Since the invention of pipelines, operators have employed a variety of repair methods to safeguard their productivity and protect against failure mechanisms. Two prominent methods have emerged as mainstream repairs for modern pipeline reinforcement: steel sleeves and composite repair systems. While steel sleeves have been a mainstay solution for decades, composite repairs have gained popularity in recent years due to their adaptability, lightweight properties, and ease of installation. This article explores elements of each repair method, discusses common applications for each, and details the advantages of composite repair systems as a long-lasting pipeline repair method.
Reinforcing Steel Sleeves: Variations and Usage
Steel sleeves, also known as full encirclement repair sleeves, have been utilized as a pipeline reinforcement method since the mid-20th century. The basic principle behind this type of repair is simple: when a section of pipe becomes damaged through corrosion, gouging, dents, or the presence of crack-like features, a steel sleeve is fitted over the affected section to safely restore its load-bearing capabilities. Specifically, two half-moon-shaped pieces of pressure vessel-quality ASTM carbon steel are welded together across the longitudinal seam. The presence of the steel sleeve transfers load from the weakened carrier pipe to the reinforcing sleeve. Steel sleeves remain a preferred method for repairing high-pressure pipelines due to their durability and ability to handle extreme conditions.
Steel sleeves fall into one of two categories, depending on their configuration: Type A and Type B.
Type A Sleeves
Type A sleeves are considered non-pressure-containing repairs because they are not welded directly to the pipe. When the sleeve is fitted over the pipeline, it is commonly milled along the edges. This slight groove allows a backing strip to slide in on the inside of the longitudinal seam of the steel sleeve. When the sleeve is welded at the longitudinal seam, the backing strip ensures that the sleeve is not welded directly to the pipe, but only to the other sleeve half.
Type B Sleeves
On the other hand, Type B sleeves are considered a pressure-containing repair because they are welded directly to the pipe at the circumferential edges. After welding the longitudinal seam, circumferential welds are installed on either end of the sleeve, permanently joining it to the carrier pipe. Pressure-containing Type B sleeves can be applied to through-wall leaking defects because of their ability to effectively hold pressure in the event of a loss of containment. Type B sleeves may be used when wall loss exceeds 80%. However, the use of Type B sleeves depends on the guidelines detailed by an operator’s integrity management program (IMP). While Type B steel sleeves are commonly used, some operators avoid them entirely because of the inherent risk of welding directly to the pipe.
Evolution of Composite Repair Systems
Over the last 30 years, composite repairs have greatly increased in popularity as a highly versatile pipeline repair method. The industry appetite for composite repair technology has spurred extensive investment into expanding their capabilities. This investment has been supported by joint industry partnerships (JIPs) led in tandem by operators, technology providers, and regulators. This coordination has both increased the rate of composite system expansion and influenced their adoption, resulting in widespread acceptance of composite repairs as a trusted, established repair method.
As their prevalence has grown, composite repair capabilities have extended beyond corrosion reinforcement to a multitude of other defects. ASME PCC-2, widely regarded as the standard for the repair of pressure equipment and piping, was first released in 2004 and became a national standard in 2011. PCC-2 is regularly updated to account for technological advancements, with the most recent update released in 2022. Composite repair systems are also listed as an accepted repair method for high-pressure pipelines, according to the PRCI Pipeline Repair Manual, 2021 Edition. Regulations and resources such as these have helped provide a growth medium for composite repair systems.
Like steel sleeves, composite repair systems also fall into two broad categories: rigid coil systems and wet layups.
Rigid Coil Systems
Before technological innovation spurred extensive expansion of wet layup composite repair properties, composite systems were initially applied in the form of rigid coil systems known as clocksprings. These rigid coil composite systems were developed as an alternative to steel sleeves and include several key components: a composite coil that uses uniaxial E-glass in a polyurethane matrix—or clockspring—forms the core of the system. A hardenable filler material and a methacrylate adhesive are then supplied to activate the curing process.
