JPS6285835A - Breakage detecting method for anticorrosive layer or parallel wire cable for mooring ocean floating structure - Google Patents

Abstract

PURPOSE:To detect the size, position, etc., of a breakage in an anticorrosive layer by measuring variation in the resistance value between a cable element wire group and a resistance detection layer. CONSTITUTION:An upper socket 5 is supported and fixed on a socket support base 6 provided to an ocean structure and a lower socket 5 is supported and fixed on a socket support base 6' installed on the sea bottom to moor the ocean floating structure. If anticorrosive layers 2 and 4 are broken for some reason at some point and sea water enters the cable element wire groups 1 to damage the group 1, the resistance value between the cable element wire group 1 and resistance detection layer 3 varies. For the purpose, the resistance value of a resistance measurement part 10 is measured to detect the abnormality of the cable element wire group 1. Consequently, the breakage state of the anticorrosive layers 2 and 4 is detected accurately to secure the safety of the ocean floating structure.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a method for detecting damage to a corrosion protection layer of a parallel cable for mooring a marine floating structure.

(Prior Art) Mooring lines 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 have high breaking strength, fatigue strength, and large modulus of longitudinal elasticity, so they have the best performance as tensile structural members. Therefore, it is possible to use this parallel cable as a mooring cable for offshore structures.

In this case, in order to maintain the above-mentioned excellent performance for a long period of time, it is necessary to cover the outer layer of the parallel cable with plastic or the like to prevent seawater from coming into contact with the parallel cable. Therefore, it is essential to use pre-corrosion-proof parallel cables.

By the way, when using this pre-corrosion-protected parallel cable as a mooring cable, it is necessary to check whether its performance is maintained over a long period of time, and the key point to check is whether or not the corrosion-protection layer is damaged. . The reason for this is that if the anti-corrosion layer is damaged, seawater may enter through the damaged portion and come into contact with the parallel cable, resulting in corrosion and an accident that may lead to wire breakage.

Therefore, it is necessary to monitor the presence or absence of damage to the corrosion protection layer over the entire life of the cable, and once damage is detected, it is necessary to pull the cable onto the platform and repair the damaged part or replace the entire cable.

In this case, what is important as a method for detecting damage to the anticorrosion layer is that it can detect not only the presence or absence of damage, but also its size and location. This is because by knowing the size of the damage, it is possible to determine the urgency of repairing or replacing the cable, and by knowing the location of the damage, it is possible to determine the length of the cable required for repair. In particular, if the damaged part is minute, it is difficult to visually detect the damaged part when pulling up the cable, and considering the harsh environmental conditions on the platform, the size and location of the damaged part must be determined from the viewpoint of workability. It is required to know this as an inspection method.

As a corrosion protection layer damage detection method, for example, U.S. Patent Nos. 4 and 2
As shown in the specification of No. 85,615, damage to the corrosion protection layer is detected by filling the inside of the corrosion protection layer with an inert gas and pressurizing it, and monitoring the pressure drop of the inert gas. However, this method requires a complicated method of constantly pressurizing inert gas for inspection, and it is also difficult to treat the blockage at the upper end, and the damage to the anticorrosion layer may be large. It is difficult to know the location.

Furthermore, in Japanese Patent Application Laid-open No. 59-176180, damage to the anti-corrosion layer is detected by measuring the electrical resistance between a conductive protective plate provided within the anti-corrosion layer and a group of wires arranged at the center of the cable. A detection method has been proposed, and although it is possible to detect the presence or absence of damage and its size (specifically, the cross-sectional area of the seawater intrusion crack), it is not possible to detect the location of the damage. Furthermore, in Japanese Patent Application Laid-Open No. 59-176181,
A pair of resistance sensing layers are provided concentrically within the anticorrosion layer, and the resistance sensing layer is divided into a plurality of units in the longitudinal direction and/or radial direction of the cable, and the electrical resistance between the resistance sensing layers of each unit is measured. proposed a method for detecting the location of damage to a corrosion protection layer. However, in order to improve the accuracy of detecting the damage location, the number of divisions of the detection layer must be increased in proportion to the accuracy, which poses many problems in terms of cable production technology and cost. For this reason, there has been a desire for a method for detecting damage that is inexpensive, technically simple, and highly accurate.

(Problems to be Solved by the Invention) The present invention has been made based on such conventional demands, and solves the problem of seawater intrusion into the parallel cable portion due to damage to the anti-corrosion layer as described above. The purpose of the present invention is to provide a method for detecting damage to the anti-corrosion layer of a parallel cable for mooring a floating structure in the ocean, which enables the maintenance and replacement of mooring cables to be performed quickly and efficiently by detecting the size and location of damage. shall be.

