The standard composite repair procedures work in most cases, especially for low-pressure pipeline applications. However, some situations require special consideration to protect long-term reliability.
Below, we describe three common challenges and the steps users can take to overcome them in the repair process.
Please note:We make recommendations for adapting the repair process for each challenge. However, every challenge in real-world applications is unique. Make sure to consult an expert to customize the solution to the application and the needs of the repair.
Application Challenge #1: Air Bubbles
Air bubbles in between layers of composite layers or between the composite and the substrate are the result of improper application. In order to better understand the impact of air bubbles and application errors on composite repair effectiveness, Advanced FRP conducted a research program, which included full-scale hydrostatic pressure and cyclic pressure tests with simulated air bubbles.
We observed several key findings:
First, air pockets in composite wraps can significantly reduce pressure capacity and compromise liquid tightness, especially in repairs for through-wall failures.
Larger air bubbles (over 1 square inch) reduce ultimate pressure capacity, with defects near the inner surface causing higher strain levels.
Smaller air bubbles (less than 0.1 square inches) had negligible impact on pressure capacity or repair longevity.
Overall, composite repair systems with higher lap shear strength perform better under pressure and reduce the likelihood of delamination due to air bubbles. When it comes to mitigating the risks of air bubble defects in the field, high-quality, well-installed composite systems are essential to long-term performance.
Applying a composite wrap to a pipe segment in a lab environment.
To Address Air Bubble Application Challenges:
Properly train repair technicians to ensure consistent mixing, saturation, and application of the carbon fiber fabric.
Apply the saturated fabric to the repair area using your hands to massage the fabric against the pipe to remove air bubbles. Always massage in the same direction and cover the entire surface area.
When considering composite wraps for high-temperature applications, the following points are important to consider:
ASME PCC-2 and ISO 24817 standards provide guidance on general composite repairs but do not provide sufficient testing requirements for high-risk composite repairs at elevated temperatures.
Composite materials perform differently at elevated temperatures compared to ambient temperatures.
As composite repair technologies and standards advance, thorough testing is integral to ensure the continued reliability of these repairs.
To Address Elevated Temperature Application Challenges:
Design your repair with the appropriate materials. Testing shows that different epoxies behave differently at different curing and operating temperatures.
Address the temperature of the curing and application environments. Accommodate elevated temperatures at any step in the process, as it may affect long-term performance.
Testing of composite wrap samples to understand the behavior of composites at elevated temperatures.
Application Challenge #3: High-Pressure Pipelines
Composite repairs may be installed on a pipeline at either full operating pressure or reduced pressure. When does each condition apply?
For high-pressure transmission pipelines, the composite wrap is installed while the pipeline is de-rated and slightly contracted. Once the composite wrap is fully cured, the pipe is re-pressurized. Re-pressurizing forces the composite system to immediately reinforce the carrier pipe in its slightly expanded state. This transfers load from the carrier pipe onto the reinforcing material.
For non-transmission pipelines operating at lower pressures, de-rating the pipeline is often unnecessary. The decision to derate a pipeline involves assessing several factors, such as the severity of the defect, the pipeline’s operating pressure, and the degree of wall loss sustained.
In both scenarios, the more effectively the composite repair “bears load” from the carrier pipe, the better reinforcement it provides.
To Address High-Pressure Pipeline Repairs:
Account for the severity of the defect, the amount of wall loss, and the operating pressure of the pipeline.
If appropriate, apply the repair while the pipeline runs at reduced pressure. Allow the repair to cure before returning to the operating pressure
Applying carbon fiber composite repairs in the field.
Questions About Application?
For questions about the application of composite repairs, or if you’re facing scenarios where special application steps might need to be taken, contact us.
Advanced FRP has advised on composite applications in wastewater, oil & gas, power generation, power transmission, and more.
Addressing Common Application Challenges
The standard composite repair procedures work in most cases, especially for low-pressure pipeline applications. However, some situations require special consideration to protect long-term reliability.
Below, we describe three common challenges and the steps users can take to overcome them in the repair process.
Application Challenge #1: Air Bubbles
Air bubbles in between layers of composite layers or between the composite and the substrate are the result of improper application. In order to better understand the impact of air bubbles and application errors on composite repair effectiveness, Advanced FRP conducted a research program, which included full-scale hydrostatic pressure and cyclic pressure tests with simulated air bubbles.
We observed several key findings:
Overall, composite repair systems with higher lap shear strength perform better under pressure and reduce the likelihood of delamination due to air bubbles. When it comes to mitigating the risks of air bubble defects in the field, high-quality, well-installed composite systems are essential to long-term performance.
To Address Air Bubble Application Challenges:
Read more about the effectiveness of composite repairs with air bubbles.
Application Challenge #2: Elevated Temperatures
When considering composite wraps for high-temperature applications, the following points are important to consider:
Read more about our comprehensive testing protocol to better understand the behavior of composites in elevated temperatures.
To Address Elevated Temperature Application Challenges:
Application Challenge #3: High-Pressure Pipelines
Composite repairs may be installed on a pipeline at either full operating pressure or reduced pressure. When does each condition apply?
For high-pressure transmission pipelines, the composite wrap is installed while the pipeline is de-rated and slightly contracted. Once the composite wrap is fully cured, the pipe is re-pressurized. Re-pressurizing forces the composite system to immediately reinforce the carrier pipe in its slightly expanded state. This transfers load from the carrier pipe onto the reinforcing material.
For non-transmission pipelines operating at lower pressures, de-rating the pipeline is often unnecessary. The decision to derate a pipeline involves assessing several factors, such as the severity of the defect, the pipeline’s operating pressure, and the degree of wall loss sustained.
In both scenarios, the more effectively the composite repair “bears load” from the carrier pipe, the better reinforcement it provides.
To Address High-Pressure Pipeline Repairs:
Questions About Application?
For questions about the application of composite repairs, or if you’re facing scenarios where special application steps might need to be taken, contact us.
Advanced FRP has advised on composite applications in wastewater, oil & gas, power generation, power transmission, and more.