EP3923303A1

EP3923303A1 - Submarine cable and preparation method therefor

Info

Publication number: EP3923303A1
Application number: EP20919372.1A
Authority: EP
Inventors: Hongliang Zhang; Yan Yan; Ming Hu; Zhiyu Yan; Hongmiao YU; Jianlin XUE
Original assignee: Zhongtian Technology Submarine Cable Co Ltd
Current assignee: Zhongtian Technology Submarine Cable Co Ltd
Priority date: 2020-06-28
Filing date: 2020-08-11
Publication date: 2021-12-15
Also published as: CN111613376B; CN111613376A; EP3923303A4; WO2021208304A1

Abstract

A submarine cable and a manufacturing method of the submarine cable. The submarine cable includes a number of structural units and the protection unit. The protection unit includes an outer protective layer and an armor layer positioned at the outer periphery. The armor layer includes an inner armor layer and an outer armor layer. An angle between a monofilament of inner armor layer and central axis of cable is larger than an angle between a monofilament of outer armor layer and the central axis, or such angle between the monofilament of inner armor layer and center axis is opposite to the angle between the monofilament of outer armor layer and center axis. The protection for the submarine cable is thereby improved.

Description

The disclosure relates to a technical field of undersea power and signal cable, in particular to a submarine cable and a manufacturing method thereof.

BACKGROUND

This section is intended to provide background or context for embodiments of the present disclosure stated in the claims. The description here is not to be recognized as prior art just because it is included in this section.
High-voltage AC and DC submarine cables are configured for marine power transmission. They have characteristics different from those of land power cables. The delivery length of submarine cables can reach hundreds of kilometers. Transportation and construction of submarine cables after production need to be handled by special construction vessels. When laying a submarine cable underwater, the gravity of the submarine cable increases with the depth of the water, which will cause damage if it exceeds the mechanical bearing capacity of the internal components of the submarine cable. Therefore, the design of submarine cables requires high axial mechanical tensile strength. At present, multiple metal wires with high tensile strength are generally used as the outer layer of the submarine cable sheath to meet the axial tension requirements.
The use of high tensile strength metal wires such as steel wire, copper wire, or aluminum alloy to form the armored layer can effectively meet the axial tension requirements of the submarine cable during construction, but the method of twisting multiple metal wires does not form a seal to protect the submarine cable against its environment. Gaps between the metal wires become weak points in the long-term operation of the submarine cable. Rocks on the seabed or other sharp objects may cause damage to the internal structure of the submarine cable through any gap.

SUMMARY

In view of the above, it is necessary to provide a submarine cable to prevent damage caused by sharp objects in the sea.
The technical solution in this disclosure is as follows:
A submarine cable, including a structural unit and a protection unit, the protection unit is positioned at an outer periphery of the structural unit. The protection unit comprises an outer protective layer and an armor layer, the armor layer is positioned between the outer protective layer and the structural layer, the armor layer comprises an inner armor layer and an outer armor layer. The angle between a spiraled or twisted monofilament of the inner armor layer and the axis of the submarine cable is larger than an angle between a spiraled or twisted monofilament of the outer armor layer and the axis of the submarine cable; or the angle between the twisted monofilament of the inner armor layer and the axis of the submarine cable is opposite to the angle between the twisted monofilament of the outer armor layer and the axis of the submarine cable. The angles referred to are those existing between a notional central axis of the cable and a monofilament crossing the central axis on a tangential plane of the inner armor layer or of the outer armor layer of the cable.
In some embodiments of the present disclosure, the monofilament of the outer armor layer is a metal wire with a circular or trapezoidal cross-section, the monofilament of the inner armor layer is a metal wire with a circular cross-section, or, the monofilament of the inner armor layer is a metal tape or metal wire with a trapezoidal cross-section. If the cross-section of the monofilament is a trapezoid, the ratio of the maximum cross-sectional width to the thickness of the monofilament is 2:1.
In some embodiments of the present disclosure, the inner armor layer and the outer armor layer are formed by twisting metal wires with circular cross-section or trapezoidal cross-section, the angle between the monofilament when twisted or spiraled and an axis of the submarine cable is 5.5-6.5 degrees.
In some embodiments of the present disclosure, when a direction of twist of the monofilament of the inner armor layer is the same as a direction of twist of the monofilament of the outer armor layer, the angle between the monofilament of the inner armor layer and the axis of the submarine cable is 8.8-10.3 degrees.
In some embodiments of the present disclosure, D is an inner diameter of the structural unit, d1 is a maximum width of the monofilament of the inner armor layer, and h1 is a thickness of the monofilament of the inner armor layer. The quantity of monofilaments of the inner armor layer is: $n_{1} = \frac{π \cdot (D + h_{1})}{2 d_{1}} - 1;$
In the following equation for the quantity of monofilaments of the outer armor layer, d2 is a maximum width of the monofilament of the outer armor layer, and h2 is a thickness of the monofilament of the outer armor layer: $n_{2} = \frac{π \cdot (D + 2 h_{1} + h_{2})}{d_{2}} - 1 .$
In some embodiments of the present disclosure, the monofilaments of the inner armor layer are metal tapes, an overlapped part of two adjacent layers of the metal tape is 15%-20% of the width of the metal tape.
In some embodiments of the present disclosure, there are three structural units, positioned in a circular array in the protection unit.
The present disclosure further discloses a manufacturing method of the submarine cable, the manufacturing method includes:

preparing a structural unit;
twisting an armor layer, a device to twist the outer armor layer and a device to twist the inner armor layer are positioned in a row along a advancing direction of the structural unit, and the inner armor layer and the outer armor layer are twisted by the respective twisting devices;
coating an outer protective layer after twisting the armor layer.

In some embodiments of the present disclosure, during twisting process, two synchronous twisting devices are positioned at an outside of the structural unit, and a rotation speed of the twisting devices for twisting the inner armor layer is twice a rotation speed of the twisting device for twisting the outer armor layer. The rotation speed of the twisting devices for twisting the inner armor layer can also be the same as the rotation speed of the twisting device for twisting the outer armor layer.
In some embodiments of the present disclosure, during twisting process, the inner armor layer is wrapped on an outer periphery of the structural unit, and then the protective unit carrying the inner armor layer is positioned in the twisting device of the outer armor layer.
The above-mentioned submarine cable includes a double-layer armor layer, and angles between the monofilaments of the two armor layers and the center axis of the submarine cable are controlled, so that gaps between the monofilaments of the two armor layers have different angles or axial directions. Penetration by sharp objects is prevented as gaps of the outer armor layer and gaps of the inner armor layer are not aligned, the protective monofilaments effectively function as a solid barrier and give greater protection for the submarine cable.

BRIEF DESCRIPTION OF DRAWING

A better understanding will be obtained by reference to the following detailed description and the accompanying drawings.

FIG. 1 is a schematic cross-sectional view of a submarine cable in an embodiment of the present disclosure.
FIG. 2 is a schematic cross-sectional view of a submarine cable in an other embodiment of the present disclosure.
FIG. 3 is a schematic structural view of a submarine cable in an embodiment of the present disclosure.
FIG. 4 is a schematic structural view of a submarine cable in another embodiment of the present disclosure.
Fig. 5 is a schematic cross-sectional view of a monofilament of an armor layer in an embodiment of the present disclosure.
Fig. 6 is a schematic structural view of a submarine cable in another embodiment of the present disclosure.
FIG. 7 is a schematic structural view of the twisting device applied to the submarine cable in an embodiment of the present disclosure.
FIG. 8 is a schematic structural view of the twisting device applied to the submarine cable in another embodiment of the present disclosure.

DESCRIPTION OF MAIN COMPONENTS OR ELEMENTS

Main components and reference numbers thereof: submarine cable 100; structural unit 10; conductor 11; inner semi-conductive shielding layer 12; insulation layer 13; outer semi-conductive shielding layer 14; semi-conductive waterproof layer15; metal shielding layer 16; plastic sheath 17; protection unit 30; strapping tape 31; optical unit 311; filler 313; armor layer 32; first armor layer; second armor layer 323; monofilament 3211; outer protective layer 33; twisted device 200.

