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The development of a Mechanistic-Chemometrics model with multi-degree of freedom for pitting corrosion of HP-13Cr stainless steel under extremely oilfield environments
Abstract
A multi-degree of freedom mechanistic-chemometrics model for predicting the pitting damage of HP-13Cr stainless steel is developed by combining the mechanistic models and chemometrics method. The mechanistic model is reconstructed by considering the effect of single factors, such as high temperature, high CO2 pressure, flow rates and complex stress distribution. The single mechanistic models are combined together considering the weight coefficients of variable interaction using the chemometrics method. Finally, the predicted results are validated by six-year-served field data, which indicates that the newly developed mechanistic-chemometrics model is accurate and highly reliable.
... In the liquid phase, CO2 and H2S dissolve in the solution to produce the corrosive ions, including HS − , S 2− , CO3 2−, and HCO3 − ions [36,37]. The cathodic and anodic reactions in the solution are as follows [38]. ...
... In the liquid phase, CO 2 and H 2 S dissolve in the solution to produce the corrosive ions, including HS − , S 2− , CO 3 2−, and HCO 3 − ions [36,37]. The cathodic and anodic reactions in the solution are as follows [38]. ...
The material selection of injection gas wells in acid gas flooding is the bottleneck of the successful implementation of the technical scheme. Through standard and literature research, the materials of the wellhead, wellbore, and packer for reinjection well in acid gas flooding are preliminarily established, and then the suitable materials are further screened by using the weight-loss and surface characterization method. Finally, a new type of packer is designed to optimize the wellbore material. The results show that 35CrMo (CR = 0.0589 mm/y) steel is used for wellhead materials, 625 alloy steel is selected as the sealing surface, and 625 or 825 alloys (with CR ≤ 0.0055 mm/y) steel is used for wellhead sealing material. The main material of the packer is 718 Alloy (with CR ≤ 0.0021 mm/y). The cost of T95 steel within 20 years (1263 ten thousand yuan) of service is much smaller than that of G3 alloy (1771 ten thousand yuan), but after 30 years of service, its cost is close to that of G3 alloy. A kind of downhole packer for acid gas reinjection is designed. Among them, G3 alloy steel tubing is used between the packer and the relief valve, T95 steel tubing is selected above the packer and below the safety valve, and the packer is set in the G3 steel tubing. The serious pitting corrosion of T95 steel in the liquid phase environment is due to the uneven deposition of FeS and FeCO3 on the steel surface.
... Hakon (Leth-Olsen, 2004) found that the formation of the corrosion product scales on 13Cr SS in formate fluids did not act as an effective barrier against corrosion, showing high-corrosion rates after several weeks of exposure, and the surface was covered by nonuniformed crystalline FeCO 3 , especially at 180°C (Leth-Olsen and others, 2005). Although the formation of the FeCO 3 layer plays a dominant role in retarding the corrosion rate, the corrosion resistance of S13Cr SS corresponds to a complicated corrosion product scales formation and evolution process, and that the amorphous/nanocrystalline inner layer provides better corrosion protection than outer FeCO 3 precipitation 21-25 under the ultradeep well conditions [temperatures beyond 180°C (Zhao et al., 2018;Yue et al., 2020aYue et al., , 2020bYue et al., , 2020cZhao et al., 2021a)]. The systematic study on the formation and evolution of the corrosion product scales on the S13Cr SS surface immersed in a formate fluid under HTHP condition, especially with the presence of aggressive substances such as sulfide or CO 2 is rare. ...
The formation and evolution of the corrosion scales on the super 13Cr stainless steel (SS) surface after exposure in a formate completion fluid with the presence of various aggressive substances was investigated. The results indicate that the formation of Fe 3 O 4 covered the surface of super 13Cr SS as the inner layer accompanied with outer scattered FeS. The corrosion rate was below 0.07 mm/year after 120 h of exposure in the formate fluid at 180°C under N 2 environments; the presence of aggressive substances such as sulfide and CO 2 in the formate fluid promoted the proceeding of anodic dissolution in the early period, and the ingress of CO 2 progressively increased the general corrosion rate to 1.7 mm/year. For CO 2 -containing conditions, the formation of FeCr 2 O 4 and Cr(OH) 3 was detected in the inner corrosion product layers, and the precipitation of “sheet”-shaped iron carbonate (FeCO 3 ) was detected as the outer layer. The accumulation rate of corrosion products increases by two orders of magnitude with the ingress of CO 2 , corresponding to thicker corrosion products, but the dissolution rate is still three orders of magnitude higher than when CO 2 was absent.
... Material degradation is one of the main issues within the EOR production systems where casting, pipelines, or tubing suffer severe corrosion attacks due to the extreme environments in terms of high CO 2 pressure beyond 28 bar, temperatures of 182-225 • C, and chloride contents beyond 80,000 ppm [3,4]. Due to these environmental effects, stainless steels (SSs) have been considered for such aggressive environments based on their good corrosion resistance. ...
