SPEL Tankstor® tanks have been developed with 60 years of experience in the market of underground GRP tanks.

In 1989 SPEL developed the technically advanced chop-hoop filament winding process to provide the most structurally sound and economic solution. This was patented in 1989 and further improved to include above and below ground fluid storage and treatment. The current range of tanks is available in five diameters 1.2, 1.8, 2.6, 3.5 and 4m internal dia.

Designed to the well-recognised British Standard BS EN 13121 they carry The SPEL 25 Year Shell Warranty and have a life expectancy of over 50 years.

SPEL are a bespoke manufacturer and Tankstor® tanks have many uses including storage, stormwater attenuation, fire sprinkler systems, spill containment, potable water and chemical spill tanks, as well as wastewater applications, contact our team for more detail.

Connections are available in a range of sizes and types to suit site drainage. Access shafts in a range of sizes, in circular, square or rectangular can be fitted to suit applications. Partitions (non-load bearing and load bearing) can be fitted to provide chambers and/or baffles. Please contact our team for your bespoke application.

Quality Control

The manufacturing process is fully ISO9001 certified and is carefully monitored with a digital read out system. Chopping glass, winding glass, the resin-rich inner layer and main laminate resins are kept within specification parameters thus minimising wastage and ensuring structural integrity.

Quality control procedures require each tank to be carefully inspected and tested. Ultrasonic thickness readings, material content weights, and more are checked and recorded against the tank’s unique serial number. Additional periodic laminate testing is carried out by independent testing facilities including stress and strain analysis and also physical property tests to meet specific design criteria.

The SPEL 5 Stage Laminate Construction

SPEL GRP chambers are built inline with the British Standard BS EN 13121, which incorporates the critical 5 Stage Laminate Construction process. This enables SPEL to offer the industry-leading SPEL 25 Year Warranty even in challenging ground conditions.

Technical Information


SPEL underground tanks are manufactured by the chophoop filament winding process developed in the US and specifically designed for underground tanks by SPEL Products, Patent No. 2233384.

GRP laminate

Design and specification for SPEL underground tanks

The SPEL underground tanks have been designed with reference to BS EN 13121, BS EN 976-1, 978 and BS EN 858-1:2002.

The quality and strength of glass reinforced plastic (GRP) laminates depends upon the following factors:

• The design criteria, eg. chemical resistance, temperature, internal and/or external loading.
• The efficiency and consistency of the manufacturing process and the high level of control to maintain resin and reinforcements within strict design parameters.
• The laminate construction from resin-rich corrosion resistant internal surface, resin-rich glass reinforced corrosion barrier, main laminate and the external resin-rich water penetration barrier providing excellent corrosion resistance from internal contents and complete sealing of laminate from ingress of water and/or contaminants externally.

Prior to determining the laminate construction and thickness using requirements, actual specimens are taken from filament wound laminates and independently tested. From the ongoing material tests and consideration of the various partial influence factors, which include the chemical resistance and a tank shell life to be excess of 25 years, a generous final design factor is determined.

The design of GRP laminates is clearly different from, for example, a steel structure where the material and loadings are clearly defined.

Tank manufacturers can cut their quality and price depending on the design factor determined.

SPEL underground tank laminates are designed to meet specific requirements, for example, hydrostatic load on tanks surrounded either in concrete or a free flowing pea

With experience gained in the United States, high quality underground tanks do not suffer from degradation to the degree envisaged in the British Standard, in fact tests carried out on laminates taken from underground tanks in the US after 25 years use, have shown very little loss of strength.

The important factors are the construction and composition of the laminate to resist the corrosive action of the internal chemicals and the water or contaminated underground water externally.

BS EN 978 – Tests to this Standard determine the alpha and beta, ‘the long term deterioration due to creep and the effects of water or chemicals on the plastics’. Tests have been carried out, on pieces of shell cut from the tank barrel, by an independent test laboratory. The results are used in the equations (BS EN 976-1) to determine the stability of underground GRP horizontal cylindrical tanks for the nonpressure storage of liquid petroleum based fuels.