DETAILED DESCRIPTION

Description of embodiments will be given with reference to the accompanying drawings. A number of specific details are set forth to enable full understanding. The described embodiments are only some of the possible embodiments and not all of them. All other embodiments obtained by those skilled in the art based on the instant embodiment without creative efforts are within the scope of the instant claims. The drawings are only for the purpose of illustration and description, and are not intended to be limiting. The dimensions shown are merely for the purpose of clarity of description.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one skilled in the art. The terms used herein are only for describing specific embodiments, and are not intended to limit the present disclosure.
The present disclosure provides a submarine cable, including a number of structural units and a protection unit. The protection unit is positioned at an outer periphery of the structural unit. The protection unit includes an outer protective layer and an armor layer positioned at the outer periphery. The armor layer is positioned between the outer protective layer and the structural unit. The armor layer includes an inner armor layer and an outer armor layer. An angle between a twisted monofilament of the inner armor layer and the axis of the submarine cable is larger than an angle between a twisted monofilament of the outer armor layer and the axis of the submarine cable; or the angle between the monofilament of the inner armor layer and the axis of the submarine cable is opposite to the angle between the monofilament of the outer armor layer and the axis of the submarine cable.
The present disclosure also provides a manufacturing method for manufacturing the above-mentioned submarine cable. The manufacturing method including the following steps:

Preparing structural units;

