Cathodic Protection Isolation for Pipe Supports

Purpose of Electrical Isolation

Cathodic protection (CP) isolation at pipe supports is required to prevent protective electrical currents from draining away from buried or submerged pipelines through grounded support structures.

Why Isolation Matters

• Preservation of CP current: Prevents CP current from short-circuiting through steel supports and being discharged into the surrounding environment.
• Effective and uniform protection: Ensures that the available CP current is directed toward the pipeline and its coating defects rather than being consumed by external steelwork.
• Reduction of galvanic interaction: Minimizes localized electrochemical interactions, particularly where dissimilar metals are present.
• Improved CP performance: Maintains the intended electrical continuity and isolation philosophy of the pipeline protection system.

Limitations of Conventional Isolated Pipe Supports

A rubber or other suitable non-conductive liner is commonly used to provide electrical isolation between the pipe and its support. However, the liner can create a narrow, enclosed crevice at the pipe surface.

This crevice presents a significant corrosion concern. Water falling onto the pipe near the support can be drawn into the gap by capillary action. Once trapped, the moisture may be difficult to remove and the area may remain wet for extended periods. This can result in:

• Localized corrosion and corrosion under the liner;
• Moisture retention;
• Reduced visibility during inspection;
• Difficulty in detecting coating degradation or corrosion at the support location; and
• Increased maintenance requirements.

Conventional U-Bolt and Cradle Arrangements

Using multiple U-bolt-type clamps can eliminate some of the problems associated with large-area support contact. However, the point of contact between the pipe and the beam, clamp, or bottom of the cradle remains a concern.

These arrangements can still suffer from:

• Moisture retention at contact points;
• Crevice corrosion;
• Limited inspectability;
• Difficult cleaning and coating maintenance;
• Restricted access for inspection; and
• Difficult replacement or maintenance of insulating materials.

Therefore, simply increasing the number of support contact points does not fully address the fundamental concerns associated with conventional pipe support arrangements.

Desired Pipe Support Characteristics

The preferred support arrangement should provide electrical isolation while minimizing the conditions that promote corrosion and simplifying inspection and maintenance.

The design objectives are to:

1. Allow easy inspection of the pipe around and beneath the support.
2. Eliminate or minimize standing water and moisture-retaining crevices.
3. Prevent metal-to-metal contact between the pipe and supporting structure.
4. Minimize the number and area of contact points with the pipe.
5. Provide simple and rapid installation.
6. Remain cost-efficient compared with conventional support arrangements.
7. Provide full adjustability to accommodate installation tolerances and pipe movement.
8. Reduce maintenance requirements and lifecycle costs.
9. Maintain reliable electrical isolation throughout the service life of the pipeline.

Design Philosophy

The preferred solution should therefore combine reliable CP isolation with minimal physical contact between the pipe and its support, while maintaining open access around the pipe.

A support that minimizes contact area, prevents water entrapment, avoids enclosed crevices, and allows visual inspection can provide a significant improvement over conventional rubber-lined cradles and U-bolt arrangements.

The objective is not simply to electrically isolate the pipe, but to achieve electrical isolation without creating a corrosion-prone environment at the support location.