In response to a requirement by a major oil company member of TWI to inspect a hydrocracker reactor vessels in-service, TWI has developed procedures for ultrasonic non-destructive testing (NDT) of ferritic steel welds at elevated temperatures. Procedures for pulse-echo shear wave and time-of-flight diffraction (TOFD) were developed on representative welded test pieces containing a range of flaw types at temperatures up to 300°C.
Since 1992, TWI's NDT specialists have successfully completed a number of inspections at refineries in the USA on vessels having a surface temperature between 250-300°C. Advanced computerised ultrasonic testing equipment such as 'P-scan' and 'Microplus' is used in conjunction with specially developed high temperature probes and scanners to enable flaws to be imaged, sized and characterised.
The objective of these inspections has been to determine the size of known flaws and to monitor these flaws periodically for signs of growth. Data interpretation and initial reporting of results is provided on-site, with a formal final report following at a later date.
With their high degree of repeatability, these elevated temperature inspections provide an accurate method of monitoring known flaws, and may also be applied for initial detection of flaws without removing the vessels from service, thereby realising significant cost savings.
For more information please email contactus@twi.co.uk.