Layer | Fill | Outline |
---|
Map layers
Theme | Visible | Selectable | Appearance | Zoom Range (now: 0) |
---|
Fill | Stroke |
---|---|
Collaborating Authors
Lu, Minxu
Effect of Aggressive Substance on the Nature of Corrosion Scales Formation on Super 13Cr Stainless Steel in Formate Completion Fluid
Yue, Xiaoqi (University of Science and Technology Beijing) | Cao, Hang (University of Science and Technology Beijing) | Zhang, Lei (University of Science and Technology Beijing) | Lu, Minxu (University of Science and Technology Beijing) | Ma, Lei (Petro China Tarim Oilfield Company) | Zhao, Mifeng (Petro China Tarim Oilfield Company) | Hua, Yong (University of Leeds)
Abstract The nature of corrosion scales formed on super 13Cr stainless steel surface after exposure in formate completion fluid in the presence of various aggressive substances was investigated by a combination of surface characterization techniques such as SEM/EDS, XRD, Raman, etc. The results indicated that the corrosion products mainly comprised Fe3O4 for super 13Cr exposed to KCOOH at 180°C under N2 environments. However, the addition of CO2 progressively increased the general corrosion rate, suggesting that the calculated high corrosion rates were attributed to the presence of CO2 in the system tested. The formation of FeCr2O4 and Cr(OH)3 were detected in the inner corrosion product layers and the precipitation of blade-shaped iron carbonate (FeCO3) was detected in the outer layer on the super 13Cr stainless steel surface. The results suggested that the outer corrosion product layer showed less corrosion protectiveness compared to the formation of nano-polycrystalline FeCr2O4 and Cr(OH)3 inner layers, based on its less compact and observed gaps between crystals from the SEM images. The presence of Sulfur on the metallic surfaces in both N2 and CO2 environments caused the increase in material degradation. Introduction The material such as super 13%Cr martensite stainless steel (SS) has been successfully used as tubing material for dowhole conditions based on its good corrosion resistance, low cost and excellent mechanical properties behaviour. The corrosion issues of high density brine-base completion fluids on tubing and casing materials in ultra-deep high-temperature wells have been a research hotspot in the course of oil and gas exploitation [1]. The considered competition fluids for the oil and gas industry are mainly the bromine salt completion fluids (KBr, ZnBr2, and CaBr2) [2], [3] and/or formate brines (NaCOOH, KCOOH and CsCOOH) [4]–[6]. In the past decades, one of the major issues is the localised corrosion by using bromine salts due to the presence of Br [7], [8]. It has become apparent that formate brines with filtrate viscosity and low water activities are more potential to be safe option for the deep wells (the average depth >6000 m) and also the operating temperature can be over 150 °C [6], [9]. Clarke states that the formate brines have many advantages during drilling and completion processes at temperatures up to 160°C, such as preventing the thermal degradation for the conventional drilling and completion fluid polymers [10].
