Corrosion in different environments

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1 Academic Year 2018-2019 Master of Science in Energy Engineering CORROSION AND MATERIAL PROTECTION Prof. A. Brenna Exercise #5 1) A coated carbon steel pipe in soil (6 ppm of oxygen) is interfered by a DC non-stationary source. What are the electrochemical reactions corresponding to the anodic and cathodic zones? Corresponding to the anodic zone, a positive potential shift of 50 mV with respect to the free corrosion potential has been measured. Calculate the corrosion rate in the anodic zone. 2) A marine concrete structure is subjected to chloride penetration. The surface chloride content (Cs) at the tidal zone is 5% by cement weight. This is the most critical zone to the simultaneous presence of chlorides and oxygen. Concrete cover and chlor ide diffusion coefficient are 40 mm and 10-12 m2/s, respectively. Calculate the corrosion initiation time considering a critical chloride content of carbon steel reinforcements of 0.4 % by cement weight. Chloride penetration at distance x from the surface and at time t can be calculated by means of the analytical solution of second Fick’s law, valid in non-stationary condition:        tD2 xerf1CC sx z erf (z) z erf (z) 0 0 0.85 0.7707 0.025 0.0282 0.9 0.797 0.05 0.0564 0.95 0.8209 0.1 0.1125 1 0.8427 0.15 0.168 1.1 0.8802 0.2 0.2227 1.2 0.9103 0.25 0.2763 1.3 0.934 0.3 0.3286 1.4 0.9523 0.35 0.3794 1.5 0.9661 0.4 0.4284 1.6 0.9763 0.45 0.4755 1.7 0.9838 0.5 0.5205 1.8 0.9891 0.55 0.5633 1.9 0.9928 0.6 0.6039 2 0.9953 0.65 0.642 2.2 0.9981 0.7 0.6778 2.4 0.9993 0.75 0.7112 2.6 0.9998 0.8 0.7421 2.8 0.9999 3) A reinforced concrete structure is exposed to an industrial atmosphere. The carbonation coefficient (K) is 5 mm·y-1/2. Calculate the initiation time considering a concrete cover of 25 mm. Carbon dioxide penetration…