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GRP / FRP Tank Companies
Fiberglass (GRP/FRP, vetroresina) tank fabricators for storage, process, and chemical service, custom-built to specification.
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GRP Tank Construction Methods: Filament Winding, Hand Lay-Up, and Design Standards
GRP (Glass Reinforced Plastic) tanks for water and chemical storage are manufactured by filament winding (for cylindrical vessels, wall glass content 65 to 72 percent by weight, wall thickness 5 to 25 mm), hand lay-up (for complex shapes, glass content 25 to 40 percent), or infusion moulding. Filament-wound tanks meet BS 4994, ASME RTP-1, or BS EN 13121 for atmospheric pressure storage. Design standards require a minimum corrosion barrier of 2.5 mm resin-rich liner (glass content below 30 percent) on the process-contact interior surface. Tanks are pressure-tested hydrostatically to 1.3 times design pressure before delivery.
Resin selection drives chemical resistance. Isophthalic polyester handles most water, aqueous acids (pH 2 to 7), and dilute alkalis. Vinyl ester (Derakane 411 or 510C) is specified for concentrated acids, chlorinated water above 5 mg per L, and hydrocarbons. Bisphenol epoxy is used for strong alkali and solvent resistance. For potable water tanks, NSF 61 and WRAS-approved resins are mandatory to prevent tainting. Tank capacity from 500 L to 10,000 m3 is achievable in GRP; beyond 5,000 m3, bolted sectional GRP panels (GRP panel tanks per BS EN 13280) or steel becomes more economic.
GRP tanks weigh 70 to 80 percent less than equivalent steel tanks, eliminating heavy foundations in many applications. Tank operating temperature limits: isophthalic polyester -20 to +70 degrees C; vinyl ester -20 to +100 degrees C. Vertical cylindrical tanks require wind and seismic anchorage calculations per local codes (EN 1998 for Europe, ASCE 7 for US). Inspection per ASME NB-23 or BSRIA guide includes visual inspection, thickness measurement (ultrasonic), and hydraulic test every 5 to 10 years. Service life of 30 to 50 years is achieved with proper liner condition monitoring. Cost per m3 of storage capacity (DN 3,000 to DN 5,000): $200 to $600 for GRP versus $400 to $1,000 for equivalent stainless steel.
Frequently Asked Questions
Are GRP tanks suitable for potable water storage?
Yes, when manufactured with NSF 61 or WRAS-approved resin systems. The corrosion liner must use food-grade isophthalic or vinyl ester resin certified to avoid extractable compounds above NSF 61 limits. Tank design must eliminate dead zones and stagnation pockets, with inlets and outlets positioned to ensure full turnover and minimum hydraulic residence time. Covers must exclude light (preventing algal growth) and be insect-proof per BS 8515. Inspection hatches must be lockable. Tanks must be disinfected before commissioning per BS 6700 (500 mg per L free chlorine, 1-hour contact, drain and rinse) and retested after maintenance. WRAS listing applies to the complete tank system including fittings.
How do GRP tanks compare to stainless steel tanks?
GRP tanks cost 40 to 60 percent less than 316L stainless steel at equivalent capacity and chemical duty. GRP is corrosion-free in aggressive process chemistries where stainless requires expensive alloy upgrades (Hastelloy, titanium). However, stainless steel offers better mechanical impact resistance, narrower wall thickness at high pressure, and simpler repair. GRP tanks cannot be repaired by welding; patch repairs use glass fibre lamination. For outdoor installation, GRP requires UV-resistant outer gelcoat or topcoat; stainless requires no surface treatment. For cryogenic service below -30 degrees C, GRP becomes brittle and stainless or carbon steel is required. For food-grade pharmaceutical water, stainless 316L with electropolished interior remains preferred for hygienic validatability (Ra below 0.8 micron).
What sizes of GRP tanks are available?
