Stainless Steel Water Gates
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THE MAGAZINE DEVOTED TO NICKEL AND ITS APPLICATIONS |
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STAINLESS STEEL is not yet the standard throughout the wastewater treatment industry, but it
has taken at least 40% of the market in the U.S.A. |
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THE MANY ADVANTAGES that stainless steel gates offer over cast iron and Ni-Resist gates include: lower
cost, lighter weight, ease of installation and lower leakage rates. |
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THE GATES pictured on this page range in size from 0.3 by 0.3 metres to 4.6 by 4.6 metres and
weigh from 580 to 3,700 kilograms. |
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For more information from the Nickel Institute on the use of nickel-containing
materials in wastewater treatment, |
A total of 520 tonnes of stainless steel were used in this wastewater treatment project in Alabama, U.S.A.
By Carroll McCormick
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 multi-billion dollar program to repair aging sewers and improve wastewater treatment capabilities in Alabama's Jefferson County in the United States, 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.
"Cast iron gates have been in use in the collection system for 70 to 80 years," says Harry Chandler, assistant director, environmental services department for the Jefferson County Commission. "We started using Ni-Resist over twenty years ago. Price became an issue and we asked ourselves if we could get the stainless steel gates at lower cost than the Ni-Resist. It was only five to six years ago that we began to look seriously at alternatives."
The County's largest treatment plants are Village Creek and Valley Creek. Village has a nominal capacity of 550 million litres per day (LPD) and a peak capacity of 1,820 million LPD. Valley has a nominal capacity 840 million LPD and a peak capacity of 1,590 million LPD.
The two plants have at least 200 fabricated stainless steel gates, ranging in size from 1-by-1 to 4-by-4 metres. They were fabricated by several manufacturers, including Whipps Inc. of Athol, MA, U.S.A. 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 200 kilograms (kg) to ones measuring 4.6 by 4.6 metres and weighing 7,300 kg each. The company also fabricated 29 gates from S31603 ranging in weight from 580 to 3,700 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 U.S. for Whipps.
Although Jefferson County has adopted stainless steel gates as the standard six to seven years ago, Whipps has been fabricating them since 1977. "We've made only 300 iron gates between 1977 and 2003, but over 6,000 stainless steel gates in that time period," Perry says. Stainless steel is not yet the standard throughout the wastewater treatment industry, but it has taken at least 40% of the market and is growing annually, according to Perry. The American Water Works Association (AWAA) recently published a standard, C-561, for stainless steel slide gates.
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 4,130 kg.
The stainless gates were fully assembled and tested before shipping to Jefferson County. Once on-site, they were bolted to thimbles, which had been set in the concrete basin walls during their construction. The thimbles were also fabricated from S31603 and range in weight from 420 kg to 885 kg.
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.
Cast iron gates, on the other hand, require on-site final assembly and adjustments to make them fit well. Although the standard for stainless gates is the same as for cast iron, Fontaine reports that its gates leak at only half of the AWAA C560 recommended leakage rate. The less leakage at the gates, the less untreated wastewater is released from the facility into the environment.
Chandler cites other reasons for choosing stainless gates: "The Ni-Resist had become adequate for corrosion, but there are a couple of other issues. The cast gates are very heavy and slide up and down in a brass frame. If the gates are not used, they freeze up. We wanted gates that were not heavy and that were easy to move," Chandler explains. "The stainless steel gates don't corrode or bind and have a seal that lets them easily move up and down."
The problem with the cast iron gates is widespread, according to Chandler. "We have 4,800 kilometres of sewers and close to 100 control structures. In the past year and a half, we looked at them, and most of them we could not operate. The stainless steel gates operated and the cast iron gates did not.
"These things are going to operate for twenty to forty years. Because you can't turn them off, maintenance is a large issue. With cast, the wedges work against brass bushings that wear. Maintenance and replacement is more expensive.
"With stainless steel gates less maintenance is required on the electrical equipment that raise and lower them. The seal on the stainless steel gate doesn't wear as much and is easier to replace than the cast seals.
"We have four treatment plants, and all have undergone expansion in the past six to seven years. We have installed stainless steel gates in all of them. Stainless steel gates are becoming the standard in our treatment plants."
The Village Creek peak flow treatment train became operational in June 2003. The part of the plant that will couple the treatment trains will be done in September 2004. Valley Creek will be completed in June 2005.
Carroll McCormick is a Montreal-based freelance writer.
PHOTOS: Whipps Inc. and H. Fontaine Limited
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George Whipps Francois Bedard Harry Chandler |
