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The role of isolation within cathodic protection systems


Isolation is often used in the form of flange isolation kits (FIK) or monolithic isolation joints (MIJs) to further reduce the cost of electricity in order to protect the pipeline and keep the electrical field to an effective level

Both products accomplish the same task, but flange isolation kits (FIKs) are predominately found in above ground installations, while monolithic isolation joints (MIJs) are commonly found below ground. FIKs and MIJs break the metallic path in the pipeline and optimise the protection of the pipeline. Because they break the metallic path, they also stop stray current up to significant voltages. Breaking the metallic path as a function of an FIK or MIJ is very important as it will stop the electrochemical reaction between dissimilar metals. By simply inserting a FIK, the metallic path between the component and the pipeline is eliminated and galvanic corrosion is then mitigated. 

There are many types of flange isolation kits and monolithic isolation joints currently available. If the pipeline is carrying a flammable material, it is recommended that a fire-safe flange isolation kit be used. If chemicals are added to the media to reduce microbial colonies from forming, act as surfactants, reduce iron sulphide build-up or for any other reason, or if chemicals such as hydrogen sulphide are part of the media stream, it is important that the isolation kit is chemically compatible with the chemicals being used.

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Role of Isolation Gasket on Emissions

Presently, many companies are attempting to achieve greenhouse gas emission reduction goals. If the pipeline is part of that effort, it is recommended that glass reinforced epoxy (GRE) based isolation gaskets and phenolic isolation gaskets be avoided as these materials are permeable. It is also recommended that when an isolation product is used (either flange isolation kit or monolithic isolation joint), that a pipeline decoupler also be used to mitigate stray current or lightning effects that are beyond the capabilities of the isolation kit or joint.

A common flange isolation kit will consist of an isolating gasket, an isolating sleeve and isolating washers (preferably fully coated and encapsulated stainless steel washers).

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