Filament-wound vertical cylindrical GRP tanks range from 500 L (DN 900) to approximately 5,000 m3 (DN 20,000) in one-piece construction. Single-lift transport is typically limited to 3.5 m diameter by road; above this, tanks are manufactured in bolted ring sections assembled on site. Horizontal GRP tanks (for transport and skid mounting) range from 200 L to 100 m3 and are available from stock in standard sizes. GRP panel tanks (bolted modular sections per BS EN 13280) scale from 10 m3 to over 10,000 m3 and are erected on site from flat panels. Above 10,000 m3, welded steel tanks (API 650) are typically more economical. Lead time for standard sizes: 4 to 8 weeks; custom filament-wound vessels: 8 to 16 weeks.
How do I maintain a GRP storage tank?
Annual inspection: internal visual check of liner condition (check for crazing, blistering, delamination, and star cracking); external visual check of outer laminate and structural fittings. Every 5 years: ultrasonic thickness measurement of critical zones (knuckle radius at base, nozzle reinforcement pads, shell bottom course). Every 10 years or after any chemical contamination incident: full hydraulic test at 1.1 times maximum working head. Liner repairs use resin-compatible glass fibre patch lamination applied to dry, abraded substrate. Nozzle gaskets and manway seals should be replaced every 5 to 10 years. Do not use mechanical abrasives on the interior liner. Cleaning uses dilute citric acid (2 percent), pH-neutral detergents, or steam-cleaning at below 80 degrees C depending on resin type.
A Northern England water treatment works required replacement of four 50,000 L steel tanks storing sodium hypochlorite (12.5 percent trade strength), sodium hydroxide (30 percent), ferric sulphate (40 percent liquid), and aluminium sulphate solution. The existing mild steel tanks were suffering from internal corrosion and external coating failure, with one tank leaking through a corroded seam. COMAH assessment was required due to sodium hypochlorite storage above 50 tonnes.
Specified four filament-wound GRP tanks with: vinyl ester corrosion liner (3 mm, glass content below 28 percent) for the hypochlorite tank; isophthalic polyester liner for the caustic and ferric sulphate tanks; and NSF 61-certified isophthalic liner for the alum tank (potable water contact). Each tank was designed to BS EN 13121-3 with 50-year design life. Bunded impermeable GRP secondary containment designed to hold 110 percent of the largest tank volume per COMAH and HSE guidance.
Tanks installed and commissioned in 14 weeks (site work 8 weeks). DWI approved the NSF 61 certification for the alum tank. COMAH notification accepted by HSE/EA. Zero in-service incidents in 3 years of operation. Total installed cost 280,000 GBP versus 380,000 GBP estimate for equivalent FRP-lined steel replacement. Elimination of cathodic protection systems saved 8,000 GBP per year in maintenance.
Questions to Ask Shortlisted Providers
- 1
What resin system does the corrosion liner use, and do you have a chemical resistance table from the resin manufacturer for our specific storage medium at our maximum operating temperature?
GRP tank failure almost always originates in the corrosion liner. Isophthalic polyester is inadequate for concentrated sodium hypochlorite above 12 percent, for which vinyl ester is required. The resin manufacturer's immersion test data at your specific concentration and temperature (not generic guidance) is the design basis for the liner life assessment.
- 2
What is the liner thickness and glass content, and how is it verified during manufacture?
The corrosion liner must be at minimum 2.5 mm thick with glass content below 30 percent by weight per BS EN 13121. Thinner liners or excess glass content provide insufficient chemical barrier. Confirm whether the liner thickness is specified in the purchase order and how it is verified: wet chemical extraction and combustion testing of production coupons is the standard method.
- 3
Does the tank carry WRAS approval or NSF 61 certification for the stored medium, and is the specific certification scope (tank, fittings, gaskets) documented?
NSF 61 or WRAS certification is required for tanks storing chemicals that will dose into potable water (alum, ferric sulphate, lime, hypochlorite). Certification must cover the complete wetted assembly: tank body, nozzle fittings, and manway gaskets. A certificate covering only the tank body without the nozzle fittings is incomplete for DWI purposes.
- 4
What secondary containment is provided, and is it designed to hold 110 percent of the largest tank volume as required by HSE and Environment Agency guidance?
