Oxides in Chloride

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08_fig17.jpg
"Iron, corroded in 0.1 n NiCl2 at 310oC. Undulating oxide is formed due to compressive growth in the outer coarse crystalline magnetite. The nickel is reduced and plated on the metal surface. Magnetite-oktaeder form on this nickel and because of the growth stresses an undulating string is formed. (foto KEMA, ref 8, 23, 61). ."
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58_11.jpg
Histogram of resistances of the steels in the KEMA database for ferrous chloride corrosion. All steels that contributed to a failure had a critical ferrous chloride value of less than 35 mmol. (foto KEMA, ref 58).
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58_12.jpg
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61_20a.jpg
Growth of magnetite cryslats in the grain boundaries of the inner magnetite causes compressive stresses. (ref 12).
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The electrochemical reactions during the corrosion in Chloride and caustic solutions. (ref 12).
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61_25a.jpg
Build-up of the stresses during the formation of magnetite in Chloride solutions. When the compressive stress exceeds the compressive strength of magnetite blistering starts. (ref 12).
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61_33a.jpg
At a critical Chloride concentration the magnetite layer cracks and fast corrosion occurs. The critical value is determined by the chemical composition of the steel according to: FeCl2 critical = 0.1 Mn + 2 P + 0.2 Cr + 0.04 Mo - 0.05. (foto KEMA, ref 12).
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2009.jpg
Typical example of the critical chloride concentration of a steel when exposed to ferrous-chloride or hydrochloric acid concentrations. When chloride concentrations are above the critical point, the weight loss increases sharply, corresponding with a laminated oxide structure. Oxide scales formed in chloride environments at 310°C. Foto a: 0.16 Mol HCL. Foto b: 0.12 Mol FeCl2. (foto KEMA, ref 58, 61).
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2013.jpg
Welded St35.8 and 14Mn4 steels tested in ferrouschloride. Only the weld material was attacked because of low resistance of the material. (foto KEMA, ref 61).
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2014.jpg
Oxide scales formed in de-aerated HCl (foto's a,b and c) and in FeCl2 (foto's d, e and f). Chloride concentrations: 0.12 mol (a and d); 0.14 mol (b end e); 0.16 mol (c and f). In the low concentration of 0.12 mol this steel formed a protective magnetite layer. At slightly higher concentrations lamination of the oxide occurred. (foto KEMA, ref 23)
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2015.jpg
Oxide scales formed in aerated HCl (foto's a,b and c) and in FeCl2 (foto's d, e and f). Chloride concentrations: 0.06 mol (a and d); 0.08 mol (b end e); 0.1 mol (c and f). In the low concentration of 0.06 mol this steel formed a protective magnetite layer in HCl and in FeCl2. In 0.08 mol chloride the FeCl2 appeared to be more agressive. (foto KEMA, ref 23).
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2017.jpg
Two different C-steels tested in ferrous chloride solutions of 3 various concentrations: 0.025, 0.05 and 0.1 Mol FeCl2. Both steels had a very low corrosion resistance (compare foto 2206 and 2207). (foto KEMA, ref 13).
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2205.jpg
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2208.jpg
Histogram of resistances of the steels in the KEMA database for ferrous chloride corrosion. All steel samples that contributed to a failure had a critical ferrous chloride value of less than 35 mmol. (ref 58).
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2212.jpg
In one of the FeCl2 experiments an oxide corrrosion crust was formed that we could not explain. Partly a blister scale was formed and partly a thick inward growing oxide layer. (foto KEMA).