Nondestructive evaluation of Delhi Iron Pillar

Abstract

We discuss results obtained on nondestructive evaluation of the Delhi iron pillar using various non-destructive techniques such as ultrasonics, impact echo, radiography, radiation gauging, X-ray fluorescence, in situ metallography and electrochemical analysis. The microstructural analysis of the ornamental portion of the pillar indicated the presence of forged structure in the main body of the pillar, whereas the top platform consists of microstructure similar to 'as cast structure'. Further, the radiation gauging, radiography, ultrasonics and impact echo testing indicated the presence of voids at different locations in the pillar. The large aspect ratio (axial to radial) of the voids indicated that the pillar could have been forged in the radial direction rather than in the axial direction. The passivation current density for the 'passive' rust scales of the pillar formed on the surface clearly indicated the protective nature of the oxide structure developed and its stability against corrosion.