HSE and EA require chemical storage tanks on water treatment sites to be bunded with containment capacity of 110 percent of the largest tank volume (or 25 percent of total volume if multiple tanks are within one bund). GRP bund lining with the same chemical resistance as the primary tank is required; concrete bunds with chemical-resistant coatings are an alternative but must be assessed for compatibility with the stored chemicals.
- 5
What is the proposed inspection regime, and do you provide an initial ultrasonic thickness baseline survey as part of the commissioning handover?
GRP tank maintenance requires periodic ultrasonic thickness measurement to detect liner degradation before it reaches a critical level. An initial baseline UT survey at commissioning establishes the reference thickness; annual or 5-yearly surveys track degradation rate. Without a baseline, the first survey cannot determine whether measured thinning occurred during manufacture or in service.
What Drives Cost in This Category
GRP filament-wound tank cost scales approximately with volume to the power of 0.6: doubling volume increases cost by about 50 percent rather than 100 percent. A 10,000 L tank costs 4,000 to 8,000 GBP; a 50,000 L tank costs 15,000 to 30,000 GBP; a 200,000 L tank costs 50,000 to 120,000 GBP for standard resins. Custom sizes (non-standard diameters or heights) add 10 to 25 percent to manufacture cost.
Isophthalic polyester resin tanks (standard water and dilute chemical duty) cost 20 to 30 percent less than equivalent vinyl ester tanks. Vinyl ester is required for concentrated hypochlorite, concentrated acids, and chlorinated solvents. Bisphenol epoxy (for strong alkali and solvent service) adds 40 to 60 percent over isophthalic. Over-specifying resin adds unnecessary cost; under-specifying risks liner failure within 3 to 7 years.
GRP-lined concrete bund: 300 to 600 GBP per m2 of bund floor area. GRP moulded drip tray (for single small tanks): 1,000 to 5,000 GBP. For a 4-tank chemical dosing area requiring a 6 m x 6 m bund, secondary containment adds 11,000 to 22,000 GBP to the project cost. COMAH-compliant bunding is non-negotiable for chemical storage above notification thresholds.
Standard GRP nozzles (threaded PTFE inserts), level gauge connections, manway assemblies, and venting arrangements add 15 to 25 percent to the bare tank cost. For hypochlorite tanks, all fittings must be in PVDF or PTFE to resist bleach degradation; standard PVC or polypropylene fittings fail within 1 to 3 years in 12.5 percent hypochlorite service. Specify fittings by material and temperature rating, not just the generic 'chemical-grade' designation.
Key Regulations & Standards
BS EN 13121-3 specifies design, manufacture, and testing requirements for above-ground GRP process tanks and vessels. It covers wall design (including wind and seismic loading), corrosion liner specification (minimum thickness and glass content), hydrostatic test requirements (1.1 times maximum filling head), and inspection intervals. UK water company procurement specifications should reference BS EN 13121-3 as the baseline standard for GRP chemical storage tanks.
Water treatment works storing sodium hypochlorite above 50 tonnes active chlorine equivalent, or chlorine gas above 10 tonnes, fall within the Control of Major Accident Hazards Regulations 2015. Lower Tier establishments must maintain a Major Accident Prevention Policy; Upper Tier must submit a Safety Report to the HSE and EA Competent Authority. GRP tank selection, secondary containment design, and leak detection must be documented in the COMAH safety report.
Chemical storage tanks whose contents will dose into potable water supply must use materials certified to NSF/ANSI 61 (North America) or on the DWI Approved Products list. NSF 61 certification for GRP tanks covers the resin system, glass reinforcement, and fittings. Non-certified materials in dosing chemical contact with potable water breach WS(WQ)R 2016 and require immediate replacement. Certification must be verified before purchase order, not assumed.
The Environment Agency requires secondary containment (bunding) for above-ground storage of hazardous liquids (oils, chemicals, trade effluent) under the Environmental Permitting (England and Wales) Regulations 2016 and associated PPG 2 guidance. Containment must hold 110 percent of the largest tank volume or 25 percent of total storage, whichever is greater. GRP bund linings must be chemically resistant to the stored liquid; concrete bunds require a chemical-resistant coating with demonstrated compatibility.
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