This paper focused on the corrosion behaviour of 15Cr stainless steel in deep/ultra-deep geological environments. The relationship between corrosion products and general/localised corrosion under various Cl⁻ concentrations at 200 oC and 28.5 bar pCO2 were systematically investigated. The results indicate that high Cl⁻ content of 81 000 ppm promoted the general/localised corrosion via precipitation of the chloride-rich products, which retarded the formation of nanocrystalline NiFe2O4 and decreased the corrosion resistance. The corrosion products consisted of outer FeCO3 and inner NiFe2O4/FeCr2O4/Cr(OH)3 in a low Cl⁻ content of 29 503 ppm. The characterisation of the corrosion products is combined with thermodynamics calculations.
... And the stress and strain distribution and K are updated after every time step. The calculated pitting depth of HP-13Cr SS depending on time with tensile stress and stress-free conditions is shown in Fig. 20, which is consistent with the literature and field date [54]. ...
The stress corrosion cracking of HP-13Cr stainless steel in the geothermal environment was studied by experimental measurements and modeling calculations. The stress corrosion cracking susceptibility of HP-13Cr stainless steel increases with both temperature and CO2 pressure, and shows a synergistic effect greater than the temperature or CO2 pressure does singly. The fracture morphologies presented quasi-cleavage fracture characteristic in the geothermal environment. The stress corrosion cracking mechanism is dominated by the anodic process. The critical stress intensity factor for stress corrosion cracking was measured and the pitting-to-cracking process was clarified by a mechanism model.
The prediction models of pitting corrosion lifetime for martensitic stainless steels (MSSs) with different N contents were developed by statistical approach. The modelling and experimental results show that after N-alloying, the metastable pit initiation time was dramatically improved, and the transformation from metastable into stable pitting was retrained, which resulted in the increase of overall stable pit initiation time from 0 to 419.05 and 459.84 days with 0.15 and 0.41 wt.% N addition, respectively. Afterwards, N significantly restrained the growth of stable pits. The present models reveal the mechanism of how N influences each stage of pitting corrosion.
The influence of chloride ion concentration in the pitting behavior of 309L cladding used in nuclear power plants has been investigated in-situ by potentiodynamic polarization and morphology observation using microscale electrodes and ex-situ 2D and 3D geometrical characterizations. The results indicate that the concentration of chloride ion affects not only the pitting potential but also the geometry of the pit. The effects of lowering the chloride ions concentration are to enhance the pit growth in depth rather than width. An extremely low chloride ion concentration (0.001 mol/L) cannot give rise to “normal” pitting corrosion but to a transpassivation-induced pit. The related mechanisms are also discussed.
In Well MJ4, Tarim Basin, the testing tubing string is 6617 m long and the bottom-hole pressure during the testing is 101.63 MPa. During the completion job, plastic deformation occurs in the tubing string, so it is very necessary to figure out at which stage of the completion job plastic deformation occurs on earth. For this reason, the three-dimension finite element analysis method was used to perform numerical calculations for the deformation of tubing string and the distribution of axial stress based on three typical load conditions (setting load, fracturing load, and well testing load of Well MJ4); a process for calculating the mechanical behavior of a completion and testing tubing string containing an expansion joint was then developed. The study content mainly includes: (1) A criterion was developed to determine the extension and closure status of the expansion joint in the tubing string; corresponding calculation mechanism and formulae were provided; and the extension–closure status of the expansion joint in the tubing string for Well MJ4 was calculated. (2) A method was developed for analyzing and calculating the additional pressure difference load in the packer annulus caused by poor engagement of the hydraulic anchor; the impact of the additional pressure difference load on the deformation behavior of the tubing string was simulated; and the significant impact of the additional pressure difference load on the plastic buckling deformation was figured out. (3) The limit of lateral buckling deformation in a calculation model was introduced, and so the impact of collar rigidity on the buckling deformation was indirectly considered; the deformation under the joint action of all loads of the tubing string was calculated, and the numerical result was the same as the observed deformation. The study results show that the plastic deformation of the tubing string for Well MJ4 occurs at the fracturing stage and the major causes are hydraulic pressure loads and gravity loads in different forms. The conclusion shows that the mechanical calculation model of the testing tubing containing the expansion joint can be used as an important theoretical tool and analysis approach in optimizing operations and designing the tubing string structure. Keywords: Completion tubing string, Well testing, HTHP, Plastic deformation, Buckling, Numerical simulation, Expansion joint
A new prediction model for pitting corrosion damage considering both pit initiation and pit growth was presented. The pit initiation was modeled based on a combination of the Sridhar model and Macdonald model, and the critical potential was redefined at the same time. The pit initiation time can be divided into the time in which the open circuit potential (OCP) exceeds the repassivation potential (Erp), and the pit induction time, when OCP > Erp. The pit growth was modeled using the Markov process and extreme value statistics were used to describe the maximum pit depth distribution. If the time–consuming pit initiation process is neglected, it results in unacceptable errors in the pit growth kinetics parameters obtained. Thus, an acceleration method, the pre-initiated pits method, was developed to eliminate this negative effect. The proposed model was validated using experimental data on the pitting corrosion of 304 stainless steel (SS) and reproduces the experimental observations with high fidelity.
