Effect of Magnetic Field on the Corrosion of API-5L-X65 Steel Using Electrochemical Methods in a Flow Loop

Limited studies have been conducted on the effect of a magnetic field on the corrosion behavior of steels. Investigating the effect on pipeline material in the oil and gas industries will be beneficial regarding corrosion prediction and control. In this work, the effect of a magnetic field on the corrosion process of API 5L X65 carbon steel was investigated in a well-developed flow loop using potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS). Using permanent magnets and a well-designed corrosion electrode set-up, the corrosion mechanism of API 5L X65 steel was studied at different magnetic orientations and different flow conditions in a NaCl solution. The surface morphology of the corroded samples was studied using a scanning electron microscope, and the micro-morphologies of the corrosion deposits and the surface elemental composition were analyzed. The results show that the presence of a magnetic field increases the corrosion rate of API 5L X65 carbon steel, and that flow velocities and magnetic orientation have a significant influence on the anodic corrosion current. The results of the polarization curves indicate a negative shift in the Tafel curve, leading to an increase in the corrosion rate with the introduction of a magnetic field in the flow system. The results of the EIS show that the charge transfer rate is decreased when a magnetic field is applied. This work provides important direction in terms of the understanding of the combined effect of magnetism and flow on the corrosion in pipelines used in the oil and gas industries.

Calibration of the AC Potential Dropping System (ACPD) for Determination of Crack Growth in API 5L X65 Steel under Cathodic Protection Effect

In this work the calibration of an Alternative Current Potential Drop (ACPD) system was performed to monitore laboratory mechanical tests on marine environment under cathodic protection. The calibration was done on CT type specimens of API 5L X65 steel dimensioned according to ASTM E1820 standard., The crack propagation during a tensile test with displacement control in an ACPD equipment was monitored through the performs points collection by two channels: one that monitors the crack growth and another that monitors a region free of crack. Using a profile projector and graphical data processing and analysis software, the area of ​​the fracture surface of the specimen was meansured, which allowed to correlate a crack size with a corresponding value of potential drop and the calibration curve. In order to verify verify the efficacy and precision of the technique, step loading tests were performed on API 5L X65 steel test specimens, submerged in synthetic sea water under the overprotection potential of-1300mVAg/AgCl. The results of the calibration showed few dispersed errors, and the main factors of this dispersion may be related to the geometry of the specimen and with variations in current flow density, which is influenced by corners and edges and by the presence of pick-up inductive. The calibration and its effectiveness can be verified through the results of the tests in marine environment, presenting crack lengths close to the actual values, confirming the effectiveness of the ACPD technique.