UTComp engineering analyst Karelle Guiao and CTO Geoff Clarkson will present a paper at the American Society of Mechanical Engineers’ (ASME) Pressure Vessels and Piping conference, PVP 2026, on the value of FRP Remaining Strength Factor calculation.
This marks the first time UTComp’s research will be featured at this important international technical forum, which marks its 60th anniversary July 19-24, 2026.
Titled “Verifying Allowable Remaining Strength Factor in Fitness For Service Assessment of Fiber Reinforced Polymer Pressure Equipment,” the paper demonstrates the value of including Remaining Strength Factor (RSF) as a key component of the new Part 16 proposed for API 579-1 / ASME FFS-1 standard.
Part 16 is advancing the science and understanding of FRP composites by providing the first-ever consensus standard for assessing in-service FRP equipment reliably, safely and non-destructively.
Failure analysis using Remaining Strength Factor
The paper discusses two recent examples of equipment failures that UTComp was asked to investigate – a pipe failure and pressure vessel rupture.
Both pieces of equipment were involved in chemical service. One operated in a more aggressive chemical environment. But in both cases it was NOT the chemical conditions that caused the failure. It was the mechanical conditions.
Here’s what happened:
FRP pipe failure in chemical service
The pipe failure was ultimately caused by an incorrectly bolted flange.
It wasn’t the flange, but the pipe that broke because the poorly installed flange added loads that the system wasn’t designed to handle. Eventually, the pipe broke from the inside-out due to polymer damage that was impossible to detect visually.
FRP pressure vessel failure
The pressure vessel failed because its construction didn’t match the design.
That is, the bottom of the tank was made only half as thick as it was supposed to be according to the design specifications.
As a result, the tank was operating under axial (vertical) stresses it was not built to withstand. Over time, polymer damage accelerated; inevitably, the tank ruptured.
Actual operating conditions a key factor
Using a combination of ultrasonic analysis and RSF calculations, as well as information about the equipment’s design and construction, UTComp engineers determined that in both cases, the equipment was doomed to fail because operating conditions didn’t match the design.
But as is often the case with FRP, the pipe and the vessel continued to operate for years without any visible problems despite doing what they were not intended to do — and then they suddenly failed.
In both cases, the UTComp team determined that the point of failure could be described using RSF. In fact, had the equipment been assessed based on Part 16 of API 579 before it failed, it would have been deemed not fit for service.
Key takeaways
Here are four key takeaways from the paper, which will be presented at PVP 2026 in July:
- The principle of RSF developed for the new Part 16 of API 579 is invaluable for determining the Fitness For Service of FRP composite equipment.
- Damage that reduces RSF is invisible; therefore, inspection tools and techniques that can collect data to determine polymer condition are essential.
- Operating conditions like pressure or flange bolt torquing or mechanical loads must be considered. Don’t count on actual conditions being the same as the design conditions.
- Many manufacturers don’t provide FRP thickness information with the equipment they supply. Thickness is a critical factor in determining RSF.
Abstract
Title: “Verifying Allowable Remaining Strength Factor in Fitness For Service Assessment of Fiber
Reinforced Polymer Pressure Equipment”
Authors: Karelle Guiao, Geoffrey Clarkson
API 579-1/ASME FFS-1 Fitness For Service Code requires that assessment of pressure equipment use Remaining Strength Factor (RSF) to determine if equipment or components may continue to operate as intended by their design. For isotropic metal alloys, RSF is often determined by applying the effects of flaws or defects in the original design engineering. In the case of fiber reinforced polymer (FRP) materials, the material properties used for design treat mixtures of reinforcement and polymer as anisotropic, homogeneous materials. When service conditions are applied, damage accumulates at different rates to each constituent, in particular polymer and reinforcement, of the mixture. Consistently, failure of polymer occurs well before the reinforcement, and this forms the basis for RSF of FRP components. When RSF is determined, what is the value of RSF that defines “End of Life”?
This paper will provide brief introduction to dominant damage mechanisms that apply to FRP equipment and the effect that they have on the structural behavior and RSF of the material. This will then lead to non-destructive evaluation of damage that allows RSF to be determined while retaining mechanical integrity. The question of determining the minimum allowable RSF value will be addressed using two different FRP failures: an atmospheric FRP storage tank and pressure piping. In both cases, non-destructive ultrasonic data was collected near the failure location and RSF was calculated for the components in accordance with Welding Research Council Bulletin 601. Similar RSF values were determined for both cases. From the findings of this work, it can be concluded that RSF for the polymer in FRP will provide reliable FFS assessment of FRP equipment. This paper also verifies and supports a conservative and effective allowable RSF value for FRP with practical failure cases.
Do you have questions about the Fitness For Service of your FRP equipment, or the changes coming with the proposed Part 16 of API 579?
Contact us or watch these videos to learn more.