For many years, ultrasound has been the go-to non-destructive testing (NDT) technology for inspecting steel pipes, tanks and vessels. However, ultrasonic testing of equipment made from fiber reinforced polymer (FRP) composites is more recent.
Below we discuss attenuation-based ultrasound (UAX), an ultrasonic testing method that is increasingly being used for FRP composite materials.
What is attenuation-based ultrasound (UAX)?
Attenuation-based ultrasound (UAX) 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. By analyzing these changes in the ultrasonic signal, trained inspectors can identify cracks, voids and other overt defects that may affect the performance of the material.
UltraAnalytix: UTComp’s patented UAX methodology
UltraAnalytix® NDT is UTComp’s brand name for the UAX method. Developed by UTComp founder Geoff Clarkson using millions of data points collected from thousands of inspections over 15+ years, 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 (RSL) assessments. This analysis provides asset owners with quantitative insights to inform decisions about FRP asset repair and replacement.
How UAX measures FRP damage
UltraAnalytix measures FRP damage in three ways:
- Creep, which relates to the loss of structural capacity and is dictated by polymer
damage. Follows a similar line to changes in bending stiffness.
- Thickness loss related to damage from abrasion and oxidation
- Corrosion barrier damage, shown as PDS related to depth of damage / thickness in the protective corrosion layer.
Learn more about how UltraAnalytix compares to other methodologies used to assess FRP composite equipment.
UAX inspection compared to conventional ultrasound: 4 key factors to consider
Detailed inspection codes developed by the American Petroleum Institute (API) and American Society of Mechanical Engineers (ASME) include standards for non-destructive ultrasonic inspection of in-service steel pipes and vessels.
However, there are currently no published consensus standards that can be used for assessing the condition of in-service FRP equipment and predicting its RSL.
When deploying a UAX inspection strategy for FRP assets, there are four key factors that must be understood compared to more conventional straight-beam UT inspection of steel alloys:
- Flaw-detector set-up differs slightly from set-ups used for metal flaw and defect detection.
- Existing UT equipment cannot display results on the A-scan that allow inspectors in the field to determine the condition of the FRP asset. Readings must be processed separately and outside of the flaw detector.
- Most indications or reflections that appear before the back surface reflection are not due to flaws or defects but are most likely from changes in resin or polymer properties along the pulse path; in reality, delaminations are rare.
- Delaminations and voids in FRP have almost no effect on the tensile strength of the material and, therefore, have a very small effect on calculations from the construction codes.
To learn about UAX inspection of non-metallic equipment, read the article in the May-June 2024 issue of Inspectioneering Journal by UTComp’s Geoff Clarkson and Ray Vermillion, Asset Integrity & Reliability Engineering Manager at Ashland.
WRC-601: guidance on new testing methods, including UAX
Welding Research Council (WRC) Bulletin 601, published in 2023, is a major step forward in addressing this gap in inspection standards for in-service FRP assets.
Authored by Clarkson, it provides technical guidance for bringing the UAX method — including techniques that form the basis of the UltraAnalytix system — and other inspection technologies into the API and ASME consensus codes that to date have focused primarily on inspecting metal pressure vessels and piping.
WRC-601 also provides further validation for the UltraAnalytix methodology for assessing FRP and other polymeric materials used in pressure vessels, piping and other assets in a wide range of industries.