Method and apparatus for diagnosing degradation of coating film on metal material

An apparatus for diagnosing degree of degradation of a coating film on a metal material, comprising:

• a grid-like jig for dividing a surface of the coating film to be measured into a plurality of small area zones of substantially same size;
• a detector having an open mouth portion in close contact with said surface of the coating film at each of said zones, when pushed against said surface, a liquid electrolyte holding chamber communication with said open mouth portion and holding the liquid electrolyte and an electrode for electrolysis disposed within said liquid electrolyte holding chamber;
• and
• AC impedance measuring means connected to said detector for measuring impedance indicative of ion transmission resistance of the coating film at the zones with which said open mouth portion of said detector is in close contact energizing said detector by an AC source voltage of a controlled frequency.

An apparatus for diagnosing degree of degradation of a coating film on a metal material, comprising:

• a plurality of detectors each having an open mouth portion in close contact with a surface of the coating film on the metal material to be measured when pushed against said surface, a liquid electrolyte holding chamber communicating with said open mouth portion and holding a liquid electrolyte, and an electrode for electrolysis disposed within said liquid electrolyte holding chamber;
• movable detector supporting means for holding said plurality of detectors such that said open mouth portions of said detectors simultaneously pushed against the surface of the coating film in close contact with the surface of said coating film;
• a multiplexer having a plurality of input terminal connected to the output terminals of said plural detectors, respectively, and an output terminal connected sequentially to said input terminals;
• and
• AC impedance measuring means connected to the output terminal of said multiplexer for measuring impedance indicative of ion transmission resistance of the coating film at the zones with which said open mouth portion of said detector is in close contact, while energizing said detector by an AC source voltage of a controlled frequency.

A method of diagnosing degree of degradation of a coating film on a metal material, comprising the steps of:

• dividing a surface on the coating film of the metal material to be measured into a plurality of small area zones at a predetermined interval;
• measuring impedance indicative of ion transmission resistance of the coating film on the metal material at each of said zones by applying an AC source voltage of a selected frequency to the coating film at said zone according to an AC impedance measuring method;
• and
• evaluating degree of degradation of the coating film based on two-dimensional pattern in distribution of the impedance values of the coating film measured at said zones, respectively.