Effects of time pressure and noise on non-destructive testing

Manual ultrasonic testing (UT) is the most frequently used non-destructive testing (NDT) method for in-service inspection of components important to safety and/or plant availability. Earlier, great variations have been found in operator performance, often attributed to operator fatigue. However, no conclusive findings have been reported. According to the Yerkes-Dodson law there is an optimal arousal level where performance is highest, for simple tasks this optimum is higher than for more complex tasks. In the present study twenty operators performed manual ultrasonic inspections of six test pieces with manufactured flaws. The operators performed the inspections under stress (high arousal - time pressure and noise) and non-stress conditions; one condition the first day and the other the second and last day. It was hypothesised that the stress condition led to a level of arousal so high that it would affect the results negatively. The results confirmed that the operators were affected by the stress condition. However, contrary to the hypotheses it was found that the manipulation increased operator performance. Operators with the stress condition the first day performed better than the other operators did (under both the stress and the non-stress condition). This was interpreted as the 'stress first' (group 1) operators had established efficient performance patterns the first day - affecting also the second day. Operators beginning with stress condition also tended to be more motivated. It was concluded that operator performance is affected by arousal. The operators with non-stress first (group 2) worked hard with the complex task but their arousal level was assumed to be above the optimal, resulting in a low hit rate