Composites are the present and future of pipeline integrity—keeping pipelines or pipeline facilities without damage or defect, two engineers assert.
Composites prove effective for a variety of issues on piping and pipelines, Aleese Post and Casey Whalen write in the 2023 AMPP conference paper “The Use of Composites in Facility Integrity Programs,” adding, “The constant advancement of this technology can lead to prolonged integrity of pipelines, facilities, and assets in general.”
Whalen, global engineering manager for CSNRI based in greater Houston, Texas, USA, presented the paper during the 2023 AMPP Conference + Expo. He says it aimed to help pipeline operators see beyond standard repair tools.
“We really wanted to show these pipeline companies that there are opportunities outside of what they may consider a previously traditional repair,” Whalen says.
Defining Terms
Simply put, composites are made from two or more different materials that, when combined, are stronger than those individual materials by themselves. Post explained that a composite for pipeline facilities could be a wet layup system with carbon fiber and epoxy, or fiberglass and polyurethane, or a rigid coil system.
Facilities refer to new and existing pipelines, rights-of-way, and any equipment or building used in the transportation of gas or in the treatment of gas during the course of transportation.
While pipelines and facilities both transport fluid from a source to a delivery point, pipeline facilities “are normally confined to privately owned areas and are usually secured, while pipelines (except for their start and end points) are often built in the public domain,” according to ScienceDirect.com. Pipelines are usually buried, the web site says, while facilities piping is normally installed aboveground and is easier to access and inspect.
Composites for Facility Defects
“We wanted to bring awareness that composites can be used in facilities, which really opens up opportunities and essentially adds another tool for these operators,” says Post, senior pipelines engineer/standards engineer for CSNRI based in Columbus, Ohio, USA.
While pipeline facilities experience many of the same defects as main pipelines, facilities often have their own unique defects such as corrosion at soil-to-air interfaces, bending at pipe supports, and corrosion at pipe supports. Composites can be used to repair these defects and are becoming more acceptable as standards address their use, the engineers say.
Examples of composites the authors cite in their paper are cement, reinforced concrete, and particle board. Within the industry, composites have a matrix phase and a reinforcing phase, with the matrix phase being the polymer/resin used and the reinforcing phase being the chosen fabric.
“The fabric contributes directional strength, binding for the resin, and increased stiffness to the repair,” Post and Whalen write. “The resin contributes environmental, chemical, impact, and abrasion resistance, as well as the temperature limit to the repair.”
Composites restore the strength of defective pipe by transferring the stress from the pipe to the load-bearing composite fabric/resin mix, the authors explain (Figure 1).
“Once the filler material, primer (two-part epoxy), and composite lay-up system have been applied, and cured, the stress will be transferred up through the filler material to the composite lay-up system,” the paper says. “The composite lay-up system will then absorb the stress, therefore increasing the life of the substrate” (Figure 2, top of page).
Post explains that the load transfer filler does exactly what it says—transferring the load from the substrate and taking that stress off of it and transferring it up to the wet lay-up system.
“Now that load is being taken by your composite, your adhesive primer is helping the actual wet lay-up system adhere to the substrate, and then your actual fabric,” she says. “So, your composite layup is what’s adding your strength. That’s what’s taking that extra stress off of the piping in this area where it has that defect and helping repair that.”
The engineers write that composites are especially useful when bending on suspended pipelines occurs as opposed to steel sleeves or full pipe replacement. Because composites are lightweight, they can land on straight and bent pipe areas.
“Steel sleeves, while a popular and good repair method, tend to be much heavier than composites, have specific landing zone criteria, and cannot be applied to bent pipe,” their paper says. “In the case of bending loads, many composite systems, specifically carbon fiber, have undergone bending load testing.”
Experimental Testing
ADV Integrity is an engineering consulting firm that provides custom-engineered solutions for asset integrity assessment and management of onshore and offshore oil and gas equipment. ADV performed tests to show the ability of a carbon fiber composite system to withstand high bending loads.
“One of the main concerns for pipeline repairs is definitely hoop stress,” Whalen says. “Most of the composites out there focus on reinforcing hoop stress-type defects. But there are definitely situations where we end up with axial loading, such as high bending loads. Working with ADV Integrity, we are developing a different system that uses the same carbon fiber, but focuses on axial reinforcements. It’s gone to show that composites can be very good at reinforcing axially as well as just in the hoop stress.”
A carbon fiber and epoxy composite repair system was used on 30-in, 0.375-in-thick, X52 pipe. An experienced composite engineer performed testing to determine the minimum repair thickness needed to ensure stress in the pipeline did not exceed 52,000 psi. ADV determined that a repair approximately 0.6 in thick would be needed to give accurate testing results and not be overdesigned.
To validate these results, ADV conducted a finite element analysis (FEA) using Abaqus FEA software. Internal pressure was applied to 72% specified minimum yield strength, and a bending load required for yield to occur was applied. Results are shown in Figure 4.
The FEA showed the max axial strain of the reinforced pipe decreased by approximately 50%, as Figure 5 shows.
“This testing shows that properly designed, engineered, and tested composites can be extremely effective in reducing axial strain,” Post and Whalen write. “This data can be used to calculate the necessary composite repair to support facility piping at pipe supports to ensure the stress is taken off the pipe and bending does not occur.”
Composites for Corrosion Mitigation
“The composite also adds extra protection for crevice corrosion and other corrosion at pipe supports,” the authors write. “By installing the composite during construction, the pipeline owner was able to prevent future problems associated with crevice corrosion, galvanic corrosion, and erosion.”
Composites can also be used to take a proactive approach to corrosion mitigation, especially at soil-to-air interfaces, they write in their paper. Composites can provide a permanent and strong repair, as well as minimize future needed maintenance.
“You’re adding the strength back to the pipe, stopping the corrosion growth, and then ensuring that no more corrosion growth will happen at that specific location,” Post says.
Editor’s note: This article first appeared in the August 2024 print issue of Materials Performance (MP) Magazine. Reprinted with permission.