اسم المؤلف:
خالد حامد رشيد عبد الخالق
اسم المشرف:
ابرائيل سركيس يارو
المستخلص:
ان وجود غاز ثاني اوكسيد الكاربون ( (CO2في طبقة الماء المالح بشكل غاز مذاب تحت ضغوط عالية والمصاحبة للنفط الخام يكون حامض الكاربونيك. الحديد المطاوع يشغل المادة الاساسية في تركيب خطوط الانابيب الناقلة في الصناعة النفطية والغازية , بسبب رخص ثمنها , مقاومته | Carbon dioxide is present in water as a dissolved gas under the high pressures common in underground oil and gas reservoirs. In the dissolved state it forms carbonic acid. The primary material of construction for pipelines in the oil and gas industry is mild steel, because of its price, strength and availability. However, carbon steel corrodes in the presence of carbonic and organic acids such as acetic acid (HAc). It is therefore important to investigate the conditions in which HAc causes corrosion damage to mild steel. The extent of HAc/CO2 corrosion depends on many other variables such as : temperature, CO2 partial pressure, pH, flow regime, etc.The corrosion rates of API X65 mild steel alloy have been studied by three different techniques : i. Weight Loss Technique.ii. Potentiodynamic Polarization Technique.iii. Characterization of the Corroded Surface Techniques.i. Weight Loss Technique : A series of experiments were performed to study the effect of simulated brines solutions on the corrosion rate of mild steel with and without acetic acid. The corrosion rates of mild steel were found to be similar in simulated brines solutions and 3.5 wt % NaCl solutions. The corrosion experiments were planned to form a second - order mathematical expression using Full Factorial Experimental Design (FFED) : a - Four variables experiments (influence of temperature, solution pH, acetic acid (HAc) concentration and speed of rotation). b - Three variables experiments (influence of temperature, solution pH and speed of rotation).The results of this investigation are summarized as follows : The second - order polynomial regression analysis of the objective function (corrosion rate), using Full Factorial Experimental Design (FFED) via STATISTICA software, gave two mathematical expressions for four and three variables experiments. Arrhenius Equation and Transition State Equation were used to evaluate the activation parameters : Activation Energy (Ea), Enthalpy of Activation (?H*) and Entropy of Activation (?S*). The values of average Equilibrium Constants (K*) were also calculated at each value of average Gibbs Free Energy Change (?G), to determine the spontaneous of corrosion reaction. The corrosion rate of mild steel in presence and absence of acetic acid were increased with increasing of temperature, acetic acid (HAc) concentration and speed of rotation, but decreased with increasing of pH of solution. Multi - variable regression analysis of objective function (corrosion rate) in presence and absence of acetic acid in weight loss technique as a function of experimental variables (temperature, solution pH, acetic acid (HAc) concentration and speed of rotation), yielded two suggested mathematical expressions.ii. Potentiodynamic Polarization Technique : In this investigation a theoretical model Equation proposed by Korobove and Medvedeva Korobove and Medvedeva, [2000] was used to analyze the shape of polarization curves. The values of polarization resistance (Rp) were also obtained, these values were increased with decreasing of temperature and speed of rotation in absence and presence of the protective film formation. The polarization resistance values in absence of acetic acid are larger than the polarization resistance values in presence of acetic acid, due to the formation of the protective film.The values of mass transfer correction factor (?) were also obtained, these values will approach unity at low overpotential and it decreases as overpotential increases in presence and absence of the protective film formation. Generally, in absence of acetic acid, the values of (?) are adjacent to each other and almost unite value compare with presence of acetic acid at different temperatures and speeds of rotation due to the protective film formation as diffusion barrier is accelerated by measures that restrict the transport of reaction products from the surface.The limiting diffusion currents of hydrogen in CO2 saturated, 3.5 wt% NaCl solutions under turbulent conditions in presence and absence of the acetic acid has been correlated. iii. Characterization of the Corroded Surface Techniques : The effect of presence and absence of the acetic acid (HAc) on the CO2 corrosion of grade API X65 mild steel alloy was investigated at optimum conditions in weight loss technique (45.4 °C, pH 4.8, 2178.5 ppm HAc and 1296.6 rpm) and in absence of acetic acid (68.7 °C, pH 7.9 and 1425.8 rpm) by using analyses of protective film thickness, porosity, roughness, Vickers micro - hardness (VMH), scanning electron microscopy (SEM), computerized metallurgical optical microscopy technique (CMOMT) and X - ray diffraction (XRD). In presence of acetic acid, a porous layer (Fe3C cementite/FeCO3 siderite layer) was formed. In absence of acetic acid, a fairly dense layer ferrous carbonate (FeCO3 / siderite layer) was formed. In absence of acetic acid, the roughness and hardness of protective film were greater than that of film formation in presence of acetic acid.
