Non-destructive

As to safety, the proportion of the components of passenger stock which develops faults or fails is very small; the incidence of defects should be decreased by better knowledge of the conditions in which they must function and by more extensive and more accurate use of non-destructive testing.

Source: wiktionary

This type of physical testing by the non-destructive test is performed to check the welding quality in a closed container such as tanks and pressure vessels.

Source: wiktionary