Improved torsional exciter for non-destructive tests of structural members

A torsional exciter for non-destructive tests on ferromagnetic tubes 1 of metal trestlework structures, comprises a set of moulded elements 3-7 with a "U"-shaped cross-section, of a flexible material, evenly positioned along the circumference of the tube 1 to induce stressing of the tube by magnetostriction. Each one of said moulded elements 3-7 has a coil 8, 9 embedded inside it in near contact with the outer wall of the tube 1 via a thin base support 12. These elements are inclined to the direction of the axis 14 of the tube at such an angle that the perpendicular to them forms an angle of 54.7 DEG with said tube axis direction, and they are connected at their ends by means of two reverse-"U"-shaped connection heads. All the coils 8, 9 are connected in series with one another, and also with an a.c. generator. In another arrangement, all the coils are encapsulated within a single moulded element encircling the tube.