Twisting a armor layer, the armor layer includes an inner armor layer and an outer armor layer, and a twisting device of the outer armor layer and a twisting device of the inner armor layer are positioned in a row along direction of advancement of the structural unit, and the inner armor layer and the outer armor layer are twisted by the twisting devices;
After twisting the armor layer, an outer protective layer is applied as a coating.
The above-mentioned submarine cable includes a double-layer armor layer, and angles between the monofilaments of the two armor layers and the center axis of the submarine cable are controlled, so that gaps between the monofilaments of the two armor layers have different angles or axial directions. Therefore, sharp objects can be prevented from entering gaps between the monofilaments of the outer armor layer and gaps between the monofilaments of the inner armor layer at the same time. The protection for the submarine cable is improved.
The following specific implementations will further illustrate the embodiments of the present application in conjunction with the above-mentioned drawings.
Referring to FIG. 1 and FIG. 2, a submarine cable 100 includes a number of structural units 10 and a protection unit 30. The protection unit 30 is positioned at an outer periphery of the structural units 10. The protection unit 30 is configured to protect the structural unit 10.
Referring to FIG. 1, in an embodiment, one structural unit 10 is positioned in the submarine cable 100. The structural unit 10 includes a conductor 11, an inner semi-conductive shielding layer 12, an insulation layer 13, an outer semi-conductive shielding layer 14, a semi-conductive waterproof layer15, a metal shielding layer 16, and a plastic sheath 17. The conductor 11, the inner semi-conductive shielding layer 12, the insulation layer 13, the outer semi-conductive shielding layer 14, the semi-conductive waterproof layer15, the metal shielding layer 16, and the plastic sheath 17 are positioned in that order from the inside to the outside. The conductor 11 is configured to carry current. In one embodiment, the conductor 11 is a solid conductor 11. In other embodiments, the conductor 11 may also be one of a round single-wire stranded conductor 11, a shaped wire conductor 11, and a split conductor 11. In one embodiment, the inner semi-conductive shielding layer 12 and the outer semi-conductive shielding layer 14 are both formed of extruded semi-conductive materials. The inner semi-conductive shielding layer 12 is configured to eliminate electric field concentration on the surface of the conductor 11 and prevent partial discharge caused by a gap between the insulating layer 13 and the conductor 11. The outer semi-conductive shielding layer 14 is configured to create a uniform electric field and prevent partial discharge caused by a gap between the insulation layer 13 and the metal shielding layer 16. The insulating layer 13 is made of lightweight polyethylene to provide insulation. In one embodiment, the semi-conductive waterproof layer 15 includes an annular corrugated metal sheath and a water blocking material, and the water blocking material is coated onto an outer wall of the annular corrugated metal sheath. The metal shielding layer 16 is configured to improve shielding of the submarine cable 100 against EMI. In one embodiment, the metal shielding layer 16 is formed by wrapping copper tape. The plastic sheath 17 is configured for protecting against compression, waterproofing, and connection and unloading protection. In one embodiment, the plastic sheath 17 is an polyethylene jacket formed by extrusion. In another embodiment, referring to FIG. 2, the quantity of the structural units 10 may also be three, and the three structural units 10 are positioned in a circular array in the protection unit 30. In other embodiments, the quantity of the structural units 10 may be different, and an optical unit 311 can be added in a gap of the protection unit 30 according to functional requirements.
Referring to FIG. 1, when the quantity of the structural units 10 is one, the protection unit 30 includes an armor layer 32 and an outer protective layer 33. The armor layer 32 is provided with two layers, and the two armor layers 32 are positioned in contact with each other. The two armor layers 32 includes a first armor layer 321 positioned on an inner layer and a second armor layer 323 positioned on an outer layer. The outer armor layer 33 is sleeved on an outer circumference of the second armor layer 323. In one embodiment, two layers of the armor layer 32 are sleeved on an outer circumference of the plastic sheath 17 of the structural unit 10, and an inner wall of the first armor layer 321 is positioned in contact with the plastic sheath 17. FIG. 2 shows that when the quantity of the structure units 10 is three, the protection unit 30 further includes a strapping tape 31, and the strapping tape 31 is wrapped around outer peripheries of the three structure units 10. A number of fillers 313 are filled in the strapping tape 31, and the filler 313 are configured to fill gaps between the structural units 10.
Referring to FIG. 3 and FIG. 4, in one embodiment, the second armor layer 323 is formed by twisting monofilaments 3211. An angle between the monofilament 3211 of the second armor layer 323 and center axis of the cable is 5.5-6.5 degrees. Specifically, the angle may be one of 5.5°, 5.6°, 5.7°, 5.8°, 5.9°, 6.0°, 6.1°, 6.2°, 6.3°, 6.4°, and 6.5°. Referring to FIG. 5, in one embodiment, the monofilament 3211 is a metal wire with a circular cross-section, and a diameter of the metal wire is 5.5±0.5mm. Specifically, the diameter of the metal wire may be one of 5.0 mm, 5.1 mm, 5.2 mm, 5.3 mm, 5.4 mm, 5.5 mm, 5.6 mm, 5.7 mm, 5.8 mm, 5.9 mm, and 6.0 mm. In other embodiments, the monofilament 3211 may also be a metal wire with a polygonal cross-section, and the maximum cross-sectional width of the metal wire is 7.0±0.5mm. Specifically, the maximum cross-sectional width of the monofilament 3211 may be one of 6.5 mm, 6.6 mm, 6.7 mm, 6.8 mm, 6.9 mm, 7.0 mm, 7.1 mm, 7.2 mm, 7.3 mm, 7.4 mm, and 7.5 mm. When the monofilament 3211 of the layer 32 is a metal wire with a trapezoidal cross-section, the ratio of the maximum cross-sectional width to the thickness of the monofilament 3211 is 2:1.
In one embodiment, referring to FIG. 3, the angle between monofilament of the first armor layer 321 and center axis of the cable is greater than the angle between the monofilament of the second armor layer 323 and center axis. Preferably, the angle between the monofilament of the first armor layer 321 and center axis of the cable is 8.8°-10.3°. A twisting direction of the monofilament of the first armor layer 321 can be same as a twisting direction of the monofilament of the second armor layer 323. Specifically, the angle between the first armor layer 321 and center axis of the cable may be one of 8.8°, 8.9°, 9.0°, 9.1°, 9.2°, 9.3°, 9.4°, 9.5°, 9.6°, 9.7°, 9.8°, 9.9°, 10.0°, 10.1°, 10.2°, and 10.3°.
When the angle between the first armor layer 321 and center axis of the cable is greater than the angle between the second armor layer 323 and center axis of the cable, the quantity of monofilaments 3211 of the inner armor layer 32 is: $n_{1} = \frac{π \cdot (D + h_{1})}{2 d_{1}} - 1;$
The quantity of monofilaments 3211 of the outer armor layer 32 is: $n_{2} = \frac{π \cdot (D + 2 h_{1} + h_{2})}{d_{2}} - 1$
