New York Codes, Rules and Regulations › Title 16 - DEPARTMENT OF PUBLIC SERVICE › Appendices › Appendix 14-D

Current through Register Vol. 46, No. 28, July 10, 2024
CRITERIA FOR CATHODIC PROTECTION
I. Criteria for cathodic protection.
Steel, cast iron, and ductile iron structures.
A negative (cathodic voltage of at least 0.85 volt, with
				reference to a saturated copper- copper sulfate half cell. Determination of
				this voltage must be made with the protective current applied, and in
				accordance with sections II and IV of this Appendix.
A negative (cathodic) voltage shift of at least 300 millivolts.
				Determination of this voltage shift must be made with the protective current
				applied, and in accordance with sections II and IV of this Appendix. The
				criterion of voltage shift applies to structures not in contact with metals of
				different anodic potentials.
A minimum negative (cathodic) polarization voltage shift of 100
				millivolts. This polarization voltage shift must be determined in accordance
				with sections III and IV of this Appendix.
A voltage at least as negative (cathodic as that originally
				established at the beginning of the Tafel segments of the E-log-I curve. This
				voltage must be measured in accordance with section IV of this Appendix.
A net protective current from the electrolyte into the
				structure surface as measured by an earth current technique applied at
				predetermined current discharge (anodic) points of the structure.
Aluminum structures.
Except as provided in subparagraphs (3) and (4) of this
				paragraph, a minimum negative (cathodic voltage shift of 150 millivolts,
				produced by the application of protective current. The voltage shift must be
				determined in accordance with sections II and IV of this Appendix.
Except as provided in subparagraphs (3) and (4) of this
				paragraph, a minimum negative (cathodic) polarization voltage shift of 100
				millivolts. This polarization voltage shift must be determined in accordance
				with sections III and IV of this Appendix.
Notwithstanding the alternative minimum criteria in
				subparagraphs (1) and (2) of this paragraph, aluminum, if cathodically
				protected at voltages in excess of 1.20 volts as measured with reference to a
				copper-copper sulfate half cell, in accordance with section IV of this
				Appendix, and compensated for the voltage (IR) drops other than those across
				the structure-electrolyte boundary may suffer corrosion resulting from the
				build-up of alkali on the metal surface. A voltage in excess of 1.20 volts may
				not be used unless previous test results indicate no appreciable corrosion will
				occur in the particular environment.
Since aluminum may suffer from corrosion under high pH
				conditions, and since application of cathodic protection tends to increase the
				pH at the metal surface, careful investigation or testing must be made before
				applying cathodic protection to stop pitting attack on aluminum structures in
				environments with a natural pH in excess of 8.
Copper structures. A minimum negative (cathodic) polarization
				voltage shift of 100 millivolts. This polarization voltage shift must be
				determined in accordance with sections III and IV of this Appendix.
Metals of different anodic potentials. A negative (cathodic)
				voltage, measured in accordance with section IV of this Appendix, equal to that
				required for the most anodic metal in the system must be maintained. If
				amphoteric structures are involved that could be damaged by high alkalinity
				covered by subparagraphs (3) and (4) of paragraph B of this section, they must
				be electrically isolated with insulating flanges or the equivalent.
II. Interpretation of voltage
			 measurement. Voltage (IR) drops other than those across the
			 structure-electrolyte boundary must be considered for valid interpretation of
			 the voltage measurement in paragraphs A(1) and (2) and paragraph B(1) of
			 section I of this Appendix.
III.
			 Determination of a polarization voltage shift. The polarization voltage shift
			 must be determined by interrupting the protective current and measuring the
			 polarization decay. When the current is initially interrupted, an immediate
			 voltage shift occurs. The voltage reading after the immediate shift must be
			 used as the base reading from which to measure polarization decay in paragraphs
			 A(3), B(2), and C of section I of this Appendix.
IV. Reference half cells.
Except as provided in paragraphs B and C of this section,
				negative (cathodic) voltage must be measured between the structure surface and
				a saturated copper-copper sulfate half cell contacting the electrolyte.
Other standard reference half cells may be substituted for the
				saturated copper-copper sulfate half cell. Two commonly used reference half
				cells are listed below along with their voltage equivalent to -0.85 volt as
				referred to a saturated copper-copper sulfate half cell:
Saturated KCl calomel half cell: -0.78 vol.
Silver-silver chloride half cell used in sea water: -0.80
				volt.
In addition to the standard reference half cells, an alternate
				metallic material or structure may be used in place of the saturated
				copper-copper sulfate half cell if its potential stability is assured and if
				its voltage equivalent referred to a saturated copper-copper sulfate half cell
				is established.