The proponents of stainless steel finishes for architectural applications exude the same evangelical loyalty as longtime users of Apple computers. In their hearts, they know they have the superior product, regardless of where it ranks in terms of market share, and they fervently want to convert you to their way of thinking.
To be fair, the champions of stainless steel finishes possess a strong case and can point to many iconic examples of their product—buildings and other structures that have stood the test of time for their longevity, beauty and prestige. A favorite word among stainless steel advocates to describe their product is “timeless.”
New York City is home to the two most famous stainless steel projects in the United States: the Chrysler Building (1930) and the Empire State Building (1931), each of which was able to lay claim to being the tallest building in the world at the time of its completion. Chrysler was the tallest for about nine months until it was overtaken by the Empire State Building, which held the title for more than four decades.
The Chrysler is one of the 20th century’s architectural trophies, a classic embodiment of the Art Deco style, and also was the first large, high-profile, stainless steel application in the world. The building’s distinctive ornamentations model themselves on features then being used on Chrysler automobiles. The stainless steel gargoyles anchored on the corners of the 61st floor are replicas of the 1929 Chrysler hood ornaments. The stainless steel arches represent hubcaps. The six rows of stainless steel arches, created using standing, batten and flat lock seams, are topped with a stainless steel spire.
One of the hallmarks of stainless steel finishes is its minimal need for maintenance. In any urban or industrial setting, all that is usually necessary is a washing with detergent and water or with one of the commercial stainless steel cleaners. In many circumstances, however, washing can be accomplished by the action of rain and wind.
In the 78-year history of the Chrysler building, the exterior has been cleaned only twice, in 1961 and in 1995. The building is considered to be in very good condition. There are some small dents from the cleaning equipment and minor pitting above the flu pipe and on the 61st story balcony. Neither adversely affects the roof integrity and the pitting could be removed with simple polishing.
The other landmark building from that era, the Empire State Building, boasts an exterior which is stainless steel, gray limestone and dark gray aluminum. It has been cleaned only once—in 1995—and is reported to be in excellent condition, with no problems ever attributed to the stainless steel other than the need to replace some panels following an accidental plane crash into the building in 1945.
There have been countless other distinctive examples of stainless steel buildings and structures, including the Petronas Twin Towers in Kuala Lumpur—the tallest buildings in the world for a time when they were constructed—Neur Zollhof in Dusseldorf, Germany; the Mapfre Tower in Barcelona; the Housing and Commercial Development, Lucerne, Switzerland; the Sun Life Centre in Toronto; the Gateway Arch in St. Louis; the Mellon Arena in Pittsburgh; the Printemps department store in Osaka, Japan; the Inland Steel Building and Millennium Park in Chicago; Jin Mao in China; the Walt Disney Concert Hall in Los Angeles; Washington National Airport; Canary Wharf and the Jubilee Line in London; and LeGeode in Paris.
More recently, in just the past several years, stainless steel has been used in projects involving public institutions such as Roger Williams University’s student union building in Bristol, Rhode Island; the University of Maryland new Dental School building; and a project that has received national attention, the recently dedicated United States Air Force Memorial in Arlington, VA. The website for the Specialty Steel Industry of North America says the new memorial “ranks as one of the world’s largest structural applications of stainless steel, along with the Dublin Spire in Ireland and America’s largest memorial, the Gateway Arch.” The Air Force Memorial, located on a promontory just west of the Pentagon, features three curved spires that arc up to nearly 300 feet in the air.
Stainless steel is finding its way in a number of other construction categories, such as airports. Such projects recently have included work for the Jamaica AirTrain JFK Terminal, and at airports in Dallas-Fort Worth, Atlanta, Detroit Scottsdale, AZ and Raleigh Durham—as well as an extensive project now underway at the Doha airport, which soon will boast the world’s largest stainless steel roof.
Why Stainless Steel?
The origin of the name is self-evident: stainless steel does not stain, corrode or rust as easily as ordinary steel. The metallurgical definition of stainless steel is an iron-based alloy with a minimum of 10.5 percent chromium content. Chromium produces a thin layer of chromium-rich oxide on the surface of the steel known as the passive layer. This reduces the possibility of corrosion of the surface. Increasing the amount of chromium gives an increased resistance to corrosion. Other alloying elements are added to enhance their structure and properties such as formability, strength and cryogenic toughness. These include nickel, molybdenum, and nitrogen.
However, this is not to say that stainless steel is invincible. In some circumstances it can corrode. To borrow a phrase from the British Stainless Steel Association , “it is ‘stain-less’ not ‘stain-impossible’.” In normal atmospheric or water-based environments, stainless steel will not corrode, but in more aggressive conditions, the basic types of stainless steel might experience some corrosion. Therefore, in those situations, a more highly alloyed stainless steel would be required for the job.
Product Characteristics
Stainless steel can be selected for use for a number of different reasons, not just its resistance to corrosion. These include:
Aesthetic Qualities – Different stainless steel finishes, along with their processing methods, can affect the visual appearance of metalwork in terms of the following:
Textures – Stainless steel comes in a variety of surface finishes. A project design team can choose textures from dull to bright (spectral gloss at 85° from 8 to 99 on a scale of 1 to 100) and smooth to rough (Ra or average surface depth <10 to >500 micro-inches). Stainless steel can even be polished to a satin or mirror finish. Processing methods include abrasive polishing, cold rolling, coining, embossing, media blasting, and colorizing. Geometric finishes and colorized stainless steels are also available.
