"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).
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).
Growth of magnetite cryslats in the grain boundaries of the inner magnetite causes compressive stresses. (ref 12).
The electrochemical reactions during the corrosion in Chloride and caustic solutions. (ref 12).
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).
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).
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).
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).
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)
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).
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).
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).
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).