In today’s rapidly changing world, industries are constantly seeking innovative solutions to enhance productivity, efficiency and sustainability. Fiber-reinforced polymer (FRP) materials are one important solution that are transforming many industries. Their growing popularity is due to the exceptional strength, durability and flexibility of FRP materials – they offer many benefits that traditional materials simply cannot match.
For chemical processing, oil and gas, mining, infrastructure, water management and other industries, FRP materials continue to unlock new possibilities and push boundaries. They are commonly used for tanks, piping systems, as an overwrap for repair and other applications.
Despite their many advantages, one drawback has hampered the adoption of FRP materials since they first appeared in the 1950s: a lack of industry-sanctioned standards for assessing fitness for service of pressure vessels, piping and other infrastructure made from FRP materials.
In this article we explore the unique characteristics, unrivaled performance, and remarkable potential of FRP materials. New fitness-for-service assessment standards coming soon will continue to fuel the rise of this durable, flexible and versatile material.
Fiber-reinforced polymer (FRP) materials boast impressive strength characteristics that make them highly desirable for a wide range of applications. Unlike traditional materials such as steel or concrete, FRP materials are lightweight yet incredibly strong. They enable engineers to create structures that are both durable and more efficient.
Unique composition of FRP materials
The strength of FRP materials comes from the combination of fibers (typically glass or carbon) embedded within a polymer matrix. This unique composition provides high tensile strength, making FRP materials ideal for applications where resistance to stretching forces is crucial.
(Note that FRP materials are less resistant to bending forces. As we’ll see below, with FRP the polymer is the first component that will experience damage. Bending actually forces more stress to flow through the polymer and this leads to more rapid weakening.)
Additionally, the polymer matrix acts as a binder. It holds the fibers together and providing protection against environmental factors such as corrosion and moisture.
As a result, FRP materials are capable of withstanding extreme conditions, making them highly suitable for applications that require long-term durability and structural integrity. This is why FRP is so useful in intensely cold or hot locales such as the Arctic or the tropics.
Whether for industrial piping, vessels or FRP wrap repairs, FRP materials offer a level of strength that surpasses traditional materials and opens up new possibilities for innovative design and construction.
We’ve only begun to tap the full design potential for FRP materials. Engineers to date have been unable take full advantage of FRP’s amazing strength-to-weight ratio because conventional design practices impose strict safety factors that effectively make the strength-to-weight ratio the same as for steel. It may be possible in future to reduce that barrier through better design and material selection practices.
Corrosion is one of the major challenges faced by industries across the globe. Traditional materials like steel are prone to corrosion when exposed to moisture, chemicals, or even atmospheric conditions. This corrosion not only weakens the structure but also leads to costly repairs and replacements. FRP materials, however, are highly resistant to corrosion, making them an ideal choice for applications where exposure to corrosive environments is common. Whether it’s offshore structures, chemical storage tanks, or wastewater treatment facilities, FRP materials provide a durable solution that withstands the test of time and reduces maintenance costs.
Traditional materials like wood or concrete can absorb moisture, leading to swelling, warping, and degradation. This moisture absorption can compromise the structural integrity of the material and result in significant damage.
In addition to corrosion resistance, FRP materials have a low moisture absorption rate and are very tolerant of moisture absorption. No dimensional changes occur. They will absorb up to about 8% of their weight of water. FRP materials are known for remaining stable and unaffected by moisture over time. This property makes FRP materials ideal for applications such as boat hulls, decks, and other marine structures, where exposure to water is inevitable.
Temperature variations can also pose a challenge to the durability of materials. Traditional materials may expand or contract when subjected to extreme temperatures, leading to cracks, fractures, and overall deterioration. FRP materials, however, exhibit excellent dimensional stability, meaning they remain unaffected by temperature fluctuations. This dimensional stability ensures that FRP structures maintain their integrity and performance even in extreme temperature conditions, making them suitable for a wide range of applications, including aerospace, automotive, and infrastructure projects.
One of the most remarkable characteristics of FRP materials is their flexibility and versatility. Unlike traditional materials, which are often rigid and limited in their applications, FRP materials can be molded, shaped, and customized to meet specific design requirements. This flexibility allows engineers and designers to push the boundaries of what is possible, creating innovative structures, components, and products that were once considered impossible.
In addition to their flexibility, FRP materials can be engineered to possess specific mechanical properties, such as stiffness, strength, and ductility, to suit the requirements of a particular application. This tailoring of material properties ensures that FRP structures and components perform optimally, providing the desired functionality and performance. FRP materials can be customized to meet the diverse needs of different industries.
FRP materials can also be combined with other materials, such as metals or concrete, to create hybrid structures that leverage the unique advantages of each material. This combination of materials allows engineers and designers to create structures with enhanced performance, improved durability, and reduced weight.
One example of the flexibility and versatility of FRP materials is its use as an overwrap to repair steel piping and other infrastructure for oil and gas, municipal water and sewage, district energy systems and other industry applications.
FRP wrap is a fast, inexpensive, reliable and safe alternative to traditional repair methods that would otherwise require engineers to remove and replace damaged sections of pipe or fix it by adding a steel sleeve or welding on a patch.
Done properly and inspected regularly, FRP wrapping provides additional structural reinforcement and leak protection that will likely outlast the steel pipe itself. See our case study of an inspection of an FRP wrap repair on steel piping.