Laboratory Experimental Method for Estimating Inhibition Performance of Corrosion Inhibitor for Deepwater Natural Gas Pipeline
Wang, Yun (University of Science and Technology Beijing) | Wang, Bei (University of Science and Technology Beijing) | Jia, Qiaoyan (University of Science and Technology Beijing) | Zhang, Lei (University of Science and Technology Beijing) | Lu, Minxu (University of Science and Technology Beijing) | Li, Qingping (CNOOC Research Institute) | Yao, Haiyuan (CNOOC Research Institute) | Chang, Wei (CNOOC Research Institute) | Hu, Lihua (CNOOC Research Institute)
ABSTRACT CO2 corrosion of mild steel pipeline a common problem that cannot be ignored in the oil and gas industry. At present, a big challenge is to simulate the real corrosive conditions in term of the solution chemistry within a closed system and high gas flow velocity for natural gas field in the deep water in the laboratory, and results in the traditional evaluation methods such as mass loss cannot be able to provide an accurate experimental results. In this paper, the corrosion behavior of carbon steel with/without the presence of corrosion inhibitor were tested in a high pressure and high gas velocity flow loop. The corrosion rates of corrosion inhibitor at different concentrations were monitored by high resolution inductance probe under different wall shear stress. The results show that the inhibitor efficiency can be achieved by increasing the concentration of the inhibitor, as well as the wall shear stress increases for the adsorption-type inhibitor. However, for the higher wall shear stress, due to the high baseline corrosion rate, it is impossible to reduce the corrosion rate to the ideal value even if the concentration of the inhibitor is too high. If the corrosion inhibitor is continuously injected, the inhibitor molecule can adsorb on the metal surface more quickly with the increase of wall shear stress, and the final inhibition efficiency is basically the same. Nevertheless, when the inhibitor is stopped, the desorption rate of the inhibitor increases with the increase of wall shear stress, and the inhibitor is more likely to fail. INTRODUCTION For the wet gas pipeline, especially the gas field or deep water gas reservoir in the late stage of development, the high water content is one of the common problem. Hence, in order to increase production and reduce liquid accumulation, it is necessary to adopt higher flow velocity. The injection-production gas flow rate is higher for gas storage, and it usually contains corrosive media such as energy water, sand, salt and so on. The string is also vulnerable to erosion threat. However, high gas velocity will inevitably result in high wall shear stress. In some gas fields, the wall shear stress generated by high gas velocity can reach as high as 300Pa. The high wall shear stress has great damage to the adsorption of inhibitor inside the pipeline. Especially in the process of wet gas transportation, high gas velocity greatly increases the risk of erosion corrosion in pipelines. For some inhibitors, when the wall shear stress is greater than the critical value, the inhibitor film will be destroyed by fluid. Some scholars believe that when the fluid velocity exceeds the critical value, the inhibitor will no longer work. The critical flow velocity for different inhibitors is different; in addition, the critical flow velocity under different inhibitor concentration is also different for the same inhibitor; and for different flow velocity, the best concentration should be determined through experiments. However, some scholars believe that the same inhibition effect can still be achieved if the inhibitor concentration is properly increased at high flow rate. Ortega-Toledo el al had studied the effect of flow conditions on the performance of a carboxyethyl-imidazoline as CO2-corrosion inhibitor for API X-120 pipeline steel using polarization curves, linear polarization resistance, electrochemical impedance spectroscopy under stirred conditions. The results show that for the uninhibited solution, corrosion rate increases with an increase in the rotation speed, but for the inhibited solution, the lowest corrosion rate is obtained at 500 rpm, and it increases at lower or higher rotation speeds. Ashassi-Sorkhabi et al investigated the influence of hydrodynamic conditions on the behavior of l-methionine (l-MTI) as a green organic inhibitor using mild steel rotating disc electrode. It was also found that the inhibition efficiencies for still electrode and low speed rotations did not have noticeable changes, but in much higher rotation speeds, increased efficiencies were observed. This behavior could be attributed to the enhanced mass transport of inhibitor molecules from bulk to the metal surface in high rotation rates.
- Asia > China (0.29)
- Asia > Middle East > Israel > Mediterranean Sea (0.24)
- North America > United States > Texas > Harris County > Houston (0.17)
- Research Report > New Finding (0.54)
- Research Report > Experimental Study (0.54)
- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (1.00)
- Production and Well Operations > Well & Reservoir Surveillance and Monitoring (1.00)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (1.00)
