The impact of corrosion on the sustainment costs of an aging fleet is significant, particularly for transport aircraft.  The presence of corrosion indicates a failure of the corrosion protection system and necessitates some sort of action in the maintenance plan.  Regardless of the corrosion control maintenance strategy, NDI plays an important role in its implementation and the need exists to quantify the corrosion detection capability of the inspection system.

Several types of corrosion are typically found in aging airframes – uniform, pitting, intergranular, exfoliation, crevice (uniform and pitting), and stress corrosion cracking.  Adaptations of the standard NDI methods discussed in Subsection 3.1.1 can be used to detect the various types of corrosion damage and new inspection methods are evolving.  Although there is a need to quantify the corrosion detection capability of an NDI system, at present there is no commonly accepted procedure for doing so.  Approaches to characterizing corrosion detection capability can be found in Alcott [1994], Howard and Mitchell [1995], Roach [1997], Komorowski, et al. [1998], and Hoppe, et al. [2000].  This subsection discusses two of the major problems in quantifying NDI capability for detecting corrosion and describes the method of Hoppe, et al. [2000].