Compared to the traditional one-by-one method, a new high-efficiency method is used to characterize large numbers of regulations varying samples. Accordingly, bump-shaped electrodes are designed using the computational fluid dynamics model, and the effect of the height and placement of these electrodes is discussed. The experimental feasibility is certified by weight loss measurement. Results indicate that flow velocities of different bump-shaped electrode surfaces are significant differences. Thus, each surface can be analyzed independently; the thickness loss of each electrode surface is consistent with that using one-by-one method, which can effectively improve the experimental efficiency 12 times.
The nature of corrosion scales formed on HP-13Cr stainless steel (HP-13Cr SS) in the extremely aggressive environment was investigated by means of microstructure characterization and high-temperature-high-pressure electrochemical measurements. The results of these studies indicated that the precipitation of Cr(OH) 3 is the dominating factor affecting on the formation of corrosion scales, and its effect can be categorized based on two compromising aspects. On the one hand, Cr(OH) 3 precipitation contributed to the increase of scales thickness. On the other hand, it inhibited the precipitation of FeCO 3 due to the hydrolysis of Cr 3+. Because of these reasons, the corrosion scales undergo significant microstructural changes, i.e., from monolayer (95 ℃/2.8 MPa) to bilayer (120 ℃/3.2 MPa and 150 ℃/3.6 MPa), then to single layer (180 ℃/3.8 MPa). Therefore, the corrosion-resistance performance of corrosion scales decreased with increasing temperature and CO 2 pressure, wherein the decreasing pitting potential and repassivation potential accompanied with the increasing density and diffusivity of acceptor in the scales.
The influence of rotation speed on the scale film and pitting mechanism of HP-13Cr SS in high temperature (>180 °C), high salinity (Cl⁻ concentration >60,000 mg/L) and high CO2 pressure (>4 MPa) oilfield environment was investigated using surface analysis and electrochemical techniques. The results delineated rotation speed decreased the mechanical properties and volume fraction of the amorphous Cr(OH)3(s) of the scale film. As a result, rotation speed increased the both nucleation susceptibility and growth probability of pitting, the serious pitting corrosion occurred and the geometry changed to shallow-disk shape.
Numerical modelling of the effects of different applied load levels on the growth of metastable single pit in stainless steel is the subject of the present work. A cellular automata model integrated with finite element analysis is used, taking into account both the electrochemical reactions during metastable pitting growth process and the real-time influence of local stress/strain distribution at pit surface on anodic dissolution. Specifically, in the current work the impacts of uniaxial load levels on pitting corrosion for various conditions of passive layer degradation extents and hydrogen ions diffusion coefficients are quantitatively assessed in terms of current transient. For a general condition with uniaxial applied load level increases from 0 MPa to 250 MPa, the ascending trend of current transient and current density transient is observed due to the increase of plastic strain accumulation at pit bottom, revealing the enhancement of metastable pit growth rate. Meanwhile, the critical magnitude of load level enabling metastable pitting to alter into the development of stable pit for each condition is discussed and predicted.
In this paper, the overall corrosion damage process is modelled sequentially using cellular automata (CA) to describe the localised corrosion component, and finite element analysis (FEA) to account for the mechanical component resulting from the stress concentration effect of the corrosion defect (pit). Synchronous execution of the CA and FEA, and provision of feedback between both provides a good approximation of stress-assisted pit development. Qualitative and quantitative comparison of simulation results with experimental measurements show good agreement. In particular, the model shows that mechanical effects, notably plastic strain, accelerates the rate of development of localised corrosion.
The reactivation of a corrosion pit under the synergetic effect of strain and electro-chemical polarisation has been observed in a type 304L stainless steel using X-ray computed tomography. The pit reactivation process was associated with the formation of a new pit, directly adjacent to a pre-existing pit. Pit growth kinetics were estimated, revealing an increase of the diffusivity parameter (Deff ΔC) from 3.0 × 10⁻⁸ mol.cm⁻¹.s⁻¹ to 4.5 × 10⁻⁸ mol.cm⁻¹.s⁻¹ with the application of strain, indicating higher metal dissolution rates. Applied strain resulted in fractured lacy metal covers, and its effect on pit growth kinetics is discussed.
In this paper, a self-built device called “full-scale tubular goods corrosion test system” was used to test a 6 m length super 13Cr tubing (with coupling) to study its corrosion performance in spent acid. The specimen fractured at the tubing and was investigated by visual inspection, optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), and mechanical test. It was the joint function of tensile force (78.6% actual yield strength), inner pressure (70 Mpa) and spent acid that induced stress corrosion cracking (SCC) of the tubing at 120 °C. Three different areas were found on the fracture surface, including crack initiation area, crack expansion area, and final fracture area. The fracture initiated from the “X” shape corrosion cracks which were evolved from small corrosion pits. The reduction of ductility and toughness may also facilitate SCC of the tubing.
An empirical formula derived from two sets of field data on tubing corrosion gives a satisfactory description for two different oil fields of the influence on corrosion of the API gravity ofthe oil and its watercut. A remarkably good level of agreement was found between predicted corrosion rates using this formula and field corrosion measurements. It reproduces the general concept that heavier oils are more protective than light ones, and that very light oils give hardly any protection at all. It also reflects the likelihood of various modes of corrosion associated with competitive wetting of the steel by water and oil arising from different modes of water entrainment. The link between API gravity, emulsion stability and water wetting of steel by an oil-water mixture is provided by considering the changes in interfacial tensions in the oil-water-steel system.
