METHOD AND DEVICE FOR NONDESTRUCTIVELY INSPECTING STRUCTURAL DEFECT OF LONG MAGNETIC MATERIAL

摘要

PURPOSE: To easily detect the structural defect of a lengthy material of magnetic body by arranging end poles having mutually reverse polarities along an axially moving matter to be inspected, and detecting the change of eddy current and magnetic flux. ;CONSTITUTION: A magnetic flux circuit is formed between positions S1, S2 along one (the other) side surface of a pipe, for example, by end poles 12, 14 (16, 18) having mutually reversed polarities, and a magnetic flux FA is induced within the pipe P. The poles 12, 14 (16, 18) induces a magnetic flux FB (FC) in the position S1 (S2) next to the magnetic flux FA. The change of longituciinal magnetic flux FA, FB (FA, FC) by the poles 12, 16 (14, 18) forms a stagnation point SP1 (SP2) where the longitudinal components of both the magnetic fluxes are 0. When the pipe P is moved from left to right, for example, a sudden reversion of magnetic flux is caused in both the stagnation points to generate an eddy current, and the eddy current induces a counter magnetic flux. The generally stable eddy current and counter magnetic flux are changed when the pipe P has a structural defect, and the eddy current and magnetic flux detecting means near the end poles detect them.;COPYRIGHT: (C)1994,JPO