Product Expertise: Rail Stress Free Temperature Measurement & Rail Crack Measurement

Stress Free Temperature (SFT) measurement and Rolling Contact Fatigue Cracks measurement with measuring devices of Metalelektro-Hungary brought to you in India by PIE (Paragon Instrumentation Engineers Pvt. Ltd.)

In continuous welded (CW) or long welded rails (LWR) compressing forces appear if the rail temperature is higher than the SFT whereas pulling forces appear if rail temperature is lower than the SFT. High compressing forces could cause buckling of the rail and the high pulling forces can cause the breakage of rails at the welding seams.

Metalelektro has different solutions to measure the Stress Free Temperature also called the neutral temperature.

The SidePull device measures the real neutral temperature, it uses mechanical chord stress principle. It measures force, displacement and temperature simultaneously. The neutral temperature can be calculated with 1°C accuracy in only 30 minutes. Track closure is needed since the measuring procedure requires the release of  the track over a  short section of about 28 meters. However no cutting of rails is required.

Another product called the RailScan device is a non- destructive measuring device for determining the SFT. It measures the magnetic characteristics of the rail without disturbing the train traffic.

Rail fractures happen because of the strengthening caused by the rolling stock load on the rail-wheel contacting surface and because of the consequently evolving rolling contact fatigue cracks. The family of defects characterized by this deformations is called Rolling Contact Fatigue (RCF).Head Check (small cracks on rail head) is the most widespread form of the RCF defects.

Head Checks evolve en masse (even 300 nos. in 1 meter) on the running and directing surface of the rail head as a consequence of the rolling contact fatigue load. The cracks progress at small angle (15⁰-25⁰) under the running surface. After reaching 2.5-3 mm depth they progress in steep angle (55⁰-65⁰) into the rail head – even into several directions. This phenomenon can generate rail cracks / fractures on the whole cross section.

Several kinds of works are executed depending on the extension and the depth of the defects: local grinding made by hand operated grinding machines or grinding made by machines on longer sections.

The product family of Metalelektro working under eddy current measuring principle – from one-channel hand-held devices up to measuring systems mounted on trolleys or grinding trains– provides up-to-date solutions for every application demand.

“One of the biggest advantages of the eddy current technology is that it can
measure the cracks in the depth zone of 0 mm to 3 mm.”

This zone cannot be detected by ultrasonic technology. However if a crack reaches the measureable zone of ultrasonic measurement then the damage of the rail is so high that it is probable that it cannot be restored any more. The detection of the cracks in their early stages (together with a maintenance strategy) could extend the lifespan of the rail remarkably.

For more details or interest please email:

This Product Expertise article is a part of our June 2020 MagazineSubscribe to our Magazine Today!