Iron rusts when exposed to oxygen, salt and water. These elements produce an electrical charge that breaks down the chemical composition of iron and causes it to corrode. Preventing the corrosion is possible, but the electrical charge has to be shifted away from the iron and absorbed by another type of metal. An electrochemical cell can be formed where the iron acts as a cathode and the absorbing metal acts as an anode.
Industries that rely on an iron pipeline to move product use a couple of different ways to protect their pipes to prevent breaks and spills. The pipeline cathodic protection methods are Galvanic (or Sacrificial Anode) and Impressed Current Systems.
Metals that have a lower electrochemical charge than iron are used to draw the current away from the iron. Zinc and magnesium are common choices for this process. The zinc or magnesium is usually buried in the ground and connected to a pipeline with wire. The electrical charge passes from the iron to the other metal via the wire. Eventually the charge is completely removed from the iron and rusting stops. The “sacrificial” metal usually rusts and corrodes over time and will have to be replaced for the pipeline to maintain its protection.
Impressed Current Systems
This process involves using a battery or power supply to stimulate the electrochemical process on larger pipelines. DC power is used to push the electrical current in the direction of anode fields made of magnesium, zinc or aluminum planted or placed at strategic spots along the pipeline. The positive end of the current is connected to the array and the negative end is attached to the pipes. The DC power moves the electrical charge off the iron and into the arrays of sacrificial metals.
These impressed current systems are used widely in large-scale operations where the pipelines are extensive and run for long distances. Galvanic systems can be used where providing power is impractical.
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