In electrified rail and tram systems, stray electrical currents, also known as dispersed dielectric currents, can escape from the rails and flow through the surrounding ground. These currents accelerate the corrosion of buried metallic structures such as pipelines, tanks, and foundations, posing long-term risks to infrastructure integrity and safety.
Stray Electrical Currents Accelerate the Corrosion of Buried Metallic Structures
Dispersed dielectric currents, also called “stray currents,” form in the ground near electric rail and tram lines.
In direct current (DC) electrified lines, the sub-station supplies current through overhead lines to train and tram motors. Most of the return current flows through the rails, but some also disperses into the ground near the tracks. These stray currents accelerate the corrosion of buried metallic structures. If metal pipes are present, the dispersed current can travel along them toward the sub-station area. This creates a negatively charged cathode where the current enters the pipe. It also creates a positively charged anode where the current leaves, causing corrosion.
Alternating current (AC) electric lines can produce similar effects, although usually less intense.
Corrosion from stray currents is much stronger than corrosion from galvanic currents. This is because stray-current intensity can reach several tens of amperes. A current of 1 ampere corrodes 9 kg of iron in one year and may also corrode 33.6 kg of lead in the same period.
Reducing Stray Current Corrosion
Reducing current dispersion is essential to prevent corrosion and interference, especially in dense urban areas with existing underground utilities. Pipes can be protected with cathodic protection or with suitable protective coatings.
When new rail or tram lines are built in residential areas, current dispersion must be minimized. This is important when old underground installations are unknown or inaccessible. In such cases, the rails of the electrified lines must be insulated to limit current leakage.
Electrochemical corrosion can also occur when the mains earth circuit of a metal pipeline is resting on the ground.
The Solution: Insulation with Sika® Icosit® Dielectric Membrane
Sika® Icosit® Dielectric Membrane is a high-performance, multifunctional waterproofing and insulating membrane designed to prevent the dispersion of electrical currents from railway and tram lines.
Made of distilled bitumen and dielectric polymers, it offers exceptional dielectric strength and high volume resistivity. This ensures effective electrical insulation and protects underground metal components from corrosion.
Its reinforced polymer–bitumen structure provides excellent durability, flexibility, and long-term resistance to moisture, chemicals, and mechanical stress.
The membrane is applied dry-laid in a horizontal position and heat-bonded with a propane torch, creating seamless and continuous protection.
Application Fields for Sika® Icosit® Dielectric Membrane
Rail and tram track beds
Underground structures and tunnels
Pipe and tank foundations
Other buried metallic structures requiring dielectric insulation
Advantages & Features of Sika® Icosit® Dielectric Membrane
- Prevents stray current dispersion from rail systems
- Protects buried metal parts from electrochemical corrosion
- High dielectric strength and volume resistivity
- Waterproof and vapor barrier performance
- Resistant to acids, bases, hydrocarbons, and site traffic
- Long-term durability even in harsh soil conditions
- Easy and efficient installation with torch-on bonding
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Author
Marco Poltera
Corporate Product Engineer
Target Market Engineered Refurbishment
Sika Services AG