Cathodic Protection Training Course

Module 01 page 3

What is a reference potential and how is it vital to electrochemical measurements?

As corrosion control engineers we must constantly be aware of the electrical energy that is around us all the time and that drives the corrosion process and affects everything we do in our everyday lives.

This pipeline test point has not been visited for some time and no measurements have been made at this location.
Pipelines are 'out of sight and out of mind' so little attention is given to the fact that metal dissolves in some solutions and gives off electrical energy.
It is left to the corrosion engineers to worry about such things until a pipeline fails, causing loss of life, environmental damage and massive financial consequences.

Consultants are then asked why the pipeline failed and the debate about the criterion for cathodic protection receives attention for a little while.

Ship and boat owners are constantly aware of the damage caused by corrosion and consequently metal boats are protected by cathodic protection. They have lumps of metal attached to hulls for this purpose. These lumps of metal dissolve in the water and give off electricity which prevents the hull from corroding.

Sir Humphrey Davy first introduced this system by attaching 'pig iron' to the copper clad hulls of ships. This was one of the first things I was told when I started as a corrosion control technician in the 1970's.

I was given a piece of copper in a plastic tube full of a saturated solution of copper-sulphate and was told that this was half of a cell and the pipeline was the other half.

This is a lie. This is NOT a half-cell. It has been called a half-cell by those who do not understand science. They have been told that this is not a half cell in science but continue the use of this term as they do not want the matter investigated.

There are many corrosion cells on every section of pipeline and steel structure to which we connect the common pole of our metering system so it is only in a laboratory that this item can possible be half of anything. The copper/copper-sulphate electrode might be 1/10th of a collection of cells or it might be 1/100th of a collection of cells, we can never know how many coating faults there are on the structure or pipeline to which wehave attached the common pole of our meter.

It is also untrue because what is described by Nerste is a 'HALF CELL REACTION' and not a physical item.

Calling this item a half-cell is like calling a thought a 'brain'. A half cell reaction is software and you cannot put it into a piece of copper in a saturated solution of copper-sulphate, no matter how you try.

To say that a ground contact electrode scans an area of pipeline is also a lie, it cannot scan anything.

To say that you can calibrate a 'half-cell' is rubbish, there is no way to calibrate it.

We can clean a Cu/CuSO4 electrode and replace the solution. We can compare the potential with another such electrode but even this is not calibration (and it is cheap and easy to do yourself).

We can make a Cu/CuSO4 electrode ourselves, the materials are readily available in ordinary shops because they all have domestic uses. You can also buy coppersylphate on line.

We can carry out tests to see the variations that we can achieve in the voltage that we can measure between each electrode.