Magnetic Particle Testing is one of the most used techniques for the detection of surface cracks. Often it is necessary to detect defects in longitudinal as well as transversal directions in very large objects. This might be achieved by using the current flow or yoke magnetizations. By rotation of the work piece and appropriate manipulation cracks with different directions can be identified. The disadvantages of these magnetization methods are: (1) Burning in by non-uniform contact, (2) Necessity of several magnetization currents, (3) Manifold manipulations of the component under investigation, (4) High investment costs. In order to avoid these disadvantages, we designed the system described in the following. The magnetic particle inspection system consists of a pair of cross coils with a magnetic field phase shift of 90-120° relative to each other together with additional orthogonal coils. The orthogonal coils are placed in approximate Helmholtz arrangement. With this arrangement magnetic fields in all directions are achieved allowing the detection of transversal as well as longitudinal surface cracks. Objects of very large dimensions can be tested for surface defects in all directions during one operation. The physical aspects as well as specific applications are presented in detail. This is including comparison of the measured magnetic fields with corresponding calculations. Various realizations of this system with cross and additional parallel coils in operation are discussed.
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