Effects of turbulent flow on the corrosion kinetics of X52 pipeline steel in aqueous solutions containing H2S

This work presents the electrochemical results obtained during the study of the corrosion of X52 pipeline steel sample, immersed in brines containing H₂S, under turbulent flow conditions. Linear polarisation resistance (LPR), electrochemical impedance spectroscopy (EIS), Electrochemical Noise (EN) and polarisation curves were used in order to determine the effect of turbulent flow upon the corrosion kinetics of the steel. It was found that flow has a considerable influence upon the electrochemical process occurring on the surface of the steel and the corrosion rate is increased.     

Corrosion study of the X52 steel immersed in seawater with a corrosion inhibitor using a rotating cylinder electrode

A corrosion study of API X52 steel was carried out in natural seawater with several concentrations of a corrosion inhibitor (10, 100 and 200 ppm) using a rotating cylinder electrode (RCE) to control the hydrodynamic conditions at environment temperature, atmospheric pressure and 24 h of the exposition time. The rotation speed used was 1000 rpm (turbulent flow). The electrochemical techniques used in the corrosion studies were: linear polarisation resistance (LPR), electrochemical impedance spectroscopy (EIS) and polarisation curves (PCs). The superficial analysis was made using a scanning electron microscope (SEM). The results show a good correlation between electrochemical techniques used. In addition, under turbulent flow, the test solution with 10 ppm had the smallest corrosion rate (CR). It is important to mention that the morphology of the corrosion in all experiments was localised corrosion.     

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 deposition of cupric ions for the determination of mass transfer rates to a stepped rotating cylinder electrode

The stepped rotating cylinder electrode (SRCE) geometry has been developed as a simple aid to the practical study of the flow-enhanced corrosion and applied electrochemistry problems commonly observed under conditions of disturbed, turbulent flow. The electrodeposition of cupric ions from an acid sulphate plating bath has been used to characterise differential rates of mass transfer to the SRCE. The variation in thickness of electrodeposited copper films has allowed the mapping of local rates of mass transfer over the active surface of this geometry. Both optical and scanning electron microscopy were used for the examination of metallographic sections to provide a high resolution evaluation of the distribution of mass transfer coefficient. Results are also discussed using the convective-diffusion model in combination with the existing direct numerical flow simulation (DNS) data for this geometry.     

Prediction models for multiphase-flow-induced corrosion of API X80 steel in CO2/H2S environment

In the offshore oil and gas industry, mainly focusing on the use of rigid or flexible pipes of subsea infrastructure applied to risers or flowlines, one of the greatest difficulties is the interpretation of the combined effects of the various correlated phenomena (hydrodynamic effects of intermittent flow, the effects of corrosivity of the environment in addition to variations in pressure, temperature, and dynamic loading). On the basis of this scenario, defining the degree of severity of each of the correlated system variables becomes of fundamental importance for establishing reliable criteria for selecting materials for subsea application. The established flow pattern directly affects the corrosion rate (or the pipe material mass loss), but the balance of other variables including possible changes in the physical and transported fluid chemical properties may increase the damage up to an order of magnitude, which is a piece of information normally not foreseen in design criteria. Therefore, to improve the understanding of the corrosion study influenced by multiphase flow, a testing loop was designed and assembled at the Corrosion and Protection Laboratory of the Institute for Technological Research, in which API X80 steel coupons were positioned in locations with a 0° and 45° inclinations. Tests were conducted by varying the partial pressure of the gaseous phase containing blends of CO₂ and H₂S with N₂ balance, mixed with the liquid phase containing light oil and heavy oil in water with salinity (NaCl)-simulating oil well conditions with 80% water cut. The main objective of this study is to establish models that can predict the corrosion intensity in conditions close to those obtained experimentally. To achieve results, the multiple regression and Box–Cox transformation methods were applied. These models will make possible damage prediction and optimization of matrix parameters for the multiphase-loop test.     

