Corrosion form

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1 Academic Year 2018-2019 Master of Science in Energy Engineering CORROSION AND MATERIAL PROTECTION Prof. A. Brenna Exercise #3 1) A coated carbon steel pipe (diameter 10 cm; wa ll thickness 3 mm) is electrically connect to a copper grounding network (about 50 cm2). Calculate the corrosion rate of a coating defect of the pipe (1 cm2) considering an oxygen content of 2 ppm (clay soil) and 5 ppm (sandy soil). Calculate the perforation time of the pipe. 2) Calculate the throwing power of a galvanic anode used to protect the external corrosion of a carbon steel pipe in the following conditions:  Bare pipe protected by a magnesium anode in aerated soil ( = 40 ·m; 5 ppm of oxygen);  Coated pipe protected by a magnesium anode in aerated soil ( = 40 ·m; 5 ppm of oxygen; coating efficiency = 99.5%);  Submarine coated pipe protected by a zinc anode ( = 0.25 ·m; i = 1 mA/m2). The throwing power ( Lmax) can be calculated as follow: i ELmax   2 The driving force ( E) is 150 mV for zinc anode and 700 mV for magnesium anode. 3) A localized corrosion attack occurred in the centre of a stainless steel plate grade AISI 304 L (PREN 18). The anodic area (the pit) can be estimated in 1 cm2. The oxygen limiting current density is 50 mA/m2.  How the current will flow in the electrolyte?  Evaluate the corrosion penetration rate in the following conditions o Fresh water (resistivity 20 ·m) o Seawater (resistivity 0.2 ·m) The throwing power ( L max, m) can be calculated as follow:    1050 2    i. E L pit max Where E is in mV, pit is in m,  is in ·m and i is in mA/m2. 4) A 20 m long pipe made of AISI 304 stainless steel (18% Cr, 10% Ni; 0.1% N) shows a localized internal corrosion attack (1 cm 2), located at the bottom of the pipe. Pipe diameter is 10 cm; wall…