Monitoring of carbon steel corrosion by use of electrochemical noise and recurrence quantification analysis

The corrosion of carbon steel in aqueous media resulting in uniform corrosion, pitting corrosion and passivation was investigated on a laboratory scale. Recurrence quantification analysis was applied to short segments of electrochemical current noise measurements. These segments were converted to recurrence variables, which could be used as reliable predictors in a multilayer perceptron neural network model to identify the type of corrosion. In addition, an automated corrosion monitoring scheme is proposed, based on the principal component scores of the recurrence variables. This approach used the uniform corrosion measurements as reference data and could differentiate between uniform and non-uniform corrosion

Similarity Analysis of Rebar Corrosion under Different Electrochemical Accelerated Method

The concrete cover cracking caused by non-uniform corrosion of reinforcing bar is one of the most important reason for structure service performance degradation. The most widely used electrochemical accelerated corrosion methods include external and internal electrode methods. The reinforcement are used as anode in both methods. The different between two methods is the position of auxiliary. In external electrode method, the auxiliary is set outside the specimen, including three methods, i.e. samples whole/part submerged in saline, samples wrapped by sponge and steel mesh. The electrochemical mechanism of these four accelerated method were analyzed by using the FE software COMSOL. According to the corrosion products distribution characteristic along the rebar circumference, the similarity of electrochemical accelerated and natural corrosion was presented. The results indicated that, rebar corrosion with external electrode method can be regarded as uniform corrosion; the internal electrode method could result in a non-uniform corrosion after optimizing, and the orientation and distance of rebar/electrode are two major influence parameters for accelerated non-uniform corrosion. In addition, based on the corrosion electrochemical principles, a modified internal electrode method was given. The stainless wire was put into the cylinder samples parallel to the rebar as a cathode. In present study, the rapid non-uniform corrosion method can play a positive role in studying the cover cracking process of reinforced concrete

NUMERICAL SIMULATION OF NON – UNIFORM CORROSION INDUCED CRACKING

This research is focused on modeling the damage of concrete due to corrosion. The load used in this paper is only focused on the internal load due to rust expansion. In this study, corrosion was modeled uniformly and non-uniformly to investigate the difference between these two configurations to the damage in concrete. The simulation in this study was carried out using the 3DNLFEA program. The results show that numerical simulation provides predictions that are in line with experimental and numerical modeling results performed by the previous study in terms of pressure and corrosion cracking patterns. From the crack analysis, the pattern found that a non-uniform corrosion model can be used to express a realistic rust corrosion development around the reinforcement. Meanwhile, uniform corrosion requires a larger loss of steel area to reach the damage stage. Therefore, for non-uniform corrosion, the corrosion rate cause cracks and reaches a limiting crack width at earlier times in the service life of the corroded part

Training Graduate Students in Utilization of Analytical Instruments in a Failure Analysis Course

Department of Engineering Technology at University of North Texas offers a graduate course on failure analysis (MSET 5150) during spring semesters. Partial requirement for the course is for students to submit a term paper based on their collected data related to a term project. Case studies are given to groups of students to work on actual failed components received from area industries. Results of their findings are presented at the end of the semester in both oral presentation form and written term paper form followed the format of a well-established technical papers. Results of such exercises allows graduate students devote skills in using scientific instruments and practice manuscript preparations for publication. This paper presents examples of a case studies done by groups of students who worked on failure analysis of components failed in an oil and gas industry. Students developed skills in utilization of scanning electron microscope (SEM), Energy Dispersive Spectroscopy (EDS), and Fourier Transform Infrared Spectrophotometry. This exercise has proven highly effective in introducing young engineers to real world problems in oil and gas industry and help them develop skills needed in performing failure analysis and steps involved.Cockrell School of Engineerin

Identifying uniform corrosion of carbon steel using electrochemical noise measurement / Shirley Arvilla Andrew, Khaidzir Hamzah and Tammie Christy Saibin

In this study, the electrochemical noise (ECN) measurement technique was utilized to identify the uniform corrosion of carbon steels in the solutions of hydrochloric (HCl), sulphuric (H2SO4), sodium chloride (NaCl), sodium hydroxide (NaOH), potassium hydroxide (KOH) and calcium hydroxide (Ca(OH)2). ECN is the fluctuations of current and potential of a corroding system. The potential of electrochemical noise was measured between a working electrode and a reference electrode whereas the current of electrochemical noise was measured between two working electrodes in an electrochemical cell. The data from the measurements were statistically analyzed using time and frequency domains. The time domain analysis reveals the characteristics of a particular corrosion type. The frequency domain analysis estimates the power spectra at various frequencies and the statistical analysis calculates electrochemical noise parameters such as the mean, standard deviation, noise resistance (RN), coefficient of variation (CoV), characteristic charge (q) and corrosion current (Icorr). The results of the time domain analysis show that uniform corrosion only occurred in acidic solutions of HCl and H2SO4. The frequency domain analysis was found to be an unsuitable method to identify uniform corrosion in the corrosion system used. The statistical analysis shows that the corrosion rate was greater when using the solutions of HCl and H2SO4 compared to NaCl, NaOH, KOH and Ca (OH)2

Investigating the spatial development of corrosion of corner-located steel bar in concrete by X-ray computed tomography

In this paper, the chloride-induced corrosion progression of a corner located steel bar in concrete is investigated by X-ray computed tomography (i.e., X-CT). Corrosion of steel bar is accelerated by placing the reinforced specimen in a wetting and drying cyclic corrosive environment, rather than by the impressed current method. 3D X-CT images are obtained and processed to characterize the different material phases, consisting of, steel bar, mortar, corrosion products and voids/cracks. The corrosion products expansion and concrete cracking are analysed and discussed. It has been found that pitting corrosion is prone to appear around the voids close to the steel bar, mainly due to the pre-existing supply of oxygen and moisture. In addition, a distinct transverse crack has been identified which is caused by non-uniform corrosion along the reinforcing steel bar. Within the cross-section, corrosion has also been found non-uniformly distributed, with the maximum rust layer pointing to the corner edge of the sample. Moreover, the corrosion rust distributions are used to parameterize a recently developed non-uniform corrosion model. This experimentally validated non-uniform corrosion model can be applied to corrosion-induced concrete cracking problems with confirmed accuracy. The combination of the use of wetting and drying cyclic corrosive environment and the X-CT scanning can provide a new method to the non-destructive investigation of corrosion process, rust distribution and corrosion-induced concrete cracking in the reinforced concrete structures