JANUARY 31 2003
be selected and applied using sound engineering practices. Once determined, the
voltage drop(s) may be used for correcting future measurements at the same location
providing conditions, such as pipe and cathodic protection system operating conditions,
soil characteristics, and coating quality, remain similar.
Note: Placing the reference electrode next to the pipe surface may not be at the pipe-
electrolyte interface. A reference electrode placed at a coated pipe surface may not
significantly reduce soil voltage drop in the measurement if the nearest coating holiday
is remote from the reference electrode location.
Sound Engineering Practices. When it is impractical or considered
unnecessary to disconnect all current sources to correct for voltage drop(s) in the pipe-
electrolyte potential measurements, sound engineering practices should be used to
ensure that adequate cathodic protection has been achieved.
In-Line Inspection of Pipes. Where practicable, in-line inspection of
pipelines may be helpful to determine the presence or absence of pitting corrosion
damage. Absence of corrosion damage or the halting of its growth may indicate
adequate corrosion control. The in-line inspection technique, however, may not be
capable of detecting all types of corrosion damage, has limitations in its accuracy, and
may report as anomalies items that are not corrosion. For example, longitudinal seam
corrosion and general corrosion may not be readily detected by in-line inspection. Also,
possible thickness variations, dents, gouges, and external ferrous objects may be
detected as corrosion. The appropriate use of in-line inspection must be carefully
Stray Currents and Stray Electrical Gradients
. Situations involving stray
currents and stray electrical gradients may exist that require special analysis.
ALTERNATIVE REFERENCE ELECTRODES
Alternative to Saturated Copper / Copper Sulfate. er standard reference
electrodes may be substituted for the saturated copper/copper sulfate reference
electrode. Two commonly used reference electrodes are listed below along with their
voltage equivalent (at 25 C, [77 F]) to -850 mV referred to a saturated copper/copper
sulfate reference electrode:
Saturated KCl calomel reference electrode: -780 mV
Saturated silver/silver chloride reference electrode used in 25 ohm-cm
seawater: -800 mV.
Alternative Metallic Material or Structure. In addition to these standards
reference electrodes, an alternative metallic material or structure may be used in place