UIC Leaflet 802-33: Standardization of Hexagonal Bolts for Railway Vehicles

What is UIC Leaflet 802-33?

UIC Leaflet 802-33 is a specialized technical standard titled “Hexagonal bolts for the construction of rolling stock – Dimensions.” While general industrial standards like ISO or DIN exist for bolts, the railway environment requires specific configurations to handle extreme vibrations and high dynamic loads.

The leaflet ensures that Fastening Systems used in Freight Wagons, locomotives, and coaches are standardized. This allows a maintenance depot in one country to replace a bolt on a foreign wagon using a part with identical mechanical properties and geometric tolerances, maintaining the vehicle’s Structural Integrity.

Technical Requirements and Mechanical Properties

Fasteners governed by UIC 802-33 must adhere to strict Technical Delivery Conditions. Because a single bolt failure in a bogie or brake system could lead to a catastrophic incident, the standard emphasizes:

• Property Classes: Mandatory use of high-strength steel grades (typically 8.8, 10.9, or 12.9) to resist shear and tensile forces.
• Thread Precision: Specifications for thread fit to ensure that nuts do not loosen under the constant 50Hz to 100Hz vibrations characteristic of the Rail Environment.
• Ductility: Ensuring the bolt can withstand impact loads without brittle fracture, especially in cold weather operations.

Corrosion Protection and Surface Finish

Railway bolts are exposed to moisture, salt, and industrial chemicals. UIC 802-33 dictates the surface treatments required to extend Maintenance Intervals:

• Zinc Flake Coating: Preferred for high-strength bolts to avoid hydrogen embrittlement while providing superior salt-spray resistance.
• Hot-Dip Galvanizing: Used for larger structural bolts where a thicker protective layer is necessary.
• Identification: Every bolt must be marked with the manufacturer’s symbol and the property class to ensure full traceability during audits or accident investigations.

Application in Rolling Stock

UIC 802-33 bolts are used in various safety-critical areas:

• Bogie Assembly: Securing axle box covers, brake rigging, and shock absorber mounts.
• Underframe Construction: Attaching secondary components to the main chassis where welding is not appropriate.
• Interior Fittings: Securing heavy equipment inside Passenger Coaches to ensure they remain anchored during high-speed collisions (crashworthiness).

Comparison: Standard Industrial vs. UIC 802-33 Railway Bolts