 Figure 1 - A scene from the trials: demonstration of TOFD inspection during TIG welding. The ultrasonic probes can be seen located behind the weld head. 
Figure 2 - a Nordon welder deliberately inserts a defect in one of the SAW test plates. |
The trials successfully demonstrated the techniques and methods developed during the four year study to undertake NDT during welding. A number of welded test plates were prepared - one set of TIG welded 25mm thick steel, the other submerged arc welded 80 mm thick steel. Defects were deliberately implanted into the testpieces by Nordon welders at various stages of weld completion - Figure 2 shows an example of this work in progress. These defects included tungsten inclusions (for TIG welds), root cracks, porosities, lack of fusion, slag inclusions (for SA welds) and lack of penetration. The techniques that are required in order to implant suitably representative defects into the welds were developed by Nordon at an early stage in the project.
Prior to the trials, Mitsui Babcock had undertaken extensive investigations into the problems of performing TOFD inspections on incomplete weld geometries, at high temperatures and in close proximity to live welding apparatus. A probe housing was designed which incorporated both water cooling and a mechanism for automatic couplant application and removal. A manipulator rig capable of being mounted on a range of automated welding machines was designed and was interfaced to an AEA Microplus data acqusisition system. The probe manipulator is shown below in Figure (3).
