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Global underground: the state of composite storage tanks

Vicki P. McConnell

Reinforced plastic underground storage tanks (USTs) have been in use since the 1960s as an alternative to steel. Vicki P. McConnell examines international technology upgrades to composite USTs and emerging market opportunities.

Of the millions of underground storage tanks (USTs), about 95% are made from steel (beginning in 1925) and 5% of glass reinforced plastic (GRP, beginning in 1965). Both tank types offer the benefits of substantial service history and product longevity, adaptability to custom fabrication, and installation that involves surrounding the tank with compacted fill material such as sand or pea gravel. Yet both types of tanks can suffer from weep, seep or leak behaviour depending upon manufacturing quality, handling during installation, operating extremes, degree of monitoring and inspection, and the effects of wear over time.

To address this reality, GRP and steel tanks must meet specific regulatory requirements to protect the environment in which they are placed. Steel tanks built and installed today require secondary containment as a means of corrosion and leak protection. This protection can take the form of internal GRP coating and external GRP overwap. Likewise, fibre reinforced plastic (FRP) tanks utilise steel components such as place/wear plates and fittings. Most of today's GRP USTs are designed as double wall tanks, comprised of inner and outer laminate walls with an interstitial space between. This lay-up essentially forms integral secondary containment.

The US underground

While GRP USTs are installed around the world, nowhere is the quantity greater than in the United States. This is due in part to the establishment of R&D for tank materials by Owens Corning in the mid-1960s. As of September 2006, the US Environmental Protection Agency (EPA) estimates the total number of active, regulated USTs stateside (both GRP and steel) is 640 000. These tanks are located at approximately 240 000 different sites, and one source for this article suggests that 500 000 of the USTs in the USA are made of composite.

Some 50 codes and standards from 12 different US organisations have been developed pertaining to USTs that specifically store petroleum products or certain other hazardous substances (HAPS). The standards most relevant to GRP USTs are the Underwriters Laboratory (UL) 1316 standard for safety, and the Fiberglass Tank and Pipe Institute (FTPI)'s FTPI T-95-02 recommended practice for remanufacturing of GRP USTs.

Representing the member companies of the FTPI, Sullivan Curran describes changes in the UST market since the first single-wall GRP tanks were installed 40 years ago:

  • tank sizes are significantly larger, on the order of 220 264 litres (50 000 gallons);
  • the majority of GRP USTs have double wall construction (ranging in wall thickness from 6.3-12.6 mm [0.25-0.5 inch], including integral ribs);
  • resins have been formulated so GRP USTs can contain aggressive fuels such as ethanol; and
  • tanks now incorporate leak detection systems and containment sumps.

Curran adds that another crucial change has been development by tank original equipment manufacturers (OEMs) of a certification programme for an estimated 30 000 third-party GRP UST installers. In his opinion, the manufacturing methods for GRP USTs at larger sizes makes GRP “price competitive with steel in these sizes typically used in today's marketplace.”

Technology upgrades

The primary methods for fabricating GRP USTs are chopped glass spray-up, rotating mandrel laydown, and filament winding. Al Dorris, former CEO of GRP tank manufacturer Xerxes, headquartered in Minneapolis, Minnesota, USA, and now a consultant to the company, finds that “technology upgrades are constant.” Among those he lists are more environmentally-friendly spray-up equipment, design of multi-compartment tanks, triple wall tanks, and the use of brine in the interstitial space between GRP inner and outer walls as a measure of tank tightness and leak detection.

Other changed market factors Dorris notes are 30-year warranties now available, and a reduction in the cost disparity between GRP and steel over the last decade to less than 5%.

Producing GRP USTs since 1972, Xerxes has just been acquired (February 2007) by Canada's largest GRP tank OEM, ZCL Composites of Edmonton, Alberta. Besides GRP USTs for petroleum fuels storage, Xerxes also manufactures tanks to store potable water, fire-protection water, waste water, landfill leachate, sewage, and chemicals. Xerxes uses different female moulds for each tank diameter, and tanks are fabricated ‘inside out.’ This eliminates stress risers between the tank wall and ribs.