The degradation of passive film on carbon steel in concrete pore solution under tensile and compressive stresses is studied using electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) techniques. As the applied stress increases, the corrosion potential and impedance of the samples decrease. When the same stress magnitude is applied, under compressive stress the samples show more negative corrosion potentials and lower impedance values than those subjected to tensile stress. Two different modes for the failure of the passive film are proposed: tensile stress creates micro-cracks perpendicular to the surface, while compressive stress induces de-bonding of the interface between the passive film and the substrate. Thus, compressive stress produces more severe degradation of the passive film than does the tensile stress.
A predictive model for pitting corrosion in buried pipelines is proposed. The model takes into consideration the chemi- cal and physical properties of the soil and pipe to predict the time dependence of pitting depth and rate. Maximum pit depths were collected together with soil and pipe data at more than 250 excavation sites over a three-year period. The time dependence of the maximum pit depth was modeled as dmax = K(t-t0) v, where t is the exposure time, t0 is the pit initiation time, and K and v are the pitting proportionality and exponent parameters, respectively. A multivariate regression analysis was conducted with d max as the dependent variable and the pipeline age, and the soil and pipe properties as the indepen- dent variables. The dependence of K and v on the predictor variables was found for the three soil textural classes identi- fied in this study: clay, clay loam, and sandy clay loam. The proportionality parameter K was found to be primarily influ- enced by the redox potential, pH value, soil resistivity, and the dissolved ion concentrations. In contrast, the pitting exponent v was found to be influenced mainly by the pipe-to-soil poten- tial, water content, bulk density, and the pipe coating type. A real-life pipeline integrity assessment is used as a case study to illustrate the application of the proposed model and to show how it can have a positive impact on integrity management programs.
The influence of metallurgical defects and residual surface stresses generated by polishing on the pitting susceptibility
of duplex stainless steels was studied by combining macro- and microelectrochemical measurements with thermal-mechanical simulation
and metallography tests. It has been shown that pits initiate in both phases at metallurgical point defects (such as oxide
inclusions in the ferrite and dislocation lines in the austenite). By contrast, the surface stress state was the driving force
for pit initiation along the austenite/ferrite interface. Experiments at the macroscale revealed that this process represents
about 40% of the total number of pits observed. It has been demonstrated that the local stress gradient was the key-parameter
in pit initiation and that the local average stress was the parameter governing the transition from metastable to stable pitting.
One of the main challenges in oil and gas wells is ensuring wellbore and casing integrity in a CO2 saturated brine environment. The integrity of a well casing relies on its mechanical properties and corrosion resistance to harsh downhole conditions. This paper discloses the results of a mathematical modeling study and experimental investigation conducted to understand the corrosion behavior of carbon steel (AISI 1045 Medium Carbon steel) in CO2 saturated brine.
Corrosion experiments were carried out at 0.83 MPa varying temperature and CO2 partial pressure (CPP). To prepare test fluid, 1 wt % NaCl was added to deionized water and thoroughly mixed. The Weight loss (WL) and Linear polarization resistance (LPR) techniques were employed for investigating corrosion. A comprehensive corrosion model is formulated to predict corrosion in a CO2 environment containing high-salt concentration.
Results indicate a strong impact of temperature on CO2 corrosion in brine environment. At low CPPs (PCO2 ≤ 0.41 MPa), the pick corrosion rate was noted at 43 °C. Furthermore, the influence of NaCl content on corrosion was strongly affected by CO2 concentration. The model is predominantly in agreement with existing corrosion measurements and it predicts the inhibiting effect of salt in CO2 corrosion.
TG-201 inhibitor could minimize corrosion of HP-13Cr SS in the process of live acid. Moreover, it accelerated the probability of serious corrosion of SS during the well completion. The failure mechanism of TG-201 inhibitor was investigated using surface analysis and electrochemical measurements. TG201 inhibitor contains amounts of Cu²⁺, which would acquire the electrons prior to H⁺ to form Cu film. The failure mechanism was due to the synergistic effect attributed to the Cu film. Cu film promoted the formation of the occluded cell and the changes of fluid state evoked by the increase in interfacial roughness during the well completion.
The soil corrosion of widely applied galvanized steel structures, such as power transmission towers, must be considered to prevent harm to their structural integrity and to mitigate the high costs associated with early failure. A full two-level factorial design was used to evaluate the relative significance of various influencing factors on the underground corrosion of hot-dip galvanized steel. Experiments were performed in simulated soil solutions. The effects of temperature and the concentrations of chloride, sulfate, bicarbonate and citric acid were evaluated using statistical analysis of the results. Using analysis of variance, temperature, citric acid and chloride were found to be individually significant. Also, temperature/citric acid and temperature/chloride significantly interacted to increase the corrosion rate. The lead-in pencil electrode technique was used to further evaluate the impact of the above mentioned factors on the dissolution behavior of the Zn coating. The results revealed that chloride and citric acid affect salt film formation at the pit bottom, while temperature alters the dissolution kinetics by changing the diffusion coefficient of the dissolving Zn(II) species. Moreover, the effect of bulk solution dissolved oxygen concentration on the corrosion rate of the galvanized steel was modeled. It was found that oxygen concentration does not have a dominant effect on the overall corrosion behavior of galvanized steel. Rather, the effect of temperature is dominant.
