METHOD AND DEVICE FOR MAGNETICALLY TESTING PRODUCTS WITH A WALL COMPRISING AT LEAST ONE LAYER OF MAGNETIC MATERIAL

摘要

Products with a wall (1) comprising at least one layer (11) of ferromagnetic material may be tested by magnetising said layer using magnetising means (30) to generate therein a remanent magnetisation (H) parallel to the wall surface, then moving magnetic field sensors (2) along the wall and measuring, in the presence of said remanent magnetisation (H) alone, the magnetic field adjacent to the product surface, whereby changes in the field measured along said wall indicate defects (22) in said layer of magnetic material. The method is particularly suitable for testing elongate products in which the layer to be tested is not on the surface. Specifically, the method is suitable for testing pipelines or tubes for transporting petroleum.