Xerxes new owner ZCL Composites Inc offers GRP UST upgrades through tank lining systems. Both the trademarked Phoenix System and LIFELINER System utilise Parabeam, a patented three-dimensional glass fabric, and a proprietary state-of-the-art curing system. These linings can be applied in situ to provide secondary containment for GRP and steel USTs. Last April, ZCL signed a five-year agreement with Tank Tech, Blodgett, Missouri, USA, to apply the Phoenix System lining technology to USTs in the state of Florida. An estimated 31 000 existing USTs need to be replaced, closed, or upgraded there, and approximately 9000 of these USTs are composite.

Originating directly from its former incarnation as the Special Products Division of Owens Corning is Containment Solutions Inc (CSI) of Conroe, Texas, USA. The company fabricates GRP and GRP-upgraded steel USTs, along with above-ground tanks. In both the USA and Canada, CSI offers single, double and triple wall GRP USTs compatible with all blends of alcohol. The OEM's ACT-100 steel USTs offer a 100 ml GRP overwrap in tank sizes up to 88 106 litres (20 000 gallons). CSI's ReTank system provides cure-in-place GRP inner steel tank coating (for 2438 mm [96-inch] diameter or smaller tanks), and the ability to make a single wall GRP UST into a double wall configuration with minimal tank downtime.

CSI's sump system from collar to the lid is UL rated, and the OEM makes GRP manholes with a 20-year warranty for use in wastewater applications.

Through its manufacturing facility in the Phillipines, Beluga Composites Corp and its wholly owned subsidiary, Panox, are producing GRP USTs via filament winding. Michael Heller, Corporate Secretary for the Montreal-based company, reports that its tank market is strongest in southeast Asia, where the estimated market for GRP USTs is US$100 million/year. In terms of GRP UST volume production, he admits that “we’re neophytes compared to Xerxes or CSI.”

Filament winding, Heller asserts, “can create optimised strength characteristics through helical and hoop angles.” Asian customers have been impressed, he says, with the consistency provided by filament winding, the complexity of integrated support ribs and structural customisation, and Beluga's proprietary process for product release from the winding mandrel.

Resins redux

Certainly fuel and chemical constituent liquids being stored in GRP USTs have become more aggressive over the decades, a factor that directly affects tank materials from a corrosion-resistance standpoint. Thom Johnson, Corrosion Industry Manager, Ashland Composite Polymers, verifies that “removal of additives such as tetra ethyl lead and MTBE simultaneous to the introduction of oxygenated additives have changed the character of gasoline. With domestically-produced ethanol as high as 85% (E85) in gasoline, resin selection to handle these aggressive fuels in GRP is more complex.”

In Europe, Johnson says, “most USTs are still constructed from steel. Ashland's DERAKANE epoxy vinyl ester resins are well suited for corrosion liner upgrades in these steel USTs. When GRP is used as a liner, as opposed to the entire tank wall, corrosion performance becomes critically important. As a result, European UST OEMs tend to trade up to the premium performance of epoxy vinyl ester resins such as DERAKANE 470 rather than using conventional polyester technology.”

Ashland's AROPOL line of low-styrene polyester resins (less than 35%) offer an economical alternative to other low-hazardous air pollutant (HAPS) resins required to meet UL 1316, especially in larger tanks. Further, AROPOL resins exhibit positive glass fibre wet-out and room temperature cure properties. Johnson explains that Ashland possesses its own UL certification for AROPOL Q-7022 and, with a joint venture partner, has also certified AROPOL 7241T-15 polyester resin for all relevant UL standards applicable to GRP USTs.

“We license these certifications to our customers globally as appropriate,” Johnson reports.