Wet Layup Systems
As technological advancements led to stronger, more versatile material properties, the wet layup technique was introduced. Wet layup systems include resin-impregnated fibers that are applied “wet” to the affected section of pipe and cure to form a hard, durable repair. This method is flexible and adaptable, allowing it to conform to irregular pipe geometries and diameter changes. This flexibility is a substantial advantage over both rigid coil applications and steel sleeves.
Application and Performance Advantages of Composite Repairs
Today, most composite systems are applied wet and allowed to cure over either a flat or contoured surface. One primary advantage of wet layup composites is their ability to conform to a wide range of pipe shapes, including those with swelling, elbows, flanged sections, wrinkle bends, tees, and multi-diameter pipelines. This makes them ideal for pipelines that are difficult to repair using traditional methods. While atypical configurations are a noteworthy application highlight for composite repairs, their cost advantages also make them ideal for repairing straight or unform pipe configurations.Composite systems can be applied to a variety of materials (such as steel, cast iron, PVC, and concrete) and are suitable for a wide range of operating conditions, including elevated temperatures and corrosive environments.
Because composite repair systems are non-metallic, they are not prone to corrosion, either internal or external. In the experience of Advanced FRP, the material properties of composite systems provide better external corrosion protection to the pipe than any other coating technology available.
Finally, composite systems are much lighter than steel, making them easier and faster to apply. This can significantly reduce labor costs and installation time. Unlike other heat-based repairs, composite repairs do not require hot work or welding, making them safer to apply and reducing the risk of sparks or fire hazards. The quick curing times of many composite systems coupled with the reduced personnel required allow for faster backfill and a speedy return to routine operations, minimizing or even eliminating downtime.
The Importance of Enabling Load Transfer Through Tight Fit-Up
The goal of any pipeline repair is to transfer load from the carrier pipe onto the reinforcing material. The more effectively the repair method bears the load, the better reinforcement it provides. By being in direct contact with the surface of the carrier pipe, the load can be effectively shared by the reinforcing material. This intimate contact between the reinforcing material and the repaired surface provides a diametric force to counter the internal stresses of the pipeline.
To enable effective load transfer, a close fit-up is essential. While the rigidity of steel sleeves can provide an effective compressive fit-up, optimal reinforcement relies on several factors: 1) uniformity of the pipe surface (meaning it cannot be swollen, bowed, or contain any bends), and 2) proper fabrication of the sleeve. To enable a close fit-up and promote effective load transfer, the outer diameter (OD) of the pipe must match the inner diameter (ID) of the reinforcing sleeve. If there is a variance between these two diameters, the annulus or voids between the sleeve and the pipe will detract from the sleeve’s reinforcing ability and increase fatigue stress where close contact is not maintained between the sleeve and the carrier pipe.
Regarding the potential for air pocket formation, Advanced FRP has performed comprehensive third-party validation testing of various diameter air pockets that can occur during composite repair application. The study showed that the impact on the composite repair’s effectiveness depends on multiple factors, including lap shear or interlaminar shear strength, the depth and diameter of the bubble, and the operating conditions of the repaired system. Larger air bubbles occurring closer to the pipe’s inner surface do negatively affect the ultimate pressure capacity, resulting in a strain level increase. Advanced FRP conducts in-depth certification training programs to instruct composite installers on avoiding issues that can result from inter-layer air pockets.
Selecting an Appropriate Repair Method
Choosing between steel sleeves and composite repairs depends on various factors, including the pipe’s operating conditions, the severity of the damage, cost considerations, and the desired longevity of the repair. From a regulatory perspective, steel sleeves can reinforce most leaking and non-leaking defects, along with wall loss exceeding 80%. However, their rigidity restricts them from reinforcing complex geometries, a significant limitation. Composite repairs are Type A repairs and can be used to reinforce defects that will not become through wall failures during the repair lifecycle. While most commonly applied to corrosion defects, composite systems can be used to reinforce dents, girth welds, wrinkle bends, mechanical damage, and seam welds, according to ASME B31.4. Their application properties will continue to grow as their usage expands over the next decade.
