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DESIGNER stainless steelHANDBOOK for coastal and salt corrosion TABLE OF CONTENTS INTRODUCTION CASE STUDY ONE STREET LEVEL APPLICATIONS CASE STUDY TWO EXTERIOR WALL PANELS AND WINDOW FRAMES CASE STUDY THREE LIGHT steel is not a single alloy but rather the The various types of stainless steels are detailed in a designer handbookname applies to a group of iron based alloys containing a Design Guidelines for the 105 chromium Other elements are added and the and Use of Stainless Steel available online at ssinacom or from the content increased to improve corrosion resistance and Steel Industry of North America SSINA byother properties There are over 50 stainless steel grades that calling the toll free number 8009820355were originally recognized by the American Iron and Steel Institute This handbook is designed to acquaintAISI Three general are used to identify stainless the reader with the 300 series stainless steels particularly grades 304 and 316steel They are 1Metallurgical structure and their applications in areas where The Unified Numbering 2 The AISI numbering system 200 300 400 series numbers coastal or salt corrosion is a factor in the life of a metal component The Specialty Steel Industry of North America SSINA and the individual companies it represents have made every effort to ensure that the information presented in this handbook is technically correct However neither the System which was developed SSINA nor its member companies 3 by the American Society for Testing Materials ASTM and the Society of Automotive Engineers SAE to apply to all commercial metals and alloys warrants the accuracy of the information contained in this handbook or its suitability for any general and specific use The SSINA assumes no liability or responsibility of any kind in connection with the use of this information The reader is advised that the material contained herein should not be used or relied on for any specific or general applications without first securing competent advice Carbon steel contains Stainless steel can be at least 95 iron with strengthened by work stainless steel up to 2 carbon The hardening the structure higher the carbon The 300 series stainless how is content the stronger steel grades 304 and applications the steel Stainless 316 contain nickel from steel also contains iron 8 to 14 in addition to stainless steel but in addition it must the chromium that mustfor coastal and contain at least 105 be present 316 contains chromium and the an additional element different from carbon content is very molybdenum from 2 to salt corrosion low usually 008 3 It is these alloying maximum Stainless elements added to the carbon steel Stainless Steel is the Grade 304 UNS 30400 steel gets it strength iron base that makes generally accepted the basic 188 alloy from the metallurgical stainless steel very terminology applied to 18 chromium 8 structure rather than different from carbon iron based alloys that nickel is the most from the amount of steel contain at least 105 common of the 300 carbon present chromium Many series and has excellent Carbon steel can be people are familiar corrosion resistance strengthened by heat The Specialty Steel Industry of North America with chromium as a in most applications treatment whereas the produces a handbook Selection and Use what is Grade 316 UNS 31600 300 series stainless of Stainless Steel available from the web at coating on the surface has an addition of at steels cannot w w w s s i n a c o m of a chromeplated least 2 molybdenum stainless part such as an which significantly automobile bumper In increases the metals stainless steel however resistance to salt steel the chromium is added corrosion during the melting of the steel and forms a homogeneous mixture with the iron and other alloying elements how It is the iron in carbon of oxide on the surface such as nickel and steel that reacts with that is several times molybdenum which the oxygen in the thicker than the original enhance the metals carbon steel atmosphere to produce iron present and often resistance to corrosion ironoxides which we results in a spalling or can see as red rust flaking of the surface corrodes on the steel surface reducing the steel Rusting creates a layer thickness The functional pier in this photo was completed in 1941 and used In the United States steel in many applica 220 tons of Type 304 reinforcing and Canada the tions Upgrading the use bar It is one of the oldest concrete structures in North America and presence of salt laden of stainless steel from is located in Progresso Mexico A casual visitor might assume that mist from the oceans 304 to 316 has shown the remnants of the nonfunctional chloride concentrations to be of significant help pier predate the functional pier but they would be mistaken The applications in rain water see map in reducing the effects nonfunctional pier was completed about 30 years ago and used on the following page of corrosion in several carbon steel rebar Corrosion of and the use of deicing applications some of the carbon steel caused the concrete to fail It would have salts in Northern or which are shown in this been much more cost effective to use stainless steel rebar mountainous regions brochure results in corrosion ofphotograph courtesy of Nickel Development Institute Because stainless steel 316 broadens the suffer any corrosion and it cannot heal the larger area where again contains at least 105 range of passivity