EN 15729-2: Rail Infrastructure – Non-Destructive Testing on Rails in Track – Part 2: Ultrasonic Testing

What is EN 16729-2?

EN 16729-2 is a critical technical standard titled “Railway applications – Infrastructure – Non-destructive testing on rails in track – Part 2: Eddy current testing of rails in track.” (Note: While Part 1 covers the general principles, Part 2 specifically focuses on the Eddy Current method, though it is often utilized alongside Ultrasonic Testing to provide a full profile of Rail Defects).

The primary objective of this standard is to provide a standardized methodology for detecting surface-initiated fatigue defects, such as Head Checking (HC) and Squats. These defects are common in the modern Rail Environment due to high axle loads and increasing traffic density.

Eddy Current Testing (ET) Principles

Unlike ultrasound, which looks deep into the rail, the Eddy Current testing described in EN 16729-2 is optimized for the “near-surface” zone (typically 0–5 mm deep). This is where Rolling Contact Fatigue (RCF) begins.

• Probe Configuration: The standard defines how probes must be oriented relative to the rail head to capture longitudinal and transverse cracks.
• Signal Interpretation: Procedures for distinguishing between actual cracks and harmless surface irregularities or rail rust.
• Detection Thresholds: Defining the minimum crack length and depth that the equipment must be capable of identifying.

Equipment and Personnel Qualification

For Infrastructure Management, the reliability of the data is paramount. EN 16729-2 mandates:

• Calibration: Equipment must be calibrated using a “reference rail” containing artificial defects of known dimensions.
• Certification: Operators must be certified according to EN ISO 9712 (Non-destructive testing – Qualification and certification of NDT personnel).
• Data Recording: Requirements for the continuous recording of test data to allow for trend analysis over multiple Maintenance Intervals.

Integration with Maintenance Strategies

The results from EN 16729-2 testing are used to categorize the severity of defects. This categorization dictates the “Action Limit”:

• Monitoring: Small cracks that are noted but left in track for observation.
• Grinding/Milling: Moderate defects that can be removed by restorative Track Quality maintenance.
• Rail Replacement: Severe or deep cracks that pose an immediate risk of rail fracture.

Comparison: Ultrasonic Testing (UT) vs. Eddy Current (ET) per EN 16729