Local Corrosion Rate Research Articles

Hydrogen Sulfide (H2S) Concentration Influence Toward Uniform and Localized Corrosion Rate of API 5L X65 Steel at Elevated Temperature

ABSTRACT Trace amounts of hydrogen sulfide (H2S) in a carbon dioxide (CO2) dominant environment reduce general corrosion rates by forming thin iron sulfide layers but increase localized corrosion. This study investigates how varying H2S concentrations affect the corrosion rates of API 5L X65 steel at 70°C. Using a 2L glass cell setup, steel coupons were immersed in a solution containing 1000 ppm NaCl and 500 ppm HAc for seven days. Corrosion rates were determined through weight loss measurements, and surface morphology was analyzed using SEM and EDX. H2S concentrations of 0, 30, 60, and 100 ppm were tested. At 0 ppm H2S, the uniform corrosion rate was 2.53mm/yr. The addition of 30 ppm H2S reduced the rate to 1.00 mm/yr, showing a 60% inhibition efficiency. However, the highest pitting corrosion rate of 6.30 mm/yr occurred at 30 ppm H2S, with a maximum pit depth of 123μm. The results suggest that lower H2S concentrations lead to localized corrosion, while higher concentrations form a protective film, reducing corrosion rates.

Study of corrosion and failure mechanism of the galvanized steel pipes of meteorological tower serviced in the South China Sea

Corrosion issues of steel in the natural tropical marine atmospheric environment widely exist, and they can easily cause the failure of engineering equipment. However, the related studies are poor. Therefore, a deep analysis of the corrosion behavior and failure mechanism of steel materials in natural environments is urgent and important. In this work, the corrosion and failure mechanisms of galvanized steel pipes of a meteorological tower in the South China Sea were deeply studied. Results demonstrated that galvanized steel pipes at a low height happen a serious uniform and localized corrosion, while the bottom surface of each pipe facing the ground is severely corroded. The damage to the galvanized layer and the subsequent steel corrosion in high temperature and humidity conditions are mainly caused by bacteria and Cl−. Some bacteria with high corrosivity, such as Desulfovibrionales, Seminibacterium, Acinetobacter, Ralstonia, Proteobacteria Streptococcus, and Lactobacillus, are found beneath the rust layer, and they can significantly accelerate steel corrosion. The maximum localized corrosion rate is 0.20 mm/y.

Research on eccentric-compressive behavior of steel stub columns with localized corrosion

To explore the impact of localized corrosion on the mechanical properties of hollow steel columns under eccentric loads, a specialized localized immersion-accelerated corrosion apparatus was developed. This device facilitated the creation of 17 locally corroded specimens, all subjected to eccentric loading. A systematic examination was conducted on various corrosion parameters including corrosion length, corrosion angle, localized corrosion rate, and corrosion location as well as loading conditions, which encompassed eccentricity and loading angle. Surface corrosion morphology and statistical parameters of the specimens were obtained using a 3D scanner. Subsequently, a nonuniform corrosion model, based on element displacement, was formulated through finite element analysis. Both experimental findings and numerical simulations indicate that localized corrosion does not alter the failure mode of locally corroded circular steel tubes (LCCSTs), which predominantly undergo local buckling in the compressed region. However, it was noted that localized corrosion leads to the elimination of the ascending segment in the load-displacement curve of the LCCSTs, thereby reducing both the ultimate load and ductility. Interestingly, the ultimate load of the LCCSTs was found to be relatively unaffected by variations in corrosion length and location but significantly influenced by factors such as localized corrosion rate, corrosion angle, eccentricity, and loading angle. Furthermore, through a comparative analysis of existing calculation models for the ultimate load of LCCSTs in major specifications, a practical model that accounts for localized corrosion is proposed. This model demonstrates high accuracy and is expected to enhance the understanding and prediction of the ultimate load capacity of LCCSTs in real-world applications.

