A rail is said to have failed if it is considered necessary to remove it immediately from the track on account of the defects noticed on it. The majority of rail failures originate from the fatigue cracks caused due to alternating stresses created in the rail section on account of the passage of loads. A rail section is normally designed
to take a certain minimum GMT of traffic, but sometimes due to reasons such as an inherent defect in the metal, the section becomes weak at a particular point and leads to premature failure of the rail.
6.7.1 Causes of Rail Failures
The main causes for the failure of rails are as follows.
Inherent defects in the rail Manufacturing defects in the rail, such as faulty chemical composition, harmful segregation, piping, seams, laps, and guide marks.
Defects due to fault of the rolling stock and abnormal traffic effects Flat spots in tyres, engine burns, skidding of wheels, severe braking, etc.
Excessive corrosion of rails Excessive corrosion in the rail generally takes place due to weather conditions, the presence of corrosive salts such as chlorides and constant exposure of the rails to moisture and humidity in locations near water columns, ashpits, tunnels, etc. Corrosion normally leads to the development of cracks in regions with a high concentration of stresses.
Badly maintained joints Poor maintenance of joints such as improper packing of joint sleepers and loose fittings.
Defects in welding of joints These defects arise either because of improper composition of the thermit weld metal or because of a defective welding technique.
Improper maintenance of track Ineffective or careless maintenance of the track or delayed renewal of the track.
Derailments Damages caused to the rails during derailment.
6.7.2 Classification of Rail Failures
The classification of rail failures on Indian Railways has been codified for easy processing of statistical data. The code is made up of two portions—the first portion consisting of three code letters and the second portion consisting of three or four code digits.
First portion of the code The three code letters make up the first portion and denote the following.
(i) Type of rail being used (O for plain rail and X for points and crossing rails)
(ii) Reasons for withdrawal of rail (F for fractured, C for cracked, and D for defective)
(iii) Probable cause for failure (S for fault of rolling stock, C for excessive corrosion, D for derailment, and O for others)
Second portion of code The second portion of code the consisting of three or four digits gives the following information.
(i) Location of the fracture on the length of the rail (1 for within fish plate limits and 2 for other portions on the rail)
(ii) Position in the rail section from where the failure started (0 for unknown, 1 for within rail head, 2 for surface of rail head, 3 for web, and 4 for foot)
(iii) Direction of crack or fracture (0 to 9)
(iv) Any other information about the fracture, where it is necessary to provide further subdivision. No specific system is recommended for this code.
6.7.3 Metallurgical Investigation
The following types of defective rails should normally be sent for metallurgical investigation.
(i) Rails that have been removed from the track as a result of visual or ultrasonic detection
(ii) Rail failures falling in categories in which cracks or surface defects develop at specified locations.