Covalence DIRAX: Why Fiber-Reinforced Heat-Shrink Sleeves Are Ideal for Directional Drilling Applications
Horizontal Directional Drilling (HDD) has transformed the way pipelines are installed beneath highways, rivers, railroads, and other obstacles.
Instead of excavating an open trench across an entire crossing, contractors can install pipelines through a drilled borehole, significantly reducing surface disturbance.
However, HDD installations introduce challenges that conventional pipeline construction methods may not encounter.
During pullback, the pipeline can be subjected to substantial mechanical forces as it moves through soil, rock, gravel, and other abrasive materials.
These forces can place considerable stress on the pipeline's external corrosion protection system, particularly at welded field joints.
Covalence DIRAX was specifically developed to address these challenges by combining corrosion protection with the mechanical durability of a fiberglass-reinforced heat-shrink sleeve.
For contractors installing pipelines through road bores, directional drills, and other trenchless crossings, DIRAX offers an engineered alternative to conventional field joint coatings.
Why HDD Installations Require Specialized Field Joint Protection
Most steel pipelines are manufactured with an external protective coating.
Common factory-applied coatings include Fusion Bonded Epoxy (FBE), polyethylene-based systems, and other specialized corrosion protection materials.
Although these coatings provide important protection against corrosion, the welded joints connecting individual pipe sections require separate field-applied protection.
During HDD installation, these joints may encounter abrasive soil, sharp rocks, and significant contact pressure.
The problem becomes particularly challenging because the pipeline is pulled through the borehole after the coating has been applied.
If a field joint coating is damaged during installation, accessing that location afterward may be extremely difficult.
Consequently, HDD field joint coatings must provide more than conventional corrosion protection.
They must also withstand the mechanical stresses associated with the installation process.
What Is Covalence DIRAX?
DIRAX is a fiberglass-reinforced, wraparound heat-shrink sleeve system specifically designed for directional drilling and related pipeline applications.
The system combines a liquid epoxy primer, a high-shear-strength adhesive, and a mechanically reinforced heat-shrinkable backing.
Unlike conventional heat-shrink sleeves that rely primarily on a polyethylene backing for mechanical protection, DIRAX incorporates fiberglass reinforcement to improve its resistance to abrasion and penetration.
This additional reinforcement makes DIRAX particularly well suited for demanding HDD applications.
The system is designed to protect the welded field joint while maintaining compatibility with specified factory-applied pipeline coating systems.
Understanding the Three-Layer DIRAX System
One of the features that distinguishes DIRAX from many conventional heat-shrink sleeves is its three-layer construction.
Layer 1: Liquid epoxy primer
The first layer is a solvent-free, two-component liquid epoxy.
Covalence S1301M epoxy is used with the DIRAX system.
The epoxy is applied to the properly prepared steel surface before the heat-shrink sleeve is installed.
This layer contributes to adhesion and corrosion protection at the steel interface.
Layer 2: High-shear-strength copolymer adhesive
The second layer consists of a specially formulated copolymer adhesive.
During installation, the adhesive is activated by heat and works in conjunction with the underlying epoxy.
This combination helps establish a strong bond between the sleeve and the coated pipe surface.
Resistance to shearing forces is particularly important during directional drilling, where the pipeline may experience substantial axial forces during pullback.
Layer 3: Fiberglass-reinforced polyethylene backing
The third layer is a thick, radiation-cross-linked polyethylene backing reinforced with fiberglass.
This reinforcement improves the sleeve's ability to resist abrasion, gouging, and mechanical damage.
The backing provides the outer protective barrier between the field joint coating and the surrounding borehole environment.
Together, these three layers provide a corrosion protection system specifically engineered for demanding installation conditions.
The DIRAX Wear Cone: Additional Protection During Pullback
Another important feature of the DIRAX system is its specially designed wear cone.
During directional drilling, the leading edge of a field joint sleeve may encounter significant forces as the pipe travels through the borehole.
These forces can create the potential for the leading edge of the sleeve to catch, lift, or become damaged.
The DIRAX system addresses this concern with an additional sacrificial heat-shrink sleeve installed over the leading edge of the main sleeve.
This wear cone provides another layer of mechanical protection at one of the most vulnerable locations.
The additional sleeve also creates a more gradual transition between the factory-applied coating and the main DIRAX field joint sleeve.
Proper positioning and installation of the wear cone are important for protecting the complete system during pullback.
Why Fiberglass Reinforcement Matters
Traditional heat-shrink sleeves provide a durable protective barrier for many pipeline applications.
However, the mechanical demands of HDD installations can be substantially greater than those encountered during conventional open-trench construction.
Fiberglass reinforcement increases the mechanical durability of the DIRAX backing.
This provides several important advantages.
1. Improved abrasion resistance
As the pipeline moves through the borehole, its exterior may come into contact with abrasive soil, sand, gravel, and rock.
DIRAX's reinforced backing is designed to withstand these conditions more effectively than an ordinary unreinforced sleeve.
2. Increased resistance to gouging
Sharp rocks and other hard objects can create concentrated contact forces during pullback.
The fiberglass-reinforced construction helps improve resistance to mechanical penetration and gouging.