Wherein, D is the inner diameter of the structural unit 10. The d1 is the maximum width of the monofilament 3211 of the inner armor layer 32, and the h1 is the thickness of the monofilament 3211 of the inner armor layer 32. The d2 is the maximum width of the monofilament 3211 of the outer armor layer 32, and the h2 is the thickness of the monofilament 3211 of the outer armor layer 32.
FIG. 4 shows another embodiment. The sum of the angle between monofilament 3211 of the first armor layer 321 and the axis and the angle between monofilament 3211 of the second armor layer 323 and the axis is equal to 180°, and the cross section of the monofilament 3211 of the first armor layer 321 is either circular or trapezoidal. The quantity of monofilaments 3211 of the inner armor layer 32 is: $n_{1} = \frac{π \cdot (D + h_{1})}{d_{1}} - 1,$
The quantity of monofilaments 3211 of the outer armor layer 32 is: $n_{2} = \frac{π \cdot (D + 2 h_{1} + h_{2})}{d_{2}} - 1 .$
Referring to FIG. 6, in other embodiments, the monofilaments of the second armor layer 323 are metal wires, and the monofilaments of the first armor layer 321 are metal tapes, and the metal tapes are wrapped to form the first armor layer 321. The overlapped part of two adjacent layers of the metal tape is 15%-20% of the width of the metal tape. In one embodiment, the width of the metal tape of the first armor layer 321 is ten times the maximum width of the monofilament 3211 of the second armor layer 323, and the thickness of the metal tape is 1/2 of the maximum width of the monofilament 3211 of the second armor layer 323.
The outer protective layer 33 is configured to protect the submarine cable 100 during transportation and deep water depositing process. In one embodiment, the outer protective layer 33 is wound or directly extruded with materials such as polypropylene, polyethylene, polyvinyl chloride, etc..
The present disclosure further discloses a manufacturing method for preparing the submarine cable 100. Referring to FIG. 7 and FIG. 8, the manufacturing method includes the following steps:
S1: preparing the structural unit 10:
Specifically, the conductor 11 is twisted; the inner semi-conductive shielding layer 12, the insulation layer 13, and the outer semi-conductive shielding layer 14 are twisted around the conductor 11 by order. In one embodiment, the inner semi-conductive shielding layer 12, the insulation layer 13 and the outer semi-conductive shielding layer 14 are co-extruded to form the three layers, then the semi-conductive waterproof layer 15 is extruded at an outside surface of the outer semi-conductive shielding layer 14, a metal shielding layer 16 is wrapped to the semi-conductive waterproof layer 15, and an outer protective layer 33 of the protection unit 30 is extruded as an outer surface layer of the cable.
In other embodiments, after the protection unit 30 is formed, the structural unit 10 is twisted, and gaps between structural unit 10 and the protection unit 30 are filled with fillers 313, and then a strapping tape 31 is wrapped around the outer periphery of the structural unit 10 and the filler 313.
S2: twisting armor layer: two armor layers 32 are selected, and a twisting device 200 of the second armor layer 323 and a twisting device 200 of the first armor layer 321 are positioned in a row along an advancing direction of the structural unit 10, and the first armor layer 321 and the second armor layer 323 are twisted.
In one embodiment, the two armor layers 32 are formed by twisting monofilaments 3211, and the twisting device 200 for twisting the armor layer 32 is a strander. During the twisting process, two synchronous stranders are positioned at the outside of the structural unit 10, and a rotation speed of strander for twisting the first armor layer 321 is twice a rotation speed of strander for twisting the second armor layer 323.
In another embodiment, the rotation speeds of the two stranders are the same.
Specifically, in production process, the quantity of the first armor layer 321 and the second armor layer 323 are calculated according to the calculation formula. During twisting processes, the monofilaments 3211 advances from a monofilament drum placed on the strander along a positioning channel in the strander, and gathers at a twisted opening. At the same time, the strander rotates counterclockwise along the axis in the cable advancing direction, a plurality of monofilaments 3211 are twisted on the cable passing through the twisted opening. In production, the structural unit 10 first enters the strander of the first armor layer 321, the monofilament 3211 of the first armor layer 321 is evenly twisted and covered on the structural unit 10, and the structural unit 10 then enters the strander of the second armor layer 323, the monofilaments 3211 of the second armor layer 323 are evenly twisted and covered on the first armor layer 321. After the structural unit 10 passes through the two stranders, the production of the double-layer armor layer is completed. In another embodiment, referring to FIG. 8, the first armor layer 321 is formed by wrapping a metal tape on the outer periphery of the structural unit 10.
Specifically, during the production process, the structural unit 10 first enters a winding machine for wrapping the metal tape to form the first armor layer 321, and then enters the strander of the second armor layer 323 after the metal tape is wrapped. During the wrapping process, the first armor layer 321 is wrapped around the outer circumference of the structural unit 10, the overlap ratio of the wrapping is controlled to be 15%-20% of the width of the metal tape, and then the protective unit 30 with the first armor layer 321 is positioned in the twisting device of the second armor layer 323.
S3: coating the outer protective layer 33:
Specifically, high-strength fiber ropes are selected to be twisted outside the armor layer to form the outer protective layer 33, or a plastic material may be extruded to from the outer protective layer 33.
The submarine cable 100 in the present disclosure includes a double-layer armor layer 32. Angles between the monofilaments 3211 of the two armor layers 32 and the center axis of the submarine cable are controlled, so that gaps between the monofilaments 3211 of the two armor layers have different angles or axial directions. Penetration by sharp objects is prevented as gaps of the outer armor layer and gaps of the inner armor layer are not aligned, the protective monofilaments effectively function as a solid barrier and give greater protection for the submarine cable. The protection for the submarine cable is improved. When there is no special or additional protection in the complex sea environment, submarine cables of the present disclosure can be meet the operation requirements. The need for secondary landfilling, heavy object protection and robot protection in conventional engineering for complex sea area conditions is also reduced, which significantly saves the cost of submarine cable engineering.
It should be noted that the above embodiments are only used to illustrate specific aspect of the present invention, and are not limitations. Those skilled in the art will appreciate that the instant disclosure can be technically modified and can accept equivalent substitutions without departing from the spirit and scope of the claims.

