Connect, no.81, November-December 1996
On-stream inspections by TWI using specialised NDT techniques are helping a major oil company make cost-effective decisions on continued operation versus repair or replacement.
Working overseas, TWI has successfully completed a series of on-stream ultrasonic inspections of a weld section in a thick-walled pressure vessel operating at elevated temperature.
The automated ultrasonic testing procedures used were developed by TWI over a period of several years. Initially, only the time-of-flight diffraction (TOFD) technique was applied using TWI's Zipscan III flaw detector. Subsequently, the inspection was enhanced using the Force Institutes' P-Scan system for pulse-echo inspection.
This year, TWI has further improved its elevated temperature TOFD capability by adding a state-of-the-art AEA Sonomatic Microplus system and developing, in-house, a simple high temperature TOFD scanner for surfaces which are typically around 250 degrees C.
Using computerised ultrasonic techniques has meant that the data acquired are highly repeatable from one in-service inspection to another. Also, the use of complementary techniques provides the optimum combination of data for flaw detection, characterisation and sizing.
The purpose of these periodic on-stream inspections is to assure mechanical integrity and allow better planning and scheduling for repair, or if necessary, replacement. Results are used in fitness-for-service evaluations, enabling the company to continue operating the equipment safely and reliably and, where feasible, defer any repair/replacement costs.
For further information contact Mark Kirby at TWI.