Potential Distribution and Polarization Effect of Storage Tank Bottoms With Cathodic Protection Applied by MMO-Coated Titanium Anode Grids
Cui, Wei (SRI (Beijing) Co., Ltd.) | Xu, Zhijun (University of Science and Technology) | Lu, Minxu (University of Science and Technology) | Dong, Liang (SRI (Beijing) Co., Ltd.) | Chen, Shaosong (Beijing Ankocorr Technology Co., Ltd.) | Qin, Runzhi (University of Science and Technology)
Abstract Mixed metal oxide on a titanium substrate (MMO/Ti) is widely used as anode material for the cathodic protection of storage tank bottoms due to its advantages such as low consumption rate, long service life and ideal current distribution. However, with the elapse of service time, the MMO/Ti CP systems have been found with such issues as low polarization level and uneven potential distribution, threatening the operation safety of storage tanks. In this study, numerical modeling and subscale experiment were chosen to clarify the main factors responsible for the aforementioned issues. The results indicated that the inadequacy of polarization and the lack of uniform potential distribution were related to a combination of multiple factors, including the anode-to-tank bottom distance, the impressed current level, and the number of current impressing points. On the basis of these systematic analyses, this paper, conclusively, proposes certain design principles and maintenance suggestions for the cathodic protection system of tank bottoms. Introduction Cathodic protection (CP) has been an effective method used for protecting the soil-side bottom of an aboveground storage tank (AST) from corrosion. Though amounting to only a small portion of the total cost of building an AST, the application of cathodic protection for the tank bottom enables to remarkably extend the service life of the structure and prevent revenue loss and environment contamination due to leakages, thereby having economic and societal benefits. CP has found its application to the external bottoms of AST’s for over half a century in Europe and North America, while it commenced to prevail in China only from the 1990’s. Currently, there have been a great number of international and industrial standards specifying that AST bottoms should be cathodically protected. Depending on the protection current demand, both sacrificial anode CP and impressed current CP can be used for the protection of the AST bottom, and regarding to the impressed current CP method, the anode bed can be installed in varied forms, such as distribution anode grid, shallow anode bed, inclined well anode bed, deep well anode bed, etc.
- Asia > China (0.52)
- North America > United States > Texas > Harris County > Houston (0.16)
Study on Dynamic AC Interference of High-Speed Railway on Pipelines
Zhang, Yuxing (University of Science and Technology Beijing / Institute of Advanced Materials and Technology) | Xing, Linlin (Beijing Gas Group Company Limited) | Lu, Minxu (University of Science and Technology Beijing / Institute of Advanced Materials and Technology) | Du, Yanxia (University of Science and Technology Beijing / Institute of Advanced Materials and Technology) | Jiang, Zitao (Safetech Research Institute)
ABSTRACT With the development of transportation industry, especially high-speed railway, the parallel or crossing between railway and pipelines system is increasing and result that dynamic AC interference on pipeline is becoming more and more serious. In this research work, nine segments of buried pipeline data in the presence of dynamic AC interference were collected. The data mainly included the parameters of cathodic protection and stray current interference. The trend of fluctuations in different areas was analyzed and the relevant interference parameters that include interference time, cycle, value were extracted. Based on the extracted parameters, we know the fluctuations of dynamic AC interference clearly and provide guidance for the parameters selection of simulated experiment. At the same time, a serious of indoor simulation experiments were operated to find out the corrosion regularity. Such as different dynamic current density from 30 A/m to 300 A/m, different interference time, different cycle, different simulated soil solution. INTRODUCTION With the rapid development of energy industry and transportation industry, large-scale construction of infrastructure such as AC electrified railway and buried pipeline had formed an intricate energy transportation network and spread all over the country. Due to the limitations of space resources and geographical environment, electrified railway and buried pipeline were often built public corridor in parallel for a long distance or intersected. This phenomenon was not only endangered the equipment and the personal safety of operators, but also the continuous dynamic AC interference would cause serious corrosion of pipeline. Dynamic AC interference was first found in Europe and then in South America. Two pipeline corrosions were identified as dynamic AC interference in a buried pipeline parallel to the 15 KV AC electrified railway in Germany. In China, a number of high-speed electrified railways have also found dynamic AC interference caused pipeline corrosion. With the appearance of domestic and foreign cases, the dynamic AC corrosion of buried pipeline has attracted more and more attention.
