Testing FRP composite materials: which method is best?

April 17, 2024

Compare reliability testing methods for FRP composites

Fiber-reinforced plastic (FRP) and other composite materials are unequaled in terms of durability and environmental benefits for many industrial applications. 

As FRP materials become more widely used for storage vessels, process tanks and pipes in a variety  of industries, choosing the right inspection method is imperative for reliability and to maximize performance, safety and return on investment. 

There are several non-destructive testing (NDT) and destructive methods to evaluate the condition of FRP composite equipment. Each approach, when used appropriately and under the right conditions, is capable of locating and/or measuring voids, cracks and other defects.

In this article we explain the differences between reliability testing methods for FRP composites.

Visual inspection of FRP

Visual inspection provides a subjective opinion focused on the state of the inner surface of the corrosion barrier.

Assumptions about the capability of the FRP to perform its function are based on appearance. It’s important to note that no research or published material has provided any scientific connection between the appearance of FRP and its reliability.

Visual inspection can’t detect flaws that are invisible to the human eye. It also often requires confined space entry, which means shutting down operations and potentially risking human health and safety.

Without data and good information, backed by verified research results, decisions based on a visual inspection of the corrosion barrier rely by necessity on hunches, intuition and guesswork. An asset may look ok from a visual inspection standpoint but not be fit-for-service:

“…one B.C. pulp mill was concerned about a line from the bleach plant and they were trying to figure out how much they had to repair or replace. So, we did ultrasonic testing with UTComp’s UltraAnalytix NDT, and, even though on a visual basis it looked pretty good, analysis of the data showed that in the bottom section of the pipe, there was basically no corrosion barrier left. So, they were able to determine that they needed to replace more than was anticipated. When they removed that section of pipe and looked at it, it was really pretty bad. If that pipe had failed, the plant would have been down for weeks. So in the end, investing in an UltraAnalytix inspection saved them time and money.”

— Daniel Tremblay, owner of Horizon Testing Inc., UTComp licensee for UltraAnalytix inspection since 2011 

Destructive testing of FRP

Destructive testing provides more information than visual inspection. However, it damages the asset that reliability engineers are trying to preserve.

For most FRP piping, it is not even possible to make these inspections unless a piece of the asset is removed. Cutting a piece from process piping and repairing it usually requires that the work be completed according to a piping code such as ASME B31.3. After the damage has been repaired, a hydrotest is required. The total cost to the facility can be enormous, considering downtime, engineering, and repairs even before any evaluation of the pipe has started. Finally, any conclusions about the piping condition hinge on the specific samples removed; if only one sample is removed, let’s hope it comes from the right place!

UltraAnalytix NDT system for FRP composites

UltraAnalytix 4 step process graphic

UltraAnalytix NDT inspection makes testing FRP assets as simple, and as reliable, as testing steel assets.

UltraAnalytix® NDT is a patented non-destructive, non-intrusive system for in-service inspection and assessment of industrial equipment made of fiber-reinforced polymer (FRP) and other composite materials.

UltraAnalytix is UTComp’s brand name for the UAX method, an attenuation-based ultrasound system for quantifying polymer damage in composite materials.

Developed by UTComp founder Geoff Clarkson, UltraAnalytix combines ultrasonic data collected in the field, external visual inspection and analysis using a proprietary algorithm. The AI-powered algorithm has been honed over 15+ years, and draws on millions of inspection data points, for accurate Fitness for Service evaluations and precise Remaining Service Life forecasting.

This method is unique in ensuring FRP and composite assets are fit for service while also calculating their remaining service life.

Clarkson drew on decades of research by leading materials scientists to develop and validate the UltraAnalytix attenuation-based method.

UltraAnalytix NDT assessment has been proven to provide safe, reliable and cost-effective reliability testing. It that ensures composite assets meet the highest standards of safety, performance, quality and regulatory compliance.

More than 4,000+ assets are now under UltraAnalytix inspection for more than 200 companies worldwide.

It’s predictive maintenance decision-making at its best for maximum return on investment (ROI).

5 questions to ask about FRP reliability testing

Here are 5 questions that every plant manager and reliability engineer should ask when evaluating a reliability testing method for their FRP assets:

  1. Can the method detect flaws that can’t be seen by the human eye?
  2. Will the structural integrity of the asset be preserved during testing?
  3. Does the method minimize or eliminate potentially risky confined space entry?
  4. Can inspection be completed while the equipment is operating (avoiding the time and expense of asset cleanout, shutdown time and lost income)?  
  5. Does the inspection provide validated data to:
    • Confirm a new asset complies with specifications?
    • Monitor the asset condition for changes over time?
    • Calculate remaining service life?

Criteria for evaluating an FRP testing system

The chart below shows how UltraAnalytix compares to other FRP inspection technologies based on the following criteria:

  • Cost
  • Speed
  • Non-intrusive
  • Inspection while equipment is operating
  • Remaining service life estimates
  • Repeatable
  • Easy, reliable data capture
  • Minimizes confined space entry

FRP testing methodologies

Attenuation-Based Ultrasonic Testing (UAX)

Attenuation-based ultrasound involves transmitting ultrasonic pulses and analyzing how the signal changes or weakens as it passes through the material being tested. This reduction in energy is known as attenuation. Analysis of these changes in the ultrasonic signal is used to identify cracks, voids and other defects that may affect the performance of the material. UltraAnalytix goes further than identifying defects in FRP. UltraAnalytix analyzes ultrasonic data using a proprietary algorithm that quantifies the condition of the polymer for reliable fitness for service and remaining service life assessments. This analysis provides asset owners with quantitative insights to inform decisions about FRP asset repair and replacement.

Ultrasonic Thickness Testing

As the name implies, ultrasonic thickness testing measures the thickness of a test piece of material. However, accurately assessing the strength and condition of composites is more complicated. In addition to measuring thickness, UltraAnalytix also calculates the Percentage of Design Stiffness (PDS) and assesses the strength and condition of bonding between layers to thoroughly evaluate mechanical integrity.

Thermography

Thermography uses infrared technology to detect external and near-surface defects in FRP and composite materials. While the technology is reliable and non-intrusive, the instrumentation is relatively complex and difficult to use.

Digital Radiography

The use of X-rays in NDT testing has a long history and the technology continues to improve. However, while it offers a dependable way to detect cracks and voids or other defects, digital radiography is relatively expensive and time-consuming.

Visual Inspection

Visual inspection is the first step in assessing the condition of equipment made from FRP and other composites. Done correctly, visual inspections are essential. However, they are by nature highly subjective and generally only detect visible surface flaws. Visual inspection also routinely requires confined space entry procedures, which can be dangerous for personnel and involves shutting down operations.

Acoustic Emission

Imperfections in FRP and composite materials can be identified using acoustic emission tests that detect mechanical vibrations generated by material defects such as cracking and debonding. This type of testing is relatively time-consuming and expensive, and it requires a great deal of skill to correlate different sounds to specific types of damage.

Unlike all other methods, UltraAnalytix NDT inspection provides asset owners with a reliable, repeatable, data-driven assessment of all facets of asset condition while saving time and money.

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