Page 693 - Corrosion Engineering Principles and Practice

646 C h a p t e r 1 4 P r o t e c t i v e C o a t i n g s 647

FIGURE 14.28
Tooke gauge.
(Courtesy of
KTA-Tator, Inc.)

Visual inspection: Visual inspection can be conducted with or without
magnification. The Tooke gauge, which makes a diagonal cut through
a coatings system to the substrate, permits measurement and iden-
tification of the coating layers under magnification (Figs. 14.28 and
14.29). These gauges are less commonly used because they are slower
to operate, and create a cut through the film.

14.9.4 Laboratory Testing
Whenever possible, standard test procedures and means of evaluation
provided by organizations such as ASTM, NACE, or SSPC should be
consulted and followed. Only in this manner can correlation with the
results of other workers be established. SSPC and NACE certified
coating/corrosion professionals are trained to investigate paint
failures and know which analytical technique or investigation method
may provide the most useful information.
For example, gas chromatography is excellent at detecting solvents,
but would be of little use in determining why an alkyd resin failed.
Another example is that only electrochemical impedance spectroscopy
(EIS) and actual exposure tests can provide a distinction between
storage-related problems and paint application/formulation problems
when white rust is formed on painted galvanized steels. Traditional
approaches cannot make such distinction. These insights could save
unnecessary effort and expense, simply by selecting the right test.