He suggests the dry weight ratio of resin/glass in a UST is 50/50. In a double wall, multicompartment GRP UST with a 3.048 m (10-ft) diameter, 88 106 litre (20 000 gallon) capacity, and dry shipping weight of about 3629 kg (8000 lbs), one could extrapolate 1814 kg (4000 lbs) for each material element, minus about a small percentage for tank system accessory components.

Terephthalate-based resins DION 490 and 495 from Reichhold address HAPS emissions in GRP USTs, such as those storing E85 fuel. Randy Slezak, Business Development Manager, tells Reinforced Plastics that less than 10% of Reichhold's total composites sales of unsaturated polyester are being used in the corrosion market (under which GRP USTs would be included). However, “Reichhold always tries to design resins to handle the worst case scenario in particular applications.” He adds that the DION resins are used both in GRP USTs and GRP overwrapped steel tanks.

Europe's largest supplier of unsaturated polyester, DSM Composite Resins of Zwolle, the Netherlands, provides isophthalic polyester as well as bisphenol-A and epoxy novolac-based vinyl ester resins for single and double wall GRP USTs that store domestic fuel and sewage. Jeroen van-Bussel, DSM Business Development Manager, calls the global market for GRP USTs huge, but agrees with Ashland's Johnson in that the market has not manifested in Europe as in the US. DSM supplies Atlac vinyl ester for GRP USTs and Synolite polyester in GRP overwrap for steel tanks.

The VIPEL line of corrosion-resistant polyester resins represents AOC's matrix material for GRP and GRP-overwrapped steel USTs, in particular, Vipel F764 high-crosslinked isopththalic resin and Vipel F774 high-crosslinked terephthalic resin. Both meet UL 1316. Ben Bogner, an AOC Corrosion and Infrastructure Market Development Specialist, reports that these Vipel resins were tested by UL in 450 and 600 g/m2 chopped glass strand mat, and UL approved for this and eight additional alternative rovings. Bogner believes a crucial aspect to keeping both existing and new USTs at optimum performance, whatever the material, is a dedicated inspection plan.

“There's a saying, ‘USTs never leak until you look,’ and over the last decade, more leaks have been found than expected, especially among steel tanks.”

He cites a stellar inspection example among the first 60 GRP USTs installed in the US. When excavated in Chicago in 1988, the tank was strong enough to be lifted by its center inlet pipe alone, and showed no signs of leaking or degradation. The resin system was developed by BP, and the inspection concluded that the tank could be recertified to provide another 25 years in operation.

Tank tightness, leak detection

Every tank OEM interviewed here emphasises the importance of tank tightness for GRP USTs, and corrosion resistance in steel USTs.

Secondary containment is now essential for steel USTs holding petroleum liquids, and that is often accomplished by fibre glass interior coating and external overwrap. Rob Pearlman, Senior Engineer for AmTech Tank Lining and Tank Repair, Plymouth, New Hampshire, USA, tells Reinforced Plastics that his company has projects ongoing in the USA, Nigeria, Canada and Mexico to provide GRP relaminating and lining systems on interior UST tank walls for both tank types. Re-gel coat application is also offered, and both upgrades extend service life. For GRP USTs, Pearlman explains that ‘repair’ per se usually involves inner laminate lining addition or fixing laminate cracks in tank structure build-up areas where accessory components such as sumps enter the tank wall.

Polyester and vinyl ester resins are used for these tank interior upgrades, as well as glass veil. Tanknology has serviced USTs from 4405-132 147 litre (1000-30 000 gallon) capacity, as well as smaller oil/water separator tanks. Pearlman points out that the application of GRP coatings with current resin formulations can allow older GRP tanks to handle the more-aggressive alcohol-based liquids and sodium hypochlorite, another extremely aggressive chemical. Not surprisingly, ethanol fuels above 10% alcohol content (such as E-85) also affect steel USTs. In Easy Being Green?, an article by Mark Ward Sr. in National Petroleum News October 2006, the author notes that steel USTs containing E85 are exhibiting the relatively new phenomenon of stress corrosion cracking at weld joints, valves, and seals.

