Fixing Myths: Dispelling Composite Repair Misconceptions Through Case Studies
Composite repair products used in oil and gas pipeline rehabilitation and restoration applications have been available for close to 30 years. In that time, multiple misconceptions have evolved regarding these products, their principles and their performance.
Myth: “Any off-the-shelf product can address my simple repair”
There are plenty of manufacturers that would have operators believe their products are adequately manufactured to handle any repair based on their one-size-fits-all construction. In reality, these types of products can provide a good repair solution only in the right conditions, but even then, that doesn’t necessarily make it right or the best option. There are many variables when considering a composite repair, including operating pressures and temperatures, defect type and severity, pipe geometry and external or internal chemical presence. Considering all these variables, it is near impossible for a single, ready-made composite to work well in every situation. A wrinkle bend case study from Ringgold, Louisiana, shows how a customized repair was necessary over a pre-designed repair.
A 24-in. OD horizontal pipeline in Ringgold needed a repair for six wrinkle bends at a crossing about 26 to 31.5 in. apart. With no visible corrosion, the distance from the center of the first wrinkle bend to the sixth wrinkle bend was 12.2 ft.
Milliken Infrastructure Solutions (MIS) engineers designed a 20-year design life repair, using 20 layers of the Atlas wrap system using the spiral method for 16 lf to restore the structural integrity of the pipeline back to pristine conditions. Wrinkle bends provide localized stress increases that can dramatically reduce the life of a pipe undergoing fatigue. The Atlas system was designed to locally reduce the stress in the buckled areas increasing fatigue life closer to that of the pristine pipe. The severity of the repair as well as operating conditions play a large part in the long-term effectiveness of the pipeline system and any composite repair needs to address these details to ensure longevity can be achieved.
The repair was completed in 13 hours by three MIS technicians and three contracted personnel. The repair area was grit blasted and wiped clean with acetone, then EP420 was applied as filler material for the load transfer at the wrinkle bends. Next, PPR epoxy coating was applied to the entire repair zone followed by a layer of fiberglass with ILI markers on both ends of the repair. The composite wrap system was applied, followed by constrictor wrap, perforation and then allowing adequate time to cure. After curing, the constrictor wrap was removed, and the team applied a topcoat with additional PPR epoxy coating.
“Pre-designed,” ready-made repair products should only be used to address very specific situations. These situations and limitations should be clearly and plainly understood. However, keep in mind that the prevailing ASME PCC-2 and ISO 24817 standards state that each repair should be properly designed in accordance with the guidelines. Finding a product that is engineered to the exact specs of a given scenario will not only offer the optimum design required to provide a sufficient repair, but it can also reduce costs. Additionally, there are many other conditions, such as bending or combined loading, that the repair must address. This is more likely to be done if the repair is custom designed by a knowledgeable engineering team versus assuming an off-the-shelf product has pre-considered every specific loading condition.
Myth: “Composite products provide only a temporary repair solution”
The largest issues with this misconception is lack of definition when it comes to the words “temporary” and “permanent.” They tend to mean something different to each operator, manufacturer and auditor. With regards to composite repairs designed for one scenario or the other, a general definition may be given as:
Temporary repair: This repair will be installed for a specified, usually short, amount of time with specialized scheduled inspections or a planned service removal.
Permanent repair: This repair will be installed without requirements for specialized scheduled inspections other than routine scheduled inspections for the entire pipe.
In either case, a “permanent” repair is only viable for a composite repair system if the defect itself has been addressed and no further damage to the pipe or composite repair is anticipated. Therefore, all internal wall loss defects, external abrasion or extremely high fatigue scenarios will be treated as temporary, requiring either a planned removal or an ongoing inspection plan. In the following case study, the operator desired a temporary repair to last until the affected system could be fully fixed.
The operator was faced with a leak in a crucial fire water system, consisting of a 10-ft carbon steel fire water line with a 0.25-in. hole. The pipe could not be immediately cut out and replaced, and a repair option was desired that would last until spring. When the company discovered this anomaly, a MIS repair team was called with an initial inquiry at 11 a.m. on one day, with design and quote completed and the order packed and shipped that same day. The following day, the team traveled to the site and completed the repair by noon the next day, finishing the repair in 25 hours from the initial call.
Based on the leaking defect, MIS engineers recommended a hybrid repair using EPRK (Emergency Pipe Repair Kit) and FormaShield. EPRK was used to stop the leak, while FormaShield was used to encapsulate and reinforce the pipe. After the contractor prepped the pipe, the EPRK items were applied as a “stop-gap.” A Butyl strip was clamped over the leak and clamp, then tented with filler putty. The team then waited 30 minutes to confirm a “drip-free” repair zone. A fast-curing, water activated wrap was applied over the clamp as an initial encapsulation, then 10 layers of FormaShield were applied to fully encapsulate and reinforce the defected area. The repair was successfully completed within two and a half hours.
To consider a repair “permanent”, any thermal and cyclic fatigue should also be considered on the pipe as well as the repair itself. Additionally, specific repair systems with known longevity issues, such as unidirectional composites that circumferentially crack or systems that allow further corrosion growth under the repair, may need to be monitored more closely and not considered “permanent.” The following case study consisting of general external corrosion could be considered “permanent” as the defect has been arrested and the repaired region is now in a static condition with no significant changes in the pipe or the composite repair anticipated.
In a case study regarding an aging pipeline in Patterson, Louisiana, MIS engineers considered the amount of corrosion it was experiencing and created a repair with an appropriate design life. A 20-in. OD horizontal gas pipeline in Patterson had been installed in 1956 and was starting to experience significant external corrosion. The damages, existing at 9 o’clock and 3 o’clock on the pipe, were 17 in. long, 15 in. wide and 0.123 in. deep for the first grid and 15 in. long, 16 in. wide and 0.066 in. deep for the second grid. The repair of the pipe, with a nominal wall thickness of 0.281 in., would require facilitating a maximum operating pressure of 1,050 psi and a pipe temperature of 50 F. MIS engineers designed a 20-year design life solution using the A+ Wrap system consisting of 17 layers for three linear feet, which would restore the structural integrity of the pipeline and bring it back to pristine conditions.
The repair was completed in two hours by a MIS technician and contracted personnel. The repair area was grit-blasted and wiped clean with acetone, followed by an application of EP420 as filler material for load transfer at the corrosion site. The repair also included repairing a girth weld and long seam welds. The technician applied a PPR epoxy coating to the entire repair zone and the 12 in. wide A+ Wrap system was applied using the layer over layer with offset method. ILI markers were installed to allow for inspection and the application was finished by applying and curing perforated constrictor wrap, which was removed the next day, and a topcoat was applied.
Years of field and third-party testing of composite repair products have shown that there are several options available that meet ASME and ISO engineering standards and are tested in accordance with ASTM and ISO. This testing shows that composites can withstand harsh elements, high pressure and the effects of long-time exposure in severe environments. Capable of providing repairs that can span decades, properly engineered composites can offer an extremely cost-effective solution.
Milliken Infrastructure Solutions, Pipe Repair, September 2018 Print Issue
Casey Whalen serves as engineering supervisor at Milliken Pipe Wrap.
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