Stainless steel will interruption It usually the environment has chromium the oxidation established by the however corrode under occurs in very tiny overwhelmed the ability of the iron is changed chromium The further certain conditions It dark brown pits on the of the passive layer to produce a complex addition of molybdenum is not the same type surface hence the to heal itself when how stainless oxide that resists further 2 minimum in 316 of corrosion as name pitting and does deprived of oxygen It oxidation and forms a further expands the experienced by carbon not interfere with the is not attractive but in passive layer on the passivity range and steel There is no mechanical properties most cases it should not steel resists surface This is a very improves corrosion wholesale rusting of of the stainless steel affect the mechanical thin layer microns resistance notable in the surface and properties of the stain in thickness but very acetic sulfuric and subsequent reduction Stainless steel can less steel Good design corrosion tenacious and will sulfurous acids and in of thickness If stainless also become subject to to eliminate sharp reform if it is removed neutral chloride solutions steel corrodes the most crevice corrosion when corners or seal them by scratching or including sea water likely form of corrosion the deposits or other will minimize this type machining The addition is pitting Pitting occurs material like a washer of corrosion of nickel to the structure If stainless steel is when the environment creates a crevice on 8 minimum in 304 properly selected and overwhelms the stain the surface It is similar and 10 minimum in maintained it should not less steels passive film to pitting but over a Chlorides in airborne metals near the site sea spray rain and dry should be evaluated salt particles carried prior to material by wind may cause selection In some pitting and rusting of locations marine salt stainless steels unless accumulations are only a sufficiently corrosion a factor within the first resistant grade is 09 miles or 15 km salt in chosen The distance from the shore In other airborne salt is carried locations salt may be can vary significantly carried much with local wind patterns inland The map below Generally locations shows the average within five to ten miles chloride concentration 9 to 18 km of salt water mg1 in rainfall across are considered at risk the United States The for chlorides in rainwater corrosion but local are primarily marine weather patterns and salts carried inland by the performance of weather patterns The above map shows This research is relevant the influence of deicing for all metals and other and marine salts types of streetlevel weather corrosive pollutants applications Please SO2 NOX H 2 S and note this is a general NH4 and particulate guideline and there damage on North American may be areas charac vehicle corrosion SO2 terized as low or high and NOX can form corrosion areas where effects sulfuric and nitric acid localized corrosion in the atmosphere and levels are different from become acid rain the level indicated Case SSINA would like to conferences One cur thank the International rent focus of IMOAs Molybdenum educational Association IMOA for is selection of providing the following appropriate grades of case studies and stainless steel for guidelines for stainless demanding architectural steel selection in applications In addition demanding exterior to these case studies environments with IMOA is providing chloride exposure architectural decision Additional case studies makers with workshops will be added to the and industry conference website as they presentations Member become available ship is broad based and Hard copes of these includes producers case studies can be consumers converters ordered from SSINA traders and assayers or IMOA Additional technical information can be IMOA coordinates found at IMOAs website promotional statistical and technical activities for the worldwide molybdenum industry Promotion of molybde IMOA num includes educat Tel 44 20 8742 2274 ing users about its Fax 44 20 8742 7345 benefits and by organ Email izing meetings and Website wwwimoainfo street level applications There is no corrosion on Deicing Salt this Type 316 bench and ModerateHigh railings in downtown Chicago after five years Urban Pollution of service A smooth LowModerate polished finish was used These Type 304 railings were corroding after one winter in Pittsburgh They are uphill from a busy highway and saltladen road mist is blown on to them The rough surface finish holds the salt on the railing making corrosion worse photographs courtesy of TMR SALT Surface contamination with URBAN salt is not limited to sites Both sites are exposed toIn many colder climates immediately beside roads moderate levels of urbandeicing salt is used to Road mist and salt pollution which does notprevent accidents contaminated airborne have an impact on salt accumu dust can carry deicing salt corrosiveness of the siteslates over time and makes significant distances fromthe environment around busy highways and as high THE and walkways much as the 12th or 13th floor of RAILINGSmore corrosive for all met adjacent closely spaced These railings are Typeals Typically deicing salt buildings Once added to 304L with a rough finishsodium chloride and the environment salt is The contractor used pipecalcium chloride deposits present throughout the with a mill finish andin cold climates can be year On building