Seawater Corrosion Rates of Metals
Seawater Corrosion Rates of Metals.
Seawater is an excellent electrolyte. The presence of a large amount of
dissolved salts, sodium chloride (NaCl), that are ionized make it an excellent
conductor and influence the Corrosion Rates and the Corrosion resistance of metals in Seawater.
The chloride ions is particularly aggressive as it causes a breakdown of passivity causing pitting, crevice corrosion and stress corrosion cracking on most stainless steel grades.
The chloride ion is also particularly aggressive as most chloride compounds are highly soluble, which limits the formation of polarizing anodic films.
Seawater also usually contains enough dissolved oxygen for reducing water to be the prevalent cathodic reaction in most cases.
The most important factors which affect the corrosion rates of metals immersed in unpolluted sea water are dissolved oxygen, velocity, and temperature.
For low carbon steel in sea water saturated with air, i.e., with dissolved oxygen concentration of 6 ml/l, the following range of corrosion rates might be expected: from 25 mdd to 125 mdd at 25°C and velocities from 0 to 2 m/s; from 15 mdd to 75 mdd at IC and velocities from 0 to 2 m/s.
In the absence of dissolved oxygen, negligible corrosion rates can be expected between 1 to 25°C.
In general, the corrosion rates of metals in seawater are increased with (a) larger concentration of dissolved oxygen, (b) higher sea water velocities, (c) raising the temperature.
Other factors which influence the corrosion rates of metals in sea water are pH, salinity, and micro-organisms.
see also Galvanic Series Metals Seawater
Source : "Corrosion Control" NAVFAC MO-307 September 1992 / "THE EFFECT OF ENVIRONMENT ON THE CORROSION OF METALS IN SEA WATER- -A LITERATURE SURVEY"
see also
Seawater Corrosion and Material Selection
Stainless Steel Corrosion Seawater
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