Module 09 Sacrificial Anodes


Metals that are less noble are sacrificed in the galvanic reaction to the more noble subject metal.

Sacrificial anodes are designed by metalurgists to inject Direct Current electricity into the ground/electrolyte.

They are connected to the pipeline or the internal tank bottom and discharge the corrosion current from the base metal which is sacrificed to protect the subject metal.

The electrolyte close to the anode is more positive that the surrounding electrolyte. It has a higher electrical potential and will show this on a digital voltmeter.

It is good to be able to imagine a groundbed as a pile of electricity and this can be displayed on a computer spreadsheet.

In the case of submarine pipelines we use 'collar anodes' that are welded to a conductor to the pipeline metal over the pipeline coating. The inside red primer of the collar anode can be seen in the diver's report on the Nord Stream Pipeline. This was mistaken as the actual pipeline metal that had ruptured.

The 48" dia Export pipeline at Forcadis leaked because the impressed current system at the shore end drew current from the nearest collar anode which depleted and then the current was drawn from the offshore pipeline metal itself.

Hybrid cathodic protection systems that include sacrificial and impressed current must be carefully and continuosly monitored.

The case of dry cell battery is sacrificed to the carbon rod in the center of the acid paste.

Battery technology is now intensly studied as a means to store energy and is developing rapidly as a very lucrative industry.