Fiber-reinforced polymer (FRP) composite tanks play a vital role in industries where corrosion resistance and long-term chemical storage performance are essential.
From chemical processing and water treatment to mining, manufacturing, pulp and paper and more, FRP storage tanks and vessels provide reliable, long-term performance in demanding environments.
The oldest tank that UTComp has inspected is nearly 70 years old! At its last inspection, it was still Fit For Service.
But, as tough and reliable as they are, FRP tanks can and do suffer from damage over time.
In fact, FRP begins to change as soon as it goes into service. Exposure to chemicals, temperature variations, pressure, mechanical loading, environmental conditions and normal operational stresses affect the polymer matrix, reinforcement and overall structural performance of FRP materials.
In this guide, we answer your top questions about testing FRP tanks and vessels to maximize asset lifespan without compromising safety or reliability.
How often should FRP tanks be inspected?
UTComp recommends inspections take place every three years due to the following factors:
- The mechanical properties of FRP can change rapidly during normal service. Assessing those changes early on provides valuable baseline data for predicting future repair or replacement needs.
- Unlike damage to steel, which is relatively predictable and linear, damage to FRP is non-linear. Small changes in the polymer can have a major impact on reliability.
- The three-year interval represents about half the time that it takes for chemical damage to cause failures in the most common types of reinforcement used in FRP.
- Unexpected changes in service conditions — due to over-pressurization, accidental impacts, damaged or faulty supports, poor installation or repairs — can cause unseen degradation that weakens FRP and leads to failures.
How is FRP tank inspection different from steel tank inspection?
Fitness-For-Service (FFS) assessment of steel tanks is relatively straightforward and backed by well-established consensus standards and codes for designing, inspecting and repairing in-service equipment.
Evaluating steel focuses on corrosion rates, thickness loss, cracks, blisters and other overt damage that can be easily compared to the equipment’s design and construction codes. For example, a steel tank that reaches its corrosion limit (as designated by code requirements and stamped on the equipment) is no longer FFS.
Assessing FRP tanks is more complex and less predictable. The kind of visible flaws that affect FFS in steel – such as thickness loss or cracking – are almost irrelevant in FRP.
FRP composites show distinct damage progression patterns. Changes to FRP’s mechanical properties – especially the strain at failure – occur at different rates in the polymer and in the fiber reinforcement. Different polymers behave and perform differently under load due to their molecular structure, flexibility and operating environment.
To determine FFS in FRP it’s necessary to identify and assess the extent of underlying polymer damage. UTComp’s UltraAnalytix non-destructive evaluation (NDE) system quantifies the condition of the polymer component of the material. This contributes to the broader assessment of the structural changes occurring within the composite structure to determine FFS as well as Remaining Life.
It’s also important to note that, unlike for steel, historically there has been very little industry guidance for objective, data-based assessment of in-service FRP. That is now changing with the publication of WRC-601 and Part 16 of API 579.
What standards and codes apply to FRP tank testing?
The National Board Inspection Code (NBIC) for boilers and pressure equipment is currently the only consensus standard that applies to inspection of in-service FRP tanks.
Other consensus FRP testing standards and codes such as ASME RTP-1 and ASTM D3299 apply only to FRP tank design and construction.
ASME RTP-1 and ASME NM.2 prescribe requirements for the design, materials, manufacturing, installation, inspection and testing of new FRP vessels and piping. However, these ASME standards do not apply to equipment after it goes into service.
Recent developments in industry guidance for FRP inspection will provide important guidance for FRP tank inspection. This includes Welding Research Council Bulletin 601 (WRC-601) and the proposed Part 16 of the API 579-1 / ASME-FFS-1 Fitness For Service standard.
Learn more about ASME standards for FRP tanks.
Which testing method should I use for an FRP tank?
There are several FRP reliability testing methods. Their usefulness varies based on the application and a variety of factors: some require confined space entry or destructive testing, while others are non-intrusive and non-destructive, so they can be used while equipment is in operation.