3. Protection of the primary corrosion barrier
The reinforced outer backing helps protect the underlying adhesive and epoxy layers.
This is particularly important because damage to the primary corrosion protection system can create potential pathways for moisture to reach the steel.
4. Protection during trenchless installation
Once a pipeline has been pulled into position, repairing damaged field joint coatings may be impractical.
Selecting a mechanically durable coating before installation helps reduce the risk of damage that cannot easily be corrected afterward.
DIRAX and Installation Efficiency
One advantage of the DIRAX system is that it combines a liquid epoxy coating with a heat-shrinkable sleeve in a coordinated installation procedure.
After the steel has been properly prepared, the epoxy is applied, and the sleeve is installed over the wet epoxy.
Heat is then applied to recover the sleeve around the pipe.
The epoxy and adhesive work together to establish a homogenous coating system.
Unlike some coating systems requiring a separate, lengthy epoxy cure before the next installation stage, the DIRAX procedure is designed around installing the sleeve directly over the wet epoxy.
This approach can support efficient field joint coating operations.
However, the completed DIRAX installation must be allowed to cool ambient temperatures before the field joint can see any forces.
Joint Specialists Inc. has extensive experience supplying DIRAX heat-shrink sleeves for pipeline construction projects.
Over a recent period of approximately two years, Joint Specialists supplied more than 75,000 DIRAX sleeves.
That represents a substantial volume of specialized field joint coating materials used to support pipeline construction and directional drilling projects.
These quantities reflect the continued demand for fiberglass-reinforced heat-shrink systems in applications where conventional coating protection may not be sufficient.
Our experience supplying DIRAX provides Joint Specialists with valuable insight into contractor requirements, project logistics, sleeve sizing, and the importance of dependable material availability.
DIRAX Is Not the Same as a Conventional Heat-Shrink Sleeve
Although DIRAX shares the basic heat-recovery technology found throughout the Covalence product family, it is designed for a different set of installation demands than general-purpose products such as WPCT.
For example, WPCT is a two-layer, mastic-based system commonly used for field joint corrosion protection on pipelines where the specified installation and service conditions are appropriate.
DIRAX, by comparison, uses a three-layer system incorporating liquid epoxy, high-shear-strength adhesive, and fiberglass reinforcement.
These differences are important when selecting field joint coatings for HDD projects.
A general-purpose heat-shrink sleeve should not automatically be considered equivalent to a specialized directional drilling coating.
Engineers and contractors should evaluate the expected installation forces, pipe coating compatibility, borehole conditions, and project specifications before choosing the appropriate product.
Important Considerations Before Installing DIRAX
Although DIRAX is designed for demanding applications, successful performance still depends on proper installation.
Important considerations include the following:
Surface preparation: Prepare the steel and adjacent factory coating according to the specified cleaning requirements.
Epoxy application: Mix and apply the approved liquid epoxy in accordance with the manufacturer's instructions.
Sleeve installation: Position and recover the sleeve using the proper heating sequence and equipment.
Wear cone installation: Apply the additional leading-edge protection as specified.
Inspection: Verify complete recovery, proper adhesion, and the absence of visible coating defects.
Cooling: Allow the completed system to cool sufficiently before subjecting it to the mechanical forces of pullback.
The current DIRAX installation instructions should always take precedence over general application guidance.
A Technology Built on Decades of Raychem Experience
DIRAX is part of the larger family of heat-shrinkable pipeline corrosion protection products that originated with Raychem.
Raychem helped pioneer the commercial use of radiation-cross-linked heat-shrinkable materials, establishing a technology platform that would eventually serve numerous industries.
Over the decades, heat-shrink systems evolved to address increasingly demanding pipeline applications.
Products such as DIRAX demonstrate how that technology can be adapted for specialized construction methods such as HDD.
Joint Specialists Inc. has been involved with Raychem and Covalence heat-shrinkable pipeline products since the company's founding in 1995.
Our experience with these products extends back even further through the original Raychem personnel who established Joint Specialists.
That history provides a depth of technical knowledge that continues to benefit customers working on demanding pipeline coating projects.
DIRAX Available from Joint Specialists Inc.
Joint Specialists Inc. stocks and supplies Covalence DIRAX heat-shrink sleeve systems for directional drilling, road bore, and other applicable trenchless pipeline installations.
DIRAX is stocked in multiple widths, including 12-inch, 17-inch, 24-inch, and 34-inch configurations, with product selection based on pipe diameter and project requirements.
Our team can assist contractors and engineers with sleeve sizing, product availability, installation information, and project-specific material requirements.
Whether your project involves a short road crossing or a major directional drilling installation, we can help ensure that the appropriate field joint coating materials are available when needed.
Contact Joint Specialists Inc. for DIRAX pricing, technical information, and availability for your next HDD pipeline project.
Contact Joint Specialists Inc.
Steve Simpson
Joint Specialists Inc.
Phone: 936-321-3333
Email: steve@jsicoatings.com
Website: www.heatshrinksleeves.com
Joint Specialists Inc. — Providing pipeline corrosion prevention solutions since 1995.
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