Ultrasonic guided wave NDE for piping

An ultrasonic guided wave nondestructive evaluation (NDE) system for rapidly detecting and quantifying the reduction in wall thickness caused by corrosion in piping under insulation is discussed. Only small, easily replaceable sections need to be removed from the thermal insulation that surrounds the pipework. The worst case scenario of the guided wave work will be a two-stage system, the first with guided waves capable of rapidly surveying the piping to indicate areas of corrosion attack and wall thinning, followed by a more quantitative technique using a more conventional normal beam ultrasonic longitudinal wave inspection. In most cases, however, the guided wave technique will be sufficient for quantitatively determining wall thickness, depending on the accuracy required and the local or global nature of the wall thinning. Drawing on guided wave experiences to date on a variety of different plate and tubing problems, preliminary feasibility experiments have already been conducted on piping under insulation in both a laboratory and a chemical processing facility field environment. Three guided wave techniaues have been introduced, one on normal beam excitation, one using a broad banded variable angle beam transducer on a curved shoe, and a third on a newly developed pipe comb system.