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  1. CathodicGuy

    Cathodic Protection - 100mV Shift

    The 850 mV criterion is applicable to coated ferrous structures. It would be inappropriate to use it, for example, on bare steel or iron pipe, where complete polarization is unlikely and it would be an overly conservative criterion. IR drops in the soil must be considered when measuring the...
  2. CathodicGuy

    Cathodic Protection - 100mV Shift

    In some cases, the 850mV criterion cannot or should not be used (that's a whole 'nother story). The 100mV shift is usually measured as the arithmetic difference between the instant off and the static potential (if you have that data). You could also measure the decay in potential from the...
  3. CathodicGuy

    cathodic protection design procedure

    Unfortunately, Ben Franklin defined current flow back in the 1700's when he was referring to positive (ion) current flow (opposite to electron flow). CP folks still use this terminology and it often confuses new engineers who are used to "electron flow." Now to answer the original post...
  4. CathodicGuy

    cathodic protection design procedure

    There are two basic methods of applying cathodic protection, although there are many variations on installing cathodic protection. These two methods are known as sacrificial (galvanic) anodes and impressed current (rectifier) cathodic protection. Sacrificial anodes are usually made of an alloy...
  5. CathodicGuy

    Corrosion Protection for Underground Compressed Air Pipe

    Galvanized CS underground will not protect the line. Have you ever unearthed an old buried galv elec conduit? "yellow jacket" is a good coating, but don't bury the line w/o adding cathodic protection. If you go w/sacrificial anodes, make sure you isolate the pipe. If not, current wil, be...
  6. CathodicGuy

    Interference on foreign structures

    Have you done a continuity test versus local and remote half-cells? If there is an anodic (DC discharge) area, there will be a local pickup (cathodic) area. Find these by P/S reads, run a temporaty drainage cable and see if you can mitigate the depressed reads.

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