FOUR PHENOMENA AFFECTING CATHODIC PROTECTION AND CORROSION RATES

THE INFLUENCE OF CATHODIC PROTECTION AND CORROSION RATE ON BURRIED STRUCTURES OF ELECTRO-OSMOSIS, COATING HOLIDAY SIZE, A-C DISCHARGE, AND UNDERFILM MOISTURE ARE OFTEN NOT FULLY UNDERSTOOD OR CONSIDERED BY CORRISION ENGINEERS. THE BACKGROUND AND SIGNIFICANCE OF THESE FOUR PHENOMENA ARE DISCUSSED. IT IS CONCLUDED THAT: (|) ELECTRO-OSMOTIC EFFECTS HAVE A DIRECT INFLUENCE ON THE OPERATION OF GROUND BEDS AND ON CERTAIN PHENOMENA AT THE PROTECTED CATHODE, (2) THE CURRENT DENSITY FOR A GIVEN DRIVING VOLTAGE VARIES INVERSLY WITH THE HOLIDAY SIZE, (3) ALTERNATING CURRENT FLOW BETWEEN A METAL AND AN ELECTROLYTE DOES RESULT IN CORRISION. THIS CAN CAUSE SEVERE CORRISION OF ALLUMINUM AT HIGH CURRENT DENSITY. FOR STEEL AND COPPER, HOWEVER, THE RATE IS OF THE ORDER OF ONLY 0.1% OF THE CORRISION THAT WOULD THEORETICALLY BE EXPECTED FROM THE SAME D-C MAGNITUDE. THIS CORROSION EFFECT ON STEEL PIPELINES IS READILY OVERCOME BY CATHODIC PROTECTION PROCEDURES. AND (4) WHILE THERE CAN BE AREAS IN CONTACT WITH MOISTURE UNDER A DISBONDED COATING THAT ARE NOT REACHED BY CATHODIC PROTECTION, THE RATE OF CORROSION AT THESE AREAS ARE, UNDER MOST CONDITIONS, INSIGNIFICANT OR SELF-LIMITING. MORE RESEACH IS NEEDED ON THE SUBJECT.

• Supplemental Notes:
  • Vol 8, No 9, PP 67-71, 6 FIG, 6 TAB, 10 REF
• Authors:
  • Hewes, F W
• Publication Date: 1969-9

Media Info

• Serial:
  • Materials Protection and Performance
  • Publisher: National Association of Corrosion Engineers

Subject/Index Terms

• TRT Terms: Aluminum; Cathodic protection; Copper; Corrosion protection; Electrolytes; Moisture content; Pipe; Steel; Underground structures
• Subject Areas: Bridges and other structures; Geotechnology; Highways; Materials;

Filing Info

• Accession Number: 00216890
• Record Type: Publication
• Files: TRIS
• Created Date: Mar 20 1973 12:00AM