Directional drilling can be unforgiving on pipeline coatings. When pipe is pulled through tight bores filled with rock, friction and abrasion can quickly expose the weaknesses of materials that weren’t designed for that kind of punishment.
A few years ago, we had the opportunity to witness exactly how different coating systems perform under those conditions during a product evaluation for Texas Gas Transmission.
The objective was straightforward: evaluate three coating systems on a 4.5" OD pipe that would pass through a 160-foot directional bore in extremely rocky soil.
As it turned out, the test became even more interesting than planned.
The Unexpected Test
Halfway through the installation, the drilling equipment failed.
At that point the pipe had already been pulled 80 feet into the bore, meaning the only option was to pull it 80 feet back out in reverse.
Instead of a single pass through the bore, the coatings experienced a 160-foot round trip—80 feet in and 80 feet out—through a very aggressive environment.
For a coating system, that’s a serious test of abrasion resistance and adhesion.
First up was cold applied tape.
Before going any further, it’s worth adding an important disclaimer:
I’m not aware of any cold applied tape manufacturer that recommends their product for directional drilling applications.
But as anyone in the pipeline industry knows, coatings sometimes get used in ways they were never intended to be used.
In this case, the result was dramatic.
When the pipe came back out of the bore, the tape coating had essentially disappeared. It had been stripped off somewhere along the 160-foot journey and deposited in the ground along the way.
Not exactly the outcome you’re hoping for.
Next up was a standard three-layer heat shrink sleeve system.
Again, another quick disclaimer: this is not a product we would typically recommend for a directional drilling application.
When the pipe came out of the bore, the sleeve was still in place, which was certainly better than the tape. However, the backing had been gouged in two locations by the rocky soil.
That kind of mechanical damage can create long-term risks if the coating barrier is compromised.
The third coating evaluated was Covalence DIRAX HDD Coating System from Seal For Life Industries.
DIRAX is a multi-layer coating system with a fiber-reinforced backing, specifically designed to withstand the mechanical forces associated with horizontal directional drilling (HDD).
And in this test, it showed why purpose-built systems matter.
Even in areas where the underlying FBE coating had been scratched by the rocky environment, the DIRAX remained fully intact and undamaged.
No gouging. No disbondment. No missing material.
Just solid protection.
The Takeaway
Directional drilling puts extraordinary stress on pipeline coatings. Materials designed for conventional trench installations often struggle—or fail entirely—when exposed to the abrasion and mechanical forces inside a bore.
This evaluation was a good reminder of an important principle:
Use coatings designed for the environment they’re going into.
In this case, the product specifically engineered for HDD applications—DIRAX—was the one that handled the challenge with ease.
Sometimes the right answer really is the purpose-built solution.
