The stray current investigation identified the following influences:
WGP personnel agreed to temporarily cut the linear anode circuit that crossed the PNG lines, disconnecting approximately 65 feet of the circuit. After the testing was completed, the following was learned:
- Peak potentials at the crossing with the WGP linear anode were reduced to approximately -2.0 Volts. Because cutting of this circuit did not actually remove any of the anode or backfill, it was suspected that some current leakage continued.
- With protective current from PNG and WGP rectifiers interrupted, the least projected potentials for the 12-in. line were positive: between +0.080 Volt and +0.120 Volt at the crossings with the WGP B and C lines.
- With protective current from PNG and WGP rectifiers interrupted, the least protected potentials for the 16-in. line were positive: between +0.150 Volt and +0.200 Volt at the crossings with the WGP B and C lines.
Because the CIS potential surveys rely on reference electrodes that travel over the surface of the soil, they are subject to measurement errors associated with current flowing through the soil from various sources. Interruption of the protective current sources is one way to reduce these errors. As a check on the CIS potential values, PNG installed new test stations, including soil access tubes to permit placement of reference electrodes close to the surface of the buried pipes. These potential measurements were in good agreement with the values obtained during the CIS testing. In addition, the test stations installations offered the opportunity to confirm that no significant corrosion damage has occurred.