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A computer-controlled system is described for the measurement of the AC impedance spectrum of coated pipe samples in the laboratory. The extent of water penetration into various coatings were compared.
Bode plots were made of the coated pipes until water penetration became excessive. Then Nyquist plots were used to demonstrate the mechanism of water penetration. The data showed that water incorporation into these thick pipeline coatings is into pores and defects rather than a uniform general penetration.
Thus, it is contrary to the observed mechanism of water penetration to calculate a penetrated thickness as recommended in the ASTM Test Method for Water Penetration into Pipeline Coatings (G 9).
AC impedance, polyethylene, coal tar, fusion bonded epoxy, extruded polyethylene, water penetration, pipeline coatings, computer control, capacitance
Senior research associate, Kendall Co., Lexington, MA