Wet layup composites edge out steel sleeves for installation over complex or atypical configurations.Even when the surface of the carrier pipe is far from uniform, the composite repair can still closely adhere to the exact contours of the pipe surface, facilitating effective load transfer and providing a close fit-up between the reinforcing material and the carrier pipe. However, the benefits of composite repairs far exceed cases of complex geometry. Their cost advantages, impressive strength-to-weight ratio, streamlined installation time, and proven longevity also make them an ideal repair option for straight, uniform pipe applications. In many cases, a composite repair can be used in place of a steel sleeve and achieve similar performance with substantial savings.
The many advantages of composite repairs include not only their structural versatility and inability to corrode over time, but also the substantial time and cost savings realized from their quick installation, minimal lead time, and deployment while a system is online and operational. Composite repairs are not only adaptable and economical—they are long-term repairs that significantly extend the service life of critical pipeline infrastructure.
Leveraging Advanced FRP’s Expertise as a Composite Solutions Provider
For complex pipeline repairs requiring high-performance solutions, partnering with an experienced composite repair provider can make all the difference. Advanced FRP Systems is a leading provider of ASME PCC-2 qualified composite repair systems. Our team of subject matter experts and knowledgeable chemists routinely engineers custom solutions for various composite repair applications. As the technology grows, Advanced FRP is executing extensive validation testing to demonstrate the versatility of composite repair systems. Testing initiatives include elevated temperature testing for composite repairs, crack reinforcement programs, air pocket analysis, and an ongoing Joint Industry Partnership (JIP) for the design optimization of composite reinforcement. Schedule your free consultation to discuss your repair requirements and create a tailored solution for your system.
To Sleeve or to Wrap: Comparing Steel Sleeves and Composite Repairs for Effective Pipeline Reinforcement
Since the invention of pipelines, operators have employed a variety of repair methods to safeguard their productivity and protect against failure mechanisms. Two prominent methods have emerged as mainstream repairs for modern pipeline reinforcement: steel sleeves and composite repair systems. While steel sleeves have been a mainstay solution for decades, composite repairs have gained popularity in recent years due to their adaptability, lightweight properties, and ease of installation. This article explores elements of each repair method, discusses common applications for each, and details the advantages of composite repair systems as a long-lasting pipeline repair method.
Reinforcing Steel Sleeves: Variations and Usage
Steel sleeves, also known as full encirclement repair sleeves, have been utilized as a pipeline reinforcement method since the mid-20th century. The basic principle behind this type of repair is simple: when a section of pipe becomes damaged through corrosion, gouging, dents, or the presence of crack-like features, a steel sleeve is fitted over the affected section to safely restore its load-bearing capabilities. Specifically, two half-moon-shaped pieces of pressure vessel-quality ASTM carbon steel are welded together across the longitudinal seam. The presence of the steel sleeve transfers load from the weakened carrier pipe to the reinforcing sleeve. Steel sleeves remain a preferred method for repairing high-pressure pipelines due to their durability and ability to handle extreme conditions.
Steel sleeves fall into one of two categories, depending on their configuration: Type A and Type B.
Type A Sleeves
Type A sleeves are considered non-pressure-containing repairs because they are not welded directly to the pipe. When the sleeve is fitted over the pipeline, it is commonly milled along the edges. This slight groove allows a backing strip to slide in on the inside of the longitudinal seam of the steel sleeve. When the sleeve is welded at the longitudinal seam, the backing strip ensures that the sleeve is not welded directly to the pipe, but only to the other sleeve half.