- Asia > China (0.38)
- Europe > Germany (0.34)
- North America > United States > Texas > Harris County > Houston (0.17)
- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Piping design and simulation (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (1.00)
Research on Parameter Fluctuation Characteristics and Effects on Corrosion Rates Under Dynamic DC Stray Current From Metro System
Du, Yanxia (University of Science and Technology Beijing) | Tang, Dezhi (University of Science and Technology Beijing) | Qin, Huimin (University of Science and Technology Beijing) | Lu, Minxu (University of Science and Technology Beijing)
ABSTRACT With the large-scale construction of metro systems in many cities of China, a growing number of buried metal pipelines are experiencing dynamic DC stray current in recent years. However, less work has been carried out on the effect of dynamic DC stray current on corrosion rate of steel structures. Therefore, there is a lack of consistent corrosion evaluation criterion under dynamic DC stray current in the world currently. Based on measured dynamic fluctuating parameters on buried pipelines interfered by dynamic DC stray current from metro system, the fluctuation characteristics, such as fluctuating period and amplitude were analyzed systemically. Corrosion coupons were buried near the pipelines interfered by dynamic DC stray current and connected electrically with the pipeline, and after 6 or 12 months, the corrosion coupons were dug out and corrosion rates of them were obtained by weight loss tests. The relationships between dynamic fluctuation parameters and corrosion rates were analyzed, which could provide reference for the buildup of corrosion evaluation criterion under dynamic DC stray current. INTRODUCTION In recent years, metro systems have been constructed in large-scale in many cities of China. A lot of buried pipelines close to the metro system have experienced dynamic DC stray current, resulting in corrosion problems. The corrosion of buried metal structures interfered by DC transit system has attracted attention since the late 1800s in North America. Corrosion on watermains as a result of dynamic stray current from a DC transit system was first reported by Stone & Forbes in 1894. After that, a lot of corrosion cases arising from DC transit system and investigation work have been reported in the world. For a metro DC transit system, with the moving of trains along metro line, both the position and the quantity of the stray current leaked from metro system change with time. So, the stray current activity on underground structures arising from metro system operation is not steady-state but dynamic in terms of current and potential amplitude. The stray current flowing into or out from underground structures often reverses direction. The corrosion process of steady-state DC current has been well understood, which is an electrolytic process following the Faraday’s law. However, for the corrosion behavior under dynamic DC stray current, because of the variable nature of the stray current activity, it is difficult to predict how much corrosion would occur. Although a lot of investigations have been conducted on the dynamic stray current from DC transit systems, most of the investigations focused on field measurements and mitigation methods. Only a little research work studied the corrosion behavior and corrosion risk evaluation method under dynamic DC stray current. McCollum and Ahlborn conducted a study in which iron samples were subjected to alternating and infrequently reversed current for different periods of time. The resulting corrosion was compared to corrosion produced by a steady-state DC of the same current density and discharge period. The results showed that for short periods of reversals, the corrosion was only a small fraction of the corrosion at steady state. For equal periods of pick-up and discharge, the corrosion coefficient remained below 20% when the cycle remained below one hour, which meant that the corrosion occurring from dynamic stray currents was a function of the frequency.
- Asia > China (0.95)
- North America > United States > Texas (0.19)
- Transportation (1.00)
- Energy > Oil & Gas > Upstream (1.00)
Study on the Corrosion Performance of C110 Tubing in Formate Completion Fluid at High Temperature
Li, Dapeng (Safetech Research Institute) | Zhang, Lei (University of Science and Technology Beijing) | Wang, Xiuyun (Safetech Research Institute) | Yang, Zhiwen (Safetech Research Institute) | Yue, Xiaoqi (University of Science and Technology Beijing) | Lu, Minxu (University of Science and Technology Beijing)
ABSTRACT Recently, there are several cracking and severe localized corrosion failures of API 5CT Grade C110 tubing in high-density formate completion fluid at high temperature, where the temperature up to 180 °C, with the possibility of CO2 mixed, and mechanical damage on the tubing surface. In this paper, the corrosion performance of C110 tubing is investigated in high-density formate completion fluid at 180 °C with different combinations of CO2 mixed and mechanical damage, and the initiation and growth of cracking and localized corrosion are studied by scanning electron microscopy (SEM),, X-ray diffraction (XRD) and stereo microscope, considering the formate decomposition at high temperature, aiming to clarify the corrosion mechanism of C110 tubing in high-density formate completion fluid at high temperature. INTRODUCTION The unique physic-chemical properties of high relative gravity, high temperature stability and low corrosivity make formate brines the ideal fluids. However, recently there are several severe cracking and severe localized corrosion failures of API 5CT Grade C110 tubing in high-density formate completion at high temperature, where the temperature up to 180 °C, with the possibility of CO2 mixed, and mechanical damage on the tubing surface. How could this happen? The formate brines could decompose in high temperature, especially up to 160 °C and the decomposition might lead to severe corrosion and cracking. Also it is possibly that the leakage of corrosive gas in the tubing brought about the decrease of pH and the susceptibility of corrosion and stress corrosion cracking. Moreover, the mechanical damage brings about the stress concentration and the damage of corrosion product, which result in the failures more likely happen in the damage region. Did the formate brines thermal degradation and cause the failure or the leakage of CO2 result in the severe cracking and severe localized corrosion of C110 tubing? And did the mechanical damage accelerate the corrosion degree?
