At the two-wire test station a test current of several A is
applied. If the measured potential on the supposedly isolated section does
not change, or if it changes to a more positive value when the test current is
applied, the insulation is effective. Special instruments have also been
specifically designed to perform the test of insulation at two-wire test
stations. As previously shown, an audio frequency pipe locator can also be
used to inspect buried insulating connections. A special test instrument is
also commercially available for underground insulator testing.
Aboveground Structures. For aboveground insulating fittings more
direct methods can be used to test the effectiveness of the insulation. If
there is an appreciable potential difference (over 100 mV) between the
isolated sections, the insulation is effective. A flange insulation tester
(instrument) that uses high frequency skin effect current is preferred if
As for buried insulating joints, special instruments have also been
developed for more precise measurement of aboveground insulating joints.
Corrosion Survey Checklist. In order to plan and design a cathodic
protection system for either an existing structure or for a structure to be
constructed, the checklists in Appendix A should be reviewed to identify the
need to determine information pertinent to the design.