High-Corrosion Environment Railway Solutions

Railway tracks in coastal areas, chemical industrial parks, humid tunnels, salt-lake corridors, and tropical regions can be exposed to salt, moisture, acidic water, industrial gases, and repeated condensation. GNEE RAIL supplies steel rails, track fasteners, and surface-treated components for these operating conditions.
The required protection depends on the actual exposure environment and the component itself. Salinity, humidity, chemical exposure, temperature, rail and fastener materials, mechanical loading, and the required maintenance interval are considered when selecting a material or surface treatment.

The type and rate of corrosion depend on where the railway is installed and what the components are exposed to. A coastal fastening system, for example, may mainly face salt and condensation, while tunnel or chemical-plant applications can involve additional moisture or chemical exposure.

For high-strength fasteners, the coating process needs to be compatible with the specified steel grade and heat treatment. Non-electrolytic zinc-flake systems may be considered where hydrogen embrittlement control is required. 

Different components can use different protection methods. The choice is normally based on the substrate material, geometry, required coating thickness, thread dimensions, mechanical requirements, and field exposure.

Zinc-Flake Coatings
Dacromet and similar zinc-flake systems use zinc and aluminum flakes in an inorganic binder and are generally applied through dip-spin and baking processes.
• Application: Track bolts, nuts, elastic clips, and other components where controlled coating thickness and thread clearance are important.
• Coating Thickness: Typically around 5–15 μm depending on the specified coating system.
• Salt Spray Performance: Approximately 500–1500 hours may be specified depending on coating type, preparation, and coating mass.
• High-Strength Fasteners: Non-electrolytic application avoids the hydrogen generation associated with electroplating. Suitability still needs to be confirmed against the fastener material and applicable specification.

Hot-Dip Galvanizing
Hot-dip galvanizing forms a zinc coating over cleaned steel by immersing the component in molten zinc.
• Typical Components: Tie plates, rail shoulders, screw spikes, fishplates, anchor bolts, and other steel hardware.
• Coating Thickness: Commonly specified according to the component and applicable galvanizing standard; approximately 45–85 μm may be achievable for many components.
• Protection: The zinc coating provides a physical barrier and sacrificial protection where the coating is locally damaged.
• Threaded Components: Thread dimensions and nut fit need to be considered because galvanizing adds coating thickness to the threaded surfaces.

Sherardizing
Sherardizing is a thermal diffusion process in which steel components are heated with zinc powder to form a zinc-iron alloy coating.
• Application: Track bolts, nuts, washers, small clips, shoulders, and components with complex surfaces.
• Threaded Parts: The process can provide relatively uniform coverage on threaded surfaces and internal geometries.
• Surface Characteristics: The coating is bonded to the steel substrate and can be specified where abrasion and dimensional consistency are important.

Polymer and Insulating Components
Polymer components are used where electrical isolation, moisture separation, or a resilient interface is required.
Typical components include:
• TPU or HDPE rail pads
• Nylon insulating gauge dowels
• Glass-filled polyamide insulator shoes
• Other specified insulating components
These parts can be combined with steel fasteners where the track design requires electrical separation or stray-current control.

The substrate material and surface treatment are selected together rather than treating the coating as a separate specification.