What Is an Abrasion Resistant Overcoat (ARO) for Pipelines?

Horizontal directional drilling (HDD) has become an important method of installing pipelines beneath roads, rivers, highways, and other obstacles without excavating a continuous trench.

However, HDD presents a challenge that conventional open-cut pipeline construction does not always encounter: the pipeline's corrosion protection coating must survive being pulled through an underground borehole.

Depending on the geology, the pipe may encounter rock, gravel, cobble, and other abrasive materials during installation.

This is where an Abrasion Resistant Overcoat (ARO) becomes important.

An ARO is an additional protective layer installed over a pipeline's existing corrosion protection coating to help prevent mechanical damage during construction.

One product specifically developed for this purpose is ScarGuard, a fiberglass-reinforced composite ARO associated with Canusa-CPS and CSNRI.

Why Do Pipelines Need an Abrasion Resistant Overcoat?

Most steel pipelines are protected by external corrosion protection systems such as fusion bonded epoxy (FBE), liquid epoxy, heat shrinkable sleeves, or other approved coatings.

These materials are designed primarily to protect the steel against corrosion.

However, corrosion resistance and mechanical damage resistance are not necessarily the same thing.

During an HDD installation, the pipe is pulled through a previously drilled borehole. Depending on the underground conditions, the coating can experience three important types of damage.

1. Abrasion

Abrasion occurs when the pipeline coating rubs against rock, gravel, or other materials.

Over a long pullback, repeated friction can wear away portions of the coating.

2. Gouging

Gouging occurs when a sharp or hard object creates a groove in the coating.

A rock protruding into the borehole can cause significant damage as the pipeline moves past it.

3. Impact

Impact damage can occur when the pipe contacts hard surfaces or debris during installation.

This can be particularly concerning around field joints, where the coating profile may differ from the factory-applied mainline coating.

An ARO provides an additional layer of mechanical protection intended to help absorb or resist these forces.

What Is ScarGuard?

ScarGuard is a composite Abrasion Resistant Overcoat developed to protect pipeline coatings during HDD and other trenchless installation methods.

The standard ScarGuard system consists of fiberglass fabric pre-impregnated with a flexible polyurethane resin.

The resin is activated by water and cures within minutes under suitable application conditions.

Because the fiberglass is already impregnated with resin, contractors do not need to mix separate resin components or saturate dry fiberglass during standard application.

Once cured, ScarGuard forms a durable composite protective layer around the pipeline.

Importantly, ScarGuard is a sacrificial mechanical protection system.

Its purpose is to protect the underlying corrosion coating, not replace it.

If the outer ScarGuard layer experiences abrasion during an HDD pull, it may still have performed its intended function by preventing damage to the corrosion protection coating beneath it.

What Types of Pipeline Coatings Can ScarGuard Protect?

ScarGuard is designed for use over approved corrosion protection systems, including:

• Fusion bonded epoxy (FBE)

• Liquid epoxy coatings

• Heat shrinkable sleeves

• Pipeline coating tapes

ScarGuard can be applied over field joints or factory-applied mainline coatings, depending on project requirements.

The underlying coating must be approved for the application, and installation procedures must follow the manufacturer's recommendations.

Why Are Field Joints Particularly Vulnerable During HDD?

Field joints are often among the most challenging areas to protect during directional drilling.

A pipeline may arrive at the construction site with a smooth, factory-applied coating. After welding, the girth weld area receives a field-applied coating system.

This creates a transition between the mainline coating and the field joint coating.

Depending on the coating design, these transitions may create raised edges or changes in surface geometry.

As the pipe travels through the borehole, these areas can encounter concentrated mechanical contact.

Applying an ARO over the field joint can help protect these vulnerable locations.

In some projects, contractors also apply ARO protection over extended sections or the entire length of the pipe being pulled.

Real-World Example: ScarGuard Protecting a Pipeline Through Granite

A documented CSNRI project involved a 24-inch steel natural gas pipeline being installed by HDD through approximately 1,600 feet of granite.

The project team was concerned that the field joint coating could be damaged during pullback.

To evaluate ScarGuard, technicians applied four layers of the composite over a test field joint positioned approximately 40 feet behind the bore head.

The test section was pulled through the borehole and subsequently inspected.

The ScarGuard composite showed areas of abrasion, but the underlying corrosion protection coating remained undamaged.

Following the successful test, the utility proceeded with ScarGuard for the installation.

This project illustrates the fundamental purpose of an abrasion resistant overcoat: allowing the outer mechanical protection layer to withstand installation damage while preserving the coating underneath.

The four-layer configuration was selected for that particular project and should not be assumed to be the correct specification for every HDD installation.

Where Are Abrasion Resistant Overcoats Used?

Although HDD is a major application, mechanical protection systems such as ScarGuard can also be used in other demanding trenchless construction methods.

Applications include:

• Horizontal directional drilling

• Thrust boring

• Microtunneling

• Direct Pipe installations

• Rocky underground crossings

• Pipeline field joint protection

• Mainline coating protection

The need for an ARO depends on the actual installation conditions and the coating protection requirements.

What Should Contractors Consider Before Selecting an ARO?

Before choosing an abrasion resistant overcoat, contractors and engineers should evaluate several factors.

Pipe diameter: The diameter affects the amount of material required and the installation procedure.

Bore length: Longer installations may create more opportunities for mechanical contact and abrasion.

Soil and rock conditions: Cobble, granite, gravel, and other hard materials can create different mechanical challenges.

Existing coating: The ARO must be compatible with the underlying corrosion protection system.

Field joint design: Weld geometry and coating transitions may influence where additional protection is needed.

Installation method: HDD, microtunneling, and thrust boring can expose pipelines to different mechanical stresses.

Project specifications: The required protection system and application thickness or layer count should be established before installation.

Why Is Protecting the Underlying Coating So Important?

A damaged corrosion coating can create significant problems after the pipeline has been installed.

During conventional open-cut construction, damaged coating may be accessible for inspection and repair before backfilling.

During HDD, the installed pipeline may be located beneath a river, highway, or other obstacle.

Accessing the damaged section may be extremely difficult.

In some situations, severe coating damage can require removing and reinstalling sections of the pipeline.

An appropriate ARO helps reduce this risk by providing an additional mechanical protection barrier during construction.

ScarGuard for Your Next HDD Project

ScarGuard provides a practical solution for contractors and engineers seeking additional mechanical protection for pipeline coatings.

Its fiberglass-reinforced construction, water-activated resin, and rapid curing characteristics make it particularly relevant for demanding trenchless installations.

When properly specified and installed, ScarGuard can help protect both mainline coatings and field joints from abrasion, gouging, and impact damage.

Contact Joint Specialists Inc. for ScarGuard

Joint Specialists Inc. supplies pipeline coating and corrosion protection materials for contractors throughout the United States.

If your next project involves horizontal directional drilling, rocky underground conditions, or other demanding trenchless construction, contact JSI to discuss ScarGuard material requirements and availability.

Steve Simpson
Joint Specialists Inc.
Phone: 936-321-3333
Email: steve@jsicoatings.com

For a ScarGuard quotation, please provide your pipe diameter, approximate length requiring protection, existing coating type, and project conditions.