Electrochemical and thermodynamic study on the corrosion performance of API X120 steel in 3.5% NaCl solution

Abstract

The present work studied the effect of temperature on the corrosion behavior of API X120 steel in a saline solution saturated with co 2 in absence and presence of polyethyleneimine (pei) as an environmentally safe green inhibitor. The effect of PEI on the corrosion behavior of API X120 steel was investigated using destructive and non-destructive electrochemical techniques. The overall results revealed that PEI significantly decreases the corrosion rate of API X120 steel with inhibition efficiency of 94% at a concentration of 100 μmol L −1. The adsorption isotherm, activation energy and the thermodynamic parameters were deduced from the electrochemical results. It is revealed that the adsorption of PEI on API X120 steel surface follows Langmuir adsorption isotherm adopting a Physichemisorption mechanism. Finally, the samples were characterized using scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques to elucidate the effect of aggressiveness of corrosive media on the surface morphology and the corrosion performance of API X120 steel. The surface topography result indicates that the API X120 steel interface in PEI presence is smoother than co 2 with cl − ions or cl − ions only. This is attributed to the compact protective film limits the aggressive ions transfer towards the metallic surface and reduces the corrosion rate. Moreover, PEI inhibition mechanism is based on its co 2 capturing ability and the PEI adsorption on the steel surface beside the siderite layer which give the PEI molecules the ability to reduce the scale formation and increase the corrosion protection due to capturing the CO 2 from the brine solution. High strength low alloy (HSLA) steels are widely finding its applications in oil & gas industry, thermal power plants and in aerospace industry etc. due to its improved mechanical properties, superior corrosion resistance and weldability when compared with plain carbon steel 1-4. Series of comparative studies have been focused on HSLA pipelines steels in order to understand the effect of alloying elements, heat treatments and other changeable factors on their mechanical properties and microstructure 5-8. it has been reported that the yield strength of the API X120 steel is in range 780-951 MPa based on the shape of the specimen. Moreover, the tensile strength is varied from 940 to 1023 MPa and the strength is more than X120 ksi and reaches to X120 grade according to the API standards 9-11. Corrosion is the major problem that compact the API X120 steel pipelines in the transportation of oil, gas. There are a myriad number of studies that investigate the influence of carbon dioxide with saline solution on the corrosion mechanism of different grades of steel pipelines employed in the pipeline applications 12,13. Additionally, it has been reported that the presence of carbonate ions in oilfield brine solution increases the corrosion rate of the pipelines 14-16. Several parameters have been noted for the corrosion of steel in CO 2 environment such as PH, temperature, CO 2 pres...

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