The evolution and characterization of films formed on super 13Cr at 90 °C and 200 °C were investigated by Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), X-Ray Photoelectron Spectroscopy (XPS), Focus Ion Beam (FIB) and Transmission Electron Microscopy (TEM) and localized Raman spectroscopy. The results show that super 13Cr maintains a passive state at 90 °C, while an active state exists with a high corrosion rate of 0.43 mm/year at 200 °C for the first 5 h, then stabilizes to a rate of 0.125 mm/year over 5 days exposure. The passive film formed at 90 °C is an amorphous-like structure with high Cr content, while the corrosion product films formed at 200 °C are mainly comprised of nanocrystalline spinel FeCr2O4 and crystalline FeCO3.
This study investigates the corrosion performance of X65 carbon steel at elevated temperatures (up to 250 °C) and CO2 partial pressures (up to 28.5 bar pCO2). A detailed appraisal of how the corrosion products can protect against general and localised corrosion is presented. The morphology and chemical composition of corrosion products were determined using various microscopic and spectroscopic techniques, with localised corrosion rates being determined by surface profilometry. An increase in temperature or reduction in CO2 partial pressure favours the formation of a protective magnetite layer. It is thermodynamically more stable and more protective than iron carbonate in these conditions.
This work investigates the effects of hydrogen and stress on the electrochemical and passivation behaviour of 304 stainless steel in 0.5 M sulfuric acid with 2 ppm sodium fluoride. Three major results are revealed: hydrogen and stress significantly increase the critical current density (icrit) and passive current density (ipass); hydrogen has a more obvious impact on icrit than that on ipass; a high synergistic effect between hydrogen and stress on current densities is observed at the intermediate hydrogen charging current densities range.
Corrosion in complex coupling environments is an important issue in corrosion field, because it is difficult to take into account a large number of environment factors and their interactions. Design of Experiment (DOE) can present a methodology to deal with this difficulty, although DOE is not commonly spread in corrosion field. Thus, modeling corrosion of Ni-Cr-Mo-V steel in deep sea environment was performed in order to provide example demonstrating the advantage of DOE. In addition, an artificial neural network mapping using back-propagation method was developed for Ni-Cr-Mo-V steel such that the ANN model can be used to predict polarization curves under different complex sea environments without experimentation. Furthermore, roles of environment factors on corrosion of Ni-Cr-Mo-V steel in deep sea environment were discussed.
The long-term shifts of corrosion potential are important in predicting the likelihood of localized corrosion and stress corrosion cracking (SCC) of carbon steel used for storing radioactive wastes in underground storage tanks. Although considerable work has been done in understanding the passivity and corrosion potential of steel in various electrolytes, an important aspect of the current work is in assessing the effects of multiyear exposures of steel in waste simulants and their effects on corrosion potential. It is shown that SCC susceptibility of steel in nitrate increases at the long-term corrosion potential in solutions without organics (either by applying that potential or letting the corrosion potential increase over time). The long-term increase in corrosion potential results principally from a decrease in the passive current density with time of exposure. The present work shows that such a reduction in passive current density is accompanied by changes in the semi-conductive properties of the passive film, which itself may be a result of changes in stoichiometry of the film over time. Nitrite reduction is the most likely cathodic reaction with a small contribution from oxygen reduction. However, the presence of organic species in the environment can result in additional anodic reactions that may decrease the corrosion potential.
https://doi.org/10.1016/j.corsci.2017.07.003
The failure mechanisms of corrosion inhibitors in highly turbulent flow remain a disputed topic. In the present study, corrosion experiments of X65 pipeline steel were performed with an imidazoline-based corrosion inhibitor using a high-shear turbulent channel flow cell, which included a flow disturbance in the form of a small protrusion. Localized corrosion was observed at the protrusion that could be mitigated with an excess inhibitor concentration. It was found that wall shear stress (up to 5000 Pa) was not the cause of inhibitor failure. The flow acceleration at the leading edge of the protrusion caused a drop in pressure and led to cavitation, with bubble collapse further downstream. This was the main cause of inhibitor failure and localized corrosion. The observed behavior was interpreted in terms of corrosion inhibitor adsorption/desorption kinetics and the associated activation energy analysis.
Frequent corrosion failures occurred on single well gathering lines in a section of the Tahe oilfield. The corrosion failures were investigated by means of experimental lab testing and numerical simulation. The electrochemical test results showed that the corrosion of the pipelines were controlled by two different mechanisms, which were influenced mainly by excessive dissolved oxygen (DO), higher temperature, lowered flow velocity and increased water cut. One mechanism was influenced by the excessive DO concentration and the higher temperature of injection water near the pipe entrance region. The corrosion rate noticeably increased at the entrance at a high temperature until DO was exhausted. The other mechanism resulted from the oil-water separation due to decreased flow velocity at the terminal climbing pipe sections. The change in flow led to the suspended particles being deposited, which caused under-deposit corrosion. The statistical analysis of the field corrosion data supported the two corrosion mechanisms.
