Bonds

Bonds are intentional electrical connections used to control continuity, current flow, and interference between metallic structures.

Quick Definition

A bond is an intentional metallic electrical connection between structures or CP system components.

Why Bonds Matter

Bonds can help a CP system function correctly, but they can also create problems if installed, adjusted, or interpreted incorrectly.

A bond may be used to ensure electrical continuity, drain interference current, control current flow, or connect related structures. However, unintended or poorly controlled bonds can increase current demand, transfer stray current, or make separate systems behave as one large structure.

Bonds must be treated as current-control features, not just wires.

Core Concept

Continuity bonds

Continuity bonds are used to electrically connect parts of a structure or system so CP current can return through a continuous metallic path.

Interference bonds

Interference bonds may be installed between structures to control stray-current effects. These bonds may include resistors, diodes, or other current-control devices.

Foreign line bonds

A foreign line bond connects the protected structure to another owner’s structure or another system. These bonds require careful monitoring because current can transfer between systems.

Current flow through bonds

Bond current direction and magnitude matter. Current flowing onto a structure may be protective. Current leaving a structure may create corrosion risk at the discharge location.

Adjustable bonds

Adjustable bonds may use resistors or other controls to limit current flow. Changing bond resistance changes current distribution and may affect both connected structures.

Field Application

Field personnel may measure bond current, bond voltage drop, bond resistance, structure potentials on both sides of the bond, and current direction.

Bond testing is common during interference investigations, facility piping evaluations, casing evaluations, pipeline crossings, and complex plant CP assessments.

Bond changes should not be made casually. Adjusting a bond may improve one location while damaging another. Results must be verified with field measurements.

Common Mistakes

Assuming every bond is beneficial.
Why it is wrong: Bonds can increase current demand, transfer interference, or connect structures that should remain electrically separate.
Changing adjustable bonds without measuring effects.
Why it is wrong: Current redistribution can create underprotection or interference elsewhere.
Ignoring current direction.
Why it is wrong: The direction of current flow determines whether the bond may be helping or harming a structure.
Assuming a bond wire proves effective continuity.
Why it is wrong: The bond may be broken, corroded, disconnected, undersized, or poorly terminated.
Failing to coordinate foreign line bonds.
Why it is wrong: Foreign structure bonds can affect another owner’s CP system and require controlled evaluation.

Standards Relevance

This page is educational and does not replace the applicable AMPP, NACE, ISO, DOT, API, regulatory, or project-specific requirements.

Bonding, interference control, foreign line coordination, and current-control documentation may be governed by applicable standards, regulations, owner specifications, and operating procedures.

Field Example

A protected pipeline is bonded to a nearby foreign pipeline at a crossing. Current measurements show current leaving the protected pipeline and entering the foreign pipeline.

That condition requires evaluation. Depending on the direction and discharge location, the bond may be transferring current in a way that creates corrosion risk. The solution may require resistance adjustment, diode control, coordination with the foreign owner, or other mitigation.

Practice Questions

What is a bond in cathodic protection?
Why does bond current direction matter?
What is one reason an adjustable bond may be used?
Why should bond changes be verified with field measurements?
How can a bond increase CP current demand?