Type B Sleeves
On the other hand, Type B sleeves are considered a pressure-containing repair because they are welded directly to the pipe at the circumferential edges. After welding the longitudinal seam, circumferential welds are installed on either end of the sleeve, permanently joining it to the carrier pipe. Pressure-containing Type B sleeves can be applied to through-wall leaking defects because of their ability to effectively hold pressure in the event of a loss of containment. Type B sleeves may be used when wall loss exceeds 80%. However, the use of Type B sleeves depends on the guidelines detailed by an operator’s integrity management program (IMP). While Type B steel sleeves are commonly used, some operators avoid them entirely because of the inherent risk of welding directly to the pipe.
Evolution of Composite Repair Systems
Over the last 30 years, composite repairs have greatly increased in popularity as a highly versatile pipeline repair method. The industry appetite for composite repair technology has spurred extensive investment into expanding their capabilities. This investment has been supported by joint industry partnerships (JIPs) led in tandem by operators, technology providers, and regulators. This coordination has both increased the rate of composite system expansion and influenced their adoption, resulting in widespread acceptance of composite repairs as a trusted, established repair method.
As their prevalence has grown, composite repair capabilities have extended beyond corrosion reinforcement to a multitude of other defects. ASME PCC-2, widely regarded as the standard for the repair of pressure equipment and piping, was first released in 2004 and became a national standard in 2011. PCC-2 is regularly updated to account for technological advancements, with the most recent update released in 2022. Composite repair systems are also listed as an accepted repair method for high-pressure pipelines, according to the PRCI Pipeline Repair Manual, 2021 Edition. Regulations and resources such as these have helped provide a growth medium for composite repair systems.
Like steel sleeves, composite repair systems also fall into two broad categories: rigid coil systems and wet layups.
Rigid Coil Systems
Before technological innovation spurred extensive expansion of wet layup composite repair properties, composite systems were initially applied in the form of rigid coil systems known as clocksprings. These rigid coil composite systems were developed as an alternative to steel sleeves and include several key components: a composite coil that uses uniaxial E-glass in a polyurethane matrix—or clockspring—forms the core of the system. A hardenable filler material and a methacrylate adhesive are then supplied to activate the curing process.
Wet Layup Systems
As technological advancements led to stronger, more versatile material properties, the wet layup technique was introduced. Wet layup systems include resin-impregnated fibers that are applied “wet” to the affected section of pipe and cure to form a hard, durable repair. This method is flexible and adaptable, allowing it to conform to irregular pipe geometries and diameter changes. This flexibility is a substantial advantage over both rigid coil applications and steel sleeves.
Application and Performance Advantages of Composite Repairs
Today, most composite systems are applied wet and allowed to cure over either a flat or contoured surface. One primary advantage of wet layup composites is their ability to conform to a wide range of pipe shapes, including those with swelling, elbows, flanged sections, wrinkle bends, tees, and multi-diameter pipelines. This makes them ideal for pipelines that are difficult to repair using traditional methods. While atypical configurations are a noteworthy application highlight for composite repairs, their cost advantages also make them ideal for repairing straight or unform pipe configurations. Composite systems can be applied to a variety of materials (such as steel, cast iron, PVC, and concrete) and are suitable for a wide range of operating conditions, including elevated temperatures and corrosive environments.
Because composite repair systems are non-metallic, they are not prone to corrosion, either internal or external. In the experience of Advanced FRP, the material properties of composite systems provide better external corrosion protection to the pipe than any other coating technology available.
Finally, composite systems are much lighter than steel, making them easier and faster to apply. This can significantly reduce labor costs and installation time. Unlike other heat-based repairs, composite repairs do not require hot work or welding, making them safer to apply and reducing the risk of sparks or fire hazards. The quick curing times of many composite systems coupled with the reduced personnel required allow for faster backfill and a speedy return to routine operations, minimizing or even eliminating downtime.
