What Does Interference Bond Mean?
An interference bond is the typical ground used for cathodic protection (CP) systems. It is a glue-less bond where two conformal surfaces are joined together with the aid of intermolecular forces.
This bond can be anodic, cathodic or a combination of the two. Determining and measuring the interference bond can help in managing factors that affect corrosion, such as direct stray current.
Corrosionpedia Explains Interference Bond
Stray currents are currents that flow within electrolytes coming from external sources. For instance, metallic substances such as a pipeline under the soil has a low resistance path and current is highly vulnerable to the stray currents’ harmful effects.
Stray current may enter buried parts in one area and leave it in another location. Severe corrosion may result when the current leaves the structure.
One classification of stray currents that produces an interference bond is direct stray current. This type of current can be found in foreign CP systems, direct current high-voltage transmission lines as well as transit systems. The types of interference bonds that can be produced by direct stray currents include:
- Anodic interference - This interference bond is typically found in buried anodes. In the region where the currents are picked up, the pipeline potential turns to the negative area and gets a boost in local cathodic protection. This could result in overprotection where excessive alkalis are produced, causing harm to lead alloys and aluminum.
- Cathodic interference - This form of interference bond is produced when there is proximity to a polarized cathode. The flow of current is always away from the area close to cathode. In this type of interference, the potential turns to the positive direction where currents leave the structure and this region will be most prone to corrosion.
- Combined interference - In this type of interference bond, greater damage is produced relative to the effects of cathodic and anodic interference.
In order to prevent corrosion related to the interference bond, countermeasures should be implemented, such as:
- Elimination of the source of stray current
- Reducing the output current
- Cathodic shielding
- Electrical bonding
- Sacrificial anodes