Visual Uniformity – Finishing methods also vary in terms of visual uniformity. The design team should take this into account. For example, elevator access doors are quite critical in terms of ensuring a pair of doors installed side-by-side will dependably look the same.
Flatness – Factors such as gauge and finishing methods have an impact on flatness.
Fire Resistance – Stainless steel exhibits better fire resistance than ordinary carbon steel, especially better strength retention at elevated temperatures. In addition, many anti-corrosion coatings are fire hazards or the materials themselves have a low melting point.
Cleanability – Stainless steel is easier to clean in terms of bacteria removal.
Weight Savings – As thinner sections can be used, more innovative design structures can be created, saving money on foundations and platform weights.
Most types of stainless steel used in architecture include a percentage of nickel, and manganese, molybdenum, or other elements. Architectural stainless steel finishes are suitable for a variety of interior and exterior applications, including roofing and wall panel systems, composite panels, elevators, coping, trim, flashing, doors and cabinets. From its inception, it became the preeminent material for projecting a progressive, modern image. That still holds true today, and the range of design options for architects has increased many fold since the 1920s.
Today’s stainless steels are produced in large volumes, offering a wide variety of steel grades and finish options, including color and texture. Architects are attracted to the product for the benefits already mentioned—atmospheric corrosion and wear resistance, strength, durability, fire resistance, cleanability, range of finishes—and for its product forms, which include structural components, precision castings, wire, cloth, panels and tubular products.
Stainless steel’s resistance to corrosion carries two attached benefits. There is no need to compensate for loss of strength due to metal deterioration, and replacement costs are virtually nonexistent. Any building owner interested in the long life of a building, rather than just a short-term gain, will be drawn to stainless steel because of its lifecycle cost payback. Stainless steel finishes last the life of the building and are low maintenance, never requiring, for instance, a fresh coat of paint.
Stainless steel’s aesthetic quality is well known. It is notable for its beauty and the ease with which it blends with other materials. It has a subtle sheen which complements, reflects and highlights surrounding materials. Because it won’t corrode, its appearance is permanent and there is no danger of streaking or staining other materials.
Stainless is one of the strongest of metals. Tensile strengths of 75,000 to 125,000 psi (or higher if needed) allow the use of gauges much lighter than are usually needed in other metals, Sturdy design elements, fabricated from thin sheets of stainless steel, can combine light weight with strength. It is produced in virtually all standard metal forms and sizes, plus many special shapes.
Stainless Steel’s Strength
Architects are catching on to stainless steel’s strength and the option to reduce gauge. Research shows that a Type 304 stainless steel sheet, for example, has at least three times greater tensile strength than aluminum sheet. This fact is percolating throughout the building industry to the point that there is now a growing tendency among architects and specification writers to write performance type specs rather than construction type specs. The advantage? Reduced costs. Construction specifications requiring stainless steel sections to be as thick as aluminum ones put an unnecessary cost disadvantage on the stronger stainless steel. However, performance type specs are based on putting strength where it is needed.
The Green Material
Stainless steel is a green material. It is 100 percent recyclable. An average stainless steel object is composed of 60 percent recycled material—25 percent of that originating from end-of-life products and 35 percent coming from manufacturing processes. Furthermore, the fact that stainless steel will last the useful life of the building limits its impact on the environment—and usually results in the least long-term costs to the building owner.
Life Cycle Costing
It’s because of this last reason that manufacturers and distributors of stainless steel believe that life cycle costing should be taken into account when designing for permanence and selecting materials for architectural applications. The Federal Highway Administration issued a report in 2001 estimating that in the United States alone, Americans spend about $550 billion a year combating metallic corrosion. Of that cost, $113 billion per year is spent on construction related metal failures ranging from roof perforation to replacement of components that have become aesthetically unattractive. Other studies conducted in recent years by both Batelle Laboratories and the National Association of Corrosion Engineers (NACE) concur that in the U.S. alone, we spend about $300 billion per year fighting metallic corrosion. The Batelle study estimates $100 billion of those costs could be avoided with proper material selection.
The history of stainless steel traces back through many discoveries and innovations that were set in motion in the 1820s by English and French scientists. Eventually, after decades of metallurgical developments in England, France, Germany and the United States, stainless steel’s birth occurred in 1913 when Harry Brearley of England created a steel with 12.8% chromium and 0.24% carbon, widely considered the first ever stainless steel.
Today, there are more than 150 grades of stainless steel, with about 15 to 20 being the most popular. The alloy is milled into sheets, plates, bars, wire and tubing for a wide variety of products and applications. The architectural possibilities for stainless steel have advanced beyond the “decorative” – it is now a vital fabric of many buildings, including its use as roofing, cladding, wall panels, composite panels, and even reinforcing bars for concrete structures for which a long design-life is required.
Stainless steel has arrived. With all of its advantages, architects, specifiers and building owners no longer ask if they can afford stainless steel – instead they now realize that, in the long run, the more pertinent question is, “Can we afford to be without it?”