Approaches to assess reliability in visual inspection

Non-destructive testing (NDT) plays an important role in quality assurance and ensuring reliable ongoing operations in many industries. Thus, the importance of reliability assessment of inspection results is increasing. Current standards and regulations provide several approaches for this purpose. For example, DIN EN ISO/IEC 17025:2018-03 provides general requirements to determine measurement uncertainty. In contrast, method-related standards such as DIN ISO 19828:2021-03 specify detailed requirements for visual inspection (VT), considering environmental conditions and other factors (for example experience of the inspection personnel). In contrast, VDA Volume 5 defines visual inspection as an attributive method, making measurement uncertainty determinations unnecessary. Instead, the reliability of the inspection process is evaluated by proficiency tests. This paper examines approaches of regulations, based on previous experiments, for their applicability and suitability for considering the reliability of visual inspections. It is shown that individual measurement values (for example illuminance) are not suitable for this purpose. Furthermore, it is shown that human factors (HFs) (for example training or experience of the inspector), considered in isolation, are also not sufficiently suitable. Hence, the combination of the qualification of inspection methods, by means of proficiency tests on reference objects, and the application of Cohen's kappa for evaluating human factors appeared to be more suitable for the investigated issue.