Ricardo Galván-Martínez

Corrosion kinetics of pipeline carbon steel weld immersed in aqueous solution containing H2S

Abstract One important challenge in the petroleum industry is reduce the problem produced by the corrosion of structures or pipeline steel caused by contact with the aggressive fluids, such as aqueous solution containing H2S or CO2. In this work, the corrosion of weldment of API X52 pipeline steel immersed in NACE solution saturated with H2S was studied. In the corrosion tests, the electrochemical techniques, polarisation curves and linear polarisation resistance were carried out in samples of API X52 pipeline steel focus in the three different zones of the weldment: heat affected zone, weld bead and base metal. In addition, a superficial analysis was made in order to identify the film of corrosion products. The temperature increment and the H2S dissolved in the NACE solution increase the corrosion rate of the three different zones. The heat affected zone was the more affected by the corrosion test and the phases mackinawite, troilite and pirrothite were identified in the film of corrosion products.

A novel experimental arrangement for corrosion study of X60 pipeline steel weldments at turbulent flow conditions

Electrochemical noise (EN) measurements were carried out to study the effect of turbulent flow conditions on corrosion kinetic of API X60 pipeline steel weld immersed in synthetic seawater. In order to control the hydrodynamic conditions, two rotating cylinder electrodes were used. The EN data were analysed by three different statistical methods: currents transients, noise resistance and localisation index (LI). On the other hand, the spectral method was used in order to get the noise impedance. The superficial analysis using a scanning electron microscopy was carried out. According to EN analyses, the current transients indicate that the aggressiveness of the corrosion increased as the rotation speed also increased. The highest corrosion rate values were obtained at turbulent flow conditions. In the superficial analysis, a localised corrosion form was found in all corrosion processes; these results are agreed with the results obtained by LI.

Electrochemical Noise Study on Corrosion of Low Carbon Pipeline Steel in Sour Solutions

Electrochemical Noise (EN) measurements for low carbon pipeline steel (X52) samples were carried out in 3.5% NaCl aqueous and NACE solutions. Both testing solutions were saturated with hydrogen sulphide (H2S) at 20 and 60 oC, under static conditions. EN data was analysed in the time domain. Parameter such as Electrochemical Noise Resistance (Rn) and Localization Index (LI) were determined from the analysis in the time domain. Also, Rn results are compared with traditional Linear Polarization Resistance (LPR) data. A superficial analysis was carried out by a scanning electron microscopy (SEM) with Energy Dispersive X-Ray analyses (EDX). A good correlation was observed among the used techniques and relevant electrochemical data related to the corrosion phenomena was obtained. According to Rn, the corrosion rate (CR) values of the steel sample immersed in 3.5% NaCl are higher than the CR of the steel samples immersed in NACE solution. The morphology of the corrosion process obtained by SEM was a localized type and this behaviour was corroborated by the results obtained by LI where these LI values are 1 or close to 1.

Electrochemical and Tension Tests Behavior of API 5L X60 Pipeline Steel in a Simulated Soil Solution

In this work electrochemical impedance spectroscopy (EIS) and slow strain rate tests (SSRT) were used for the evaluation of API 5L X60 carbon steel in contact with a simulated soil solution called NS4. EIS monitoring before and after performing the tension tests was carried out. SSRT were carried out in NS4 solution at room temperature to simulate dilute ground water that has been found associated with stress corrosion cracking (SCC) of low carbon steel pipelines. A strain rate of 1x10-6 sec-1 was used. According to the analysis of SSRT, the X60 pipeline steel is highly resistant to SCC. In order to perform the electrochemical test, two working electrodes were considered, a complete specimen, before the SSRT and a fractured specimen after the SSRT. The analyses of results show that the electrochemical response was different in each samples. The corrosion rate (CR) obtained by the two corrosion techniques revealed that the CR of the fractured specimen was higher than the CR of the complete specimen. This behavior is attributed to the fact that the fractured specimen present a high degree of tortuosity and this condition activate the corrosion process. In addition, according to the cathodic Tafel slope, the reduction reacction was influenced by a difusion process. A combine fracture type in SSRT was observed: ductil and brittle with a transgranular appearance. Some pits and internal cracks close to the fracture zone were observed. The failure process and mechanism of X60 steel in NS4 solution are controlled by dissolution and hydrogen embrittlement.

Electrochemical Characterization of the Structural Metals Immersed in Natural Seawater: In Situ Measures

This work presents the electrochemical corrosion results of the structural metals, aluminium (Al), brass and copper (Cu), immersed in coastal waters of Veracruz Port in Mexico at room temperature, atmospheric pressure and eight weeks of the exposition time. The electrochemical technique used was electrochemical noise (EN). A typical three-electrode electrochemical cell was used. Where the reference electrode was the silver/seawater (Ag/SW) and two nominally identical metallic samples were used as working electrodes (WE1 and WE2). The metallic samples of Al, brass and Cu were used as working electrode. The potential and current fluctuations were measured simultaneously between the two working electrodes (current measured) and the Ag/SW electrode (potential measured). The electrochemical noise measurements (ENM) were analysed by three different methods: Potential and current versus time (transients), Localization Index (LI) and Electrochemical Noise Resistance (Rn). The results shown a good correlation between the superficial analysis and the results obtained by the ENM. In addition, Cu presents the highest corrosion rate and, a corrosion attack was obtained by localization index; this behaviour was confirmed by superficial analysis.