exteriors applied a rough polishheavier than the sea salt salt concentrations and over it The round bar hasdeposits found in coastal corrosion are usually a smoother finish and wasareas Both of these salts greatest between street not as badly corrodedare corrosive to architectural level and the third floor Type 304L will corrode ifmetals Salt begins to but this can vary with the exposed to deicing saltabsorb water from the air location and can require annualand forms a chloride solutionabove specific humidityand temperature levelsCalcium chloride at 00C 320F and45 humidity and sodiumchloride becomes corrosiveat 100C 500F and 76humidity Illustrated diagram of airborne road mist and contaminants being carried a significant distance from a busy cleaning to Index of Corrosion Resistance restore its appearance 35The pictured Type 304railings are approximately 30300 feet 91 meters uphillfrom a busy highway Wind 25blows deicing salt mist upthe hill and deposits it on 20the railings was not an isolated 15incident and and the 10 304 316 317L 317LMN 2205resulting corrosion are grades of stainless steelusually worse closer off after the last snowfall sheltered areas are alsoto where salt is applied of the season The use of beneficial in reducing risk Type 316 the specification of corrosion If there willTHE CHICAGO of a smooth finish rain be regular cleaning and maintenance Type 316 with rougherThe bench and railings are keep the bench and railings surface finishes to a sidewalk and attractive applications or a few feet of a busy surfaces can be usedroad where deicing salt is STAINLESS STEEL If there will not be regularused They are Type 316L SELECTION maintenance a morewith a smooth finish In applications with corrosion Type 304 Type 316L moderate deicing salt stainless steel should becontains molybdenum exposure and urban improves resistance pollution Type 316 isto pitting and crevice usually adequate if and is particularly surface finishes Ra 20helpful in preventing salt microinches or 05damage Type 316L is microns are suitable for street horizontal surfaces thatlevel applications where collect salty deposits aredeicing salt is used avoided and the if a smooth grain is vertical Designssurface finish is used and that encourage naturalsalt deposits are washed rainwashing by MOLYBDENUM STEEL INDUSTRY OF NORTH AMERICA exterior wall panels and window frames When these photos were Deicing Salt taken it had been five Moderate years since both the Type 304 window frame right Urban Pollution middle and the Type 316 Moderate wall panel right bottom had been washed Both have a smooth No 4 finish and are on the second floor of neaby buildings exposed to deicing salt in Minneapolis Minnesota The wall panel is from the Frederick R Weissman Art Museum right top The Weissman is exposed to higher levels of deicing salt than the window frame DEICING SALT chloride are used for deicing contaminated airborne dustEXPOSURE and are both corrosive can carry deicing has long cold Salt begins to absorb water significant distances fromwinters with significant from the air and form a busy highways and assnowfall Large quantities concentrated corrosive high as the 12th or 13thof deicing salt are used on chloride solution above floor of adjacent closelyroads and sidewalks to specific humidity and spaced buildings Onceprevent accidents Deicing temperature levels added to the accumulates over time Calcium chloride becomes salt is present throughoutand makes the environment corrosive at 00C 320F and the year On buildingaround roads and 45 humidity and sodium exteriors salt corrosive for all chloride becomes corrosive and corrosion are usuallymetals Road mist and salt at 100C 500F and 76 greatest between airborne dust humidity level and the third floor butcan carry deicing salt as this can vary with thehigh as the 12th or 13th Surface contamination locationfloor of adjacent closely with salt is not limited tospaced buildings Sodium sites immediately beside URBAN and calcium roads Road mist and salt Both sites are exposed to moderate levels of urban pollution which does not have an impact on the corrosiveness of the sites THE FREDERICK R WEISSMAN MUSEUM The museum is adjacent to a busy major road and bridge Road mists laden with deicing salt rise from the road and are diagram of airborne road mist and salt contamination being onto the building as high as the 12th or 13th floor of closely spaced winter The architect street with less traffic so risk of corrosion If thereFrank O Gehry recognized less saltladen road mist is will be regular the deicing salt would generated The window Type 316 with roughercreate a corrosive environ frame is badly stained by surface finishes shelteredment and selected Type corrosion Type 304 does applications or horizontal316 for the building Type not provide sufficient surfaces can be used316L contains molybdenum protection from salt corrosion If there will not be regularwhich improves resistance for this application and maintenance a moreto pitting caused by salt annual remedial cleaning corrosion resistantand crevice corrosion The after the last snowfall would stainless steel should bemuseum panels have a be required to keep these No 4 finish average window frames attractiveRa 03 microns and Cleaning quarterly wouldvertical grain orientation provide the most attractiveThe building has some surfaces butgenerally encourages STAINLESS STEELnatural rainwashing Some SELECTIONdirt accumulation was In applications withobserved on the