Definition - What does Foreign Structure mean?
A foreign structure is any type of metallic structure that is not planned as an element in a cathodic protection system (CPS).
In a corrosion protection system, these are metals or metallic structures that surround the system despite the fact that they are not considered to be primary parts. These structures may be found in the water or on the ground.
Corrosionpedia explains Foreign Structure
Cathodic protection systems are typically utilized in environments with minimal current requirements, as brought about by partial current output and fixed voltage. It is mainly intended for the protection of electronic structures that are isolated and small in nature. Steel structures need up to 2 milliamperes for every square foot in order to meet the criteria of cathodic protection. Thus, absolute electrical isolation should be achieved to achieve efficient cathodic protection against corrosion.
This means that a particular structure that is to be protected should be separated from any foreign structures in order to reduce the demand for current. Other than this, the structure that requires protection should be appropriately and adequately coated. Large exposed surfaces need current that surpass the power of cathodic protection against corrosion.