A 12-in. diameter pipeline in Missouri had a section become exposed to the environment as a result of soil erosion and water flow from a nearby creek. That section needed to be replaced by means of horizontal directional drilling (HDD), but the soils present and the elevation change posed hazards to the long-term integrity of the pipe.

The operator used a newer technology to ensure the integrity of the pipe and its protective coating, resulting in a successful installation after the pilot hole was completed. This experience made the operator aware of some of the key risks that exist when using HDD for pipe installation and introduced the company to specific product solutions to overcome those risks.

When the problem with the aging pipeline crossing was identified, the damage was deemed irreparable, and thus it had to be replaced due to corrosion from failed coatings and environmental exposure.

After a review of the area and evaluating the expected further erosion, the pipeline operator opted to install the new pipe by HDD at approximately 50 ft deeper than the original line. The pipeline section to be replaced was 12 in. diameter and needed to be nearly 1,200 ft long in order to safely reach the depth and to minimize the radius of the curve.

The installation also had another issue to contend with. The current erosion of the soil was partially due to the creek laying at the base of a hill where the water runoff from the nearby creek, was making the soils move to the lower side. This created a rather large difference in the elevation between where the pipe needed to enter the ground versus the elevation of the exit.

The reason this becomes such an issue, is because the installation methodology chosen was HDD. When pipe is trenched into the ground, elevation changes aren’t much of an issue because the pipe is simply getting laid into the trench, then backfilled. But with an HDD method, the pipe will literally be pulled through the ground via a hole slightly larger than the diameter of the pipe.

In a typical HDD installation, damage can occur while pulling the pipe through the soil. Damage can be mitigated by filling the hole with smooth drilling mud. This type of mud has many benefits, which include lubricating the hole to reduce abrasion and providing some buoyancy to the pipe to help keep it centered in the pull-through hole. Yet, on this project, the elevation change made it so that nearly half of the hole’s length wouldn’t hold the drilling mud because gravity due to the elevation change was making the drilling mud slide out before any pull through could happen. This means that the pipe would have no protection when it would be pulled through the ground for over 500 ft.

During the drilling for the HDD installation, it was discovered that the ground contained cobble and the rocks in the area were fracturing into sharp shards. Knowing that the rocks could easily damage the pipe and its coatings, the contractor decided to take additional steps to protect the pipeline’s coating, which was being field applied, to ensure that it would survive the installation.

Another challenge the contractor had to face with the HDD installation was that sections of the pipe was already shop coated, per the operator’s specification, and was not in the contractor’s scope of work. In order to address this issue and provide protection to the shop coating, the contractor applied Denso Bore-Wrap, a field-applied abrasive resistant outer wrap, over the weld coatings to protect them from damage during the HDD installation. This was a means of ensuring that the contractor’s work was of the highest quality after the pipe was pulled through the bore hole.

Once the line was pulled through the hole and exposed on the exit, it was found that the shop applied mainline coatings, which was not wrapped with Denso Bore-Wrap, had experienced significant damage to the fusion-bonded epoxy (FBE) coating resulting in gouges and scrapes down to the bare steel.

Having exposed steel, due to the HDD installation, is a potentially dangerous and costly situation due to the potential for corrosion. Typically pipe that is installed by HDD is inaccessible for repair, meaning that the pipe must survive the entire expected lifespan without issue. Too much exposed steel, caused by pulling the pipeline through soil, can be difficult to protect using cathodic protection (CP). With a coated pipeline, the likely corrosion would form pits in the steel, degrading the pipelines integrity and increasing its failure. This is a scenario that no party involved wants to occur, especially around a water source.

To evaluate the extent of the damage caused from the HDD pullback, the contractor pulled out additional footage to determine if the damage was just on the leading edge or if it continued down the length of the pipe. As they extracted more and more of the pipe, it was evident that the coating damage was likely on much of the length that was now underground. Yet, to the contractor’s and operator’s surprise, they’d discovered that the welds that had been protected with Denso Bore-Wrap, had no damages, to the coating underneath.

The pipeline operator made the difficult decision to extract the newly installed line and repair all the damaged coatings. After several days of repairing the epoxy and checking for coating holidays, the pipeline operator chose to follow the contractor’s lead and wrap the entire HDD section with Denso Bore-Wrap. It took the contractor two days to protect the 1,200 ft of pipe with two layers of the wrap, at which time it was ready to be pulled through the hole once again. Although they did all they could to mitigate the threats from shear, abrasion, impact and gouge (SAIG) by using the industry best SAIG coating, the potential for damage was still elevated because of the presence of rocks and the dry hole that still needed to be passed through.

This time, the installation was under continual observation from the operating company’s project manager, as well as third-party inspectors. All parties were in attendance during the HDD installation, as there were obvious concerns of the condition of the coating as it exited the bore hole. When the pipe exited the hole, the contractor quickly disconnected the drill rig and pulled the pipe out 50 ft to begin the spray cleaning to clear off any drilling mud for inspection. The Denso Bore-Wrap was completely intact with only negligible damage visible to just the outermost layers. The success of the Bore-Wrap in protecting the pipeline’s coating on this project spurred the drilling contractor to request additional product information so he could present and offer it to every project in which they encounter cobble in the soil.

Ron Raphoon is the managing member of Raphoon LLC. He works in the oil and gas sectors providing consulting services on anti-corrosion coatings, inspection and applicator training. Contact him at ron@raphoon.com or (832) 928-2786. To learn more about Denso Bore-Wrap, visit www.densona.com.

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