Fiber optic technology has advanced to be a versatile solution for many operations. While most think of fiber optic cables as an essential part of high-speed internet and cellphone technology, that is only a small part of what the technology can be used for. For instance, on pipelines, many operators use these lines to help detect leaks and strain in the pipeline.
To further examine the challenges in laying fiber optic cables for pipeline monitoring, CCI Inc., a leading expert in trenchless pipeline design and execution, studied the issues.
Understanding Fiber Optic Cable
Fiber optics can help monitor pipeline performance based on subtle "tone” changes. Fiber optic monitoring detects differences in vibration, temperature, sound, and strain. Any change in the frequencies allows pipeline operators to see there are issues in the line.
As there is no electrical power required to use the cable, it is the safe choice for pipeline integrity monitoring. With pipelines being an integral part of the world’s infrastructure, having a reliable means of damage detection is essential.
Yet, some challenges arise when trying to install fiber optic cabling on the pipeline. CCI Inc. decided to look at some of these challenges and develop a solution to help protect the cabling.
Challenges for Fiber Optic Installation
While fiber optic cables are typically installed within conduits alongside the pipeline, there are significant challenges to installing the conduits along trenchless installations, such as horizontal directional drills (HDD).
The typical method utilized for HDD conduit installation is to attach a coated stainless steel conduit to the pullhead of the pipe section and pull it through the borehole along with the pipe. The success of this method is variable, as borehole conditions can cause considerable damage to the conduit. A common mitigation for this is to pull through multiple conduits in the hopes that one or more are pulled through the borehole in adequate condition.
CCI leveraged their experience in trenchless pipeline installation design and execution to develop a solution to increase the success of conduit installation through HDD boreholes.
To address this issue, CCI created the Trenchless Integrity Pipeline System (TIPS). This system allows for continued trenchless installation of conduits for fiber optic cables with pipeline installation. TIPS consists of steel conduits, 0.5” in diameter, which are encased in a protective profiled fiberglass wrapped polymer adhered directly to the pipeline coating.
To ensure the TIPS conduit adheres to the exterior of the pipeline, CCI employs a two-part adhesive resin. This resin was formulated in-house to obtain a balance that ensures adequate adhesion to the coating while still allowing this bond to break prior to creating any coating disbondment from the steel in the event of significant shear forces on the conduits occurring within the borehole.
The resin, fiberglass, and polymer casing all provide additional support and protection for the encased conduits, vastly increasing the probability that an acceptable conduit is installed within the borehole.
To address the potential for disbondment of the TIPS conduit bundle due to shear forces which may occur while moving the drag section through the roller cradles during pipe handling, CCI designed the profile of the polymer extrusion so that hard edges were eliminated. This smooth profile allows the system to pass through or over obstacles without becoming caught on a hard edge which may shear the conduits from the product pipe.
Dimensional consistency, a challenge when extruding dissimilar materials at the same time, was obtained by designing the polymer casing with two interlocking parts that accept the stainless-steel conduits after extrusion. Dimensional consistency improves adhesion of the profile to the pipeline by providing a uniform bonding surface.
Splices that are required for segmented pipeline drag sections were considered while developing the TIPS system. The selected polymer used for the profile belongs to the Thermoplastic family.
When a splice is required, the stainless-steel conduits are welded together with an orbital welder and snapped into the two-piece polymer profile casing. The casing itself is then fused together with heat, prior to being wrapped in fiberglass and finally adhered to the pipeline.
This complete product is then strung out along the entire drag section prior to the drag section being pulled into the hole. The pipe coating is prepared by cleaning and lightly abrading. The resin is then pressured into the fiberglass wrap and then laid onto the prepared pipe section. The cure time for the resin to the pipe length depends on the dew point. Once it is cured and the hardness is confirmed to be within specifications, the pipe can be installed.
Conclusion
CCI has installed and tested several different design modifications to the TIPS model. All have been generally successful, but small upgrades and improvements have built the version that is currently in use. The resin, fiberglass, and polymer casings providing strength and protection to the 0.5” stainless tubulars all add reassurances the product will endure the strains of the annular space in the borehole.
Being able to provide support for the fiber optic cable conduits helps to mitigate damage to the line. With this system, owners and contractors can count on having a successfully installed conduit to install fiber optic lines at the end of the project.