Standard Practice for Conducting a Coating/Lining Detachment Acoustical Sounding (Tapping) Inspection

Abstract

5.1 Coating condition assessments are based, in large part, on visual observation of defects in or damage to the coating/ lining system. The visual observation process also identifies precursors of defects (discoloration, cracking, etc.). Such visual inspections may be augmented with destructive adhesion testing on a case-by-case basis. Acoustical sounding (tap testing) provides a non-destructive alternative to destructive testing to quickly identify areas of potential coating/lining film detachment for more intrusive examination, since poor adhesion to the substrate may not be visually evident. 5.2 Areas of suspect coating or lining adhesion revealed by the tap test may be overlooked during normal visual observation until visual indicators of failure (for example, blisters, cracks, peeling, or the presence of corrosion) become evident. Acoustical sounding can be a predictive go/no examination, in that it provides indication of a reduced bond between the coating/lining system and the substrate before disbonding becomes visually evident. 5.3 Acoustical sounding inspection is particularly useful when assessing the condition of immersion service linings that may be covered with corrosion product, staining, or other tenacious deposits that obscure small defects (Note 1). High performance coatings and linings can also visually mask disbondment and under-film corrosion due to high cohesive strength. 5.4 Although the use of acoustical sounding (tapping) to determine potential coating detachment is relatively simple, the extent of the noted detachment is subject to the inspector’s interpretation of the tonal differences in the produced sound. Likewise, areas with high levels of ambient background noise make tonal differences of the produced sounds difficult to distinguish. Furthermore, data recording must be done manually using sketches and photographs. Note 1: For best results, the coating or lining should be cleaned prior to or in combination with acoustical sounding, as effective use of tap testing should include a concurrent visual examination.