Valve sets are the service portals for pipelines, providing access and control for maintenance, safety, and transmission efficiency. As crucial as they are, valve sets can cause maintenance nightmares for pipeline companies, especially when aboveground.
When ground conditions allow, most of a pipeline is underground except for aboveground maintenance points such as valve stations, compressor stations, and metering stations. In these maintenance areas, pipes are elevated to aboveground access points through transitions called "risers," where 45-degree pipe bends shift the pipe at an angle to bring the pipe aboveground and eventually back underground.
Risers are highly susceptible to axial displacement. When fluids are pumped at high velocities through these transitions, the sudden change in direction causes vibration in the pipe, resulting in differential settlement and deterioration from abrasion. Risers are also susceptible to shifting when repairing or replacing valves or other aboveground components, which leads to significant difficulties in realigning the riser to complete the maintenance.
When constructing 190 miles of pipeline in Wyoming, LOENBRO pipeline company decided to try an innovative method for supporting the risers using polyurethane. Typically, buried pipelines are fully restrained by the soil and are not susceptible to axial displacement, but the angle of a riser is difficult to adequately compact and confine using backfill, cementitious grout, or sandbags. Polyurethane offered the pipeline company something they didn't have, the ability to encapsulate the pipes on a slope and provide long-term structural stability and padding that would stop axial displacement.
LOENBRO contacted White Construction, LLC, a Wyoming-based contractor that specializes in polyurethane applications to install the system. White Construction was tasked with stabilizing 17 valve sets. They were to stabilize the risers for each location, a total of 34 risers, as the pipeline was constructed.
The risers stabilized using NCFI Polyurethanes' 24-023 Strata-Fil low-exotherm system. White Construction sprayed the polyurethane in place below and around the pipes, encapsulating the pipe at 6ft before and after the riser fitting, an 18" pillow below the pipe, and stabilizing the pipe the entire width of the trench. The encapsulation purpose was to place the pipe's vertical and horizontal loads into the compacted soil and stop axial displacement.
"Encapsulating the pipe in polyurethane was a perfect solution for preventing long-term degradation, and the NCFI Strata-Fil 24-023 was the perfect polyurethane for the job," stated Nick White, President of White Construction, LLC. "Because of Strata-Fil's low-exothermic properties, we were able to build the pipe supports without the polyurethane overheating, and we were also able to complete the project efficiently due to the system's high expansion."
All of the riser points were stabilized in progression with the pipeline construction schedule. Since the polyurethane is subgrade, the system is expected to last indefinitely. The risers will be protected against axial displacement and abrasion or corrosion of its coating. The pipe will also be stabilized against shifting during maintenance and component replacements, providing oil and gas customers with a system that has easier service ability and long-lasting integrity.