rotational moulded polyethene water storage tanks
1996 Edition

Polyethylene utilized in these tanks must be of rotational moulding grade resin, stabilized with no more than 0.3% by mass of physiologically safe anti-oxidants as listed under IS 10141:1982. Tanks intended for outdoor use require polyethylene compounded with carbon black, with content and dispersion validated following IS 2530:1963 to ensure UV resistance and durability. The tanks are designed to operate effectively within a nominal temperature range of +1ºC to +50ºC, ensuring longevity and safety for potable water storage.

For cylindrical vertical tanks, the wall thickness up to the effective height must meet or exceed the values specified in Table 1 of the standard, while above the effective height it should be at least 75% of those values. Rectangular loft tanks follow thickness requirements outlined in Table 2. Thickness measurements are taken at a minimum of 20 points distributed across the sides, top, and bottom surfaces, with lid thickness checked at no fewer than 4 locations. A dial gauge micrometer with spherical anvils is used after the tank has rested for 48 hours post-moulding to ensure accuracy, compensating for variations due to rotational moulding processes.

To ensure structural integrity, a compression test is performed where the tank, filled to 98% of its capacity, is subjected to a 100 kg load for at least four hours at ambient outdoor temperatures, followed by a 4-hour recovery period to confirm the surface returns to its original flat condition without cracks. Additionally, impact resistance tests, as detailed in Annex C, simulate impact scenarios using standardized weights dropped from specified heights. Tanks must exhibit no cracking or puncturing to pass these tests, confirming their durability and toughness under operational stresses.

The fittings and threaded connections must be full-threaded G.I. brass components, conforming to IS 554:1985 for thread dimensions and IS 1879:1987 for fitting shapes such as elbows and couplings. Thread sizes vary with tank capacity, ranging from 12.5 mm bore for tanks up to 750 liters, to 75 mm bore for tanks exceeding 10,000 liters. Overflow pipes require mosquito-proof devices with a maximum mesh clearance of 1.6 mm. Installation guidelines recommend using rubber gaskets and hexagonal check nuts, avoiding jointing compounds, and employing PTFE tape for sealing to ensure leak-proof, corrosion-resistant connections.

According to the standard, only up to 10% of the manufacturer’s own reworked material generated during tank production is allowed to be reused in manufacturing. The inclusion of any other recycled materials, fillers, or waste sourced externally is strictly prohibited. This restriction safeguards the quality, safety, and suitability of the tanks for potable water applications, ensuring compliance with the standard’s durability and health requirements.