Friday, July20, 2018


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DESIGNER stainless for coastal
and salt
LIGHT steel is not a single alloy but rather the The various types of stainless steels
are detailed in a designer handbook
name 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 by
other properties There are over 50 stainless steel grades that calling the toll free number originally recognized by the American Iron and
Steel Institute
This handbook is designed to Three general are used to identify stainless the reader with the 300 series stainless
steels particularly grades 304 and 316
steel They are
and their applications in areas where
The Unified Numbering
The AISI numbering system
200 300 400 series
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 3 by the
American Society for
Testing Materials ASTM
and the Society of Automotive
Engineers SAE to apply to
all commercial metals and
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
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 must
for 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 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 chloride 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
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 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
passive layer on the passivity range and steel There is no mechanical properties most cases it should
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
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 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 The above map shows This research is
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 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 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 street
There is no corrosion on Deicing Salt
this Type 316 bench and railings in downtown
Chicago after five years Urban Pollution
of service A smooth 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
photographs courtesy of TMR SALT Surface contamination with URBAN salt is not limited to
sites Both sites are exposed to
In many colder climates immediately beside roads moderate levels of urban
deicing salt is used to Road mist and salt pollution which does not
prevent accidents contaminated airborne have an impact on salt accumu dust can carry deicing salt
corrosiveness of the sites
lates over time and makes significant distances from
the environment around busy highways and as high THE and walkways much as the 12th or 13th floor of RAILINGS
more corrosive for all met adjacent closely spaced These railings are Type
als Typically deicing salt buildings Once added to 304L with a rough chloride and the environment salt is
The contractor used pipe
calcium chloride deposits present throughout the with a mill finish and
in cold climates can be year On building exteriors applied a rough than the sea salt salt and over it The
round bar has
deposits found in coastal corrosion are usually a smoother finish and was
areas Both of these salts greatest between street not as badly corroded
are corrosive to architectural level and the third floor Type 304L will corrode if
metals Salt begins to but this can vary with the exposed to deicing salt
absorb water from the air location and can require annual
and forms a chloride specific humidity
and temperature chloride at 00C 320F and
45 humidity and becomes corrosive
at 100C 500F and 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
The pictured Type 304
railings are approximately 30
300 feet 91 meters uphill
from a busy highway Wind 25
blows deicing salt mist up
the hill and deposits it on 20
the railings was not an isolated 15
incident and and the 10
304 316 317L 317LMN corrosion are grades of stainless worse closer off after the last
snowfall sheltered areas are also
to where salt is applied of the season The use of beneficial in reducing risk
Type 316 the specification of corrosion If there will
THE CHICAGO of a smooth finish rain be regular cleaning and maintenance Type 316
with rougher
The 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 used
road where deicing salt is STAINLESS STEEL If there will not be regular
used They are Type 316L SELECTION maintenance a more
with a smooth finish In applications with corrosion Type 304 Type 316L moderate deicing salt stainless
steel should be
contains molybdenum exposure and urban improves resistance pollution Type 316 is
to pitting and crevice usually adequate if and is particularly surface finishes Ra 20
helpful in preventing salt microinches or 05
damage Type 316L is microns are suitable for street horizontal surfaces that
level applications where collect salty deposits are
deicing salt is used avoided and the if a smooth grain is vertical finish is used and that encourage natural
salt deposits are washed rainwashing by MOLYBDENUM STEEL INDUSTRY OF NORTH AMERICA
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
DEICING SALT chloride are used for deicing contaminated airborne dust
EXPOSURE and are both corrosive can carry deicing has long cold Salt begins to absorb water
significant distances from
winters with significant from the air and form a busy highways and as
snowfall Large quantities concentrated corrosive high as the 12th or 13th
of deicing salt are used on chloride solution above floor of adjacent closely
roads and sidewalks to specific humidity and spaced buildings Once
prevent accidents Deicing temperature levels added to the accumulates over time Calcium chloride becomes
