270

Increases in temperature also tend to increase the corrosion rate. For example, an increase in temperature of 10°C will tend to double the corrosion rate. Such effects are, however, not universal as increasing the temperature of a solution affects the concentration of gases dissolved in solution, notably oxygen. Increased corrosion rates are the result of increased mass transport, which for oxygen reduction controlled reactions, occurs at about 80°C [20].

Solution velocity effects the corrosion rate of metals by affecting the rate of mass transport of species to and from the reaction sites and also by affecting the stability of passive films. In addition, increased flow rates affect whether or not corrosion products remain at the anode/cathode sites, thereby affecting the ability of subsequent electron transfer processes. Oldfield and Todd [21] proposed the following equation to predict the corrosion rate of mild steel in flowing seawater:

D0.75

Corrosion rate (mm/y) = 1.17 x 1(T2 C02 U0 9 -, (11.12)

v where CO2 = concentration of oxygen, ppb U = flow rate, cm/s D = diffusion coefficient, cm2/s v = kinematic viscosity, cm2/s

0 0

Post a comment