Beneath the vast oceans, millions of kilometers of submarine optical and power cables crisscross the seabed, acting as the Earth's "neural network," carrying over 95% of international data traffic and cross-sea energy transmission. These cables traverse continental shelves, trenches, and even volcanic zones, enduring extreme conditions such as high pressure, low temperatures, and high salinity. They must also resist scouring by ocean currents, dragging by fishing nets, bites from sharks, and disturbances caused by earthquakes. The protective material enveloping these cables must be flexible, sealed, corrosion-resistant, and capable of preventing biofouling. In this demanding role, silicone rubber stands out with its unique advantages, becoming a key choice for advanced submarine cable sheathing.

Structure and Challenges of Submarine Cables

Submarine cables typically consist of layers from the inside out: conductor/fiber optics, insulation, armor wires, and an outer sheath (sheath). Traditional sheaths are often made of polyethylene (PE) or polyvinyl chloride (PVC), which are cost-effective and easy to extrude. However, they exhibit aging, embrittlement, poor tear resistance, and vulnerability to marine life erosion over long-term use. Silicone rubber sheaths provide more reliable solutions at the molecular level.

1. Superior Resistance to Seawater Corrosion: Seawater contains about 3.5% salt, with chloride ions being highly penetrative and electrochemically active, accelerating metal corrosion and degrading organic materials. Silicone rubber features inorganic Si–O bonds in its backbone and saturated methyl side chains, making it chemically inert and resistant to reactions with saltwater and swelling. Even after prolonged immersion in simulated deep-sea hydrothermal environments at 60°C, its mechanical and electrical properties degrade minimally, far surpassing most carbon-chain polymers.

2. High Elasticity and Fatigue Resistance: Submarine cables are not stationary; they sway continuously with ocean currents, especially in shallow-water landing areas or uneven seabeds, where repeated bending can lead to sheath cracking. Silicone rubber boasts a break elongation exceeding 500% and remains flexible at –40°C, effectively absorbing dynamic stresses and preventing microcrack propagation. This "softness conquers hardness" characteristic significantly extends cable lifespan under complex marine conditions.

3. Biofouling Prevention Potential: Marine organisms like bacteria, barnacles, and algae tend to attach and grow on cable surfaces, forming biofilms that increase water resistance and may secrete acidic metabolites that corrode the outer layer. Although pure silicone rubber is not inherently antimicrobial, its low surface energy (about 20–24 mN/m) makes it difficult for fouling organisms to adhere firmly. Further enhancements include blending slow-release antifouling agents (e.g., copper compounds, organosilicon quaternary ammonium salts) or employing biomimetic surface designs (mimicking shark skin textures) to achieve long-lasting antifouling without relying on toxic TBT (tributyltin) paints.

Electrical Performance: While silicone rubber as an outer sheath does not directly insulate, its high volume resistivity and low dielectric constant prevent external stray currents from interfering with internal signals, particularly suitable for high-voltage direct current (HVDC) submarine cables. Additionally, its flame-retardant and low-smoke characteristics comply with safety regulations for ships and offshore platforms (such as IEC 60754 and IMO FTP Code).

Manufacturing Process: Silicone rubber sheaths for submarine cables are usually produced using continuous extrusion vulcanization lines combined with electron beam or hot air vulcanization systems to ensure thick-walled (2–5 mm) sheaths are free of bubbles and defects. Some high-end products adopt dual-layer structures: an inner layer of high-adhesion silicone rubber ensures tight bonding with steel armor, while an outer layer of wear-resistant and tear-resistant modified silicone rubber enhances mechanical protection.

Cost Considerations: Despite higher raw material costs compared to PE, considering lower lifecycle maintenance costs (reduced retrieval and repair frequencies) and longer service lives (up to 30 years or more), the overall benefits are significant for critical communication trunk lines or deep-sea energy projects.

In applications like deep-sea exploration devices, remotely operated vehicles (ROVs), and ocean monitoring sensors, silicone rubber sheaths are widely used due to their flexibility, ease of winding and unwinding, transparency for visual inspection, and biocompatibility suitable for deployment in ecologically sensitive areas.

Conclusion

Silicone rubber as a submarine cable sheath represents not just a material upgrade but a redefinition of "deep-sea reliability." It silently protects every bit of data transmission and every watt of power delivery across thousands of meters underwater, ensuring that human civilization's connections remain unbroken, even across abyssal depths.



3120 Phenyl Methyl Vinyl silicone Gum