A field study was conducted to evaluate the effect of induced alternating current (AC) voltage on a cathodically protected pipeline paralleling an electric power transmission line. The study used the instant-off method, with steel probes simulating coating defects. Data regarding probe potentials and currents were compared with the proposed tentative criterion for cathodic protection (CP). Positive proof of the adequacy of CP was obtained after field testing for 1 year, when probes were removed to ascertain corrosion rates. Synchronous fluctuation of induced probe potential and current with the sinusoidal frequency of 50 Hz, corresponding to the power-line frequency, was observed. The higher the AC probe current density, the greater the amount of DC cathodic current density to the probe was, together with sufficient off-potential more negative than -1.12 VCu-CuSO4), indicating a decrease in AC corrosion. Proof of the adequacy was obtained after field testing for 1 year, when the probe was removed to ascertain corrosion rates. Uniform corrosion rates were <= 0.032 mm/y. On the basis of the results obtained from field studies, laboratory studies should follow with simulation experimentation to establish the criteria to assess the effect of induced AC voltage on A CP system.
Effect of induced alternating current voltage on cathodically protected pipelines paralleling electric power transmission lines
Einfluß induzierter Wechselspannung auf kathodisch geschützte Rohrleitungen parallel zu Elektroenergieübertragungsleitungen
Corrosion, Houston ; 55 , 2 ; 200-205
1999
6 Seiten, 8 Bilder, 2 Tabellen, 6 Quellen
Aufsatz (Zeitschrift)
Englisch
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