From the results of Case I and Case II, it can be roughly concluded that SYMADEC has advantages in dealing with complicated polarization curves under the effect of AC, due not only to that it is robust but also to that it can reveal more information about the anodic and cathodic reactions by deconstructing the curves. Despite the results of SYMADEC are remarkable, more polarization data still need to be studied to furtherly validate its effectiveness. Therefore, two more sets of polarization curves subject to AC that have been presented in different published literatures were also treated by SYMADEC and the results were compared with their originals. One set consists the polarization curves of X60 pipelinesteel immerged in a simulated soil solution under the condition of AC densities of 50 and 100A/m 2 .  The other involves the polarization curves of X70 pipelinesteel tested in 3.5wt% NaCl
In this work, the coupling effect of stress and stray current on corrosion of X80 pipelinesteel was investigated in soil-simulating solution by open circuit potential (OCP) and corrosion potential test, potentiodynamic polarization measurement and surface characterisation technique. A mathematical relationship between corrosion rate and yield strength, direct current (DC) stray current density was obtained through multiple linear regression. The results indicate that, the corrosion potential of X80 pipelinesteel with and without superimposed DC stray current all shift negatively, and the corrosion rate increases with the enhancement of tensile stress in solution. Moreover, the above laws become increasingly obvious with DC stray current density form 0.5 to 3.5 mA/cm 2 . Comparing with the stress, the effect of stray current on corrosion rate of X80 pipelinesteel is more significant in elastic deformation. Mutation in corrosion potential and corrosion rate appeared when the strain reaches plastic deformation. This study provides important recommendations for pipeline safety design and operation, where the corrosion enhancement due to the coupling effect of stress and stray current should be considered.
Pipelinesteel has been used in the transport of petroleum, petrochemicals, natural gas and water supplies. Due to different service environments, there is always a temperature gradient across different pipe sections, which has a great influence on corrosion behavior[2-4].A previous study has indicated that temperature has an obvious influence on the limiting diffusion current density. With increases in temperature, the concentration of oxygen and thermal motion of molecules change a lot, which are key factors in corrosion behavior. Yuan has suggested that high temperature increases the corrosion activity of the steel and affects its reaction kinetics. In this work, polarization curve and electrochemical impedance spectroscopy(EIS) measurements were used to analyze the influence of temperature in the range of 20~95℃ on X65 steel.
inhibitor for API X-120 pipelinesteel has been evaluated by using electrochemical techniques. Techniques includes polarization curves, linear polarization resistance, electrochemical impedance spectroscopy and electrochemical noise measurements, whereas the rotation speed were 0, 250, 500, 1000 and 2500 rpm. Different techniques show that for uninhibited solution, the corrosion rate increases with an increase in the rotating speed, but for the inhibited solution, the lowest corrosion rate is obtained at 1000 rpm, but it increases with a further increase in the rotating speed. Electrochemical noise measurements shows that in absence of inhibitor, the steel is susceptible to uniform corrosion, whereas when the inhibitor is present, the steel is highly susceptible to localized type of corrosion.
Buried pipelines steels for oil and gas transport suffer near neutral pH SCC in their external surfaces. API (American Petroleum Institute) steel grades ranging from X52 to X100 were worldwide used that exhibit the classical ferrite + pearlite microstructures to complex constituent microstructures. Advances in alloy design technique and the adoption of new controlled rolling processes leads to a new generation of pipelinesteel with higher strength and toughness. Fine-grained acicular and bainitic microstructures and most recently martensitic microstructures were developed by rapid cooling after controlled rolling. In the present work the hydrogen effects under stress as by products of the corrosion mechanisms in NS-4 solution, related to microstructural factors of a recently developed microalloyed pipelinesteel were studied. Involving Polarization Curves (PC), Electrochemical Impedance Spectroscopy (EIS) and Slow Strain Rate Testing (SSRT). Hydrogen embrittlement cracking mechanisms were identified in both rolling directions. Some evidence seems to indicate that the HELP (Hydrogen Enhanced Local Plasticity) mechanism is present. This mechanism interacts with several steel ferrite types promoting hydrogen ingress minimizing their mechanical properties.
