The problem: The city of Minneapolis needed to construct a new surface water treatment plant, replacing a sand filter operation that had been in operation since 1913.
The solution: Stainless Steel for Ultrafiltration
Minneapolis constructed the largest surface water treatment plant in the U.S., the Minneapolis Water Works, incorporating advancements in membrane technology—a process called ultrafiltration—that was originally developed for purification in the beer and wine industries. The treatment plant’s surface water is transported through the ultrafiltration process in more than 9,000 feet of large stainless steel tube and pipe, some of which was provided by Outokumpu’s Wildwood, Florida stainless steel pipe facility. Outokumpu stainless steel pipe for the water treatment plant ranged from 2-inch to 60-inch in diameter.
Stainless Steel for Municipal Water Projects
For the corrosive environments of salt water and brackish water, stainless steel is a necessity in the desalination and other particle removal processes. Now stainless steels are increasingly being used for processes like water re-use, softening, and the removal of organic matter through a variety of filtration technologies such as microfiltration, ultrafiltration, nanofiltration, and reverse osmosis.
Outokumpu is one of the world’s largest producers of duplex stainless steels, many of which are used in clean water processing around the world. In the United States, three duplex stainless steels from Outokumpu have been added to ANSI/NSF Standard 61, the American National Standard that ensures products that come into contact with drinking water do not contribute levels of contaminants that could cause adverse human health effects.
These three duplex stainless steels for safe drinking water include LDX 2101® (a proprietary lean alloyed duplex with high mechanical strength, good weldability and machining properties); 2205 Code Plus Two ® (a proprietary duplex combining excellent resistance to pitting, crevice corrosion, and chloride stress corrosion with high strength); and Outokumpu 2304 (a proprietary duplex with high surface hardness).
Outokumpu now has seven grades of stainless steel acceptable for municipal water systems:
• 304
• 304L
• 316
• 316L
• LDX 2101
• 2205 Code Plus Two
• Outokumpu 2304