As a result, most inspectors and reliability engineers don’t have the information they require to recognize and understand the changes that occur in FRP composites over time in response to the mechanical and chemical stresses that take place due to normal operating conditions.
WRC Bulletin 601 a major step forward for FRP assessment
This situation is changing following the publication of a Welding Research Council Bulletin (May 2023), authored by UTComp founder Geoff Clarkson, an FRP subject matter expert. WRC Bulletin 601 — “Assessment of Existing Fiber Reinforced Polymer Equipment for Structural Damage” — addresses the gap in standards for assessing fitness for service of pressure vessels, piping and other infrastructure made from FRP composite materials.
The bulletin describes the challenges and solutions involved in determining the condition and fitness for service of aging pressure vessels, piping and other equipment made from composite materials. It provides reliability engineers with a technically valid, quantitative and repeatable process for evaluating in-service FRP material assets.
“Until now, there has never been a comprehensive resource that identifies the damage that occurs to the polymer and how to detect it in FRP equipment after it is in service, and nothing that provides a rational, quantitative basis for determining fitness for service of these assets.”Geoff Clarkson, UTComp founder and CTO
Clarkson said WRC-601 is structured to provide guidance for including new methods for assessing FRP equipment in the consensus codes developed by the American Petroleum Institute (API) and American Society of Mechanical Engineers (API 579-1/ASME FFS-1), which are focused primarily on fitness for service assessments of metal pressure vessels and piping.
He notes the bulletin follows in the footsteps of 600 other bulletins that inform the code, providing technical background and validation for a methodology developed over 20 years of assessing FRP and other polymeric materials used in pressure vessels, tankage, piping, vehicles, building structures, and other assets in a wide range of industries.
FRP materials are different from metal alloys in a number of important ways, including how they change in response to chemical and mechanical stresses. Historically, the underlying damage mechanisms affecting FRP were little understood due to the material’s complex, multilayered structure.
Each component operates separately and has different mechanical properties: the reinforcement provides most of the structural strength, while the polymer binds it all together, prevents leakage and provides corrosion protection against harsh chemicals.
Damage mechanisms affecting FRP are completely different from the mechanisms that damage metal alloys. In general, steel loses thickness over time but not strength; FRP won’t usually lose thickness but the polymer will lose stiffness and strength in ways that until recently were difficult to measure without destructive testing. Damage always starts in the polymer and is detectable. As the polymer loses stiffness and strength, even normal service conditions may lead to cracks.
What are damage mechanisms in FRP?
Damage mechanisms are the underlying processes and changes that lead to the appearance of a failure mode (the way that failure appears to the naked eye, such as blistering or cracking.)
The naked eye cannot usually detect damage mechanisms. They often require techniques such as non-destructive evaluation and analytical techniques involving destructive testing, including microscopy.
Three main damage mechanisms can occur in FRP materials:
- Damage to the polymer / resin: this shows up as a reduction in stiffness (and, therefore, strength) caused by chemical attack, stress, strain and temperature over time.
- Damage to the reinforcement: reinforcement fibers are much stronger than the polymer. They are also protected by the corrosion barrier from chemical attack. As a result, the reinforcement won’t fail before the polymer, which undergoes more drastic viscoelastic changes.
- Damage to the interface of the matrix and reinforcement: this also shows up primarily as damage to the polymer. Exposure to corrosive chemicals and mechanical loads over time can weaken bonding between polymer and reinforcement layers, leading to cracking, swelling, and delamination.
FRP composite tanks, piping, ductwork, reactors and other equipment require evaluation of both mechanical and chemical damage mechanisms.
Mechanical damage mechanisms
Mechanical damage mechanisms include high stresses, bending movements, fatigue, compression loads, and defective installation.
Chemical damage mechanisms
Chemical damage is the main risk factor in FRP chemical processing equipment such as reactors, scrubbing columns and piping with injection points where chemical reactions are taking place. In some cases, damage due to chemical attack is also magnified where damage to the protective inner surface has occurred due to leaks along internal bonds, leaks in thermoplastic lining welds, cracks and abrasion.
What is Creep Rupture in FRP materials?
“Creep Rupture” is the term for a common result of these damage mechanisms that leads to failure of FRP materials.
The damage mechanisms identified above all relate to the components of FRP materials that combine to give it strength and stiffness. For this reason, changes in stiffness, also known as creep, will generally result from damage.
Visual inspections for FRP materials are highly subjective and often require confined space entry (with added costs and safety issues). While destructive testing methods are well-developed for steel and FRP materials, by definition they require equipment to be made “unfit” for service during an inspection and then made fit for service once again. This adds costs for repairs and downtime.
UTComp’s UltraAnalytix® NDT system is the leading NDT methodology capable of assessing the mechanical integrity of FRP by determining the condition of the polymer. While conventional ultrasonic testing can be used to measure thickness and find defects in materials, UltraAnalytix uses ultrasound differently. Like conventional ultrasonic testing, UltraAnalytix can identify thickness changes, cracks, delaminations and other defects. But by measuring changes in stiffness (PDS), thickness and the depth of corrosion barrier damage, it quantifies the condition of the material, calculates remaining service life (RSL), and provides fitness for service assessments that allow end-users to make data-based decision about their FRP assets.
Questions about your FRP assets?