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MAR -30-99 TUE 06:30 PM I' RO COMPANIES INC FAX NO. 5104J1 3698 P. 06/07 4.2 Criteria for Steel Structures 4.2.1 Corrosion control can be achieved at various levels of cathodic polarization depending on the environmental conditions. However, in the absence of data which demonstrate that adequate cathodic protection has been achieved, one or more of the following shall apply; 4.2.1.1 A negative (cathodic) potential of at least 850 mV with the cathodic Protection applied. This potential is measured with respect to a saturated copper/copper sulfate reference electrode contacting the electrolyte. Voltage drops other than those across the structure -to -electrolyte boundary must be considered for valid Interpretation of this voltage measurement. 4.2.1.2 A negative polarized potential (see definition in Section 1.2) of at least 850 mV relative to a saturated copper/copper sulfate reference electrode. 4.2.1.3 A minimum of 100 mV of cathodic polarization. The formation or decay of polarization can be used to satisfy this criterion. 4.3 Alternative Reference Electrodes 4.3.1 Other standard reference electrodes may be substituted for the saturated copper/coppar sulfate reference electrodes. However, their voltage equivalents need to be converted to the referenced equivalents. 4,41 Special Considerations 4.4.1 Special cases may exist such as stray currents and stray electrical gradients that require the use of criteria different from those listed above. Measurements for current loss and gain on the structure and current tracing in the electrolyte have been useful n such cases. 4.4.2 Abnormal conditions in which protection is ineffective or only partially effective sometimes exist. Such conditions may Include elevated temperatures, disbonded coatings, shielding, bacterial attack, and unusual contaminants in the electrolyte. DATA INTERPRETATION rho assessment of cathodic protection effectiveness is based on the interpretation of structurt-to-soil potentials gathered at points of access to the protected structure. Normal survey techniques require, as a minimum, measurement of a sufficient number of potentials at strategic locations to give a reasonable certainty the measured potentials are representative for the area and structure of concern. This procedure permits the general status of cathodic protection to be assessed on any stricture based on a minimum number of gathered potentials, but it does not prOvidc tine actual status of cathodic protection at all points. In reality, the gathered potentials aro Only valid at the point of measurement,