This slide speaks for itself. Corrosion is expensive and it can be avoided by designing with stainless steel.
Correctly specified stainless steel will last well beyond a century. Copper and Zinc may approach 100 years service in certain applications while painted materials like carbon steel and aluminum can last 30 years before their coatings have generally degraded to the point where expensive restoration is required to achieve their original aesthetic.
Now that we’ve reviewed this nearly overwhelming selection of stainless steelalloys let’s take a moment to simplify the grade selection process with some suggestions for various types of environments.
The designer should be aware of a materials physical properties when considering it for use in architectural applications. Stainless steel shines, at least figuratively, in a comparative analysis with other metals commonly used in architectural applications. Yield strength can be a major consideration for specified thickness. Stronger materials can utilize lighter thicknesses in many cases. The thickness specified is also influenced by an applications need to withstand impacts that lead to dents in service. For example a light or thin gauge of any metal wouldn’t be suggested for below eye level installation in high traffic areas. High traffic areas are often serviced better by thicknesses of .059”/ 1.5mm or heavier. Stainless steel’s high strength properties mean that it can excel at lighter gauges in applications like roofing where wind uplift requirements favor stronger metals. Naturally density will determine weight per square foot at any given thickness. Percent elongation is an important indicator of how much bending or forming an alloy can withstand during fabrication. Low elongation limits a materials design possibilities somewhat.
Thermal expansion figures are in inches per degree Fahrenheit. When long panel lengths are being considered stainless steel’s relative advantage in lower rates of thermal expansion can be important. Also when dissimilar metals are used in together in assemblies allowances must be made for the different rates of expansion/contraction. Note that if 304 and 316 are held at temperatures between 800F and 1200F for extended periods of time they can become sensitized which reduces their corrosion resistance. Likewise the Duplex UNS 32003 can become embrittled if held at temperatures above 650F for extended periods. Applications above 650F should be avoided for UNS 32003. Areas exposed to exhaust venting from emergency generators should be designed to avoid direct contact with hot gasses for sustained periods of time.
It’s always better to be able to visualize what we’re talking about so we’ve included pictures of results from ongoing testing at Kure Beach, NC. The painted aluminum and carbon steel coupons were scored to show the effect of a compromised coating.
There are some relative measures which help us evaluate the general corrosion resistance of different alloys.The pitting resistance equivalent number or PREN gives a relative comparison on resistance to pitting corrosion among different stainless steel alloys. There are standard tests like the ASTM G48 which are used to establish relative pitting resistance among alloys and validate the relative PREN rankings. The higher the PREN number - the higher the pitting resistance. Crevice corrosion develops in crevices of a couple millimeters or less. These are areas where a contaminant can enter and become stagnant. The corrosion mechanism for crevice corrosion is similar to the mechanism of pitting corrosion so crevice corrosion is sometimes also associated with the PREN formula.
430 is generally recommended for interior applications. It is very popular with kitchen and restaurant equipment that is cleaned daily. Exterior application would require a rural environment, no sheltered areas, and regular cleaning.Type 304/304L has been successfully used for curtain walls, and roofing in urban areas with modest pollution and limited exposure to de-icing salts. Some examples of type 304 architecture are the Gateway Arch, Ronald Reagan National Airport, and the Pittsburgh Civic Center. T304 is suitable for almost any interior feature. For marine environments in temperate climates or polluted urban environments where metal is not in continuous contact with salt water but may have some exposure to de-icing salts T316 is often specified. However when conditions become more corrosive due to high salt and temperature combinations, as for example, in the Persian Gulf, a move up to a lean duplex alloy can be a sensible consideration.
This picture was taken in 1997. The steel still looks the same today.
By contrast painted panels at this Hyatt Hotel in Tampa built in 1982 had already begun to exhibit coating failure after only 20 years. Expensive restoration will be required to rehabilitate the building’s appearanceto its original condition . Interestingly the restoration cost can easily be more expensive than what the raw material cost would have been for stainless steel if it had been used in the first place.
Austenitic stainless steels have exceptional elevated temperature properties compared to commonly used building materials like aluminum, zinc or copper.
This is the Sacony Mobil building which is across 42nd street from the Chrysler Building. It was designed by Harrison and Abromovitz and built in 1956. This is a picture of it being cleaned in 1997. Cleaning was mostly done with cotton cloth, soap and water. Ammonia was used on the deposits that were more difficult to remove. It was cleaned again in 2007.
Here is the Sacony Mobil Building with a completed wash job.
