Causes of defects:
The origin and development of such cracks is due to:
Material defects originating during the manufacturing process such as clusters of nonmetallic inclusions, hydrogen flakes, rolling marks, guide marks etc. which may be present in spite of successful non-destructive tests carried out on the rails during quality assurance examination.
Residual stresses induced during manufacture (cooling, rolling, gas pressing and straightening).
Defects due to incorrect handling e.g. plastic deformation, scoring, denting, etc.
Defects associated with faulty welding i.e. gas pores, lack of fusion, inclusions, cracks etc.
Dynamic stresses caused by vertical and lateral loads particularly by vehicles with wheel flats or when the vehicle runs over poorly maintained rail joints etc.
Excessive thermal stresses due to variation in rail temperature beyond specified limits.
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