UTComp’s UltraAnalytix NDE is a patented, non-destructive ultrasonic (UAX+) system that provides quantitative data to accurately assess the FFS of in-service FRP storage tanks and pressure vessels.
UltraAnalytix aligns with both WRC-601 and the proposed API 579- Part 16, and is the only proven method that provides the comprehensive data required to calculate Remaining Strength Factor (RSF) and Remaining Life.
What role does Barcol hardness testing play in FRP tank inspection?
One factor that has often been used to determine the condition of FRP is the hardness of the resin, called Barcol hardness.
However, Barcol testing provides surface hardness values to a depth of only 0.25 mm and it is strictly related to how well the polymer has been cured (hardened).
Barcol hardness testing does not provide data or information about deeper polymer condition. No engineering analysis exists using Barcol values.
In spite of the importance traditionally placed on Barcol hardness, no agreed criteria exist that define whether any particular Barcol hardness value is acceptable for in-service equipment. It becomes a matter of the inspector’s opinion.
Plus, even as polymer damage increases and causes the strength or elasticity of the polymer to decline, surface hardness remains generally constant until a certain point and then it drops off severely.
So there may be a significant change in the strength of the polymer even while we don’t see a direct relationship to Barcol values.
How do you inspect the corrosion barrier of an FRP tank?
In the 1960s, as FRP composite tanks and other equipment became commonplace in chemical processing and other industries, the corrosion barrier emerged as a key design feature to improve reliability of FRP.
Monitoring the corrosion barrier condition has been critical to ensuring FFS of FRP tanks ever since.
Conventional approaches to corrosion barrier inspection usually require shutdowns and entering the tank so it can be assessed based on visual appearance, as well as surface hardness and damage depth.
In general, these methods allow reasonable evaluation of visible surface damage, but determining how much damage is acceptable remains subjective.
UTComp’s patented method for evaluating corrosion barrier condition takes a data-based approach based on two key parameters:
- Damage Depth: the depth that damage extends into the corrosion barrier resin
- Polymer Damage Status (PDS): relative stiffness (compared to new) of the resin within the damaged depth
Learn more about corrosion barrier assessment best practices here.
Can I rely on visual inspection alone to determine FRP tank reliability?
On its own, visual inspection is not enough to determine FRP Fitness For Service.
Damage affecting in-service FRP tanks may include:
- Resin degradation without a corresponding, easily measurable reduction in wall thickness.
- Matrix cracking and microcracking.
- Delamination between laminate layers.
- Fibre damage or breakage.
- Changes in stiffness, strength and strain capacity.
- Blistering or bubbling due to chemical attack
Some of these changes may occur beneath the surface or within the laminate, making them difficult to identify through visual inspection alone.
An FRP tank can retain much of its apparent shape and thickness while its material properties and ability to withstand operating loads have changed.
An effective FFS assessment must consider more than whether the tank looks acceptable. For more, see our investigation of a chemical storage tank failure.
How do I determine if an FRP tank is Fit for Service?
FFS requires an engineering assessment. The assessment determines whether an FRP tank with known or suspected damage can continue to perform its intended function under the relevant loads, pressure, temperature, contents and environment.
Traditional inspection methods that rely heavily on subjective visual observations, destructive testing and other limited testing tools provide only part of the information needed to make confident FFS decisions. Lacking objective FFS data can lead to premature equipment replacement or continued operation with unknown risks.
For an FRP tank, a FFS inspection and assessment may need to consider:
- The significance and location of the identified damage.
- The condition of the structural laminate and corrosion barrier.
- The tank’s operating loads and environmental conditions while in service, which may be different from its design conditions
- The tank’s current material condition, as determined by the inspection, and its required performance.
- Whether changes to operating conditions could affect the assessment.
- Whether additional inspection, analysis, repair or restrictions are necessary.