- Well Drilling > Drilling Fluids and Materials > Drilling fluid selection and formulation (chemistry, properties) (1.00)
- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (1.00)
- Well Completion > Completion Fluids > Completion fluids (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (1.00)
Some Considerations on the Use of Coupon Under Stray Direct Traction Current Interference
Tang, Dezhi (Petrochina Planning and Engineering Institute) | Du, Yanxia (Institute for Advanced Materials and Technology) | liu, Jie (Institute for Advanced Materials and Technology) | Lu, Minxu (Institute for Advanced Materials and Technology) | Chen, Shaosong (Beijing Safetech Pipeline Co., Ltd.)
ABSTRACT Coupons have been widely used for cathodic protection evaluation of buried metallic pipelines. Under stray direct traction current condition, however, the application of coupon techniques faces some challenges due to IR drop errors caused by the inherent stray current which cannot be interrupted. In this work, factors affecting the measurements of coupon polarization potential in the existence of stray direct traction current were investigated through field experiments. The results showed that the measured coupon polarization potential was significantly influenced by multiple parameters, such as polarization retention period, “instant-off” potential sampling delay, coupon burial depth, coupon-to-CSE interval, and the proximity of groundbeds. Based on the experimental results, practical suggestions were proposed for improving the proper use of coupons under dynamic stray direct current interference. INTRODUCTION It has been acknowledged that buried metallic pipelines would experience accelerated corrosion, especially pitting corrosion, in the presence of stray direct traction current. Moreover, the stray direct traction current would affect the performance of cathodic protection (CP) system and shifts the CP potential applied on pipelines to deviate from the design value. The identification and evaluation of stray direct traction current interference was a research hotspot. Nowadays, the most accepted method for identification and evaluation of stray direct traction current interference was to measure polarization potential of the interfered-pipeline by coupon technology. However coupon technology faced some challenge due to the IR drop caused by the stray current which could not be controlled or interrupted during field test. Besides the measured coupon polarization potential would be affected by multiple parameters, such as polarization retention period, instant-off potential sampling delay, coupon burial depth, coupon-to-CSE interval, and the proximity of groundbeds. Unfortunately, very few literatures were available to provide practical suggestions for effective measurement of coupon polarization potential. In this work, factors that affected the measured coupon polarization potential under stray direct traction current interference were discussed and some practical suggestions were proposed.
