Acoustic emission testing (AT) is in Europe an already well established non-destructive
testing (NDT) method. Qualification requirements as well as certification of testing personnel are
laid down in European standard EN 473. A widespread application of AT deals with testing of
unfired pressure vessels for re-qualification after a certain period of service (repetition test). The
advantages of applying AT compared to the traditional procedure of hydrostatic test plus visual
inside inspection are numerous. Just to name the most important: reduction of downtime, omitting
of residual humidity and no risk of product contamination with water. It is a fact that AT provides
much more useful information concerning the condition of the pressure vessel under test than a
simple ‘passed’ or ‘not passed’ obtained usually by a hydrostatic test. This contribution gives two
examples of practical experience, where severe corrosion defects have been detected by AT. The
defects have been found in both cases on the vessel’s shell under the thermal insulation, where they
have been hidden undetected for years. It can be assumed that even the vessel with the most severe
damage (loss of more than 50% of the nominal wall thickness) would have passed the traditional
repetition test procedure and that failure within the following service period would have occurred.
In contrary to this scenario, AT enabled the vessel operator to perform appropriate repair in time.