Influence of turbulent flow on the corrosion of Al‐Zn‐Mg galvanic anode in artificial seawater media

The effect of hydrodynamics on the corrosion of Al(14 wt%)‐Zn(8 wt%)‐Mg alloy in artificial seawater media at room temperature was studied in a rotating cylinder electrode (RCE) system under turbulent flow conditions. Five different rotation rates were studied: 100, 1000, 3000, 5000, and 7000 rpm. The corrosion rates were measured by electrochemical impedance spectroscopy (EIS). For the system studied, the steady‐state corrosion potential increased with increase in rotation rate. The effect of increasing the rotation rate is to increase the availability of oxygen at the surface, which in turn will polarize the corrosion reaction in the more noble direction. The corrosion rate also increases with increase in RCE rotation rate. This reflects the fact that the rate of corrosion is controlled, at least in part, by the rate of mass transfer. In this case, the effect of increase in the rotation rate on the corrosion rate is to increase the interfacial concentration of the reactant (oxygen).     

偏析对X65管线钢抗氢致裂纹性能的影响

通过LIBS-OPA-100原位分析仪、扫描电镜(SEM)、透射电子显微镜(TEM)等方法,从显微组织、硬度、偏析元素3方面研究了X65管线钢中心偏析带马奥岛(M/A)组元对氢致裂纹性能的影响,偏析与硬度以及偏析与氢致裂纹(HIC)之间的关系。结果表明:X65管线钢中C、Mn、S、Si元素在中心偏析后形成硬度较高的带状组织是导致抗HIC性能不合格的主要原因;显著的中心偏析马奥岛、铁素体带状组织和大尺寸的相颗粒析出不利于抗HIC性能;带状的马奥岛组织是氢原子的聚集场所,是导致氢致裂纹萌生与扩展的源头。     

Study on the corrosion behaviours of API X65 steel in wet gas environment containing CO2

An impingement jet system was used to study the corrosion of API X65 steel in a wet CO₂-containing environment via electrochemical tests, surface analysis technique and computational fluid dynamics simulation. The corrosion rate decreased in the wet environment compared to that in the bulk solution. When under flow condition, corrosion rate increased with the flowing velocity, especially when above the critical flowing velocity. Continuous electrolyte film was formed and electrochemical reaction started to occur in about 70% RH, and the critical RH appeared at 70–80%, above which pit size and amount remarkably increased with flow velocity.     

多相流动状态下温度对X70钢CO2腐蚀的影响

目的提高多相流动状态下温度对X70钢CO2腐蚀机理的认识。方法采用自制实验装置和挂片实验,模拟起伏管路段塞流动条件下X70钢的CO2腐蚀状态,通过电子显微镜和电化学在线监测等手段对试样表面形貌、腐蚀速率以及在线腐蚀情况进行观察和分析,侧重研究多相流动状态下温度对X70钢CO2腐蚀速率的影响。结果当温度达到90~98℃时,由于腐蚀产物膜的影响,CO2分压对腐蚀速度影响甚微,腐蚀速度降至较低水平。当温度在60~80℃之间时,腐蚀挂片表面的腐蚀状态不稳定,出现局部腐蚀或均匀腐蚀,当CO2分压较低时(如0.15 MPa),易形成均匀腐蚀;当CO2分压较高时(如0.6 MPa),易形成局部腐蚀。当温度在40~80℃之间时,随着CO2分压的增加,腐蚀速率达到最高值的温度越来越高,腐蚀速率达到最高值的温度范围一般保持在40~80℃之间。结论温度对X70钢CO2腐蚀的影响与CO2分压密切相关,相同温度下,随着CO2分压的增加,腐蚀速率增大,相应的腐蚀速率达到最高值的温度也越来越高;孤立地说某一温度值下,CO2腐蚀速率达到最高值这一说法不准确。     

The study of the La(NO;3)3 inhibition on X70 pipeline steel in 3.0(wt.%) NaCl solution

Lanthanum nitrate has been investigated as corrosion inhibitor of X70 pipeline steel in 3.0 (wt.%) NaCl solution using electrochemical techniques such as potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) in conjunction with scanning electron microscopy (SEM) and energy dispersive X‐ray detector (EDX) techniques. The results showed that La(NO₃)₃ belonged to the film‐formed mixed inhibitors, which can form a compact network over the whole surface of X70 pipeline steel. The inhibition effect of La(NO₃)₃ on X70 steel reinforced with the increase of the concentration itself. The EDX analysis showed that lanthanum ions were found to participate in the network film formed on the sample surface.