New Rapid Nondestructive Testing Method for Detecting and Quantifying with Material Property Changes Using Vipulanandan Impedance Corrosion Model

Abstract

In this study, carbon steel corrosion was evaluated in salt water solutions using the newly developed non-destructive electrical method which can be easily adopted in the field for real-time monitoring and the results were compared to some standard test methods such as weight loss, corrosion rate and potential difference. The average weight loss in 10% salt solution (accelerated corrosion and also representing the hydraulic fracking fluids) in one year was 1.05% and corrosion rate was 1.54 mm/year, using the ASTM G1 method. Vipulanandan correlation model was used to represent the weight loss versus time relationship. The potential difference between the corroding steel and standard calomel electrode in 1M salt solution reduced from -0.680 V to -0.791 V in two years, a 15% total change. The use of the new nondestructive electrical method was to detect and quantify the surface and bulk corrosion in the field. Tests were performed to first verify the best electrical property that will be highly sensitive and represent the steel corrosion. The findings from this study indicated changes in the newly developed electrical corrosion index for the surface (2D representation) and the resistivity (second order tensor, 3D representation) for the bulk material using the Vipulanandan Impedance Corrosion Model. Corrosion development in 30 inches long steel specimens were studied in the 3.5% salt solution (simulating sea water) for 500 days. The changes in the specimens were monitored at regular intervals using the new two probe method and measuring the impedance-frequency relationship using alternative current up to a frequency of 300 kHz. The surface corrosion was quantified using the new electrical corrosion index parameter, which changed from point to point on the surface of the corroding steel and the change was over 200%. The change in the bulk resistivity along the length of the steel specimen was over 40,000 times (4,000,000%) in 3.5% salt solution compared to the weight loss and reduction in the potential difference. Hence the electrical resistivity for the bulk material and the new corrosion index for the surface corrosion are highly sensing parameters for detecting and quantify the corrosion in the steel.