Chemical resistance and long term degradation

Further independent tests have been carried out in accordance with BS EN 858-1:2002 Section 8.1.4 ‘Chemical resistance of internal surfaces’. The tests involve full immersion of three test specimens for 1000 hours in four solutions; de-mineralised water at 40°C, fuel oil at 23°C, unleaded fuel at 23°C, caustic solution at 40°C.

The requirement in Section ‘Plastic materials’ (BS EN 858-1) is for the glass reinforced test specimens under test to retain 80% of their strength when compared with the control specimen. The results of tests for tensile strength and flexural modulus have shown very little reduction, if any, in performance. In each case there was a reduction in flexural strength but an increase in modulus. Initially this might seem odd but it is possible that this could be part explained by at least two samples being immersed at 40°C hence a post cure compared to the control. All samples appeared to have passed seeing they came within the 80% retention of the control specimen.

Workshop conditions, Health & Safety and Environmental considerations.

Included in process controls is work shop temperature, fume extraction to keep within Health & Safety occupational exposure limits and odour control to meet the strict Environmental Protection Act 1990 Part 1 requirements as dictated by the Local Authority ‘Authorisation’ requirements. The record maintained since 1989, when the chop-hoop filament winding process was introduced, is that no tank has failed due to a design or manufacturing fault. Since 1989 thousands of underground tanks have been manufactured. The few tanks damaged were due to faulty installation or handling.

With this exceptional track record we are fully satisfied and confident that we have a specification and process control that produces exceptionally high quality laminates that have a life expectancy well in excess of 50 years.

The SPEL underground tank shell carries a 25 year warranty.

Laminate Specifications

GP – General purpose applications

Constructed throughout with orthophalic polyester resin and glass reinforcement.

Applications – potable water, sewage, surface water and mild chemicals.

CR – Chemical resistant lined tanks

The smooth moulded resin-rich corrosion resistant internal surface and the resin-rich glass reinforced corrosion barrier are constructed from isophthalic polyester resin or terephthalic NPG polyester resin.

Applications – suitable for silage effluent, chemicals (acidic) and hydrocarbon materials.

HCR – Highly chemical resistant

Aggressive chemicals and/or high temperatures. The smooth moulded resin-rich corrosion resistant internal surface and the resin-rich glass reinforced corrosion barrier are constructed from vinyl ester resins dependent upon chemical resistance and/or high temperatures.

Applications – transformer oil dump tanks, highly aggressive chemical process or holding tanks, and accidental chemical spillage containment tanks.

Suffix CG – Contaminated ground conditions

The external resin-rich water penetration barrier can also be in chemical resistant or highly chemical resistant where tanks are to be installed in contaminated ground.

Chop-hoop Filament Wound Shells

Laminate struction to BS4994

SPEL Tankstor® underground tanks and separator shells are chop-hoop filament wound in quality glass reinforced plastics in accordance with the British Standard BS EN 13121.

To ensure a life expectancy in excess of 50 years underground and containing contaminated water or chemicals, the laminate construction must incorporate a chemical or corrosion barrier as defined in: Section two (BS EN 13121) 7. Construction of chemical barrier

7.3 Where a thermoset lining is used, in order to achieve the optimum properties, the construction of the laminate in contact with the corrodent shall consist of the following:

(a) Surface layer

A resin-rich surface layer reinforced with C glass surfacing mat, synthetic fibres or other suitable material, with a thickness between 0.25mm and 0.50mm.

(b) Backing layer

A backing layer normally containing a minimum of 1.2kg/m2 chopped glass strand or CSM with a soluble binder with between 25% and 33% glass content, by mass.

For tanks and vessels which are constructed in accordance with categories II and III, it is permissible to reduce the backing layer to 0.6kg/m2 chopped glass strand or CSM if agreed between the purchaser and the manufacturer.

SPEL Laminate Construction

A Competitor Laminate Construction