The problem

At the turn of the century, water utility company, E.D.A.R. de Bens, based in the town of A Coruña in northwestern Spain, realized they would need to expand to handle the municipal wastewaters of the 600,000 inhabitants of five surrounding towns; A Coruña, Cambre, Culleredo, Arteixo and Oleiros.

They needed to grow to meet the demands while, at the same time meeting the EU regulations concerning effluents from wastewater treatment plants.

The expansion project was awarded to Cadagua S.A by the Spanish Ministry of the Environment. The engineering company specializes in water purification, wastewater treatment, and desalination.

Planning for a minimum plant life of 25 years, the Spanish Ministry of the Environment specified the austenitic grade EN 1.4404 (ASTM 316L) for gates, suction precipitator bridges, sand removers and lamellas.

Between the time of initial planning and when Cadagua S.A took over the project engineering in 2006, the price of 1.4404 had skyrocketed due to high nickel prices.

Stainless steel is still a relatively new material in wastewater treatment, but it is fast becoming the standard in plant hardware. Stainless is ideal because it fights corrosion and abrasion while lowering maintenance needs and life cycle costs.

The solution

Cadagua S.A then approached Outokumpu, aware of the company’s extensive track record in desalination and unique capabilities in duplex grades.

Duplex grades have a low nickel content, and thus better price stability than austenitic grades. And they offer 90 percent higher strength and considerable weight savings.

Based on corrosion tests, Outokumpu convinced E.D.A.R de Bens, Cadagua and the project contractor that the right grade was Duplex 2304 (EN 1.4362). Outokumpu was awarded the contract to supply approximately 360 tons of Duplex 2304 sheet and plate to the wastewater treatment project.

The result

Duplex 2304 offers the water utility company multiple benefits in addition to vast savings in the initial price compared to 1.4404.

Its high surface hardness allows it to withstand the abrasion caused by solid suspended particles.

Because the completed structures are lighter in weight there is less need for edge preparation and thus less need for welding consumables, welding hours, lower-capacity cranes can be used, and overall the structures are easier to handle. It also promises a longer life cycle for the wastewater treatment plant.

To date, Cadagua S.A has built 170 wastewater treatment plants, with a total processing capacity of 8,000,000 cubic meters per day.