The corrosion behavior of metal is closely related with its polarization behavior in a corrosive solution. The polarization behavior is also useful for understanding pitting corrosion or stress corrosion cracking in particular. Stainless steel was adopted as the testing material in the experiment reported in this paper, and the anodic polarization curves were measured under various constant loads applied on the specimen in 3% NaCl solution. The pitting initiation potential, passivity, passivity maintaining current, the change in roughness of specimen surface and the difference in pitting corrosion depth were also measured. Study materials, methods and results are discussed.
Response surface methodology (RSM) is introduced into corrosion research as a tool to assess the effects of environmental factors and their interactions on corrosion behavior and establish a model for corrosion prediction in complex coupled environment (CCE). In this study, a typical CCE, that is, the corrosion environment of pipelines in gas field is taken as an example. The effects of environmental factors such as chloride concentration, pH value and pressure as well as their interactions on critical pitting temperature (CPT) were evaluated, and a quadratic polynomial model was developed for corrosion prediction by RSM. The results showed that the model was excellent in corrosion prediction with R
2 = 0.9949. CPT was mostly affected by single environmental factor rather than interaction, and among the whole factors, chloride concentration was the most influential factor of CPT.
A new Markov stochastic process is developed for the description of the growth with time of maximum pit depths in pitting corrosion systems. The Markov model is fully operational with the determination of two parameters, λ and κ, that constitute the corrosion system paameters. Also described is an experiment that was undertaken to determine these characteristics for a specific pitting corrosion system. With their determination, the stochastic model predicts the future time evolution of the probability distribution describing the maximum pit depths. In this way, a new method of describing pitting corrosion, in general, is established.
The influence of chloride ion concentration on the passivation film and corrosion product film of martensitic stainless steels (SS) (13% Cr, modified 13% Cr-1% Mo, modified 13% Cr-2% Mo, and 15% Cr SS) have been investigated using immersion tests and electrochemical measurements in sweet environments at temperatures of 150 degrees C and 180 degrees C in the presence of carbon dioxide (CO2). The corrosion rate of conventional 13% Cr SS was found to increase with increasing chloride ion concentration at 150 degrees C. However, the corrosion rates of modified 13% Cr SS and 15% Cr SS were independent of the chloride ion concentration at 150 degrees C. The corrosion rates of modified 13% Cr SS increased with increasing chloride ion concentration above 1,000 ppm at 180 degrees C. The corrosion rate of 15% Cr SS slightly increased at high chloride ion concentration at 180 degrees C. Chromium-enriched corrosion product films were produced on all alloys considered, except for 15% Cr SS, at 180 degrees C. A passivation film was maintained for 15% Cr SS at 180 degrees C. In addition, the pitting corrosion behaviors were investigated by potentiodynamic polarization curves and open-circuit potential measurements. The behavior of the current density of anodic curves corresponded to the immersion test results. Pitting corrosion on modified 13% Cr-2% Mo SS is considered to repassivate because of low potential compared with pitting potential.
The Tazhong area, at the center of the Tarim basin, western China, contains abundant hydrocarbon resources, principally in Ordovician carbonate reservoirs. The geological conditions for hydrocarbon accumulation in the area are quite complicated and are characterized by multiple stages of hydrocarbon generation, accumulation, adjustment and alteration. Despite decades of exploration and production in the region, the mechanisms of hydrocarbon accumulation and their controlling factors are still not well established. The geological setting and the distribution characteristics of the reservoir, have been used to investigate the mechanisms of accumulation, to quantitatively describe the main controlling factors, and to predict potential favorable hydrocarbon accumulation zones in Ordovician carbonate rocks of Tazhong. Our results show that the hydrocarbons in the Ordovician reservoirs came from mixed sources including middle-lower Cambrian and middle-upper Ordovician source rocks within the Majiaer Sag. Four stages of accumulation are recognized and hydrocarbons migrated into the Tazhong area along six intersections of NE and NW fault sets, principally from the northeast to the southwest but then, locally, from the northwest to the southeast. The Ordovician carbonate reservoirs are typically lithologically defined and the dynamic force of hydrocarbon accumulation is primarily reflects differential capillary forces. The accumulation and distribution of hydrocarbons was controlled by the petrophysical properties of the reservoir and by hydrocarbon supply/charge energy. The petrophysical properties of the reservoir controlled the hydrocarbon accumulation threshold with the maximum differential capillary pressure force, on average, approximately 13 MPa. The supply or charge energy of the hydrocarbons controls the accumulation distribution range. The daily production of individual wells decreases with increasing distance from the fault intersections and the maximum hydrocarbon migration distance is about 35 km. Reservoir properties and the hydrocarbon supply/charge Energy coupling Index (REI) appear to control hydrocarbon accumulation and distribution. Accumulation does not occur when the value of REI is <= 0.6, but is favored when values are higher.
The effects of applied tensile and compressive stresses and surface finish on pitting susceptibility, hence stress corrosion crack initiation of 34CrNiMo6 and 26NiCrMoV145 steam turbine disk steels were studied in an aerated wet steam environment. Four-point bend specimens and scanning electron microscopy (SEM) was used. 34CrNiMo6 is more susceptible to pitting than 26NiCrMoV145. Testing time influences the degree of pitting on differently machined surfaces. Pitting susceptibility increases with increasing applied tensile stress.
