Welcome, Guest

• Forgot your password?
• Apply for membership

1. • CommentAuthorzee
   • CommentTimeJul 10th 2009

    permalink
   An electric potential difference between galvanized steel and copper grounding exists when they are exposed to chloride containing soil or water table. When these metals are in electrical contact, the potential difference produces electron flow between them. Accelerated corrosion takes place on galvanized surface adjacent to copper grounding. This is called galvanic corrosion.
   
   The nature and corrosivity of the soil environment largely determines the degree of galvanic corrosion due to copper grounding. Usually the galvanized steel becomes anodic member of galvanic couple. The severity depends on moisture content, chloride content, temperature, soil resistivity, the oxidizing or reducing nature of the soil.
   
   Another important factor in galvanic corrosion is the ratio of cathode (copper grounding) to anodic areas (galvanized steel). A small cathode draws less current than a large one and hence more slowly dissolves the galvanized steel anode. Therefore, a large anode (galvanized pole) and small cathode (copper grounding) will create a favorable area ratio. It should be noted that galvanic corrosion requires electrical contact between two metals.
   
   As corrosion progresses, corrosion products may accumulate at the galvanized surface or copper grounding or both depending on oxidizing or reducing nature of the soil/water table. This accumulation may reduce or increase the corrosion rate. Therefore, the best way to determine the acceleration of corrosion due to galvanic action is to measure the current between galvanized steel and copper grounding in field soil environment. Matco has developed novel techniques to perform this type of testing in the field.
   
   It should be noted that in chloride containing corrosive soils, the bare galvanized surface is prone to corrosion attack and should be coated and cathodically protected to prevent further accelerated corrosion due to galvanic action.