This Chrysler Building feature is a nice example of stainless steel’s ability to be formed into a variety of shapes by various fabrication methods. Stainless Steel is easily fabricated. It can be formed and joined with the same equipment and methods used for carbon steel with appropriate modifications and handling. Remember too that because of its high strength lighter gauges can be specified.
The increased spring back will require modifications to set ups used for carbon steelThe PVC coating also prevents contamination of the stainless steel surface by carbon steel tooling. This type of contamination can lead to rust stains developing when the carbon steel particles oxidize on the surface of the stainless steel. Galvanic corrosion can also be controlled by including insulation between dissimilar metals at contact points.
Require that sub contractors have current AWS certifications for welding stainless steel by the welding method being employed. Write your spec to require that bidders are competent fabricators.
Unpolished mill finishes exhibit a wider range of visual variability than polished finishes. They can be tricky to utilize architecturally unless cosmetics are absolutely unimportant.Polished finishes provide a means to make stainless steel’s surface more uniform. It is better to orient linear polished finishes vertically on exterior applications to facilitate natural cleaning. Horizontal orientation of linear polishes tend to hold more dirt and will not clean as easily. Wet polishing with silicon carbide belts is suggested for architectural applications in more corrosive environments. For a starter always specify polishes per ASTM A-480 and utilize control samples, try and limit sourcing to a single vendor since there is wide variability among the various suppliers in the polishing business.
This whimsical design included a bit more reflectivity than the neighbors wanted to be exposed to. The remediation solution used to eliminate the unwanted glare from the mirrored finish stainless steel gives us a very interesting study of some common finishes. The first thing one needs to know is that the building has two finishes on the exterior, a mirror product and an abraded non-directional finish with low reflectivity. Both cases are on stainless steel.Originally the mirror finish was more extensively utilized than shown in the above photograph. Reflected light from the some mirrored areas were annoying the neighbors. So, the offending areas had to be refinished with a more non-reflective finish.
This view gives us a composite view of reflectance for direct and indirect light as well as gradations of shade. This is a low reflecting, non-directional abrasive finish.
The solution was to refinish the problematic exposures of the mirror in the same duller finish that existed on other parts of the building. In this view we can see the contrast between the dull finish and the mirror finishes reflectivity. The dull finish still provides a very muted and subtle reflection of the sky and clouds while the mirror finish picks up the shrubbery and the banners with relative clarity.
How did they do that?This picture plays a trick on the eye. The two panels on the left separated by the overlapping seam near the top of the picture are the dull finish. The right hand side of the picture with the curving lines is actually the mirror finish reflecting an adjacent wall. Although, on a glance it gives the appearance of an impossibly tricky fabrication job.
Abrasive blasted finishes cannot be made in lighter gauges. If weight is a consideration the embossed finishes can be supplied down to .018” or lighter.Utilize one mill source and utilize control samples.
Colorized stainless can add attractive detail to many designs. Stainless steel colorized by the anodic process has a wider range of visual variability than the sputter coated ceramic colors. However there is also a cost differential, the anodic coatings are less expensive and exhibit wider process variability. On the other hand the sputter coated products are more uniform and scratch resistant. Both types of coatings are only on the surface of the sheets. Any drilling, perforating or shearing will reveal the brighter stainless substrate on the edges where metal has been removed. So designs should conceal processed edges and cover or cap holes.
Life is like a box of chocolates. Colorized stainless is available in a variety of textures and the techniques can also produced intricately etched designs. The circular etched piece shown here has an actual diameter of only 2.5” however surface areas of 4’ x 14’ are possible.
The panels on this roof are made with a non-directional finish on T316 stainless steel. Note the panels are made from coil stock and long continuous lengths are no problem.
This addition to the Fletcher Allen Hospital blends in nicely with the pre-existing structure. Most stainless steel finishes have the attribute of reflecting aspects of their surroundings. In this way stainless components blend into the pre-existing design while still retaining a distinctive stainless steel character. This job was produced with a light gauge (.024”) panel system which gives a interesting soft pillowy effect.
These composite panels with a ASTM #4 polish at the Dallas Fort Worth Airport deliver a crisp clean look. The picture does a good job of conveying the bright shiny appearance of a linear abrasive polish. You’ll also notice that the panels on the lower left still have PVC protection. This is an example of a good workmanship practice – that is keeping protective coatings on the metal until installation has been completed. Stainless steel composite panels can also be used on the building envelope.
Here we see the effect of light and shadow on a non directional, non reflective matte finish. The tower has a skin of perforated metal catching direct light. The cone at left-center is the same finish without perforations illustrating the appearance of the finish as it looks in the shade.