- Asia > China (0.31)
- North America > United States > Texas > Harris County > Houston (0.16)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (1.00)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (0.89)
- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (0.86)
The Effect of Corrosion Product Formation Mode at the Early Stage of Sour Corrosion of Pipeline Steel
Li, Huixin (Institute of Advanced Materials and Technology) | Zhang, Lei (Institute of Advanced Materials and Technology) | Shi, Fengxian (Aircraft Engine Corporation of China Shanghai) | Liu, Jiancang (Goertek Inc) | Wang, Zhu (Institute of Advanced Materials and Technology) | Lu, Minxu (Institute of Advanced Materials and Technology)
ABSTRACT The rapid process at the initial stage of sour corrosion on carbon steels and the relatively low uniform corrosion rate show the change of corrosion mechanism and the effect of corrosion products over time. In this paper, the scaling mode at the early stage of carbon steel exposed to H2S environments with short exposure time were investigated. Corrosion exposure tests and linear polarization resistance (LPR) techniques were performed. The corrosion products of pipeline steel formed under sour corrosion conditions were analyzed by scanning electron microscopy (SEM), and X-ray diffraction (XRD). Based on corrosion rate and the parameters of water chemistry, solubility limits of iron sulfide (FeS) were calculated. A preferred orientation of mackinawite appeared after 30 min of immersion. After exposure for one hour, the solution supersaturated and the corrosion product began to precipitate on the steel surface. Assuming the corrosion film covered the matrix layer by layer, the thickness of FeS were calculated based on water chemistry input. There was a significant difference between the calculated result and the film thickness of the cross-section. The corrosion product layers were loose and covered the matrix incompletely at the early stage of H2S corrosion. The rapidly scaling mode derived by the experiment and theoretical works is expected to improve the understanding of the mechanism of H2S corrosion at early stage and the possibility of the nucleation of the pitting under sour conditions. INTRODUCTION Sour corrosion has become one of the most important topics during the recent decade due to demands of oil and gas industry. The rapid process at the initial stage of sour corrosion on carbon steels and the relatively low uniform corrosion rate show the change of corrosion mechanism and the effect of corrosion products over time. Numerous studies have investigated the initial stage of corrosion and the sensitivity of localized corrosion under sour conditions. Shoesmith reported that there are two types of scaling mode of mackinawite at the initial stage, one is solid-state reaction and the other is precipitation processes. Smith, Sun and Cancio have also provided data that support the direct reaction between the H2S and the steel surface. Sun proposed a plausible mechanism for H2S corrosion of mild steel and suggested that a very thin (<1 µm) but dense and protective non-stoichiometric iron sulfide film forms rapidly. Smith found that the dimensions for a tetragonal mackinawite crystal is very close to the dimensions of ferrite which means a bare ferrite surface is almost a perfect template for the nucleation of mackinawite. Bai observed that H2S corrosion begins at the grain boundary as the preferential site of dissolution. However, the understanding of the initial stage of sour corrosion and the key factors inducing pitting are still poorly understood because of the high toxicity and the rapid dissolving properties of H2S. This paper investigated the scale formation of iron sulfide at the early stage of sour corrosion. The property and structure of corrosion scales and the water chemistry of precipitated mackinawite are discussed in details.
- Asia > China (0.31)
- North America > United States > Texas > Harris County > Houston (0.17)
- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (1.00)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (1.00)
The Pitting Failure Boundary of Duplex Stainless Steel Under Sour Condition
Zhang, Ziru (Institute for Advanced Materials and Technology) | Wang, Zhu (Institute for Advanced Materials and Technology) | Xue, Junpeng (Institute for Advanced Materials and Technology) | Zhang, Lei (Institute for Advanced Materials and Technology) | Tang, Xian (Institute for Advanced Materials and Technology) | Lu, Minxu (Institute for Advanced Materials and Technology)
ABSTRACT In this paper, the pitting failure boundary of duplex stainless steel under sour condition was investigated by electrochemical and immersion tests. Polarization measurements are employed to investigate the effect of temperature and H2S on the corrosion behavior of Duplex Stainless Steel. And the pitting susceptibility is estimated by the further analysis of polarization curves and surface characterization. The results show that the pitting resistance of S31803 duplex stainless steel decreases with the increase of temperature and the H2S partial pressure. S31803 duplex stainless steel is pitting sensitive at around 85°C in 50kPa H2S, 130,000ppm Cl condition. INTRODUCTION The fast increasing energy demand has boosted the exploitation of much deeper and sourer oilgas field with high pressures, high temperatures and extreme corrosive environments, which brings potential threat of sudden material failure. The typical failure cases for stainless steels are caused by pitting and stress corrosion creaking (SCC) . Due to