Detecting defective rail welds
RADIOGRAPHIC non-destructive testing of aluminothermic welds is being carried out by AMEC under a £1m contract from Railtrack. Ultrasonic methods are unsuitable for analysing welds because of the heterogeneity of the metal, but radiography takes less than 30min to check a weld.
A selenium isotope is supported above the rail by a jig, and a digital film on the opposite side of the rail records an image. The data is studied by image analysis software housed in a road-rail Land Rover, adapted by Aquarius Road Rail Technologies. This contains PC equipment for film scanning and on-site image evaluation. Images can be electronically transferred to a central laboratory for storage and further analysis. GPS is used to locate the weld accurately.
Marketed under the name of CAmera, radiographic analysis of rails was developed by AMEC and CoMech. The aim is to bring to the railway environment established testing methods from the chemical and power industries. Small area gamma radiography is proven technology, using portable equipment and leaving no residual effects. A barrier marks out the test site, and exposure levels at the barrier are no more than 75