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Photo Samples, Stainless Steel
Stainless steel is quite an amazing
group of alloys. Containing at least 12 %
chromium (Cr), stainless steel is by far the most widely used group
of materials within all types of "critical industry", such as the dairy and
medical businesses. Unfortunately, stainless steel is not always as
stainless as the name would suggest, and, depending upon the steel type and
the environment, corrosion may take place. And, as stainless steel is a
so-called passivating alloy, this corrosion is sometimes very decorative -
and equally expensive! As always, the photos are © Claus
Qvist Jessen. Any copying is illegal without my written permission. Should
you want to know more about stainless steel and corrosion, please check "my"
company Damstahl a/s at
www.damstahl.com. |
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One of the most common types of stainless steel corrosion, pitting
corrosion is caused by a partial activation of the steel. The result is
small pinholes, a small loss of material and a very rapid penetration.
Not a very good combination; this case is an EN 1.4301 steel (AISI 304,
18/8-steel) which has been subject to hot tap water containing 500 mg/L
chloride. © Claus Qvist Jessen |
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Pitting corrosion in an EN 1.4301-steel (AISI 304) after a simple
corrosion testing in a NaCl solution containing hydrogen peroxide (as
oxidant). Note the penetration - it took just four days! © Claus Qvist Jessen |
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Pitting corrosion caused by heat tinting from welding. Steel type
EN 1.4301 (AISI 304); all the black spots are pits - some of them
penetrating. © Claus Qvist Jessen |
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Micro section through corrosion pit in austenitic 1.4301 steel. © Claus Qvist Jessen |
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Crevice
corrosion (CC) on a stainless steel axel (acid resistant EN 1.4404 /
AISI 316L) which has been subject to natural saltwater. It looks like a
beaver has been working here! © Claus Qvist Jessen |
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Crevice
corrosion (CC) on a flange of acid resistant EN 1.4404 / AISI 316L used
for transporting natural seawater. © Claus Qvist Jessen |
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Intergranular corrosion (IGC) in a 1 inch bend (EN 1.4301 / AISI 304)
which has been subject to an unfortunate heat treatment. This process is
called sensitization, and the subsequent corrosion has been caused by
pickling acid. © Claus Qvist Jessen |
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Intergranular corrosion (IGC). Same case as above. © Claus Qvist Jessen |
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Stress corrosion cracking (SCC) in a tank made of stainless steel type
EN 1.4301 / AISI 304. The corrosion reveals itself as fine cracks and
the main cause is a high temperature (just 70 ºC). © Claus Qvist Jessen |
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Micro section through stainless steel
EN 1.4301 / AISI 304 suffering from stress corrosion cracking (SCC).
The corrosion runs from the outside (top) and in (down) and is caused by
splash from plain water combined with the heat from the 60 ºC
water inside. © Claus Qvist Jessen |
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General corrosion
(GC) caused by diluted (10-20 %) sulphuric acid. Steel type EN 1.4401 /
AISI 316L. © Claus Qvist Jessen |
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General corrosion
(GC) in a bolt made of EN 1.4301 stainless steel (AISI 304). The
corrosive environmen was pickling acid; nitric acid + hydrofluoric acid.
© Claus Qvist Jessen |
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An unusual case of general corrosion
(GC) in a pipe made of EN 1.4404 / AISI 316L. The pipe was dug into the
ground, and the corrosion was caused by electrical currents from an
electricity wire in the ground, just a few inches away from the steel
pipe. © Claus Qvist Jessen |
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