الفهرس 
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Abstract
The produced petroleum oils from Oilfields are generally associated with formation waters which are distinguished by its high salinity and contained high percentage of chlorides and other soluble salts. These waters are responsible for the corrosion of most steel structures in the petroleum industry. In our present study we are concerned with the electrochemical behavior of the steel alloy in the formation waters which delivered from different areas in the western and eastern desert in Egypt.
Two different types of steel samples, which utilized in the pipeline manufacture, were used in our experimental studies. On the other hand, six formation water samples were under test, three from the eastern desert and the other three from the western desert.Our study was divided into three parts. In the first part the Open Circuit Potentials (OPC) were measured against standard calomel electrode (SCE). The OCP was found to be about (-) 580 mV, at the beginning of immersion and then shifted towards negative direction of the potential due to the aggressive action of sodium chloride which leads to corrosion simulation. The potential decreases after three months to values ranging between (-) 710 and (-) 650 mV for samples delivered from western desert and to values between (-) 690 and (-) 660 mV for that delivered from eastern desert.
After the second three months, the OCP shifted to more negative values due to the formation of oxide film on the steel surface, which increases the resistance of the anodic surrounding area.
After nine months, the potential shifts to more positive values (still negative values) ranging between (-) 390 mV and (-) 475 mV for both deserts. This sudden shift is explained by the breakdown of the oxide film (passive layer) which protects the metal surface from corrosion and then after the oxide layer fragmentized completely, the corrosion starts again. The variation in the OCP from cathodic to anodic and vice versa, explains the active behavior of the corrosion at the interfacing layer between the metal and solution. In the second part, we studied the variations of the weight loss for the two coupons corresponding to the time of immersion. The obtained data showed three stages, the first was characterized by the increase in weight loss by time, the second clarified sharp decrease in weight loss by time, and the third stage revealed sudden increase in weight loss.
In the third part of the study, the measurements of the potentiodynamics were completely carried out and the obtained data clarified that the coupons immersing for long time leads to rapidly corrosion and formatted Fe (OH) 2 which responsible for the corrosion rates. Therefore, one important reason for the increasing of corrosion rate value attributed to the initial formation of pits on the surface of the steel.