WEAR AND FAILURE IN RAILS: RAIL WEAR, TYPES OF RAIL WEAR, DEFECTS IN RAILS AND RAIL FAILURE

WEAR AND FAILURE IN RAILS

RAIL WEAR 

Due to the passage of moving loads and friction between the rail and the wheel, the rail head gets worn out in the course of service. The impact of moving loads, the effect of the forces of acceleration, deceleration, and braking of wheels, the abrasion due to rail-wheel interaction, the effects of weather conditions such as changes in temperature, snow, and rains, the presence of materials such as sand, the standard of maintenance of the track, and such allied factors cause considerable wear and tear of the vertical and lateral planes of the rail head. 

Lateral wear occurs more on curves because of the lateral thrust exerted on the outer rail by centrifugal force. A lot of the metal of the rail head gets worn out, causing the weight of the rail to decrease. This loss of weight of the rail section should not be such that the stresses exceed their permissible values. When such a stage is reached, rail renewal is called for. 



In addition, the rail head should not wear to such an extent that there is the possibility of a worn flange of the wheel hitting the fish plate.

RAIL WEAR





 Types of Wear on Rails 

A rail may face wear and tear in the following positions: 

(a) On top of the rail head (vertical wear) 

(b) On the sides of the rail head (lateral wear) 

(c) On the ends of the rail (battering of rail ends) 

Wear is more prominent at some special locations of the track. These locations are normally the following: 

(a) On sharp curves, due to centrifugal forces 

(b) On steep gradients, due to the extra force applied by the engine

 (c) On approaches to railway stations, possibly due to acceleration and deceleration 

(d) In tunnels and coastal areas, due to humidity and weather effects

 Measurement of Wear 

Wear on rails can be measured using any of the following methods:

 (a) By weighing the rail 

(b) By profiling the rail section with the help of lead strips 

(c) By profiling the rail section with the help of needles 

(d) By using special instruments designed to measure the profile of the rail and record it simultaneously on graph paper 

Methods to Reduce Wear 

Based on field experience, some of the methods adopted to reduce vertical wear and lateral wear on straight paths and curves are as follows- 

(a) Better maintenance of the track to ensure good packing as well as proper alignment and use of the correct gauge 

(b) Reduction in the number of joints by welding 

(c) Use of heavier and higher UTS rails, which are more wear resistant 

(d) Use of bearing plates and proper adzing in case of wooden sleepers 

(e) Lubricating the gauge face of the outer rail in case of curves 

(f) Providing check rails in the case of sharp curves 

(g) Interchanging the inner and outer rails 

(h) Changing the rail by carrying out track renewal 



Rail End Batter 

The hammering action of moving loads on rail joints batters the rail ends in due course of time. Due to the impact of the blows, the contact surfaces between the rails and sleepers also get worn out, the ballast at places where the sleepers are joined gets shaken up, the fish bolts become loose, and all these factors further worsen the situation, thereby increasing rail end batter. Rail end batter is measured as the difference between the height of the rail at the end and at a point 30 cm away from the end. If the batter is up to 2 mm, it is classified ‘average’, and if it is between 2 and 3 mm, it is classified as ‘severe’. When rail end batter is excessive and the rail is otherwise alright, the ends can be cropped and the rail reused.

OTHER DEFECTS IN RAILS 

Rail wear and battering of rail ends are the two major defects in rails. However some other types of defects may also develop in a rail and necessitate its removal in extreme cases. 

These are as follows: 

Hogging of rails 

Rail ends get hogged due to poor maintenance of the rail joint, yielding format, loose and faulty fastenings, and other such reasons. Hogging of rails causes the quality of the track to deteriorate. This defect can be remedied by measured she packing. 

Scabbing of rails 

The scabbing of rails occurs due to the falling of patches or chunks of metal from the rail table. Scabbing is generally seen in the shape of an elliptical depression; whose surface reveals a progressive fracture with numerous cracks around it. 

Wheel burns 

Wheel burns are caused by the slipping of the driving wheel of locomotives on the rail surface. As a consequence, extra heat is generated and the surface of the rail gets affected, resulting n a depression on the rail table. Wheel burns are generally noticed on steep gradients or where there are heavy incidences of braking or near water columns. 

Shelling and black spots 

Shelling is the progressive horizontal separation of metal that occurs on the gauge side, generally at the upper gauge corner. It is primarily caused by heavy bearing pressure on a small area of contact, which produces heavy internal shear stress. 

Corrugation of rail: 

Corrugation consists of minute depressions on the surface of rails, varying in shape and size and occurring it irregular intervals. The exact cause of corrugation is not yet known, though many theories have been put forward. The factors which help in the formation of rail corrugation, however, are briefly enumerated here, 

a) Metallurgy and age of rails 

(i) High nitrogen content of the rails 

(ii) Effect of oscillation at the time of rolling and straightening of rails

(b) Physical and environment conditions of track

(i) Steep gradients 

(ii) Yielding formation 

(iii) Long tunnels 

(iv) Electrified sections 

(c) Train operations 

(i) High speeds and high axle loads 

(ii) Starting locations of trains 

(iii) Locations where brakes are applied to stop the train 

(d) Atmospheric effects 

(i) High moisture content in the air particularly in coastal areas 

(ii) Presence of sand 



RAIL FAILURE 

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. 

(b) Physical and environment conditions of track 

(i) Steep gradients 

(ii) Yielding formation 

(iii) Long tunnels 

(iv) Electrified sections 

(c) Train operations 

(i) High speeds and high axle loads 

(ii) Starting locations of trains 

(iii) Locations where brakes are applied to stop the train 

(d) Atmospheric effects 

(i) High moisture content in the air particularly in coastal areas 

(ii) Presence of sand The corrugation of rails is quite an undesirable feature. 

When vehicles pass over corrugated rails, a roaring sound is produced, possibly due to the locking of air in the corrugation. This phenomenon is sometimes called ‘Roaring of rails’. This unpleasant and excessive noise causes great inconvenience to the passengers. Corrugation also results in the rapid oscillation of rails, which in turn loosens the keys, causes excessive wear to fittings, and disturbs the packing.

Causes of Rail Failures 

The main causes of failure of rails are as follows: 

Inherent defects in the rail 

These are due to 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 soots in tvres, engine burns, skidding of wheels, severe braking, etc. 

Excessive corrosion of rails 

This 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 

The rails are damaged during derailment. 

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 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 consisting of three or four digits gives the following information, 

(i) First digit indicate the 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) Second digit indicate the 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) Third digit indicate the 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. 



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

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