salt is present makes the environment corrosive at 00C 320F and the year On roads and 45 humidity and
sodium exteriors salt corrosive for all chloride becomes corrosive and corrosion are Road mist and salt at
100C 500F and 76 greatest between airborne dust humidity level and the third floor but
can carry deicing salt as this can vary with the
high as the 12th or 13th Surface contamination of adjacent closely with salt is not limited to
spaced 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 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 there
Frank O Gehry recognized less saltladen road mist is will be regular the deicing salt would generated The window Type 316 with
a corrosive environ frame is badly stained by surface finishes and selected Type corrosion Type 304 does applications or
for the building Type not provide sufficient surfaces can be used
316L contains molybdenum protection from salt corrosion If there will not be improves resistance for this application and
maintenance a more
to pitting caused by salt annual remedial cleaning corrosion crevice corrosion The after the last snowfall would stainless steel
should be
museum panels have a be required to keep these No 4 finish average window frames 03 microns and Cleaning quarterly
grain orientation provide the most building has some surfaces encourages STAINLESS STEEL
natural rainwashing Some accumulation was In applications on the building moderate deicing salt
but there is no evidence of exposure and pollution Type 316 is
usually adequate if smooth
THE WINDOW surface finishes Ra 20
FRAME microinches or 05 microns
The Type 304 stainless are specified window frame is on a surfaces that collect salty
nearby building and has a deposits are avoided and
smooth No 4 finish and is the finish grain is the same Designs that above the sidewalk natural rainwashing by
as the wall panels on the avoiding sheltered areas It is on a smaller also beneficial in MOLYBDENUM STEEL INDUSTRY OF NORTH AMERICA
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 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 humidity
Sea salt contains a mixture assessment If a laboratory
of salts including sodium is used they will need a JONES calcium chloride sample that has been near AND MIAMI BEACH
and magnesium chloride the test site and has not LIGHT POLES
It is carried inland by wind been washed Care must be The Jones Beach Type 316
rain and fog The distance taken so that chlorides are light poles were is carried can vary not inadvertently removed at
Jones Beach New with local from the surface before in 1967 They have a
weather patterns Generally testing If there is industrial very smooth No 4 within five to ten or urban pollution the level Although they
are in the
miles 9 to 18 km of must be determined to parking area water are at risk for assess corrosion potential adjoining
the beach by sea salts In is no corrosion They are
some locations marine salt Evaporation and infrequent not cleaned but are are only a rain increase salt washed by
rain Urban
factor within 09 miles or on exterior pollution levels are
15 km from the shore In surfaces and corrosion salt deposits have rates Sheltered measured 27 miles generally have
heavier salt A Type 304 light pole
50 km or more inland deposits because the salt was installed within a few
Sea spray and deposits of is not removed by rain blocks of Miami Beach
dry salt particles can lead Humidity fog and light rain Florida in a sheltered
to pitting and unsightly can dampen the deposited location It has a rough mill
rusting of some stainless salt and create a concen finish which was trated very corrosive salt blasted
Higher levels of
solution on the surface salt collect on the rough
The performance of metals Salt solutions begin to form finish and in a the site should be at temperatures above
location they are not
evaluated prior to material 0 C 32 F and humidity
0 0
washed away by 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 one
surfaces around the site combined year chloride corrosion is
Portable chloride test kits with high ambient BEACH a smooth surface finish
suggested if the and washing to remove appear of Type 304 and contaminants If with a
smooth 2B some discoloration may Rough surfaces and
finish were installed occur after longterm horizontal grain lines retain
250 meters 820 feet from exposure more salt and usually have
mean high tide at Kure higher corrosion rates In
Beach North Carolina Higher levels of molybdenum coastal locations surface
When this photo was taken and chromium increase finish roughness should not
they had been in place for corrosion resistance If exceed Ra 20 years with only rain the location appears more
05 microns unless a Like the Jones aggressive a more highly alloyed stainless steel
Beach 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 more
exposed Type 316 with a resistance of Type 304 316 corrosive and require a
smooth 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 corrosion
A very smooth should be used and Relative Corrosion Resistance
frequent washing assumed
if Type 304 is used in a
moderate coastal location 30
Type 316316L is preferred
for most coastal because
it contains increases resistance 15
to pitting caused by In moderate 10
304 316 317L 2205
coastal locations a pristine grades of stainless steel
Note Determined using ASTM G48 can usually

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