Inspectors having knowledge of Above-ground fiberglass storage tanks (ASTs) are a critical asset in industries such as chemical processing, oil and gas, water treatment, and pulp and paper.
Known for their corrosion resistance, lightweight construction, and customization potential, fiberglass-reinforced plastic (FRP) tanks have been a reliable alternative to steel. Ensuring their long-term integrity requires rigorous inspection protocols, particularly as many tanks in service today are aging and lack detailed documentation. This article explores the inspection needs of above-ground fiberglass storage tanks, the evolution of design standards, the challenges posed by legacy tanks, and the critical knowledge inspectors must possess to prevent failures.
Early fiberglass tank design and evolution of standards
Early applications focused on *centrifugal-cast fiberglass piping for the crude oil industry, addressing corrosion issues that plagued metal systems. By the mid-1950s, advancements in polyester and epoxy resins enabled the production of larger, more robust FRP tanks. These early designs were one-offs, based on personal knowledge and designed independently and individually.
It was a time where manufacturers experimented with resin formulations, fiber reinforcements, and construction techniques, and were basically all on their own.
*Centrifugal-cast fiberglass piping is, in short, a 3D hollow shape, pipe or tank, created by rotating a mold while applying resin and glass fibers, creating a dense, uniform composite structure with high strength and corrosion resistance on the inside of the form.
John Cornell
The 1960s marked a turning point as the industry recognized the need for consistent standards to ensure safety and reliability. Engineers began developing guidelines for FRP tank design and fabrication, but not specifically for field inspections of already, in-service FRP tanks.
Early standards aimed to address critical design elements such as resin and fiber selection etc.
Over-time, standards evolved to incorporate lessons learned from field performance. For example, early designs often didn’t appreciate the impact of certain environmental factors such as sunlight exposure, leading to issues such as resin degradation and delamination.
Today’s in-service inspection needs for fiberglass ASTs
Fiberglass ASTs require specialized inspection protocols due to their composite construction. FRP tanks consist of multiple layers, typically an inner corrosion barrier, a structural layer, and an outer protective layer, each susceptible to unique failure modes.
Reputable modern industry recommended practices expound upon comprehensive internal and external inspections, with intervals that vary based upon tank size, entrance and egress abilities and of course the nature of the stored product. Simply mandating a specific number of years between inspection, without regards of the aforementioned variables, may be costly and unnecessary.
For internal, or out-of-service inspections, the inspectors must be provided with a safe-working environment. Tanks must be emptied, cleaned, and verified free of hazardous residues, with air quality tested before entry. If access is via a roof manway, the inspector should also be equipped with safety devices as required to prevent a fall.
Challenges with legacy fiberglass tanks
One of the most significant challenges in inspecting above-ground FRP tanks is the lack of documentation for older installations. Many older tanks in service today were built before modern standards were widely adopted. Records of resin types, wall thicknesses, layer count and etc are often incomplete or nonexistent, complicating assessments of *remaining service life.
*Remaining service life predictions are generally based upon the past several years simply being repeated. For FRP tanks, this is not really a possibility and the owner should not rely closely upon these “prediction”.
John Cornell
For example, early tanks may have used poor quality resins, inadequate wall thicknesses and other potential failure modes. Without historical data, inspectors must rely on visual and NDT methods to infer material properties and membrane suitability. This increases the risk of overlooking critical defects.
Inspector knowledge and failure prevention
Effective inspection of FRP tanks demands a broad skill- set, as inspectors must understand not only fiberglass construction but also the behavior of other tank types, to draw meaningful comparisons.
Inspectors should also be familiar with NDT techniques, including ultrasonic testing (although this may yield only limited information) along with sounding methodologies and possibly acoustic emission, to detect subsurface flaws. Credible certification programs, must first of all, demand that the inspection candidates hold certifications from other industry leaders, such as but not limited to API, STI, and EMMUA. Training programs for FRP tank inspectors should not enroll individuals having only an understanding of fiberglass manufacturing, but also years of general tank experience.
Training individuals to understand the issues with fiberglass is one thing, teaching them to understand tanks, takes years
John Cornell
Training and experience, the required combination for a FRP inspector.
- A training course and the subsequent written examination shall be administered to ensure the knowledge of a Trained Inspector.
- A successful applicant must also meet the requirement of a work history / education matrix.
Conclusion
Above-ground fiberglass storage tanks are vital to modern industry, but their inspection needs are complex and distinct from those of steel tanks. The evolution of design standards has improved tank reliability, but legacy tanks pose unique challenges. Inspectors must possess a deep understanding of FRP construction, failure modes, and have a comparative knowledge of other tank types to ensure safety and compliance. By adhering to rigorous inspection protocols and leveraging non-destructive testing (NDT), industry can mitigate risks and extend the service life of these critical assets. As the global inventory of FRP tanks ages, prioritizing inspector training and standardized inspection procedures will be essential to preventing failures and ensuring operational integrity.
This article was developed by specialist John Cornell and published as part of the sixth edition of Inspenet Brief September 2025, dedicated to technical content in the energy and industrial sector.
