Non-destructive testing.

摘要

The invention relates to non-destructive testing particularly of the material. It is known to test bar material utilising two coils and a common saturation with the bar passed through the coils, any detected difference in field strengths signifying the presence of a defect. However such method can only test for discontinuous defects, a continuous defect would have equal effect on the field strengths of both coils. The object of the invention is to provide for the detecting of both continuous or discontinuous defects which objective is met by apparatus comprising a search coil (4) and a reference coil (2) having substantially identical field strengths said search coil (4) being adapted to be sited in an inspection line for bar material (1) and said reference coil being adapted to be sited off line for use with a reference sample (3). Thus, with the reference sample of known quality of surface finish and chemical and physical consistency, any deviation from the readings emitted between the search coil and the reference coil signifies a defect in the bar material (1), a continuous difference signifying a continuous defect and a discontinuous difference signifying a discontinuous defect.