In the late 1940s, fiberglass-reinforced thermosetting plastic or fiberglass was first used as an alternative to stainless steel. Around the same time, centrifugal cast fiberglass piping was introduced in the production of crude oil. Fiberglass piping promised to an effective solution to corrosion problems, typically experienced with steel piping. Soon, fiberglass tanks and piping systems became widely popular for water and fuel storage purposes. Upon seeing the popularity and usage of FRP tanks, manufacturers began developing standards and testing methods for fiberglass storage tanks. Worldwide inspection services providing agencies have to follow inspection standards when undertaking tank assessment and evaluation.
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What are Fiberglass Tanks?
Fiberglass or FRP Storage tanks and piping systems are made of glass fiber reinforcement inserted in a thermosetting resin. Fiberglass tanks are complex storage containers made from different components layered together to form a robust, corrosion-free yet lightweight material.
An FRP tank can be divided into four layers: an inner layer, interior layer, structural layer, and outside layer. Speaking of the material used to produce the FRP tanks, the inner surface has rich resin content. The interior layer of the tank contains 20-30% chopped glass. The chopped glass offers strength to the fiberglass tank. The structural layer is made of 60-70% continuous strand filament winding. The outside layer is primarily made of resin and coated with corrosion resistance and UV protectant.
Types of Inspection Required for Fiberglass Storage tanks
Quality Control Inspection
For fiberglass tanks, Quality Control inspections may vary according to the requirements of the end-users. Most often, FRP tanks have to undergo a 3-stage inspection process. The initial assessment is performed after the corrosion barrier has been added to the tank. The second round of inspection takes place before any nozzles are attached to the tanks. Final quality control assessment happens before the shipment of the tanks.
Quality Control inspections are generally performed by third-party tank inspection companies with a minimum 5-year of FRP vessel inspection experience.
Internal and External Inspections
According to the guidelines set up by ASTM and RTP standards, if you own or manage fiberglass storage tanks, you are required to get the tanks inspected every five years. Regular FRP tank inspections allow on to identify defects that have the potential of turning into hazards. Before undertaking FRP tank inspection, inspectors follow pre-inspection safety measures to ensure the storage tank does not have toxic chemicals or hazardous gas. When conducting FRP tank inspection, the tank’s interior is accessed through either roof manhole or ground level manhole. The inspectors look for possible signs of corrosion, deterioration to the structure or environment, structural damage, leakage, or erosion.
Fiberglass Tank Acoustic Emission Testing
Fiberglass Tank Acoustic Emission testing is yet another crucial test performed on FRP tanks. This test is typically done after the fabrication of the tank or during in-service. The tank inspection professionals follow ASTM standard practice to check for resin cracking, fiber breakage, pullout debonding, delamination, wear, and nozzles.
In acoustic emission testing, the FRP tank is filled with water in incremental steps. As the tank is filled with water, it’s tested for any possible flaw. The flaws in a tank emit acoustic emission, which is captured by sensors.
