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III.    ANALYSIS AND CONCLUSION:

A   

Criteria for Cathodic Protection:
A change of potential in the negative direction of -300mv or more is one criteria for full cathodic protection.

B   

Structure-to-Water Potentials:
The structure-to-water potentials after the coupling halves and the bolt units were connected range from a low of -720mv to a high of -810mv. This indicates that a high level of cathodic protection has been achieved on the stainless steel bolt units. The average potential shift of change in the negative direction of stainless steel bolt units was 494mv. This indicates that the stainless steel bolt units are receiving a full level of cathodic protection from the couple with the cast-iron coupling.
C    Inspection of Test Samples:
All test samples were inspected after testing and found to have no visible corrosion attack of the stainless steel bolt units. Through testing and inspection, it has been determine that the MG Coupling, consisting of a cast-iron body and stainless steel bolts, acts as a galvanic corrosion cell. The stainless steel bolt units, being lower in electromotive series, are cathodic to the cast-iron coupling halves making the coupling the anode.
his type cathodic protection is considered sacrificial. The anode (in this case the cast- iron coupling body) protects the stainless steel bolt units. The cast-iron coupling body is acting like the anode in the sacrificial system.

D    Conclusion:
It is concluded that due to the relative size differential and potential difference between the coupling and stainless steel bolt units, that the bolt units will be cathodically protected and the resultant corrosion rate on the coupling should be minimal. It is anticipated that the MG Coupling will have a life expectancy as great or greater than that of a pipe to which it is attached in the small soil environment.