Some current developments in NDE of corrosion

There is increasing concern about the economic and safety-related implications of hidden corrosion in ageing civil and military aircraft, and interest in non-destructive testing methods for detecting and characterising such corrosion is increasing. There are however practical difficulties in trying to detect and characterise hidden corrosion, in all its forms, particularly the difficulties involved in working with second- or third-layer problems. This paper discussed two promising methods for the detection and assessment of hidden corrosion. The first is based on detecting the acoustic emission generated by active corrosion cells, and using triangulation methods to determine the location of significant areas. The second methods is Compton backscattering of X-rays, which offers a means of detecting corroded areas on the basis that the corrosion product has a lower effective density of free electrons. With respect to the detection of corrosion damage, Compton scatter imaging offers the following advantages over conventional radiography: 3-D reconstruction without complex computations; imaging from one side of the object; imaging of low-density materials and, imaging of low-density materials is not affected by intervening higher density materials. 8 refs., 5 figs