Above: A composite structural section of reinforced concrete and 2205 duplex stainless steel plate provides a 120-year design life for the Stonecutters Bridge in Hong Kong. Photo: John Nye
Reflecting on the metal’s lustrous past sheds light on things to come
February 2013 - For most, Harry Brearley is considered the inventor of stainless steel for his “rustless” steel of 1913, but many were experimenting with chromium at that time. A century later, the alloy continues to adapt and thrive in a global market. According to an International Stainless Steel Forum presentation at the BIR World Annual Conference in May 2012, world consumption of stainless steel has grown faster than most metallic materials at a compound annual growth rate of 4.6 percent, since 1980.
During that time, stainless has progressed from a specialized product to a diverse material for numerous industries. “And it’s starting to be accepted as a sustainable material because people have realized it’s 100 percent recyclable and it’s based on predominantly recycled scrap,” says Poul-Erik Arnvig, vice president, market development for Outokumpu North America, Itasca, Ill.
Outokumpu is as old as stainless steel itself, taking its name from a town in the eastern part of Finland where a rich copper ore deposit was discovered in 1910. Today it produces stainless steel and high-performance alloys in many countries, with a product offering of austenitic, ferritic and duplex stainless steel grades, and nickel, titanium and zirconium alloys.
Three types of stainless steel are most common today. Arnvig says austenitic steels are popular for their formability, strength and weldability. Ferritic stainless steels are stronger, which Arnvig says is often an advantage, “but they’re impossible to produce and work with in heavy sections, so products in ferritic grades are limited in thickness. They also are limiting with regard to ductility and weldability.”
He says austenitic grades make up “the biggest chunk of global consumption, followed by ferritics.” Duplex stainless steels are growing in popularity as a strong hybrid, balancing the fabrication properties of austenitic grades with the price stability of ferritic grades. Arnvig says duplex was a niche product at the time of its creation in the 1930s, but “we are seeing that niche become bigger and bigger, and it is no longer a niche material. Its consumption is growing faster than other types of stainless steel.”
Stainless steel is used in a variety of chemical and process industries including oil and gas, pulp and paper, food and beverage, and pharmaceutical. “Even in the thinner gauge items, we’re starting to see duplex considered, especially in the oil and gas industry but also in building and construction industries,” says Arnvig.
Catherine Houska, senior market development manager for TMR Stainless, Pittsburgh, specializes in architectural and construction metals. “In architecture, the sustainability, longevity and corrosion resistance benefits of stainless are a driving force in using it for exterior applications such as roofs and wall panels,” she says. In addition, new seismic construction and rehabilitation projects use stainless steel because of its ductility and ability to perform well under cyclic loading conditions.
Tapping the construction market
“The construction industry is just learning about these new materials,” says Arnvig. “For them, stainless steel was something very avant-garde that was mostly used in specialized architectural projects.” He says, “builders want longer lifetimes than what the design criteria were just 10 to 15 years ago. Green thinking forces the industry to use recyclable, longer lasting and less maintenance demanding materials.”
Arnvig cites lack of design standards as a major holdback in the aggressive use of stainless in construction. “Even if you have a great material you don’t just put it in a building’s specifications because it’s great,” he says. “You need design standards and official codes to be adopted that allow and utilize the new material’s properties. Getting accepted into standards and codes is a relatively slow process, but nonetheless, it’s ongoing with the upcoming publication of the new AISC stainless steel structural design guide in 2013.”
Houska says builders sometimes overlook the total life cycle cost benefits of stainless. “From the standpoint of sustainability, the rating systems, ASTM and the green building code are starting to look at a 75-year design life as the requirement to call a structure sustainable.” Selecting a long-lasting material lessens the carbon footprint and total cost of a building because there is no replacement required. “So I think those requirements will help to increase the visibility of stainless steel as an option because it can provide hundreds of years of life,” she says.
Misunderstandings and preconceived notions also have led builders to shy away from stainless. “There has been a tendency to think of it as just a material for big corporate office buildings and practical applications like airports and kitchens, but the increased awareness of its sustainability should help increase its specification,” says Houska.
“Many of the leading international architecture firms know about stainless steel’s longevity and have been designing with it,” she says. However, “it is not uncommon for the typical architect to think of it as a material that is only used for those big high-profile projects. They’re not aware of its advantages for everyday applications and range of finish options, so we’re trying to educate them about these aspects.”
As a large producer of duplex stainless steels, “Outokumpu realizes architects need more information to select the right stainless steel,” says Houska. “They’ve done recent atmospheric corrosion testing in the U.S., the Middle East, China and other places where construction is occurring to help specifiers make better material decisions.”
According to Arnvig, 2205 is the most widely used duplex stainless steel today, offering higher corrosion resistance and double the strength of austenitic stainless steels. “On top of that, it is weldable and ductile,” he says. Outokumpu provided 2205 for the Stonecutters Bridge, Hong Kong. “Being close to the sea and high off the bridge deck, portions of the bridge’s stainless are difficult to reach for regular maintenance. So a material with better corrosion resistance than ordinary stainless steel was necessary, and 2205 was the obvious choice,” he says.
In the 1980s, duplex 2507 was developed for higher strength and seawater corrosion resistance. Another duplex, 2304, “was a leaner version of 2205,” says Arnvig, “putting it, corrosion resistance-wise, on the level of traditional stainless steels but with the added strength from the duplex.”
Outokumpu released a third generation of duplex stainless steels in the early 2000s with its LDX 2101 grade. “We developed a totally new strategy for how to add the alloying elements together, with the intent of utilizing more cost optimal alloying elements, [while] keeping the duplex structure and adding more strength,” says Arnvig.
The company also introduced LDX 2404, which is similar to 2205, but uses the same alloying philosophy as LDX 2101. Reducing carbon content while adding nitrogen and manganese as a constituent to the metal structure has strengthened these duplexes and achieved a more cost optimal product.
Houska says many builders look at the initial cost of stainless steel without completing a full cost analysis over the life of a product or application. “Not having to replace materials that fail and having less maintenance pays for that cost difference,” she says. “The actual long-term cost of stainless steel is less in many common applications. Additionally, stainless steel roofing, wall panels and sunscreens can help to reduce energy requirements, reduce toxic runoff from construction and provide other environmental and cost benefits. Stainless steel has a high recycled content, and it is recaptured and used to make new stainless steel of the same high-quality level at the end of life, making it a very sustainable material.”
Built to last
“Stainless steel producers, like Outokumpu, have developed U.S. Green Building Council LEED statements and have been involved in ASTM E60, which is the ASTM sustainability standards,” says Houska, noting similar efforts in Europe. According to the Green Material handbook from the Specialty Steel Industry of North America’s Stainless Steel, “all stainless steel products are 100 percent recyclable and have value even after a very long life as capital goods or consumer products.”
Houska adds, “Stainless steel’s recycled content and end-of-life recapture rates have continued to increase.” In fact, a 2009 ISSF and Yale University study found 8 percent of stainless steel used in building went to a landfill, while 92 percent was collected for recycling and of that, 95 percent was collected as stainless steel at end of life.
“Because of the combination of its high sustainability and its strength but also because of the industry work in establishing design standards, duplex stainless will be more available and more frequently applied to construction projects in the next few years,” Arnvig says. He wants industry leaders “to realize that stainless steels aren’t just stainless.” Applying the material’s numerous properties to appropriate applications, including construction, is essential to its future success. “They have a lot more to give,” he says. MM
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