For round bars or wires, corrosion proceeds radially inward at essentially a uniform rate around the entire circumference. The result is

• A. A circular pitting ring forms
• B. A bar or wire of progressively smaller diameter
• C. A hollow cylinder forms
• D. A bar with constant diameter

Answer: (B)

Uniform radial inward attack on a round bar means material is removed evenly from the outside toward the center all around the circumference. As time passes, the outer surface recedes uniformly, shrinking the cross-sectional diameter but keeping the bar solid and its length unchanged. So the result is a bar or wire that becomes progressively smaller in diameter over time. This differs from forming pits (localized spots around the circumference), or creating a hollow interior (which would require material to be removed from an inner surface to leave a cavity).