Comparison of 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.
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
UTComp’s UltraAnalytix NDT system combines ultrasonic data collected in the field, external visual inspection and analysis using a proprietary algorithm. This non-intrusive, non-destructive method is unique in ensuring FRP and composite assets are fit for service while also calculating their remaining service life (RSL).
UTComp founder Geoff Clarkson drew on decades of research by leading materials scientists to develop and validate the UltraAnalytix system. UltraAnalytix inspection has repeatedly proven to provide safe, reliable and cost-effective reliability testing 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.
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:
- Can the method detect flaws that can’t be seen by the human eye?
- Will the structural integrity of the asset be preserved during testing?
- Does the method minimize or eliminate potentially risky confined space entry?
- Can inspection be completed while the equipment is operating (avoiding the time and expense of asset cleanout, shutdown time and lost income)?
- 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:
- Inspection while equipment is operating
- Remaining service life estimates
- Easy, reliable data capture
- Minimizes confined space entry
FRP testing methodologies
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 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.
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 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.
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.
First published January 4, 2022