Corrosion Detection by Real-Time Neutron Imaging

Abstract

Neutron radiographic imaging offers advantages for the detection of corrosion in metallic assemblies because of the excellent neutron sensitivity for the hydrogen in the corrosion product. Corrosion products usually are mixtures of hydroxides and often contain extra water from the moisture in the associated environment. The relatively high slow-neutron attenuation for hydrogen coupled with the relative neutron transparency for many metals leads to the prospect for early detection of hidden corrosion in assemblies. Neutron detection of corrosion depends on the hydrogen content of the corrosion product buildup whereas other nondestructive methods for corrosion detection, such as x-ray imaging, ultrasonics or eddy currents, depend on metal loss as the principal means for detection. These nondestructive testing approaches are compared to real-time neutron radiographic methods for the detection of corrosion. Real-time imaging methods offer advantages in prompt response at a remote location, capability for scanning and the presentation of an electronic signal that lends it-self to image processing. Enhancement techniques such as frame averaging, beam flattening, and gray-level stretching are all shown to be effective in bringing out neutron radiographic corrosion images. Detection capability in aluminum is shown to be at least 0.18 mg H/cm2, representing an aluminum metal loss of about 25 µm.