Corrosion at Top-of-the-Line in High Pressure and Dense CO2 Environments

This study presents unique data on top-of-the-line corrosion (TLC) occurring in high-pressure environments where CO2 was in the gaseous, liquid, or supercritical state. While CO2 is traditionally in a gaseous phase, this form of degradation is referred to as TLC. In this study, similar phenomena with different mechanisms were observed in liquid CO2 and supercritical states all of which are referred to as TLC due to the location of specimens and ease of comprehension. Experiments were conducted to investigate the effect of CO2 partial pressure (ranging from 20 bar to 100 bar) with temperatures (30°C to 50°C) relating to different water condensation rates (0.001 mL/m2/s to 0.1 mL/m2/s). Uniform and localized TLC rates increased with a higher water condensation rate and surface temperature. As long as CO2 remained gaseous, its partial pressure (pCO2) showed a negligible influence on both uniform and localized TLC rates. At the highest gaseous CO2 content tested, the formation of a protective iron carbonate (FeCO3) layer decreased the TLC rate, with this effect being more pronounced at lower water condensation rates. The risk of localized corrosion for specimens exposed to this environment at high and medium water condensation rates remained an issue. In the dense phase CO2 environment, the difference in temperature between the bulk environment and the specimen’s surface caused a similar phenomenon to water condensation, termed water drop-out, which resulted in corrosion. The rate of water drop-out could not be measured experimentally or estimated theoretically but is a complex function of temperature, pCO2, and CO2 physical state. The interplay between high pCO2 and low pH of the dropped-out water led to elevated uniform and localized corrosion rates. The depth of localized corrosion, at the high and medium water drop-out conditions, reached its maximum at the surface temperature of ca. 45°C. At a lower surface temperature of ca. 25°C and a higher surface temperature of ca. 65°C, the maximum penetration rate was decreased due to slower kinetics of reactions and the formation of a more protective FeCO3 layer, respectively. The results presented in this study highlight the significant difference between corrosion rates, especially in the form of localized damage, in gaseous and dense-phase CO2 environments.

Corrosion reason analysis and countermeasures of buried oil unloading pipeline in an oilfield

The material, corrosion morphology and characteristics, as well as the compositions of corrosion products of a 20# steel unloading pipeline were studied using on-site C-scan detection, laboratory corrosion morphology analysis, material metallographic analysis, chemical composition analysis and tensile testing. The uniform corrosion and pitting behavior of 20# steel were studied using a high temperature and high pressure autoclave under conditions of 50 °C and CO2 partial pressure of 0.05 MPa, 0.1 MPa, and 0.2 MPa, respectively. The microstructure and composition of the surface and cross-section corrosion product film were analyzed by SEM. The results show that the uniform corrosion rate of 20# steel increases with the increase of CO2 partial pressure. When the CO2 partial pressure reaches 0.2 MPa, there are a large number of corrosion pits on the surface of the sample, and the maximum local corrosion rate reaches 1.8719 mm/a. The corrosion product film has a multi-layer structure, with a surface layer of FeCO3 corrosion product films and an inner layer of (Ca, Mg)CO3 deposition layer. There are obvious corrosion pits at the interface between the corrosion product film and the substrate locally. The severe thinning of the on-site pipeline wall is mainly caused by CO2 corrosion. The defects of the corrosion product film and the deposition of scale layer accelerate local corrosion.

Experimental teaching design of weightlessness method to determine the corrosion rate of metal

Abstract When exposed to corrosive environments, metals, which are relatively common industrial materials, undergo serious corrosion, leading to significant economic losses. Therefore, studying the corrosion rate of metals in their early stages holds great pedagogical significance. This study employs a standard specimen of 20# steel as an experimental object, designing the experimental teaching of metal corrosion rate under varying temperatures, PH levels, and hydrated salt materials. The weightlessness method determines the overall corrosion rate of the metal, while the electrochemical method determines the localized corrosion rate of the metal. When the experimental temperature is 80℃ and 100℃, the corrosion rate of 20# steel is the largest; both are 0.00800g·m−2·d−1, and the charge transfer resistance increases gradually when the temperature is −20℃~5℃, and decreases gradually when the temperature is 5℃~100℃. The corrosion rate of the metal did not change much at pH=7 and 8, and the corrosion rate reached 0.688 mm/a, and the impedance curve polarization resistance Rp was the smallest when pH=5, and its corrosion resistance was poor under acidic conditions. The average corrosion rates in MgSO4·7H2O, and CaCl2·6H2O and Ba(OH)2·8H2O were 0.0030g/m−2h−1, 0.0018g/m−2h−1, and 0.0050 g/m−2h−1, respectively. Teaching experiments were used to carry out the present study. The study aims to let students experience the process of metal corrosion through teaching experiments and better help them solve cognitive difficulties in metal corrosion.

