On-stream inspections by TWI using specialised NDT techniques have helped a major oil company to make cost-effective decisions on continued operation versus repair or replacement.
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. Subsequently, the inspection was enhanced using a pulse-echo imaging system.
The use of computerised imaging systems 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.