Cathodic Protection Training Course

Module 4

8 cathodic protection models

Coated pipe with coating faults.

In order to study the behaviour of corrosion and cathodic protection at a coating fault on a steel pipeline we can make a scale model that will behave in a similar way that we observe in field work.

We take a short length of pipe and wrap it in insulating tape after making a good electrical contact facility to the pipe metal. We 'bury' this pipe in a model of the electrolyte consisting of a super absorbant cloth held close to the taped metal surface by pressing it into a slot cut in a sponge bed set in a metal box.

the result is similar to the circumstances found in reality where the only thing you see is the metal connection poking from the surface of the electrolyte.

Single coating faults can be subjected toa variety of conditions to produce corrosion showing both anode and cathode.

Or making the coating fault all anodic, seeing that the result is totally covered by corrosion products.

To do this we make another coating fault and force it to be cathodic by imposing an 'interference current'.

The picture above shows the bottom of the pipe with the cathode and the anode.

This picture shows a pipe with two coating faults that each have both anode and cathode.

The original coating fault has been cut out to reveal the metal surface below the coated area.

This can be examined to see the effects of 'cathodic disbondment' and 'over protection'

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