The focus in this paper is on the effects of multiphase flow on CO2 corrosion of mild steel pipelines. The significance of mass transfer in turbulent flow is discussed first: (i) when an increased rate of mass transfer of corrosive species, such as H+ ions, to the steel surface leads to an acceleration of the cathodic reactions and a higher corrosion rate and (ii) when an increased mass-transfer rate of the corrosion product, ferrous ions (Fe2+), away from the steel surface makes it harder to form protective ferrous carbonate layers. The mechanical interaction of the flow with the pipe walls is discussed next, where the wall shear stress is often blamed for removal of protective surface layers, such as iron carbonate or inhibitor films. Using macroscopic as well as atomic scale measurements [atomic force microscopy (AFM)], it was found that it is very unlikely that truly protective surface layers can be removed by mechanical forces alone. The other multiphase flow effects on corrosion, such as the effect of condensation on the top of the line corrosion (TLC) in wet gas pipelines, the effect of water settling and wetting in oil-carrying lines, and the effects of sand on erosion–corrosion and underdeposit corrosion in production pipelines, are outlined at the end.
We study the corrosion performance of Cr bearing low alloy pipeline steel (Cr3MoNi) in CO2 saturated formation water, under both static and flowing conditions. Cross-sectional morphologies of corrosion scales at progressively increased test duration are observed by scanning electron microscopy. The characteristic of the corrosion scales are investigated by energy dispersive X-ray spectroscopy and X-ray diffraction. Our results show that the corrosion rate of Cr3MoNi steel at flowing condition is higher than that of static condition, and the degree of Cr enrichment in the scales at flowing condition is also higher. Flow also makes ions distribute evenly in the solution close to the specimen, leading to a uniform distribution of Cr compound in the amorphous corrosion scales. In this way, flow suppresses the presence of the potential pits and also leads to a more flat scale/substrate interface.
Integral damage functions for Type 403 stainless steel (SS) in borate buffer solution containing chloride ion have been experimentally determined. The pits are of an open morphology, thereby rendering effective determination of the damage functions using optical microscopy. Extensive pit coalescence caused the measurement of the damage functions to be less accurate than desired and, in some instances, rendered their measurement impossible. Accordingly, the Deterministic Extreme Value Statistics (DEVS) protocol of Damage Function Analysis (DFA) is adopted as a convenient means of presenting pitting damage in terms of the growth of the deepest pit in the population. A similar analysis is reported for A470/471 steel, where an insufficient population of shallow, pan-shaped pits precludes DFA, which requires a large population. In this case, too, DEVS is used to extrapolate maximum pit depth to a longer time (750 h) after calibrating the model on shorter term data (24 h and 240 h). The experimental maximum pit depth distribution for 750 h is in good agreement with that predicted from the calibrated DEVS, thereby demonstrating the veracity of the method. The maximum pit depth distributions on Type 403 SS and A470/471 steel surfaces do not display the increasing trend with increasing applied potential and chloride concentration. The large depth distribution and/or a large ohmic potential drop inside a pit under a thick adherent layer of corrosion product, probably have “buried” the effects of applied potential and chloride concentration.
The galvanic corrosion of copper/AISI 316L stainless steel couples has been studied under different temperatures and flowing conditions in heavy LiBr brines. The mixed potential theory, zero-resistance ammeter and weight loss measurements were performed. Temperature and Reynolds number increase galvanic corrosion rates of copper. Statistical analysis by means of multilevel factorial design reveals that temperature greatly affects galvanic current densities. Additionally, the mixed potential theory suggests that thermogalvanic corrosion may occur when the materials of the pair work at different temperatures. The most important increase of current densities due to thermogalvanic effects takes place at high Reynolds numbers with the highest difference of temperature between copper/AISI 316L pairs and the anode operating at 25 °C. The results obtained with the different techniques are in good agreement.
In this work, the effect of uniaxial elastic stress on corrosion of X100 pipeline steel in a near-neutral pH solution was investigated by localized electrochemical impedance spectroscopy (LEIS), corrosion potential and electrochemical impedance measurements, surface analysis techniques as well as finite element analysis. No effect of the static elastic stress on electrochemical corrosion potential of the steel is detected. The critical failure strain of corrosion scale formed on the steel surface is calculated to be 0.00357–0.00417, which is higher than the maximum strain of 0.0029 generated on the specimen. Thus, corrosion scale does not fracture during loading. No difference in the steady-state corrosion potential could be detected upon application of an elastic tensile or compressive stress. If the scale is pre-formed on the steel surface, the applied dynamic elastic load would “weaken” the scale by expanding its pores, and thus, increase the steel corrosion. While a dynamic tensile stress enhances the steel corrosion, the dynamic compressive stress would inhibit corrosion of the steel. This work provides important recommendations for pipeline safety design, where the corrosion enhancement due to the dynamic elastic stress should be considered.
