Published: 2025-08-11 09:25:49
Cables resistant to seawater (such as those used in marine engineering, underwater detection, ship communication, and other scenarios) need to withstand long-term exposure to seawater corrosion, water pressure impact, marine organism attachment, and complex marine environments (such as salt spray, tides, and temperature changes). Their structural composition needs to be specially designed to address these characteristics.
It usually includes the following core components, from inside to outside:
1. Conductor (conductive core)
Material Selection: High-purity oxygen-free copper (OFHC) or tin/silver-plated copper is mostly used to ensure excellent electrical conductivity while reducing electrochemical corrosion of copper by seawater ions (the tin/silver plating can form a physical barrier to slow down copper oxidation). For scenarios requiring high strength (such as deep-sea cables), copper-clad steel or copper alloys may be used, balancing conductivity and mechanical strength.
Structural design: Usually consists of multi-stranded braided conductors (rather than single solid copper) to enhance the flexibility of the cable, in order to accommodate swaying, dragging, or bending in a seawater environment (such as ship cables swinging with the hull).
2. Insulation layer (conductor protection)
The insulation layer directly wraps the conductor, and its core function is to isolate the conductor from the external environment, prevent short circuits and leakage, while also withstanding seawater penetration and chemical corrosion:
Common Materials:
Polyethylene (PE): Especially high-density polyethylene (HDPE) or cross-linked polyethylene (XLPE), which has excellent water resistance, insulation, and chemical stability, and is reasonably cost-effective, suitable for medium and low voltage cables.
Polytetrafluoroethylene (PTFE, fluoroplastic): extremely corrosion-resistant (resistant to almost all chemicals), high-temperature resistant (long-term service temperature up to 260°C), but relatively costly; suitable for high-pressure or special requirement cables (such as deep-sea exploration and high-temperature seawater environments).
EPDM rubber: highly elastic and weather-resistant, suitable for scenarios requiring flexibility (such as marine mobile cables).
Design key points: The insulation layer must be uniform and dense, free of pinholes or bubbles, preventing seawater from seeping into the conductor through tiny gaps.
3. Shielding Layer (Signal / Anti-Interference Protection)
For seawater-resistant cables transmitting signals or high-frequency currents (such as communication cables and sensor cables), shielding layers must be installed to resist electromagnetic interference (EMI) and radio frequency interference (RFI):
Materials and Structure:
Tin-plated copper wire braided mesh: combines shielding and flexibility, effectively blocking external electromagnetic signals, while the tin-plated layer enhances resistance to seawater corrosion.
Aluminum-plastic composite tape (AL-PET): Shielding formed through longitudinal or winding with good sealing properties, helping to block seawater infiltration.
Copper tape wrapping: Strong shielding effect but relatively poor flexibility, suitable for fixed cable installation.
Special requirements: The shielding layer must be connected to the grounding device to avoid amplification caused by interference caused by seawater conductivity.
4. Lining Layer (Structural Cushioning and Sealing)
The inner lining layer is located between the shielding layer and the outer sheath, and its main functions are:
Buffers external pressure (such as deep-sea water pressure), protecting internal insulation and shielding layers;
Enhances adhesion between layers to prevent seawater from seeping in through interlayer gaps;
Isolates the shielding layer from the outer sheath to prevent chemical reactions between different materials (such as corrosion reactions between metal shielding and sheath materials).
Common materials: Polyethylene (PE), polyvinyl chloride (PVC, oil-resistant model), or neoprene, which must have water resistance and a certain degree of elasticity.
5. Armor Layer (Mechanical Strength Enhancement)
For deep-sea, seabed, or mechanical impact scenarios (such as cables near ship anchor chains), additional armor layers are needed to resist water pressure, drag, collisions, or abrasion from marine organisms (such as shells and corals):
Materials and Structure:
Galvanized steel wire armor: Wound by twisting or interlocking to enhance tensile and impact resistance, with the galvanized layer improving seawater corrosion resistance.
Steel belt armor: mainly used for compression resistance, suitable for underground submarine cables laid underground (to prevent damage to fishing boat trawlers or anchors).
Aramid fiber (Kevlar): lightweight, high-strength, suitable for scenarios requiring weight reduction (such as underwater robot cables).
Design points: The armor layer must be tightly integrated with the inner lining and outer sheath to prevent seawater from stagnating in the armor gaps and causing corrosion.
6. Outer Sheath (Outermost Protection)
The outer sheath is the "first line of defense" for seawater protection cables, directly exposed to seawater, salt spray, sunlight, etc., and must have core properties such as seawater corrosion resistance, weather resistance, wear resistance, and UV resistance:
Common Materials:
Neoprene rubber (CR): seawater-resistant, oil-resistant, aging-resistant, and highly flexible, suitable for ship decks and shallow sea cables.
Polyurethane (PU): Highly wear-resistant, tear-resistant, and remains elastic at low temperatures, suitable for cables for underwater equipment that require frequent movement (such as submersible cables).
Polyethylene (PE): Especially the weather-resistant PE (with added carbon black or antioxidants), low cost and excellent water resistance, suitable for deep-sea fixed cable laying.
Fluoroplastics (such as FEP, PFA): highly corrosion-resistant, able to withstand long-term immersion in seawater and extreme temperatures, but costly, suitable for special environments (such as areas with chemical pollutants).
Special treatment: Some outer sheaths contain anti-biological adhesions (such as copper ion compounds) to reduce adhesion of marine organisms like seaweed and shells (biofogging increases cable weight and resistance, and can even damage the sheath).
7. Auxiliary Structure (Special Scenario Requirements)
Water-blocking filling: fills the gaps between cable cores with water-blocking yarn, water-blocking powder, or hot melt adhesive. When the outer sheath is damaged, the water-blocking material expands into water to form a seal, preventing seawater from penetrating further.
Central reinforcements: such as steel wire ropes and fiberglass rods, to enhance the overall tensile strength of the cable (especially deep-sea cables, which must bear their own weight and the tensile force during installation).
Summary
The composition of seawater-resistant cables results from multi-layer protection and functional synergy: conductors ensure conductivity and transmission performance, insulation and shielding layers guarantee electrical safety, armor layers enhance mechanical strength, outer sheaths resist seawater and environmental corrosion, and inner lining and water-blocking structures reinforce sealing.
Cables in different scenarios (such as shallow sea/deep sea, fixed/mobile, signal/powered) are targeted for protection by adjusting materials and structures (such as armor type, outer sheath materials) to meet the needs of long-term reliable operation.