the higher mechanical properties and excellent general and localized corrosion resistance comparing with either austenitic stainless steels or ferritic stainless steels, S31803 duplex stainless steel is widely used in the extreme oil-gas conditions to meet the requirement for exploitation . The high pitting corrosion resistance of duplex stainless steel is related to the composition and microstructure, formed by roughly equal percentages of austenite and ferrite, which is the reason why the material is widely used in oil-gas industries . Duplex stainless steels (DSSs) are characterized by the precipitation of many secondary phases, carbides and nitrides for tempering temperatures. This phenomenon implies a high susceptibility to localized corrosion, however better than austenitic and ferritic grades. Many recorded researches and case studies have been conducted on the corrosion failures of duplex stainless steels, and most of these failures started with pitting attacks and then developed to stress corrosion cracking . Substantial efforts have been made in the past to investigate the service temperature conditions on DSS. Elsaady et al. found the resistance of the S31803 duplex stainless steel to pitting corrosion decreased with the aging temperature till 850°C. Tsai et al. found the duplex stainless steels are susceptible to SCC at ambient and elevated temperatures with chloride/sulfide environments. Oltra et al. found the cracking is not only dependent on the mechanical events but also on the effect of H2S upon the electrochemical conditions. A number of studies were devoted to the problem of high temperatures on pitting resistance of DSS. Deng et al. studied the critical pitting temperature (CPT) of S31803 duplex stainless steel in NaCl solution. Geng studied the pitting corrosion resistance in different zones of the S31803 duplex stainless steel’s weld joint and base metal was evaluated by the polarization technique in 3.5% NaCl solution at 25°C. Matteo Gastaldi investigated the effect of temperature in the range 20~60°C on the resistance to chloride-induced corrosion of low-nickel duplex stainless steel. M. Barteri studied the engineering stability diagrams of duplex stainless steels for down-hole simulated environments and investigated the sulphide stress corrosion cracking (SSCC) morphology. The critical partial pressure for the extruded and quenched materials was around 0.070.35 bar (1-5 psi) at 80°C. The standard of NACE MR0175 gave recommendations and requirements for the selection and qualification of CRAs (corrosion-resistant alloys) for service in equipment used in oil and natural gas production in H2S-containing environments. In this standard the application boundary for S31803 was T<232°C and PH2S<10 kPa.
ABSTRACT AC corrosion experiments were carried out in two kinds of typical soil simulated environments with different contents of calcium ion (Ca), magnesium ion (Mg) and sodium ion (Na) to study the effects of environmental and cathodic protection parameters on AC corrosion rates. Based on the weight loss experiments results and corrosion morphology analyses in two different environments, as well as under different CP polarized potentials and AC current densities, the difference of AC corrosion behavior in different environments and CP levels were analyzed. Besides, the effective CP polarized potentials under different AC current densities in two environments were explored. INTRODUCTION In the recent twenty years, AC corrosion problem has drawn wide attention in the international corrosion field. Many AC corrosion cases indicated that AC corrosion could occur when protection criterion was met, which means the industry accepted CP criterion was not suitable to decrease the corrosion rate to negligible level under AC interference. However, how to evaluate the corrosion risk and how to choose CP parameters to protect pipeline from corrosion under AC interference have not reached an agreement currently. One paper noted that the “conventional” -0.85 V (referenced to copper/saturated copper sulfate reference electrode, abbreviated as CSE) CP criterion was not adequate in the presence of AC interference. Based on weight loss and electrochemical measurements, the paper concluded that AC corrosion rate could be decreased to negligible level at potentials more negative than -1.15 V (CSE). Carpentiers et al. also suggested that the off-potential of the pipeline should be more negative than -1.15V (CSE). Fu et al. concluded that if AC current density was less than 30 A/m, CP polarized potential should not be positive than -0.95 V (CSE), and if AC current density was more than 500 A/m, CP polarized potential should not be more negative than -1.25 V (CSE). Xu et al. indicated that when AC current density was less than 400 A/m, AC corrosion could be mitigated well if CP polarized potential was more negative than -1.07 V (CSE). Based on the results of field measurement, Nielsen proposed that “the CP level has a dramatic influence on the AC corrosion process” and that “excessive” CP can exacerbate AC attack and thus should be avoided. The paper reported that corrosion rates gradually increased to as high as 10 mm/y at direct current (DC) about 10 A/m and off-potentials of approximately -1.10 V (CSE) (measured by electrical resistance probes over a two-week period). From the above researches, it could be seen that the published papers regarding to the appropriate CP levels in the presence of AC interference are seemingly contradictory.
- Europe (0.68)
- North America > United States > Texas > Harris County > Houston (0.17)