A total of 520 tonnes of stainless steel were used in this wastewater treatment project in Alabama, USA, according to an article by Carroll McCormick in Nickel Magazine, July 2004. Modern wastewater treatment plants, designed to handle peak flows after rain storms, need sluice gates to control the movement of wastewater between storage basins. In a programme to repair aging sewers and improve wastewater treatment capabilities in Alabama’s Jefferson County in the USA, S30400, S31600 and S31603 stainless steel have become the material of choice for gates, replacing traditional cast iron and F47006 (Ni-Resist D-2). Although fabricated stainless steel gates have been in use for only a short time, experience has quickly shown that they are less expensive, lighter, easier to install, and less prone to leaking. They also are more resistant to corrosion in the presence of hydrogen sulphide and require less maintenance. The County’s largest treatment plants are Village Creek and Valley Creek. The two plants have at least 200 fabricated stainless steel gates, fabricated by several manufacturers, including Whipps Inc. of Athol, MA, USA, and H. Fontaine Limited in Magog, Quebec, Canada. Whipps fabricated 111 gates from 9.5-mm-thick S30400 plate for Valley Creek. They range from small 0.3-by-0.3-metre gates, weighing 200kg to ones measuring 4.6 by 4.6 metres and weighing 7300kg each. The company also fabricated 29 gates from S31603 ranging in weight from 580 to 3700 kg each. “The choice of stainless steel depends on the corrosive conditions and whether they require a lot of welding,” says Fred Perry, regional sales manager for the southeastern USA for Whipps. Fontaine, meanwhile, supplied 72 flange-back design gates, ranging in size from 1.22-by-1.22 metres to 3.05-by-3.05 metres, to the Village Creek treatment plant. The gates’ weights range from 820 kg to 4130kg. The plate from which the gates are constructed using a combination of bending and welding, range in thickness from 6.3 millimetres (mm) to 9.5 mm. Each gate is passivated before leaving the plant, and further passivated on-site.
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