Defining "Electrical Isolation" for a Cathodic Protection System

With respect to cathodic protection systems, the term "electrical isolation" relates to confining the (cathodic) protective current to the structure being protected.

In terms of electrical separation this could mean isolating;

• Two (or more) cathodic protection systems from one another
• Buried / immersed structures from above ground appurtenances
• Cathodically protected structures from earthing systems
• Owner / Operator interfaces

Electrical isolation is a key factor in the successful application of cathodic protection where it has been included at the design stage. For the purposes of this blog article we assume that the structure is intended to be electrically isolated.

That is not to say that electrical isolation is always required, as long as the designed system has taken this into account.

There are times when it may not be desirable, or even practical, to isolate protected from unprotected structures. Examples are refineries, industrial plants, large tank farms and similar complex facilities. 

How to Electrically Isolate the Cathodically Protected Structure

Commercial fittings for providing electrical isolation of pipework include;

• Insulating Flange Kits (IFK)
• Monolithic Isolation Joints (IJ)
• Non-metallic pipe sections

Cathodically protected structures can be electrically isolated from earthing systems via;

• Decoupling Devices

Other solutions, e.g. non-conductive membranes, are available as methods of electrical isolation depending on the system in question.

Insulating Flange Kits (IFK)

The kit comprises of the following;

• Insulating Gasket
• Non-Metallic Sleeves for Assembly Bolts
• Non-Metallic Washers
• Metallic Washers
• Nuts & Bolts

Monolithic Isolation Joints (IJ)

The isolation joint is fabricated as a ready to install section of pipework.

The joint consists of;

• Forged Rings
• External Coating
• Internal Coating
• Adhesive Sealant
• Di-Electric Filler
• Insulating Rings
• O Rings

Decoupling Devices

Corroconsult recommend only solid-state devices, as this eliminates the maintenance requirements and hazardous electrolytes of electrochemical polarisation cells.

Solid-state DC decoupling devices can be used for;

• Electrically isolating from from utility earthing (grounding) systems
• Electrically isolating from electrical equipment earthing (grounding) systems
• Induced AC voltage mitigation
• Isolation joint protection

How can electrical isolation be compromised?

Incorrect Installation

An incomplete kit installation for an IFK will result in the flanged joint being electrically continuous.

Earthing / Grounding

The most common failure of installed electrical isolation is through incorrect earthing of cathodically protected structures.