NDE Methods for Detecting In-Service FRP Damage
September/October 2023
Despite the success of fiberglass reinforced polymers (FRP) in many applications over many decades, there is considerable uncertainty about the capability of aging FRP pressure vessels, piping, and tankage to continue in service. Practices for how to detect and assess flaws and damage have not been consistent nor well-understood and accepted, and have often relied on subjective opinions that impose the expected behavior of metallics onto these materials. Damage to FRP from service conditions and material properties is usually completely different from damage that will occur to metal alloys, so using techniques and procedures developed for metals will produce unsatisfactory results.
This article explores the dominant damage mechanisms experienced by FRP during service. It also describes several detection methods and how they can be used to provide information on the size, magnitude, and extent of damage to FRP. Finally, the article identifies what inspection information is required to allow FFS assessment of equipment made from FRP.
Practical External Inspection of FRP Vessels
January/February 2021
Since the chemical processing industry started using fiberglass reinforced plastic (FRP) composites for vessels and piping in the 1950s, many users have experienced reliability problems. In response, there has been significant work to establish standards and codes for FRP vessel design that have contributed to increased reliability of FRP equipment.
Even with improvements in reliability, some vessel failures still occur. Many failures could be prevented or mitigated by following a systematic external inspection program.
However, codes and standards that are typically used for design of FRP vessels limit their inspections to those required for the design and manufacture. No guidance is provided for fitness for service inspections or inspections after commissioning of the equipment. The American Petroleum Institute (API) has several inspection codes for vessel that focus on steel or metallic vessels. No explicit coverage is provided for FRP vessels.
This article provides a systematic process/program for these external inspections that serves to increase reliability.
FRP Corrosion Barrier Inspection: Non-destructive & Non-intrusive Technique
March/April 2020
One of the design features that evolved to significantly improve reliability of FRP equipment is to incorporate a corrosion-resistant barrier onto the surface of the FRP that is to be exposed to corrosive chemical conditions—usually the inner surface of pipes, tanks or process vessels.
Proper maintenance of the corrosion barrier became a critical component of FRP reliability. The challenge was that monitoring the condition of the corrosion barrier almost always required an outage and confined space entry.
This article describes the construction of corrosion-resistant FRP and the practices used for inspecting corrosion barriers, starting from the original visual inspection, to microscopic evaluation of sections through cut-outs, to advanced ultrasonic techniques that provide results that can be directly related to an ASTM standard used globally to provide quantitative performance of FRP in corrosion service.
Bridging Acoustic Emission Testing and Ultrasonics for FRP
July/August 2019
From early in the use of fiberglass reinforced polymers (FRP) for corrosion resistant equipment, engineers developing new design and construction methods for the material faced numerous challenges. Early design approaches included use of metal vessel design standards which did not suit the properties and behaviors of FRP composites, which are fundamentally different from metals.
The early legacy of these challenges was numerous FRP failures which in the 1970s led some major owners of FRP assets in the chemical processing industry to place a moratorium on using the material until its reliability could be improved. While design and construction standards evolved to address the early flaws, a non-destructive testing (NDT) method using acoustic emission (AE) technology was developed to ensure that final commissioning and proof testing of new FRP equipment did not cause any damage before it was put into service.
Since the early 1980s, AE has been adopted by many FRP users and incorporated into relevant codes and standards. However, periodic AE cannot predict changes in FRP over time. This paper examines how AE can be combined with an attenuation-based ultrasound technique to reliably predict changes to in-service FRP.
Fitness for Service of FRP: Moving Towards Best PracticesBridging Acoustic Emission Testing and Ultrasonics for FRP
May/June 2018
A Fitness for Service (FFS) assessment of an asset requires the use of certain best practices to determine whether the asset can continue to operate as intended by its design. Best practices have been shown by research and experience—including empirical data—to reliably lead to a desired result. Often these best practices are formalized through consensus of experts into codes and standards that relate original designs to current condition and provide guidance to engineers and operators. There are currently no industry consensus documents that provide this guidance for fiberglass reinforced polymers (FRP) assets.
This article provides a case study that illustrates how the European design standard “glass reinforced plastic (GRP) tanks for use above ground” designation EN 13121 can be used to calculate expected changes in FRP for FRP vessels.
However, use of codes such as EN 13121 requires destructive testing of the FRP to be evaluated. This approach involves significant costs for removal of test specimens, testing and subsequent repair. In addition, this type of testing, after the vessel has been in service, requires shutdown, de-inventory and a safe work plan to obtain the test specimens and repair the assets.
Therefore, in parallel with the testing described above, a non-destructive and non-intrusive test method was used to determine changes in bending stiffness of FRP in the same tank. The non-destructive and non-intrusive test method provided similar results at significantly lower cost and no disruption to the service of the equipment.
Non-intrusive FRP Inspection for Avoiding Premature Asset Retirement
November/December 2017
UTComp’s UltraAnalytix® NDT provides accurate, actionable information that not only helps prevent catastrophic failures but also saves companies millions of dollars in unnecessary replacement costs.
This article provides a case study of an ultrasonic inspection of an FRP vent scrubber at a large chemical facility. The scrubber was used to neutralize hazardous gas with sodium hydroxide solution in a countercurrent flow.
The equipment had been in service since 1995, but the lower section was replaced in 2002. All sections of the scrubber were manufactured by the same manufacturer. In 2015, the scrubber was replaced because the structural integrity was suspect based on visual inspection of the corrosion barrier. Since it was no longer in service, the scrubber was made available for a comparison of non-destructive and destructive evaluation techniques.
The results provided a good match between information provided by UTComp’s ultrasonic readings and the actual retained mechanical properties of the cut-outs. The examination of the cut-outs also indicated minimal damage to the corrosion barrier, thereby suggesting the vessel actually had significant remaining service life — and did not need to be replaced — which testing also predicted.
Novel Inspection System Aligns FRP and Metallic Asset Management Approaches
May/June 2017
Asset management for steel piping and vessels relies on well-established systematic approaches that have proven effectiveness. Many operators with fiberglass reinforced plastic (FRP) piping and vessels in their facilities desire the same quality of reporting and advice regarding FRP condition as they receive for their steel assets.
Ultrasonic inspection techniques for FRP equipment that are both non-destructive and non-intrusive are available to meet that demand, backed by thousands of inspections to provide reliable asset management information. Owner/operators can now receive inspection reports for FRP that are similar to those for metallic assets, including the measured effects of damage and the remaining structural capacity compared to the new asset, whatever its age.
This article provides an overview of a systematic inspection approach for FRP that aligns FRP mechanical integrity results with those for metallic mechanical equipment.