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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.

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

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

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

Micro section through corrosion pit in austenitic 1.4301 steel.  Claus Qvist Jessen

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

Crevice corrosion (CC) on a flange of acid resistant EN 1.4404 / AISI 316L used for transporting natural seawater.  Claus Qvist Jessen

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

Intergranular corrosion (IGC). Same case as above.  Claus Qvist Jessen

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 C).  Claus Qvist Jessen

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 C water inside.  Claus Qvist Jessen

General corrosion (GC) caused by diluted (10-20 %) sulphuric acid. Steel type EN 1.4401 / AISI 316L.  Claus Qvist Jessen

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

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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