ULTRASONIC GUIDED-WAVE NDE FOR PIPING

An ultrasonic guided wave nondestructive evaluation (NDE) system for r apidly detecting and quantifying the reduction in wall thickness cause d by corrosion in piping under insulation is discussed. Only small, ea sily replaceable sections need to be removed from the thermal insulati on that surrounds the pipework. The worst case scenario of the guided wave work will be a two-stage system, the first with guided waves capa ble of rapidly surveying the piping to indicate areas of corrosion att ack and wall thinning, followed by a more quantitative technique using a more conventional normal beam ultrasonic longitudinal wave inspecti on. In most cases, however, the guided wave technique will be sufficie nt for quantitatively determining wall thickness, depending on the acc uracy required and the local or global nature of the wall thinning. Dr awing on guided wave experiences to date on a variety of different pla te and tubing problems, preliminary feasibility experiments have alrea dy been conducted on piping under insulation in both a laboratory and a chemical processing facility field environment. Three guided wave te chniques have bee 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.