In 2019, TWI conducted a three-phase project aimed at determining the feasibility of using alternating-current field measurement (ACFM) testing, a non-destructive testing (NDT) technique, to inspect train bogies without the need to remove the surface coating.
Conventionally, train bogies are inspected using visual and magnetic particle inspection (MPI) where paint coatings have to be removed prior to inspection. Otherwise, probability of detection (POD) will be low, or the indication of defects might be inaccurate.
Under this project, the client asked TWI to firstly explore the feasibility of using ACFM testing on the train bogie without coating removal. Secondly, if proven feasible, TWI was asked to produce the defect specimens and perform the ACFM testing blind trial test on the train bogie. TWI demonstrated that it was possible to detect defects, through surface coatings, with a high POD of 91% over MPI, without coating removal. The variety of ACFM testing probes with differently angled/lengthened heads also further expedites the inspection on weld joints and areas previously difficult to accessusing MPI. This reduces the overall downtime and the extra cost for productionthat is associated with removing coatings.