Here is a closer shot of the tower showing the perforation effect in both light and shadow.
Educational Presentation High Performance Metals
High Performance Architectural Metals<br />51 QSi Lane Allison Park, PA 15101 (724) 779-5100 www.metalresources.net<br />
Cost of Corrosion<br />Battelle Laboratories and the National Association of Corrosion Engineers (NACE) concur that in the United States alone, we spend $300 billion per year repairing metallic corrosion. <br />The Battelle study estimates that at least $100 billion of this cost can be avoided with proper material selection.<br />Stainless steel when properly specified decreases life cycle costs and increases sustainability. <br />
Environmental Responsibility<br />Our philosophy regarding materials is to select a product that will last the useful life of the building with little or no maintenance. This usually results in the least long-term cost to the building owner. In addition, significantly less harm can be made to the environment by using permanent materials as opposed to more commonly used materials that require maintenance and replacement. Specifically, our portfolio of high performance metals serves this philosophy well. Beyond offering permanence, these materials are by their nature, environmentally “green” materials.<br />
Leadership in Energy & Environmental Design (LEED)<br /><ul><li>Established by the US Green Building Council
Architects as well as government agencies are adopting LEED
Consumers are embracing environmentally sensible products
Stainless steel will last the useful life of a building with little or no maintenance
Stainless steel is 100% recyclable after the building is torn down
With respect to LEED credits, our products are eligible for two to four points based on what material is selected, how it is used and where the building is located. Please contact us for assistance in pre-qualifying LEED points for your specific project </li></li></ul><li>Green Globes<br />There are a number of ways in which our materials can contribute to the accumulation of Green Globes Design points: <br /><ul><li>Environmental Purchasing
Low Environmental Impact</li></li></ul><li>What is Stainless Steel?<br />Stainless steel is an iron based alloy with a minimum chrome content of 10.5%<br />An invisible chrome oxide film covers stainless steel’s surface and protects it from discoloration and rusting.<br />Therefore a protective surface coating is not needed.<br />More Chrome = More corrosion resistance <br />
Who should consider specifying stainless steel for their designs?<br />Anyone who is designing for:<br /><ul><li> Sustainability
When is grade selection an important consideration?<br />Type 316 with a matte finish on the restored <br />Carousel at Santa Monica Pier<br />
Grade Selection<br />Type 304 is sufficient for most all exterior applications <br />Type 316 should be used in normal seacoast environments<br />Specify 304L or 316L if welding will be employed<br />Corrosive environments like seacoast locations subject to ocean spray and chemical processing plants may require higher alloys<br />Any grade, including Type 430 may be used in interior applications<br />
Comparative properties of architectural metals<br /> Coefficient of Melting Thermal Expansion Point <br />Stainless Steels<br /> Austenitic - 304/316 9.6 X 10-6 2500° F<br /> Ferritic - 445M2 5.4 X 10-6 2600° F<br /> Duplex – UNS 32003 7.2 X 10-6 2550° F<br />Others<br /> Carbon steel - 1020 7 X 10-6 2760° F <br /> Aluminum - 5005, H-16 12.9 X 10-6 1220° F<br /> Copper - Roofing 1/8 hard 11.3 X 10-6 1984° F<br />
Factors effecting grade or finish selection<br />air pollutants humidity<br /> marine salt rainfall<br /> deicing salt wind erosion<br /> quantity required temperature<br />Classification of service environments<br /> rural industrial<br /> urban marine<br />
Sustainability<br />Stainless Steel is an outstanding sustainable material <br />It is one of the few 100 plus year materials<br />Scrap is a primary production input.<br />It is 100% recyclable <br />Requires no coatings so it has no VOC’s<br />
Chrysler Building<br /><ul><li>Completed in 1930
Type 302 (304 is the modern version) Stainless Steel
1995 cleaning involved replacing a few panels that exhibited pitting corrosion at the location of heating system exhausts
Its good to go for another 70 years - evidence of stainless steel’s low life cycle cost </li></li></ul><li>304 SS (59 yrs.)<br />Painted Cast Aluminum (12 yrs)<br />Examples of relative corrosion resistance among architectural metals.<br />At the LaQue lab facility in Kure Beach, NC. These test coupons are exposed to the marine environment 820’ from high tide.<br />316 SS (59 yrs.)<br />Painted Cold Rolled Carbon Steel (12 yrs.)<br />
