Radiograph — Definition & NDT Use

From the inspector's bench, Radiograph is run as a defined sequence: equipment verification on a known reference, scan setup against the procedure, scanning the part, and writing the indications into the report. The magnetising current creates a field that runs continuous through the part; at a discontinuity the lines of flux squeeze around the gap and break the surface as a leakage field, where dry powder or wet-suspension particles cluster and outline the flaw to the inspector's eye. Radiation passes through the part and a dense region (more material, more attenuation) records as a lighter band on film or digital detector, while a void, lack of fusion, or porosity records as a darker area; an image quality indicator (IQI) verifies that the technique was sensitive enough to be trusted. Procedure writing, inspector qualification, and the reference block establish the chain that lets a remote engineer trust an indication called a kilometre away from the office.

Radiograph is selected when the failure mode the engineer cares about — surface crack, internal void, wall loss, lack of fusion — lines up with what the technique is physically capable of detecting. On welded fabrication it is most often paired with VT and one volumetric method (RT or UT) so surface and internal defects are both addressed.

The most expensive mistake with Radiograph is treating it as a yes/no test rather than a characterisation — an indication called without a sizing strategy forces a repair where a fitness-for-service review might have left the part in service.