The experimental material was commercial X52 pipelinesteel with the microstructure of typical ferrite and pearlite. The chemical composition of X52 is listed in Table 1. The specimens for the hydrogen permeation experiments were 55-mm-diameter plates with a thickness of 0.7 mm. The plates were then subsequently ground with 300, 600, 800, and 1200 grit silicon carbide paper. Specimens (10 mm ×10 mm× 3 mm) for the wet H 2 S corrosion tests were pre-treated in a manner
trend removal has to be applied over an average baseline as previously established . It has been demonstrated that the noise signal contains information about the dynamics that occur on the surface of the electrode, giving information about the type of corrosion that is occurring, either uniform or localized. Thus, the aim of this work is to study the performance of a simple organic compound, carboxyethylimidazoline, as an H 2 S corrosion inhibitor of API X-120 pipelinesteel by using different
High-temperature and high-pressure electrochemical measurement techniques, scanning electron microscopy and X-ray diffraction were applied to investigate the effects of the corrosion product films formed on the surface of L360NCS pipelinesteel at different temperatures on the hydrogen permeation and the corrosion rate in high pressure H 2 S environments. The results indicate that hydrogen
The variation of the topsoil pH value in the X70 steel surface was studied under the AC corrosion process. The cyclic voltammetry technique was employed to investigate the AC action mechanism on the X70 pipelinesteel in a soil environment. The results show that the alternating current has a great effect on the surface soil pH value. The corrosion mechanism of a metal suffered AC interference in an alkaline environment is that the AC changes the polarization potential and reduces the pH value of the surface soil. The coupling potential of the mixed alternating and direct currents presents a periodic oscillation in the electrode surface, which destroys the passivation of the X70 steel. The electrode surface is covered with a large amount of Fe (OH) ads, when the potential is in the range of the active dissolution potential of the X70 steel. In this condition, the hydroxides and oxides will form preferentially. In a different charge transfer process, the hydroxide, as the inhibitor of the passivation film, has an important impact on the metal corrosion. The increase of the corrosion rates is under the control of the transfer process.
This paper aims at exploring the electrochemical role of carbonate in driving the corrosion reactions in aerated solutions. Different from the conventional solutions prepared for SCC tests, no bicarbonate was introduced in order to understand corrosion from narrower chemistry perspectives. If the electrochemical results in this paper are combined with future SCC studies’, the already determined role(s) of the environmental factors on the electrochemistry of cracking steels would alleviate the difficulty of analyzing the results. API-X100 is a new pipelinesteel of special alloying element content (table 1), and is being considered in some new projects for its high strength, but its corrosion resistance is a new research subject and this paper serves this respect.
Commercial X70 pipelinesteel manufactured by BlueScope Steel Ltd, with the nominal composition given in Table 1, was received in the form of transfer bar and strip. Simulations of coarse-grained heat affected zone (HAZ) and normalising of transfer bar (950°C, 20 minutes) were carried out using tubular furnace with either quenching or slow cooling, respectively. The details are available elsewhere . Electrolytical charging of 1 mm thick samples was carried out at a current density of 50 mA/cm 2 in 1M H 2 SO 4 with 250 mg/L of NaAsO 2 .
The surface coverage characteristics of the pseudo anaerobic corrosion inhibi- tion of pipelinesteel in petroleum pipeline water in the presence of various con- centrations of Brassica oleracea and Citrus paradise mesocarp extracts were cal- culated using Equation (3). The results obtained are presented in Figure 6 and Figure 7. Sel vi et al. ,  previously reported that inhibitors act by separating metal surface from the corrodent covering its surface. The surface coverage of BO and CPM extracts increased with increase in their concentrations. This trend must have resulted from the availability of more inhibitive phyto molecules which covered the surface of pipelinesteel as concentration increased. The dras- tic increase in surface coverage from concentration of 0.00 g/l to 0.2 g/l of both extracts further confirms the effectiveness BO and CPM as corrosion inhibitors. The result of weight loss data with time can be related to the kinetics of corro- sion. Figure 8 and Figure 9 present the plot of log(W − W 1 ) versus time (weeks)
Abstract: With the continuous development of urban city, more and more subway lines are applied in the urban rail transit systems. During the daily operation of metro, the insulation performance between running rails and earth is gradually decreased. Thus, the stray current is generated at where the current flows out of the running rail. Stray current leakage and the corrosion caused by it are not negligible negative effects. Stray current corrosion will cause severe electrochemical corrosion to the metallic structures in and around the subway system, such as buried pipelines, running rails and concrete reinforcement etc. In view of the current situation of buried pipelines being affected by stray current corrosion, this paper starts with the stray current corrosion experiment of X20 pipelinesteel. The experimental system was built up to simulate the stray current corrosion on the buried metallic pipeline. Electrochemical measurements including Tafel method and electrochemical impedance spectrum (EIS) were conducted in this study. Based on the measurement results and microscope morphology, the electrochemical corrosion process of X20 steel was discussed in detail Then the equivalent circuit model of the corrosion system was fitted and analyzed. It was found that the Nyquist plot of X20 corrosion system shows the characteristics of double capacitive reactance arc, and the corrosion system can be equivalent to a R s (CPE pore R pore )(CPE dl R ct ) model. Finally, the stray current corrosion in the subway was