Claims

A submarine cable, comprising:
a structural unit; and

a protection unit, positioned at an outer periphery of the structural unit;

characterized in that, the protection unit comprises an outer protective layer and an armor layer, the armor layer is positioned between the outer protective layer and the structural layer, the armor layer comprises an inner armor layer and an outer armor layer, an angle between a twisted monofilament of the inner armor layer and the center axis of the submarine cable is larger than an angle between a twisted monofilament of the outer armor layer and the center axis of the submarine cable; or the angle between the monofilament of the inner armor layer and the center axis is opposite to the angle between the monofilament of the outer armor layer and the center axis.
The submarine cable as claimed in claim 1, characterized in that, the monofilament of the outer armor layer is a metal wire with a circular or trapezoidal cross-section, the monofilament of the inner armor layer is a metal wire with a circular cross-section, or, the monofilament of the inner armor layer is a metal tape or metal wire with a trapezoidal cross-section, if the cross-section of the monofilament is a trapezoid, the ratio of the maximum cross-sectional width to the thickness of the monofilament is 2:1.
The submarine cable as claimed in claim 2, characterized in that, the inner armor layer and the outer armor layer are formed by twisting metal wires with circular cross-section or trapezoidal cross-section, the angle between the monofilament and the center axis of the submarine cable is 5.5-6.5 degrees.
The submarine cable as claimed in claim 3, characterized in that, a twisting direction of the monofilament of the inner armor layer being the same as a twisting direction of the monofilament of the outer armor layer, the angle between the monofilament of the inner armor layer and the axis of the submarine cable is 8.8-10.3 degrees.
The submarine cable as claimed in claim 4, characterized in that, D is an inner diameter of the structural unit, d1 is a maximum width of the monofilament of the inner armor layer, and h1 is a thickness of the monofilament of the inner armor layer, a quantity of monofilaments of the inner armor layer is: $n_{1} = \frac{π \cdot (D + h_{1})}{2 d_{1}} - 1;$
d2 is a maximum width of the monofilament of the outer armor layer, and h2 is a thickness of the monofilament of the outer armor layer, a quantity of monofilaments of the outer armor layer is: $n_{2} = \frac{π \cdot (D + 2 h_{1} + h_{2})}{d_{2}} - 1 .$
The submarine cable as claimed in claim 2, characterized in that, the monofilaments of the inner armor layer are metal tapes, an overlapped part of two adjacent layers of the metal tape is 15%-20% of the width of the metal tape.
The submarine cable as claimed in claim 1, characterized in that, a quantity of the structural unit is three, three of the structural unit are positioned in a circular array in the protection unit.
A manufacturing method of a submarine cable as claimed in claim 1, characterized in that, the manufacturing method comprising:
preparing a structural unit;

twisting an armor layer, a twisting device of the outer armor layer and a twisting device of the inner armor layer are positioned in a row along an advancing direction of the structural unit, and the inner armor layer and the outer armor layer are twisted by the twisting devices;

coating an outer protective layer after twisting the armor layer.
The manufacturing method as claimed in claim 8, characterized in that, during twisting process, two synchronous twisting devices are positioned at an outside of the structural unit, and a rotation speed of the twisting devices for twisting the inner armor layer is twice a rotation speed of the twisting device for twisting the outer armor layer; or the rotation speed of the twisting devices for twisting the inner armor layer is the same as the rotation speed of the twisting device for twisting the outer armor layer.
The manufacturing method as claimed in claim 8, characterized in that, during twisting process, the inner armor layer is wrapped on an outer periphery of the structural unit, and then the protective unit carrying the inner armor layer is positioned in the twisting device of the outer armor layer.