One way to detect such cracks and avoid damaging tank leaks comes via inspection and leak detection monitoring products and services. Tanknology, Austin, Texas, USA, has licensed its storage tank testing methods to customers in more than 20 countries for use at nearly 40 000 sites a year. Tank owners include petroleum companies such as ExxonMobil, BP, and Shell; convenience stores such as 7-11; transportation companies like Hertz and Alamo; and ‘Big Box’ US retailers such as Sam's Club and Costco. Last September, Tanknology achieved the milestone of its millionth UST test at a convenience store in Canton, Massachusetts, USA.

Brad Hoffman, Tanknology's Vice President of Engineering and R&D, explains that testing is important for both newly installed and older FG USTs.

“Some end users are unaware that fibreglass USTs can encounter deflection and flattening of the tank bottom over time, which can place undue stress on the fibreglass shell,” he says. “Our bottom flatness test and trademarked PetroScope video inspection method assess the complete tank system in situ and can detect deflection, water intrusion and cracks.”

The testing company also offers its trademarked SureTest and VacuTect processes to measure tank tightness.

GRP UST OEMs Xerxes and CSI both offer brine solution leak detection technology contained within the interstitial space between inner and outer laminate walls. CSI's HydroGuard System puts the brine under hydrostatic pressure in both tank and sump walls to achieve reliable monitoring 24/7. Generally, USTs can be hydrostatically, dry or electronically monitored.

New markets

What's clear to new customers of GRP or GRP-overwrapped steel USTs is the versatility and longevity of the glass-reinforced material option. And while the US predominates in embracing GRP USTs, new installations are reaching far and wide. Reichhold's Slezak describes developing market opportunities in densely populated urban areas with a growing concentration of gasoline-fueled transportation activity and ongoing infrastructure development. China and India come immediately to mind.

Ashland's Johnson adds Brazil to the emerging marketplace. In the mature US market, he cites the changeover from smaller gas stations to ‘Big Box’ grocery stores and discount retailers as “an opportunity for fabricators to supply GRP USTs to these developing distribution sites.”

If ethanol develops as expected in becoming a more widely used automotive fuel due to its price and renewability benefits, this could create a need for additional UST capacity. Key to this opportunity will be more defined guidelines for composition and quality of E-85, followed by verification that existing tanks have compatability for this fuel and conducting thorough tank cleaning and tightness testing. Obviously, new tanks to contain E85 will reflect compatible resins, and likely a change in monitoring sensors specifically designed for high-alcohol fuel.

Beluga Composites reports signing a contract with Royal Dutch Shell in April to supply petroleum GRP USTs for Shell International Petroleum Co Ltd in India, Pakistan and Indonesia. ZCL Composites is selling its LIFELINER system to CALTEX for use in single wall GRP USTs in southern Asia, south China and Thailand.

In Australia and New Zealand, over 6000 double-wall GRP USTs have been produced by two licensees of Containment Solutions Inc (CSI): Envirotank down under and Maskell Productions Ltd in New Zealand. According to Dale Timms, Envirotank's General Manager, fibreglass has captured 95% of the UST market in these countries over the past 19 years. That's how old Envirotank's first installed GRP UST is, “which is still in service and going strong,” he says.

Timms adds that GRP USTs now store a variety of flammable liquids, and 30-year OEM warranties on the tanks prove the corrosion resistance of this material. Problems with tanks, he says, “are usually related to poor installation techniques, but even this can be seen favourably compared to steel tanks, which don’t accommodate in situ repair. When storing petroleum fuels, they also create a danger of flame and explosion, whereas GRP USTs are inert to gasoline and so provide a safe working environment for upgrades and repair. Fortunately, repairs are a rare occurrence.”

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