For all electrochemical experiments, an Autolab Potentiostat (PGSTAT20 computer controlled) operated by the general purpose electrochemical software (GPES) version 4.9 was used to perform the electrochemical experiments. The open-circuit potential (OCP) of the API X65 pipelinesteel was measured versus time for 1350 min. The cyclic potentiodynamic polarization curves were obtained by scanning the potential in the forward direction from -1.200 V to 0.250 V against Ag/AgCl at a scan rate of 0.003 V/s. For the back scan, the potential was reversed in the backward direction at the same scan rate in order to understand the possibility of the occurrence of pitting corrosion. Chronoamperometric current-time experiments were carried out by stepping the potential of the steel samples at – 0.50 V vs. Ag/AgCl for 4000 sec. The electrochemical impedance spectroscopy (EIS) tests were performed at corrosion potentials (OCP) over a frequency range of 100 kHz to 100 mHz, with an ac wave of 5 mV peak-to-peak overlaid on a dc bias potential, and the impedance data were collected using Powersine software at a rate of 10 points per decade change in frequency. All experiments were carried out at room temperature in a cell contains 100 ml of the freely aerated stagnant NaCl solutions.
The selected samples for the examination are summarized in Table 1. They were provided by the institute of Venezia Technology, Italy. Two specimens were cut from the field service samples [called, Ragusa and Pakistan] and four samples (VETEC J55, X65 samples 1, 2) were prepared in the laboratory with two different conditions, as will be described in the next section 2.2. Samples are made in Steels X65 (pipelinesteel) and J55 (casing steel). The chemical compositions of the steels are presented in Table 2. Specimens are squares 20 x 20 x 3 mm. Substrates were polished up to P600 grade and degreased with acetone.
The specimens were cut from hot-rolled plate of API X80 pipelinesteel. The chemical composition of the steel is (wt%): C 0.070,Si 0.216, Mn 1.80, P 0.0137,S 0.0009,Mo 0.182,Cr 0.266,Cu 0.221, Ni 0.168, Nb 0.105, Al 0.026, Ti 0.013, V 0.001, N 0.003 and Fe balance. The microstructure of the steel is mainly composed of polygonal ferrite, acicular ferrite and a number of granular bainites (Fig.1).
Figure 3 shows the polarization curves of X100 pipeline steels under three different simulated soil solution environments. It is obvious that the polarization curves have similar shapes and two inflection points a and b are present. The portion of the polarization curve above the point a is characterized as the anodic polarization, and the portion below the point a belongs to the cathodic polarization. In the a-b section, the cathodic potential shifts negatively and the cathode current density is quite stable. At this time a large amount of electrons are accumulated on the cathode which strengthens its polarization and protects the metal. When the potential is negative to point b, the cathodic current density increases sharply and the magnitude of negative shift of the cathode potential is not large. Hydrogen bubbles appear on the surface of the pipelinesteel which is not conducive to metal protection.
Along with the advent of the fourth industrial revolution, the processing capacity of "big data" is highly demanded in industry community. Compared with the traditional computing and programming model based on serial program, parallel computing is based on heterogeneous architecture and runs in a completely different way from CPU, which has greatly enhanced the processing speed of large-scale data sets. Therefore, parallel computing has been developing dramatically in recent years, and has been favored by all walks of life. In the future, large-scale data processing must belong to parallel computing. Set on LAMMPS (large-scale atomic/molecular massively parallel simulator) as an example, this paper described the technique of establishing parallel computing platform, and applied it on simulated test on fracture process of lamellar structure from gas-pipelinesteel.
All electrochemical characterizations were carried out in an electrochemical cell with 4 electrodes arrangement as is shown in Fig. 1. The working electrode (WE) was a rod X52 pipelinesteel. A steel surface area of 0.5 cm 2 was mechanical grinding using emery papers of grade 180, 240, 500 and 600 to obtain a flat, homogeneous and clean X52 steel surface. A rod graphite as auxiliary electrode (AE) and saturated calomel electrode (SCE) as reference electrode (RE) were used.
the simulated soil solution. The changes in the corrosion potential of the X80 pipelinesteel in the different solutions were not obvious and ranged from −800 mV to −700 mV (vs. SCE). By contrast, the anodic polarization curves varied greatly and showed passivation to different degrees. When the HCO 3 – concentration was 0.072 mol/L, the anodic polarization curve exhibited active–passive