An appraisal of ultrasonic wall thickness measurement practices

There are many forms and manifestations of corrosion which can affect the useful lives of pressure vessels, pipes and other components used in harsh environmental service. In-service inspection procedures commonly use thickness measurement as a guide to present and future component life. This notion arises from Code design calculations which take no account of surface condition and other features, which can seriously affect life predictions and lead to continuing risk and unplanned, let alone wasted effort spent on the collection of erroneous data. The paper examines some of the shortcomings of conventional ultrasonic wall thickness measurement and the need for more advanced methods of corrosion mapping. This approach, combined with sophisticated assessment methods within a risk management framework, can lead to significant cost savings and life planning.