For our underground piping, we are told to install a cathodic protection system with an external coating. The piping is electrically isolated by installing the insulating flanges at the ends. However, the liquid in the pipeline is phosphoric acid, an electrically conductive liquid. Does it require electrical isolation in the internal surface also? If so, how is this done?
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Re: Can you help with underground piping questions?
15 August 2011 at 1:29pmMost modern buried pipelines are coated with an organic coating that is supplemented by a cathodic protection system to prevent external corrosion. The coating protects most of the external pipe surface and the cathodic protection system prevents corrosion at the gaps or holidays in the coating. Both the coating and the cathodic protection system protect only the external part of the pipe. The internal surfaces of the pipe will receive no protection even if the pipe contains a conductive material. This is because the pipe intercepts the current and carries it back to its source. Cathodic protection systems can do more harm than good if they are not designed and installed properly. I suggest you refer to a standard, such as NACE SP0169 "Control of External Corrosion on Underground or Submerged Metallic Piping Systems," for more information.
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