The objective is not simply to determine whether a defect or damage exists. It is to establish what that defect means for the tank’s ability to perform its required function.
Determining FFS of in-service FRP tanks involves collecting and analyzing engineering data that takes into account the unique mechanical properties of FRP composites and the damage mechanisms and failure modes that affect these materials over time.
Learn more about UTComp’s recommended FRP tank inspection process.
When should an FRP tank be repaired vs. replaced?
A damaged FRP tank can still be FFS. Replacing a tank based solely on its age or the presence of visible damage may be unnecessary and expensive.
However, continuing to operate a tank without understanding the extent and significance of any deterioration may pose serious safety, environmental and operational risks.
That’s why regular FFS inspection and assessment is essential.
As noted above, the UTComp approach to assessing FRP tank integrity focuses on quantifying the condition of the polymer component of the material. By identifying and evaluating the significance of polymer damage, UTComp’s UltraAnalytix NDE system helps asset owners make data-based decisions about inspection, repair and replacement of FRP tanks and vessels.
Learn how an UltraAnalytix inspection saved Ashland €1.5M in planned capital expenditure for an FRP tank.
For another client – a global chemical and food processing company – we inspected more than 200 tanks over a three year period. Our inspection program showed that only seven of the tanks actually required replacing, saving the client a minimum of $33 million, based on their planned replacement schedule.
FRP tank inspection case studies
UTComp and our licensees conduct FRP tank inspections for customers in a wide range of industries around the world. In addition to the examples provided above, our FRP tank case studies includes the following applications:
Case study: Sodium hydroxide (NaOH) storage tank inspection
FRP is widely used for storage vessels that contain chemicals used in water treatment and disinfection, as well as NaOH (sodium hydroxide, or caustic soda), a highly corrosive substance used in the desalination process. Sodium hydroxide can damage fiberglass resins over time, making regular inspections essential.
For more on inspection of sodium hydroxide tanks, see our case study on an UltraAnalytix non-destructive inspection of two atmospheric FRP tanks used to store sodium hydroxide at a water desalination facility in Australia.
Case study: Monochloroacetic acid (MCA) storage tank
Monochloroacetic acid (MCA) is a highly hazardous, toxic, and corrosive substance. Confined space entry of an MCA tank to conduct a comprehensive mechanical integrity assessment is considered highly risky from an environmental, health, and safety standpoint.
UltraAnalytix licensee Nordic Glasfiber conducted an UltraAnalytix NDE of an above-ground storage tank containing MCA at an Ashland facility in France in 2023. See the MCA storage tank case study.
Case study: Hydrochloric acid storage tank
UTComp founder Geoff Clarkson published a case study on a glass reinforced plastic (GRP) storage tank containing hydrochloric acid in Inspectioneering Journal in 2018. The case study compares both destructive test results and UltraAnalytix non-destructive, non-intrusive results to assess the tank’s fitness for service.
Also see a case study on using UltraAnalytix to monitor the condition of an HCl FRP tank, recommend repairs to the tank and provide structural data on the repaired tank.
Case study: Ageing aluminium sulphate tanks
UltraAnalytix licensee RPC Technologies Pty inspected five 50,000-litre storage tanks that appeared to be ready for replacement. The tanks, used to store aluminium sulphate, were each about 45 years old and showing their age with visible weathering, dirt, mould and cracks in the surface coating.
However, the UltraAnalytix inspection and assessment found:
- lowest PDS values were around 60%, well above the minimum 40% threshold
- Estimated Remaining Life for each of the tanks was more than 6 years.
The results demonstrate that visual appearance does not always reflect structural performance.
UTComp FRP tank inspection services
UTComp engineers and licensees are certified in accordance with SNT-TC-1A to provide FRP inspection and assessment services using the UltraAnalytix NDE system.
Contact us for answers to all your FRP tank questions and to arrange an inspection.