The Importance of Enabling Load Transfer Through Tight Fit-Up
The goal of any pipeline repair is to transfer load from the carrier pipe onto the reinforcing material. The more effectively the repair method bears the load, the better reinforcement it provides. By being in direct contact with the surface of the carrier pipe, the load can be effectively shared by the reinforcing material. This intimate contact between the reinforcing material and the repaired surface provides a diametric force to counter the internal stresses of the pipeline.
To enable effective load transfer, a close fit-up is essential. While the rigidity of steel sleeves can provide an effective compressive fit-up, optimal reinforcement relies on several factors: 1) uniformity of the pipe surface (meaning it cannot be swollen, bowed, or contain any bends), and 2) proper fabrication of the sleeve. To enable a close fit-up and promote effective load transfer, the outer diameter (OD) of the pipe must match the inner diameter (ID) of the reinforcing sleeve. If there is a variance between these two diameters, the annulus or voids between the sleeve and the pipe will detract from the sleeve’s reinforcing ability and increase fatigue stress where close contact is not maintained between the sleeve and the carrier pipe.
Regarding the potential for air pocket formation, Advanced FRP has performed comprehensive third-party validation testing of various diameter air pockets that can occur during composite repair application. The study showed that the impact on the composite repair’s effectiveness depends on multiple factors, including lap shear or interlaminar shear strength, the depth and diameter of the bubble, and the operating conditions of the repaired system. Larger air bubbles occurring closer to the pipe’s inner surface do negatively affect the ultimate pressure capacity, resulting in a strain level increase. Advanced FRP conducts in-depth certification training programs to instruct composite installers on avoiding issues that can result from inter-layer air pockets.
Selecting an Appropriate Repair Method
Choosing between steel sleeves and composite repairs depends on various factors, including the pipe’s operating conditions, the severity of the damage, cost considerations, and the desired longevity of the repair. From a regulatory perspective, steel sleeves can reinforce most leaking and non-leaking defects, along with wall loss exceeding 80%. However, their rigidity restricts them from reinforcing complex geometries, a significant limitation. Composite repairs are Type A repairs and can be used to reinforce defects that will not become through wall failures during the repair lifecycle. While most commonly applied to corrosion defects, composite systems can be used to reinforce dents, girth welds, wrinkle bends, mechanical damage, and seam welds, according to ASME B31.4. Their application properties will continue to grow as their usage expands over the next decade.
Wet layup composites edge out steel sleeves for installation over complex or atypical configurations. Even when the surface of the carrier pipe is far from uniform, the composite repair can still closely adhere to the exact contours of the pipe surface, facilitating effective load transfer and providing a close fit-up between the reinforcing material and the carrier pipe. However, the benefits of composite repairs far exceed cases of complex geometry. Their cost advantages, impressive strength-to-weight ratio, streamlined installation time, and proven longevity also make them an ideal repair option for straight, uniform pipe applications. In many cases, a composite repair can be used in place of a steel sleeve and achieve similar performance with substantial savings.
The many advantages of composite repairs include not only their structural versatility and inability to corrode over time, but also the substantial time and cost savings realized from their quick installation, minimal lead time, and deployment while a system is online and operational. Composite repairs are not only adaptable and economical—they are long-term repairs that significantly extend the service life of critical pipeline infrastructure.
Leveraging Advanced FRP’s Expertise as a Composite Solutions Provider
For complex pipeline repairs requiring high-performance solutions, partnering with an experienced composite repair provider can make all the difference. Advanced FRP Systems is a leading provider of ASME PCC-2 qualified composite repair systems. Our team of subject matter experts and knowledgeable chemists routinely engineers custom solutions for various composite repair applications. As the technology grows, Advanced FRP is executing extensive validation testing to demonstrate the versatility of composite repair systems. Testing initiatives include elevated temperature testing for composite repairs, crack reinforcement programs, air pocket analysis, and an ongoing Joint Industry Partnership (JIP) for the design optimization of composite reinforcement. Schedule your free consultation to discuss your repair requirements and create a tailored solution for your system.