building moderate deicing saltbut there is no evidence of exposure and urbancorrosion pollution Type 316 is usually adequate if smoothTHE WINDOW surface finishes Ra 20FRAME microinches or 05 micronsThe Type 304 stainless are specified window frame is on a surfaces that collect saltynearby building and has a deposits are avoided andsmooth No 4 finish and is the finish grain is the same Designs that above the sidewalk natural rainwashing byas the wall panels on the avoiding sheltered areas areWeissman It is on a smaller also beneficial in MOLYBDENUM STEEL INDUSTRY OF NORTH AMERICA light standards These Type 316 light poles Coastal were installed at Jones Medium Beach New York in 1967 with a smooth No 4 finish Urban Although they are in the Medium parking area immediately adjoining the beach and are exposed to coastal salt there is no sign of corrosion A similar light pole of Type 304 shown in closeup view right middle was installed in a sheltered location a few blocks from Miami Beach Florida After one year chloride corrosion is visible Samples of Type 304 and 316 with a smooth 2B finish were installed 250 meters 820 feet from mean high tide at Kure Beach North Carolina When this photo was taken they had been photographs courtesy of Nickel Development Institute in place for 56 years with only rain cleaning Like the Jones Beach light poles they illustrate the performance advantage of Type 316 in a coastal SALT can be used or a laboratory temperatures and can provide a more accurate humiditySea salt contains a mixture assessment If a laboratoryof salts including sodium is used they will need a JONES BEACHchloride calcium chloride sample that has been near AND MIAMI BEACHand magnesium chloride the test site and has not LIGHT POLESIt is carried inland by wind been washed Care must be The Jones Beach Type 316rain and fog The distance taken so that chlorides are light poles were installedsalt is carried can vary not inadvertently removed at Jones Beach New with local from the surface before in 1967 They have aweather patterns Generally testing If there is industrial very smooth No 4 within five to ten or urban pollution the level Although they are in themiles 9 to 18 km of must be determined to parking area water are at risk for assess corrosion potential adjoining the beach therecorrosion by sea salts In is no corrosion They aresome locations marine salt Evaporation and infrequent not cleaned but are are only a rain increase salt washed by rain Urbanfactor within 09 miles or concentrations on exterior pollution levels are15 km from the shore In surfaces and corrosion moderateothers salt deposits have rates Sheltered locationsbeen measured 27 miles generally have heavier salt A Type 304 light pole50 km or more inland deposits because the salt was installed within a fewSea spray and deposits of is not removed by rain blocks of Miami Beachdry salt particles can lead Humidity fog and light rain Florida in a shelteredto pitting and unsightly can dampen the deposited location It has a rough millrusting of some stainless salt and create a concen finish which was abrasivesteels trated very corrosive salt blasted Higher levels of solution on the surface salt collect on the roughThe performance of metals Salt solutions begin to form finish and in a shelterednear the site should be at temperatures above location they are notevaluated prior to material 0 C 32 F and humidity 0 0 washed away by rainselection If possible levels above 45 The There is no if there are salt most aggressive conditions cleaning A deposits on are created by high salt view is shown After onesurfaces around the site concentrations combined year chloride corrosion isPortable chloride test kits with high ambient visibleKURE BEACH a smooth surface finish suggested if the and washing to remove appear severeSamples of Type 304 and contaminants If unwashed316 with a smooth 2B some discoloration may Rough surfaces andfinish were installed occur after longterm horizontal grain lines retain250 meters 820 feet from exposure more salt and usually havemean high tide at Kure higher corrosion rates InBeach North Carolina Higher levels of molybdenum coastal locations surfaceWhen this photo was taken and chromium increase finish roughness should notthey had been in place for corrosion resistance If exceed Ra 20 microinches56 years with only rain the location appears more 05 microns unless a morecleaning Like the Jones aggressive a more highly alloyed stainless steelBeach light poles they corrosion resistant stainless is used or regular the performance may be required Chart 1 is planned of boldly shows the relative corrosion applications are moreexposed Type 316 with a resistance of Type 304 316 corrosive and require asmooth finish in a coastal and two common and more higher grade of corrosion resistant stainless unless regular cleaning is steels 317L and 2205 planned Crevices STEEL The advice of a stainless be sealed to avoid steel corrosion expert is corrosionA very smooth surfacefinish should be used and Relative Corrosion Resistance frequent washing assumed 35if Type 304 is used in amoderate coastal location 30Type 316316L is preferred 25for most coastal because 20it contains increases resistance 15to pitting caused by saltexposure In moderate 10 304 316 317L 2205coastal locations a pristine grades of stainless steel Note Determined using ASTM G48 can usuallybe maintained by MOLYBDENUM STEEL INDUSTRY OF NORTH AMERICA

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