Corrosion ResistancePitting/Crevice corrosion<br />Resistance against pitting and corrosion is estimated with the pitting resistance equivalent number (PREN):<br />W = % Cr + 3.3 x % Mo + 16 N*<br />Nickel does not prevent pitting/crevice corrosion, it just inhibits its growth.<br />*N = Nitrogen in Duplex Alloys<br />
Aluminum, zinc, galvanized steel and fiberglass have been performance tested along with the T316 stainless steel at temperatures exceeding 1,000°F. This test shows that significant failure begins on all materials except T316 stainless steel within five minutes of exposure to temperatures over 1,000°F. After 45 minutes the T316 stainless steel ladder is still standing while the gas supply for the test has run out. <br />
Stainless Steel is low maintenance<br />Cleaning Guidelines:<br />Utilize natural rainwater<br />A mild detergent or degreasers can be used for more tenacious spots. Thinners can be used for ink or paint.<br />Always rinse thoroughly after using any cleaning agent.<br />Test abrasives first. <br />Never use solutions containing chlorides, hydrochloric acid, or muriatic acid.<br />Additional information is available at ssina.com <br />
Stainless steel, on the other hand, can be cleaned. It will not fade, chalk or chip. <br />
150 East 42nd Street, NYC<br />June 2008 <br />
Dedicated equipment and production area if possible</li></li></ul><li>Stainless SteelCutting<br />Incoming coils are slit to ordered width by the supplier.<br />Shearing is the most common type of cutting during fabrication.<br />Blanking, perforating, and nibbling are also effective forming operations.<br />
Stainless SteelForming<br />Most common method is brake forming<br />Roll forming is also economical when large quantities are produced<br />Press forming for drawn panels<br />Extrusion is possible but not always practical due to tooling costs, finishing costs and geometry limitations <br />
Stainless SteelDesign Considerations<br />Stainless steel has a greater spring back than carbon steel<br />Plastic coatings prevent galling (metal to metal contact) during fabrication. Plastic also protects the surface during handling. It is removed upon installation.<br />Use stainless steel fasteners & clips<br />Prevents rusting and galvanic corrosion <br />
Stainless SteelWelding, Brazing, Soldering <br />Proper techniques can prevent distortion during joining. <br />Specify low carbon grades where applicable<br />Weld wire must be chemically compatible.<br />
Stainless SteelWelding<br />The heat tint formed during welding is mechanically removed to prevent future corrosion. Traditional methods are glass bead blasting, flapper wheels, grinding, stainless steel wire brushes and pickling where feasible.<br />Welding damages the finish. Ability to repair limited. Consider in design.<br />
Stainless SteelChoosing a Finish <br />The project architect should specify the finish and identify it by its industry standard designation or its trade name if specifying proprietary finishes. <br />Request control samples from the supplier.<br />When high gloss or low gloss is an option, consider the application.<br />
Stainless SteelIndustry Standard Finishes<br />Unpolished finishes are less directional. They range in appearance from rough & dull (no. 1) to smooth & dull gray (2D) or smooth & bright gray (2B), to a near mirror finish (Bright Anneal).<br />Polished finishes are produced by abrading the surface of the steel. They range in appearance from heavy, directional grit lines (#3, #4) to dull satin (#6), to reflective with some grit lines (#7), to reflective with faint grit lines (#8).<br />
Our Variety of Rolled-in Metal Finishes Differ Distinctly In Appearance. <br />Its All About Reflectivity.<br />
Abrasive Blasted Appearance finishes are non-directional and one or two sided.
Textured finishes are two sided with the texture reversed on the obverse side. </li></li></ul><li>Stainless SteelOther Specialty Finishes<br />Colorized: black, blue, bronze, pink, gold and nickel silver<br />Methods: anodic and sputter coated<br />Graphic: etched patterns, custom artwork<br />
Where can stainless steel be used?<br />Any component of a building envelope. Roofing systems, curtain walls, column covers, rain screens, railings and grip bars as well as sun screens are all natural applications for stainless steel. <br />Interior features that require a decorative element and durability such as elevator cabs, ceilings, sound proofing, wall treatments, tabletops and shelving.<br />Any area where sustainability and lifecycle cost are key design criteria.<br />Where fire resistance is important.<br />
…..<br />Scottsdale Air Center<br />Scottsdale, AZ<br />
If you wish to learn more about Contrarian Metal Resources, please call or visit our website<br /><ul><li>Contrarian Metal Resources</li></ul> 51 Qsi Lane <br /> Allison Park, PA 15101<br /><ul><li>Metalresources.net
(866)-360-5100</li></li></ul><li>High Performance Architectural Metals<br />51 QSi Lane Allison Park, PA 15101 (724) 779-5100 www.metalresources.net<br />