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Inspection of cast high-manganese steel railway crossings

A railway project co-funded by the UK’s innovation agency, the Technology Strategy Board, called RailSAFT has been successfully completed. The consortium is pleased to report the successful development and implementation of an ultrasonic technique capable of reliable inspection of cast high-manganese steel railway crossings. The developed system utilises a combination of low-frequency ultrasonic transducers and a post-processing image reconstruction technique known as Synthetic Aperture Focussing Technique (SAFT). The system has been shown to reliably detect and locate real sub-surface and surface breaking defects in critical regions of manganese steel crossings.

Cast high-manganese steel railway crossings are employed at safety critical locations throughout the UK and European railway infrastructure due to their work hardening material properties. Repetitive high velocity collisions from rolling stock, act as a catalyst for fatigue cracking which can compromise the structural integrity of such components. Due to the fully austenitic coarse grained structure of cast manganese steel crossings, examination of the material sub-surface is ineffective using current industry standard ultrasonic techniques.

Inspection of in-service crossings is limited to visual and dye-penetrant surface inspection. With no practical sub-surface inspection method available, the structural integrity of in-service crossings remains unknown, resulting in conservative service life estimates and high life cycle costs for railway operators and infrastructure owners.

Pre-service examination may be performed using radiographic methods capable of full volumetric imaging. However, these require highly trained personnel, specialist equipment, have strict health and safety regulations due to radiation exposure and can be very expensive to setup and maintain.

 

 

Inspection of side-drilled holes at 80mm depth in a high-manganese steel railway crossing sample using conventional ultrasonic testing (top) and SAFT (bottom)
Inspection of side-drilled holes at 80mm depth in a high-manganese steel railway crossing sample using conventional ultrasonic testing (top) and SAFT (bottom)

The RailSAFT consortium has successfully developed an ultrasonic SAFT inspection system, capable of full-volume inspection from the top surface of manganese steel crossings. The team used low-frequency ultrasonic transducers in combination with

SAFT image reconstruction in order to minimise coherent noise contributions emanating from material back-scatter. An encoded 4 axis scanner system and a conformable membrane water wedge configuration were used in order to allow reliable coupling to the complex geometry top surface of the crossings.

The signal response from side-drilled holes, ranging between 5mm and 25mm in diameter at 80mm depth in manganese steel clearly indicate the improvement in SNR achievable using ultrasonic SAFT inspection over conventional ultrasonic testing.

For more information please email contactus@twi.co.uk.

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