APPENDIX E (continued)
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 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. A. 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
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 volt.
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
[Amdt. 192-4, 36 FR 12305, June 30, 1971]
Each component in the pipeline system must be provided with protection
against external corrosion.
(a) No pipeline system component may be buried or submerged unless that
component has an external protective coating that-
Is designed to mitigate corrosion of the buried or submerged
(2) Has sufficient adhesion to the metal surface to prevent
underfilm migration of moisture;