Study of the Mass Transport on Corrosion of Low Carbon Steel Immersed in Sour Solution Under Turbulent Flow Conditions

A corrosion process can be influenced, in different ways, by the relative movement between the metal and the corroding environment. This relative movement can increase the heat and mass transfer of reactants towards and from the surface of the corroding metal, with a consequent increase in the corrosion rate. Also, if solid particles are present, removal of protective films, erosion and wear on the metallic surface can occur. The corrosion of the metallic structure under turbulent flow is complex, but this problem has been studied mainly in the oil industry (Garnica-Rodriguez et al., 2009; Genesca et al., 2010; Mora-Mendoza et al., 2002; Papavinasam et al., 1993; Poulson, 1993), where, the flow and some gases are very important in the behaviour of the phenomenon processes. This oil industry has processes that involve the movement of corrosive liquids in metallic structures, for example, the transport of mixtures of liquid hydrocarbons and gas with water through pipes. Therefore the influence of flow on the corrosion processes is an important issue to be considered in the design and operation of industrial equipment. This influence is complex and many variables are involved. Many observations of flowaccelerated corrosion problems have been documented (Dean, 1990; Garverick, 1994; Poulson, 1993). One aim that has been so much studied in the petroleum industry is the effect of flow and dissolved gases, such as hydrogen sulphide (H2S) and carbon dioxide (CO2). The most common type of flow conditions found in industrial processes is turbulent and according to increasing of the necessity to describe the corrosion of metals in turbulent flow conditions some laboratory hydrodynamic systems have been used with different degrees of success (Poulson, 1983, 1993, 1994). Among these hydrodynamic systems, rotating cylinder electrodes (RCE), pipe segments, concentric pipe segments, submerged impinging jets and close-circuit loops have been used and have been important in the improvement of the

The Role of Residual Stresses in Circumferential Welding Repairs of Pipelines in SCC Susceptibility

The main objective of the present study is to measure the residual stresses in the circumferential welding joints of X52 pipeline steel with multiple welding repairs, and then relate these residual stresses to study the influence on the high pH stress corrosion cracking (SCC) susceptibility. Four conditions of shielded metal arc welding (SMAW) repairs of the girth weld were evaluated. The residual stresses were measured through X-ray diffraction (XRD) on the internal side of the pipe in longitudinal and circumferential direction. Residual stresses in the circumferential and longitudinal direction reach values of about 98 and 74% of the yielding strength (360 MPa) respectively. The effect of residuals stresses in the high pH-SCC susceptibility of X52 pipeline steel was evaluated through slow strain rate tests (SSRT) in a simulated soil solution. Relation between SCC index and residual stresses on the SCC susceptibility was analyzed. Results of SCC index taking account the ratios obtained from the mechanical properties of the welding joints evaluate (containing different levels of residual stresses) showed good SCC resistance. It was observed that increasing the magnitude of residual stresses, the SCC susceptibility increases. For all the SSRT specimens the failure occurs in the base metal and heat affected zone (HAZ) interface.

Characterization of the Corrosion Kinetic of X52 Steel in Seawater with Biocides

Corrosion study of the API X52 pipeline steel immersed in seawater without biocide and with 0.25, 0.5 and 0.75 ppm of biocide, under static and dynamic (turbulent flow) conditions was carried out at room temperature and atmospheric pressure. The hydrodynamic conditions were controlled by a rotating cylinder electrode (RCE) and the rotation speed was 1000 RPM. I order to analyse the corrosion process, linear polarization resistance (LPR), and polarization curves (PC) were made. This work investigation shown that the corrosion rate is higher under turbulent flow conditions than static conditions. A localized corrosion attacks was found in the superficial analysis.

Electrochemical Characterization of the Aluminum–Copper Composite Material Reinforced with Titanium Carbide Immersed in Seawater

This work shows the electrochemical study of Al–Cu/TiC composite and Al–Cu alloy immersed in synthetic seawater. Polarization curves (PCs) and the corrosion potential as a function of the time were the electrochemical techniques used to characterize the corrosion process. A typical three-electrode electrochemical cell was used, where the working electrodes (WE) were made from Al–Cu alloy and composite samples, the reference electrode was the saturated calomel electrode (SCE) and a sintered graphite rod was used as auxiliary electrode. The electrochemical measures were carried out at atmospheric pressure and room temperature, and the total exposure time was 24 h. In addition, in order to analyze the corrosion form, a superficial analysis using scanning electron microscopy (SEM) was carried out. The electrochemical results showed that the highest corrosion rate corresponding to composite samples and the global corrosion process is a mix process, that is to say, the charge transfer resistance is limited by diffusional resistance. Pitting corrosion type was observed.

Residual Stress Assessment of Multiple Welding Repairs of Girth Welds in Pipeline Used in Oil Industry

This work presents the residual stress assessment of multiple welding repairs in the same area in seamless API X52 low carbon pipeline. Four conditions of shielded metal arc welding (SMAW) repairs and one as welded specimen of the girth weld were evaluated to determine changes in the microstructure (metal base, weld bead and heat affected zone) to evaluate their effect on the residuals stresses and mechanical properties of the welded joints. One of the mainly adverse effect of residuals stresses are in the susceptibility of stress corrosion cracking (SCC) of buried pipelines. The residual stresses were measured through X-ray diffraction (XRD). Samples were evaluated on the internal side of the pipe in longitudinal and circumferential direction. Circumferential residual stresses are greater than longitudinal stresses. Microstructural characterization of the welding joints through scanning electron microscopy (SEM) was performed. Relation between microstructure, mechanical properties and residual stresses was carried out. In general, the grain size increases with the number of repairs, and consequently there is an increase in residual stresses. Significant reduction in Charpy-V impact resistance with the number of weld repairs was observed overall in the weld fusion line. The hardness and strength increase in the first repair and in subsequent repairs decrease. As increasing the average grain size, the hardness and the absorbed energy decreases. Generally, the residual stresses showed a tendency to decrease in the first repair and after showed an increase with the number of repairs. It is clear that residual stresses depend more than the position of measurement than the welding repair number, which is directly relate with the microstructure and phases presented.