(Means for Solving the Problems) The present invention provides a marine floating cable in which a group of cable wires is arranged at the center, an anti-corrosion layer is surrounded therearound, and an electrically conductive resistance sensing layer is provided within the anti-corrosion layer. In the cable for mooring a structure, an electrical resistance measuring device is connected between the cable wire group and the upper end of the resistance detection layer, and between the cable wire group and the lower end of the resistance detection layer, and each electrical resistance is measured. This method is characterized by detecting the location and size of damage to the anti-corrosion layer by measuring the values.

The present invention will be explained in detail below with reference to the drawings.

Figures 1 and 2 show a longitudinal section and a cross section of a cable to which the present invention is applied, in which a group of parallel cable wires 1 is arranged in the innermost layer, and around it a corrosion protection layer 2 made of plastic such as polyethylene. , a conductive resistance sensing layer made of a button or aluminum, etc.3. A corrosion protection layer 4 having the same quality as the corrosion protection layer 2 is arranged concentrically. 5, 5' are the upper socket and lower socket 1 connected to the upper and lower ends of the cable.
. . . , whereby the cable is supported and fixed to the upper socket support 6 and the lower socket support 6'.

The cable wire group 1 is cast with a bonding alloy in a branched state within the sockets 5 and 51 in order to equalize the tension applied to each wire.

Further, although the surfaces of the wires are usually plated, since no insulating coating is particularly applied, the cable wire group 1 is all electrically conductive and short-circuited.

On the other hand, the resistance detection layer 3 is made by wrapping a metal tape whose surface is coated with a hot-melt adhesive around the anti-corrosion layer 2 like a bandage. is electrically isolated. Further, 7 and 7' are lead wires for resistance measurement drawn out from the upper and lower ends of the resistance detection layer 3, respectively, 8 is a lead wire for resistance measurement drawn out from the cable wire group 1, and 9 is a changeover switch.

10 is an electrical resistance measuring section, and 11 is a calculation display section.

To use the above-mentioned cable, the upper socket 5 is supported and fixed to a socket support 6 installed on the offshore structure, and the lower socket 5 is supported and fixed to a socket support 6' installed on the seabed. The object is to be moored, but the anti-corrosion layers 2 and 4 are damaged for some reason, and seawater intrudes into the cable group 1.
If damage occurs to the cable wire group 1, the resistance value between the cable wire group l and the resistance detection layer 3 changes, so that an abnormality in the cable wire group can be detected.

First, when there is no damage to the cable, the electrical resistance R between the cable wire group l and the resistance sensing layer 3 is approximately expressed by the following equation.

Ro = po X (d/A) (1) However,
R0 is the specific resistance of the anti-corrosion layer 2 between the cable wire group 1 and the resistance sensing layer 3, and d and A are the equivalent spacing and cross-sectional area of the electrical resistance layer, respectively.

However, as shown in Fig. 3, for some reason a crack 12 occurs at a distance @ The resistance is as shown in the equivalent circuit of FIG.

In FIG. 4, R1 represents the electrical resistance of the resistance sensing layer 3 from the upper end of the cable to the crack 12, R2 represents the electrical resistance of the resistance sensing layer 3 from the lower end of the cable to the crack I2, and RW represents the electrical resistance from the upper socket to the crack 12. It shows the electrical resistance of cable wire group 1.

ΔR is the electrical resistance of the crack I2 and is expressed by the following formula.

ΔR=ρX(d/S) (2) However, ρ is the resistivity of seawater, and S is the average cross-sectional area of the cracks. In addition, in FIG. 4, strictly speaking, the electrical resistance Ro of the anticorrosive layer 2 is applied to the electrical resistance measuring section in parallel (not shown), but R1,...
Since it is very large compared to R2 and ΔR2Rw, it can be ignored.

Therefore, when the changeover switch 9 is connected to the upper end side of the resistance sensing layer 3 (the state shown in the figure), the electrical resistance measuring section 10
The resistance R measured by is expressed as the following formula (Rw is R++
(omitted as it is smaller than ΔR).

R=R1+ΔR (3) Furthermore, the measured resistance R' when the changeover switch is connected to the lower end side of the resistance sensing layer 3 is expressed by the following equation.

R' = R2 + ΔR (4) Next, by adding the measured values R and R' of the above two states using the calculation display unit 10, the following equation is obtained.

RA = R+ R' = R1, + R2+ 2Δ
From equations R(5)(2) and (5), the cross-sectional area S of the seawater intrusion crack can be calculated using the following equation.

