Comprehensive Analysis of Stainless Steel Corrosion Resistance in Sixteen Environments

The ability of Stainless Steel to resist atmospheric corrosion is largely controlled by the chloride content present in the air—so proximity to the sea or other chloride-pollution sources is extremely important.

Fresh water environments—such as rivers, lakes, ponds or wells—corrode metals depending on pH, dissolved oxygen, and tendency to scale.

Acidic waters (for instance those leached from ores or coal and containing free sulfuric acid or dissolved iron sulfates) are much more aggressive than natural fresh water.

In saline water environments, localized pitting is common due to breakdown of the passive film—particularly when chlorides are present. Bio-fouling and marine deposits may set up oxygen-concentration cells, accelerating attack. When stainless steel is used in high-flow conditions (for example pump impellers) the corrosion rate of suitable austenitic alloys can be very low. Good design—such as avoiding crevices and using sufficiently thick sections—also helps.

The corrosion of buried stainless steel depends on variable and complex soil conditions.

Both ferritic and austenitic stainless steels with at least ~14 % chromium content resist nitric acid well.

Standard stainless steels have only very limited application in sulfuric acid. One of the better standard grades (0Cr17Ni12Mo2) is adequate at room temperature for concentrations below ~15 % or above ~85 %.

Austenitic stainless steels are broadly used and effective in phosphoric-acid environments, sometimes at temperatures up to ~107 °C and various concentrations. Minor halide (fluoride or chloride) impurities can, however, degrade performance. Ferritic and martensitic steels are noticeably inferior in phosphoric acid service.

Stainless steels are virtually unsuitable for hydrochloric-acid service—even at ambient temperature and moderate concentrations—because the passive film cannot maintain integrity in such reducing, chloride-rich acidic environments.

Austenitic stainless steels generally resist corrosion from boric acid, carbonic acid, chloric acid and chromic acid across a broad range of concentrations and temperatures (except 100 % chloric acid). Lower‐alloy ferritic/martensitic stainless steels perform less well against chromic acid, though they may still resist boric or carbonic acid satisfactorily.

Austenitic stainless steels exhibit excellent resistance to acetic acid corrosion, even at room temperature across the full concentration range.

At ambient temperature, any common austenitic stainless steel can satisfactorily handle formic acid. However, in hot formic acid service non-molybdenum austenitic steels degrade quickly—so molybdenum-bearing grades become necessary. Martensitic and ferritic types fare poorly across temperatures in formic acid.

At room temperature and concentrations up to about 50 %, stainless steels typically show good resistance to oxalic acid corrosion. But at higher temperatures and concentrations (for example ~100 %) they may experience significant corrosion across virtually all grades.

Some austenitic grades (e.g., 0Cr18Ni9) can be employed in lactic-acid storage at moderate temperatures (up to ~38 °C).

Stainless steels typically resist mild alkalis (such as ammonium hydroxide) quite well.

Stainless steels generally offer very good corrosion resistance in many acidic salt solutions—but one must account for the effect of hydrolyzed acids formed from salts and pay special attention when chlorides or other halides are present. Under elevated temperatures, molybdenum-bearing austenitic grades outperform many others.