Current distribution and electrochemical environment in a cathodically protected crevice
- Clarkson Univ., Potsdam, NY (United States). Dept. of Chemical Engineering
Current and potential distributions inside the crevice of a simulated disbonded coating with a holiday during cathodic protection (CP) of steel were measured experimentally in 0.001 M to 0.6 M sodium chloride (NaCl) solutions covering a range of conductivity from 0.012 {Omega}{sup {minus}1} m{sup {minus}1} to 5.1 {Omega}{sup {minus}1} m{sup {minus}1}. The circular crevice was 95 mm in radius, 0.8 mm in thickness, and open to the test solution through a holiday of 5 mm in radius on the center of the coating. Microelectrodes mounted on the steel surface were used to determine the local current densities inside the crevice. change in the concentration of dissolved oxygen inside the crevice was monitored with a micro-oxygen electrode. Current distribution was extremely nonuniform. Depending upon NaCl concentrations, the local current density on steel exhibited a 100-fold decrease from that at the holiday opening within 20 mm to 40 mm into the crevice. Current and potential distribution curves became less uniform with a decrease in NaCl concentration and solution conductivity. In 0.6 M NaCl, the steady-state local current density on steel at the sealed end of the crevice was 200 times smaller than that at the holiday opening. In 0.001 M NaCl, the local current density at the sealed end became 1,000 times smaller than that at the holiday opening. The dissolved oxygen within the crevice was consumed largely by local corrosion cells when the crevice was consumed largely by local corrosion cells when the crevice was formed initially. Any oxygen needed for the reduction reaction during CP had to be transported into the crevice by diffusion through the holiday opening.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 349896
- Journal Information:
- Corrosion, Journal Name: Corrosion Journal Issue: 3 Vol. 55; ISSN 0010-9312; ISSN CORRAK
- Country of Publication:
- United States
- Language:
- English
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