S=2ρd/ (Ra (R1+R2)) (
6) In the above equation, R1+R2 is the electrical resistance of the resistance detection layer 3 over the entire length of the cable, and can be measured in advance, so the situation of seawater intrusion and the damage of the corrosion protection layer can be quantitatively detected by equation (6). can do.

Further, the above-mentioned measured value R is displayed by the calculation display unit 10.

By subtracting R', the following equation is obtained.

RB=RR'=RI R2 (7) On the other hand, the seawater intrusion potential [X is expressed by the following formula, where r is the resistance of the resistance detection layer per unit length of the cable.

X=Rt/r (8) Therefore, from equations (7) and (8), X= (Ra +R1+R2) / 2 r (
9) The above formula is found, and as mentioned above, R1+R2 is known, and r is the total length of the cable, then r = (R1
+R2)'/L.

The seawater intrusion position X can be detected by equation (9).

(Example) Next, examples of the present invention will be shown.

In the structure shown in Figure 1, the diameter of the cable wire group is 160 mm.
■φ, the diameter of the protective layer is 180+++o+φ, the total length of the cable is 500 m, the anti-corrosion layer is made of high-density polyethylene, and the resistance detection layer is coated with a hot-melt adhesive and has a thickness of 50 μm.

Using lead laminate tape with a width of 60+w+m, anti-corrosion layer 2
Wrapped half-wrap around the area like a bandage. The electrical resistance over the entire length of this resistance sensing layer is approximately 658Ω, and the resistance per meter of cable is 1.32Ω.

The interlayer resistance of the above cable before use was 1000MΩ or more, but the cross-sectional area of 100m from the top of the cable was
When seawater enters the surface of the cable wire group, a crack with a diameter equivalent to 1.5 mm is generated, and the measured value of the interlayer electrical resistance is approximately 2480 Ω between the upper end of the resistance sensing layer and the cable wire group, and 2480 Ω at the lower end of the resistance sensing layer. The interlayer resistance significantly decreased to approximately 2870 Ω between the wires and the cable wire group, and the intrusion of seawater was significantly detected.Furthermore, the calculation display section uses these measured values to determine the above (6).
Calculate equation (9) and calculate the size of the crack as S = 0
．． 98mm”.

X = 101.5m was displayed as the damage location.

From this result, by using the corrosion protection layer damage detection method of the present invention, if damage to the corrosion protection layer is detected during use, the location and degree of damage can be quickly and accurately determined. Measures such as repair and replacement can be taken to prevent accidents.

Furthermore, it goes without saying that the method of the present invention can be used not only in seawater but also on land for inspections during manufacturing of mooring ropes, intermediate inspections after use, and the like.

(Effects of the Invention) As explained above, the present invention can accurately detect the damage state of the corrosion protection layer in a corrosion protection parallel cable whose usability is determined by the soundness of the corrosion protection layer. The contribution to ensuring safety is significant.

[Brief explanation of drawings]

Fig. 1 is a longitudinal cross-sectional view of a cable for mooring a marine floating structure embodying the present invention, Fig. 2 is a cross-sectional view of the same, Fig. 3 is a longitudinal cross-sectional view showing a state in which the anti-corrosion layer is damaged, and Fig. 4 is a longitudinal cross-sectional view of a cable for mooring a marine floating structure according to the present invention. FIG. 3 is an electrical circuit diagram showing an equivalent circuit of the measurement system when damaged. l: Cable wire group 2, 4: Corrosion protection layer 3: Resistance detection layer 5.5': Upper and lower sockets 6.6': Upper and lower socket support bases 7.7': Resistance detection layer pulled out from the upper and lower ends Measurement lead wire 8: Measurement lead wire drawn out from the cable wire 9: Changeover switch 10: Electrical resistance measurement section 11: Calculation display section, 12: Crack patent applicant Nippon Steel Corporation 2 Company 1 Te. Agent: patent attorney Nobuoki Sugi. Frost 1■ 13 circles

Claims (1)

[Claims] In a cable for mooring a floating structure at sea, which has a group of cable wires arranged in the center, an anti-corrosion layer surrounding it, and an electrically conductive resistance detection layer within the anti-corrosion layer, the group of cable wires and the resistance An electrical resistance measuring device is connected between the upper end of the detection layer and between the cable group and the lower end of the resistance detection layer, and by measuring the respective electrical resistance values, it is possible to determine the location of damage to the corrosion protection layer and the location of the damage. A method for detecting damage to a corrosion protection layer of a parallel cable for mooring a floating structure in the ocean, characterized by detecting the size.