The carbon dioxide corrosion behaviour of HP13Cr110 stainless steel in simulated stratum water is studied by potentiodynamic curve and electrochemical impedance spectroscopy (EIS); the micro-structure and composition of the corrosion scale formed at high-temperature and high-pressure are analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results show that 13Cr stainless steel is in passive state in the stratum water, the passive current density increases and the passive potential region decreases with increasing temperature. The corrosion scale formed at high-temperature and high-pressure is mainly composed of iron/chromium oxides and a little amount of FeCO3.
The effects of chromate on the open-circuit repassivation of the guillotined aluminium electrode in chloride solutions are presented. The presence of chromate causes the entire transient to lie at higher potential, thereby accelerating repassivation. Reactivation of the repassivating surface observed in pure chloride solution is eliminated by the presence of chromate. Some implications of the results are discussed.
A theoretical carbon dioxide (CO2) corrosion model was used to conduct numerical experiments, which allowed total in- sight into the underlying physicochemical processes. The focus was on factors influencing protective iron carbonate film formation and the effect that these films have on the CO2 corrosion process. It was confirmed that high bulk pH, high temperature, high partial pressure of CO2, high Fe 2+ concen- tration, and low velocity all lead to favorable conditions for protective iron carbonate film formation. The model can be used to identify threshold values of these parameters. Corro- sion rate was not strongly correlated with protective film thickness. The so-called surface film "coverage" effect ap- peared to be more important. Corrosion rates decreased rap- idly as the film density increased. It was shown that in the presence of dense films diffusion of dissolved CO2 through the film is the main mechanism of providing the reactants to the corrosion reaction at the metal surface. It was demon- strated that "detached" films have poor protective properties even when they are very dense. Serious errors in prediction/ reasoning can be made by operating with bulk instead of surface water chemistry conditions. The former is made possible by using advanced models such as the one used in the present study.
A stochastic model previously developed by the authors using Markov chains has been improved in the light of new experimental evidence. The new model has been successfully applied to reproduce the time evolution of extreme pitting corrosion depths in low-carbon steel. The model is shown to provide a better physical understanding of the pitting process.
Relationships are established which describe the evolution of the corrosion potential of freshly generated aluminium with time during repassivation. The relationships explain quantitatively the empirical observation that the free corrosion potential of freshly generated aluminium surfaces increases linearly with log t during repassivation by oxide film growth. In some solutions deviation from this linearity towards higher values of ∂E/∂ log t is caused by the presence of dissolved oxygen.
The influence of applied macrostress on the pitting susceptibility of a 12%CrMoV martensitic stainless steel in a de-aerated caustic solution containing chloride at 373K has been investigated and discussed.
A recently developed model for predicting the repassivation potential has been applied to stainless steels and nickel-base alloys in aqueous environments containing chlorides and various inhibiting anions. The model accounts for the effects of solution chemistry and temperature on the repassivation of localized corrosion by considering competitive dissolution, adsorption, and oxide formation processes at the interface between the metal and the occluded site solution. An extensive database of repassivation potentials has been established for six alloys (UNS 31603, N06600, N06690, S31254, S32205, and UNS S41425) in contact with solutions that combine chlorides with hydroxides, molybdates, vanadates, sulfates, nitrates, and nitrites at various concentrations and temperatures. Also, repassivation potentials are reported for four alloys (UNS N08367, N08800, N06625, and N10276) in chloride solutions. The database has been used to establish the parameters of the model and verify its accuracy. The model quantitatively predicts the transition between concentrations at which localized corrosion is possible and those at which inhibition is expected. It is capable of predicting the repassivation potential over wide ranges of experimental conditions using parameters that can be generated from a limited number of experimental data. The parameters of the model have been generalized as a function of alloy composition, thus making it possible to predict the repassivation potential for alloys that have not been experimentally investigated.
Potentials for the thermal cell (25°C)
as a function of the concentration of
and temperature
are reported. The thermal cell potentials are combined with isothermal potentials for the silver‐silver chloride electrode
at elevated temperatures to calibrate external
electrodes as pseudothermodynamic standards for the investigation of electrochemical processes in high temperature aqueous
systems.
In this paper, we provide an alternative, more general theoretical basis for damage function analysis (DFA), by drawing an analogy between the growth of a pit and the movement of a particle. In contrast to our previous formulation of DFA, which was developed specifically for enabling the damage function for localized corrosion to be calculated from the point defect model for passivity breakdown, the coupled environment pitting model for pit growth, and the theory of prompt and delayed repassivation, the new formulation readily incorporates any theories or models (deterministic or empirical) for these stages in the development of a pit. We show that the new formulation leads to the original expressions for the damage functions for active (living) and passivated (dead) pits, and hence for the differential and integral damage functions, as were obtained from the original theory. We also describe the unification of deterministic (damage function analysis, DFA) and empirical, statistical (extreme value statistics, EVS) methods for predicting the development of localized corrosion damage on metal surfaces. In particular, we have devised a means of estimating the central and scale parameters of EVS directly from DFA in a “first principles” manner, as well as from fitting the EVS distribution function to experimental data for short times, in order to predict the extreme value distributions at longer times. The techniques have been evaluated on EVS data for the pitting of manganese steel in CO2-acidified seawater and for the pitting of aluminum in tap water. Finally, we outline the generalization of pit nucleation, as described by the point defect model, for external conditions that depend on time.