All metals (and alloys) are subject to deterioration caused by corrosion. Corrosion is generally defined as a degradation of a material or its properties because of its reaction with the environment. Buildings, ships, machines, power plant equipment, oil and gas pipelines, bridges and automobiles are all subjected to be attacked by the environment. It is estimated that the total annual corrosion costs in the industrialized countries amount to about 4.6% of gross national product. Radiography unlike other non-destructive testing methods allows insulation to be left intact. They also cannot give profiles of corrosion in terms of area or depth. Radiography with the wide range of radiation energy available, from low kilovolt X rays to Co-60 gamma rays, can be safely applied even with insulation in place.
