Nature of defects in welds:
Joining rails by improper welding may introduce a variety of
defects on the joints as well as in the heat affected zone (HAZ) e.g. lack of fusion, cracks,porosity, slag inclusion, structural variation, etc.
The quality of weld depends to a large extent on the careful execution of the welding operation. USFD testing done by manual rail tester suffers from following deficiencies:
(i) Full cross section of weld is not covered by normal USFD examination using manual tester thereby leaving areas in head and foot, which may have flaws.
(ii) Micro structural variations in the weldment cause attenuation of ultrasonic energy.