Abstract
The influence of soil moisture content on the corrosion behavior of X60 steel in soils of different cities of Saudi Arabia (Riyadh, Rabigh and Jeddah) was investigated at ambient temperature (29 +/- 1 degrees C) using weight loss (WL) method and various electrochemical methods [open circuit potential (OCP), potentiodynamic polarization (PDP), and electrochemical impedance spectroscopy (EIS)]. Optical photographs for X60 steel surface at different conditions were obtained. It was found that WL data followed the power law kinetic relationship with a penetration factor (n) more than unity. The data of EOCP and E-corr revealed that with increasing the soil moisture content, the corrosion of X60 steel becomes under cathodic control. The EIS spectra suggested two corrosion processes. One process related to the dissolution of corrosion products formed on the metal surface and the other process related to the charge transfer process at the metal/film and metal/soil interfaces. WL, PDP and EIS measurements indicated that the corrosion rate of X60 increases with increasing the moisture content of the studied soils up to critical limit (10 wt%), then it starts to decrease with further increase of moisture content. Various corrosion patterns (general, striations, general deep pitting and channel form corrosion) were detected on X60 steel surface after prolonged immersion in the studied soils at different moisture contents. At the critical moisture content, the corrosivity of the studied soils is given in the order: Jeddah > Rabigh > Riyadh. Correlation between the soils variables and the order of soils corrosivity was achieved.