change rate ΔR/R due to tension fluctuation is ΔR/R = β・(Δl/l)=β・
(ΔT/E)=3×(40/20000)=0.006. Therefore, even when compared with the above-mentioned embodiments, it can be seen that accurate fracture detection is impossible unless the resistance changes caused by these are corrected.

Note that the cable wire group 1 is connected to the upper end socket part 4.
The method described above can be achieved by dividing the wires into a plurality of wire bundles, insulating them with a heat-resistant insulating material such as ceramic, and switching and connecting the constant current generating source 7 between each wire bundle and the measurement cable wire 2. In the same manner as above, it is possible to detect the breakage status of each wire bundle.

In addition, it is possible that the measurement cable wire may break, but this can be easily detected by the measurement shown in Figure 3b, and can be easily detected by preparing multiple measurement cable wires. Can be exchanged.

As explained above, since the present invention can accurately detect the situation of parallel cables in which the breakage of each cable strand decisively affects its usability, it will greatly contribute to ensuring the safety of marine floating structures. It is what it is.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional plan view of the parallel wire cable, Fig. 2 is also a vertical cross-sectional side view, Fig. 3 a is an equivalent circuit diagram when measuring the electrical resistance of the parallel wire cable in the present invention, and Fig. 3 b is the same. FIG. 2 is an equivalent circuit diagram when measuring the electric resistance of a measuring cable element wire. 1 is a group of cable wires, 2 and 2' are cable wires for measurement, 3 is an anti-corrosion layer, 4 and 4' are upper and lower end sockets, 5 and 5' are upper and lower end socket supports,
Reference numeral 6 indicates an outlet hole for the measurement cable wire, 7 indicates a constant current source, 8 indicates a voltage measuring device, 9 indicates a signal analysis section, 10,
10' is an interlocking changeover switch.

Claims (1)

[Scope of Claims] 1. Consists of a group of cable wires that are insulated from each other except for the conductive socket portions at both ends, and a plurality of measurement cable wires that are insulated from other wires except for the lower end socket portions. In a parallel cable for mooring a marine floating structure, a constant current generation source is provided at the upper end socket and the end of the measurement cable strand, and the upper end socket and the measurement cable strand are different from the measurement cable strand. A voltage measuring device was connected to each end of the cable to measure the electrical resistance of the cable group, and a constant current source and a voltage measuring device were connected to the ends of the two measurement cables, respectively. Therefore, measure the electrical resistance of the measurement cable wire,
Parallel wires for mooring floating structures in the ocean, thereby correcting changes in electrical resistance due to temperature and strain in the group of cable wires, and making it possible to detect cable breakage from the electrical resistance of the group of cable wires. Cable break detection method. 2 A group of cable wires that are insulated from each other except for the sockets at both ends is divided into multiple wire bundles that are mutually insulated at the upper end socket, and a constant current is generated at the ends of each wire bundle and the measurement cable wire. source,
In addition, a voltage measuring device was connected to the end of each wire bundle and a measurement cable wire different from the measurement cable wire, and the electrical resistance of each wire bundle was measured.
By connecting a constant current source and a voltage measuring device to the ends of the measurement cable strands, the electrical resistance of the measurement cable strands is measured, and the temperature and temperature of the cable strands are thereby measured. 1. A method for detecting breakage of a parallel cable for mooring a floating structure in the ocean, comprising correcting changes in electrical resistance due to strain and detecting the state of breakage of the cable from the electrical resistance of the bundle of cable strands.