UIC Leaflet 844-1: Technical Specification for Steel Tubes for Rolling Stock

What is UIC Leaflet 844-1?

UIC Leaflet 844-1 is a specialized metallurgical and engineering standard titled “Technical specification for the supply of unalloyed or low-alloy steel tubes for rolling stock.” While the 500-series leaflets focus on the assembly of the vehicle, the 800-series, including 844-1, focuses on Technical Delivery Conditions for the raw materials and semi-finished products.

These tubes are the “arteries” of the train, used in critical systems such as the main brake pipe, pneumatic suspension lines, and heating systems. Because a tube failure could lead to a loss of Operational Safety (e.g., brake failure), the quality standards are significantly higher than for standard industrial piping.

Material Grades and Mechanical Properties

The leaflet specifies the chemical composition and mechanical requirements to ensure the tubes can withstand the unique Rail Environment, which includes constant vibration and high-pressure cycles.

• Ductility: Tubes must be capable of being bent to tight radii without cracking or wall thinning, which is essential for routing pipes through the complex Underframe of Passenger Coaches.
• Impact Toughness: Ensuring the steel does not become brittle at low temperatures (down to -40°C), which is vital for trains operating in Nordic or Alpine climates.
• Weldability: The low-carbon content is strictly controlled to allow for high-quality Welding during assembly without the risk of hydrogen cracking.

Testing and Quality Assurance

To ensure Structural Integrity, every batch of tubes must undergo rigorous Non-Destructive Testing (NDT) and physical validation:

• Hydrostatic Testing: Every tube is subjected to internal water pressure significantly higher than its working pressure to check for leaks or microscopic pores.
• Flattening and Flaring Tests: Samples are crushed or expanded to confirm the material’s structural homogeneity.
• Dimensional Tolerances: Strict limits on wall thickness and eccentricity to ensure that standardized fittings and couplers can be attached securely.

Corrosion Protection and Surface Finish

Given the long Maintenance Intervals of modern rolling stock, the standard mandates specific surface treatments:

• Internal Cleanliness: Tubes for pneumatic systems must be free of scale and rust to prevent debris from damaging sensitive brake valves.
• External Coating: Requirements for galvanization or specialized primers to protect against salt, moisture, and debris impact under the train.

Comparison: Standard Industrial Pipe vs. UIC 844-1 Tube