When a leading civil engineering operator, charged with maintaining one of the UK's most notable bridge structures, needed to detect and size service induced fatigue cracks, it turned to TWI to perform the task.
Hanger boxes, A-frame assemblies and lighting columns all came within the scope of the work as well as an inspection of the deck structure's welds from within the box sections.
TWI produced an inspection procedure for each of the inspection tasks identified, often with the help of specially constructed test pieces. These procedures involved the use of both Ultrasonic and Eddy current methods. A field trial was also carried out using the ultrasonic Phased Array technique on selected hanger box welds. The purpose of this was to demonstrate that a more advanced inspection could replace the current manual ultrasonic inspection procedure.
TWI was able to assure its client that there was no evidence of service induced planar flaws in the deck welds, the lighting column bases or the A-frame assemblies. Detailed inspection of the hanger box welds in regions where the paint had cracked showed no associated fatigue related flaws.
Most interestingly, this work showed that high quality images of the critical welds in the hanger boxes could easily be obtained using Phased Array technique. Due to the permanent record and guaranteed scan coverage, this approach provides a much higher integrity inspection than the more traditional manual ultrasonic technique used to date. However, Phased Array data requires time to process and evaluate. It was concluded that, per metre of weld, the time required for each technique was comparable.
For information about TWI's capabilities please contact us.