Ultrasonic Measurement of Thick Walled Pipe Diameter Changes

Abstract

Thickwalled, main stream pipelines are key elements in many power and chemical plants. Operating for a long time in high temperature and subjected to internal pressure such pipes are subjected to creep resulting in material degradation and strain. The most common method of pipe state evaluation is pipe diameter monitoring. Usually such measurements are performed with micrometer gauge in locations where special “pipsâ€‌ were earlier installed. Other methods are also tested to monitor creep progress like various temperatureresistance strain gauges or eddy current sensors. The paper examines a new ultrasonic technique to evaluate thickwalled pipe diameter changes. Pipe diameter evaluation is based on time of flight of bulk ultrasonic waves propagating in circumferential direction along the polygon, reflecting on the pipe external surface only. Presented are results of experiments performed on 100 mm diameter pipe subjected to internal pressure to generate small diameter changes and on 273 mm diameter and 40 mm wall thickness pipe section. Measurements were performed with longitudinal, shear SV and shear SH waves. Described are advantages and disadvantages of various ultrasonic wave types for pipe diameter evaluation in practice. Discussed is the influence of residual stresses and temperature on accuracy of pipe diameter evaluation with proposed technique. Shear SV wave was chosen as the most easily applicable ultrasonic wave on thickwalled tubes.