The Alternating Current Field Measurement (ACFM) technique for public safety applications

The use of NDT is well-known in the oil and gas industry, petrochemical industry, shipping and aerospace. Theme parks are visited by thousands of people worldwide and the rides are becoming more adventurous by demand. This places a greater strain on the material being used. Fracture mechanics analysis is being carried out to determine the critical defect size that can be allowed to exist. From a customer satisfaction point of view, the rides must be available when the theme park is open, which in some cases is all year. This means inspection techniques have to be used which are non-invasive but which can reliably detect even the smaller defects required to be detected. Bridges are even greater people-carriers, rail and road, and are often coated and have difficult access. Interest has been recently aroused in the structural integrity of high-rise buildings constructed with low-toughness weld metal. The majority of buildings constructed in the West Coast of America have used this material and several, especially in the California area, have been subject to seismic shocks. Tests carried out have shown that these shocks would be greater than those applied during the toughness tests which produced low values. This has led to the belief that some of these buildings will have defects present in their welded joints. The problem that now exists is one of inspection and determining if defects of a significant nature are present. The Alternating Current Field Measurement technique has been used successfully to inspect through coatings and, with rope access techniques, can be applied to these public safety applications.