Defect detection using magnetic field and particles

A defect detection apparatus for detecting defects 5 in a Ferromagnetic or non Ferromagnetic test object 2 comprises magnetic flux generator 12 for inducing magnetic flux lines 14 in the object and a viewing device 20 that includes magnetic particle medium 21 in a casing 25. The casing has a transparent surface 26 which in use faces away from the object and through which encased magnetic medium can be observed and a second surface 27 which in use faces towards the test object. When the apparatus is placed near a test object, distortions of the induced magnetic flux lines by defects observably influence the alignment of the magnetic medium to enable detection of defects. A camera with light source may be used to observe the transparent surface. The apparatus may be used to inspect tubes and internal surfaces.