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.
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
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.
Damages caused to the rails during derailment.
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)
for withdrawal of rail (F for fractured, C for cracked, and D for defective)
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
of the fracture on the length of the rail (1 for within fish plate limits and 2
for other portions on the rail)
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)
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.
The following types of defective rails should normally be sent
for metallurgical investigation.
that have been removed from the track as a result of visual or ultrasonic
failures falling in categories in which cracks or surface defects develop at