Corrosion Evolution mechanism of N80 tubing steel under supercritical CO2 and H2S environment

The corrosion evolution mechanism of N80 tubing steel in 8 MPa supercritical CO2 and 0.1 MPa H2S environment was investigated. The results show that although the corrosion rate of N80 steel decreases with the prolonged corrosion time, it still maintains a high level of about 1.06 mm/y after a long period of 360 h. As the corrosion progresses, the corrosion products change from FeS to a mixture of FeS and FeCO3. The corrosion form of N80 steel changes from uniform corrosion to localized corrosion. The origin credited for localized corrosion is the detachment of large particles of FeS in the early corrosion stage. A double-layer film consisting of an outer layer of FeS and an inner layer of FeCO3 forms in the area of corrosion pits after a prolonged period of corrosion, which provides protection for the substrate, thereby causing the decrease of localized corrosion rate of N80 steel.

Determination of Chemical Species Dominating the Corrosivity of Japanese Tap Water by Multiple Regression Analysis

Japanese tap water is Ca2+-poor and SiO2-rich in comparison with that of other counties. Thus, there have been few studies on its corrosivity. We sampled tap waters at 70 different sites and in different seasons in Japan, subjected the samples to chemical analysis and measured localized corrosion depth and the total corrosion loss of carbon steel placed in these waters. The average corrosion rate vavg and maximum localized corrosion rate vmax were calculated. The ratio of vmax to vavg, which was defined as localized corrosion factor LCF (=vmax/vavg), was also studied. The multiple regression method was applied to obtain the dependence of vavg (objective variable) on concentrations of chemical species (explanatory variables). In the same manner, the relation of vmax and LCF to concentrations of chemical species was derived. As a result, we showed that SiO2 and SO42− mainly dominate the corrosivity of Japanese tap water. In particular, as SO42− increased, vavg became larger and vmax became smaller. Also, as SiO2 increased, vmax became larger and vavg became smaller. The behavior of LCF was similar to that of vmax. The findings of this study will be useful for estimating the corrosivity of tap waters that have low Ca2+ and high SiO2 concentrations.

Nondestructive detection and quantification of localized corrosion rates by electrochemical tomography

Localized corrosion is one of the most common causes of early degradation of engineering structures. To non-destructively determine the location, size and rate of localized corrosion in porous media, a new technique, electrochemical tomography (ECT), has been theoretically and numerically formulated. The current work shows the application of ECT to measure corrosion rates in a controlled laboratory setup, with a stable electrolyte and well-defined macro-cell. The results show that ECT is able to replicate the corrosion size and location and can give a good estimation of the corrosion rate. Moreover, the validation of ECT on a well defined localized corrosion system, brings the technique closer to future field applications.

Model for corrosion of copper in a nuclear waste repository

A mathematical model for corrosion of copper under a droplet, developed in a previous paper, was applied for conditions suitable for the Canadian nuclear waste repository under two models for oxygen decay. The influence of temperature was included, and the model accounted for the influence of films on reaction rate constants. The model shows the time-dependent localized corrosion rates and depths, calculated here for an elapsed time of ten years. Preliminary results show that the corrosion of copper is almost uniform on the electrode surface. Temperature and oxygen concentration is shown to have a strong contribution to copper corrosion.

Experimental and numerical research on the static behavior of locally corroded OSBD

Corrosion can accelerate the deterioration of the mechanical properties of orthotropic steel bridge decks (OSBDs), seriously affecting the service safety of steel bridges. In this paper, thirty Q345C steel and four OSBD specimens with various corrosion levels are designed to investigate the effect of corrosion on the static behavior of OSBDs. Then, corrosion damage and its influence on mechanical properties are explored by static loading experiments. The constitutive model for Q345C steel is built considering the impact of corrosion. Finally, a numerical analysis considering geometric initial defects is employed to compare the effect of corrosion location on bearing capacity degradation. It is observed from the tested results that the corrosion led to the failure mode of Q345C steel changing from plastic failure to brittle failure. The ultimate bearing capacity of specimens with a local corrosion rate of 7.92%, 12.05%, and 16.24% decreased by 11.08%, 14.45%, and 17.82%, respectively. Corrosion leads to stress concentration in the top plate area, causing local instability of the structure. The degradation degree of the bearing capacity of the top plate is greater than that of the U-rib corrosion corresponding to the same corrosion conditions.

Corrosion inhibition study of marine Streptomyces against sulfate-reducing bacteria in oilfield produced water

A marine Streptomyces sp., which has an inhibitory effect on sulfate-reducing bacteria (SRB), was selected to study inhibitory effect and mechanism of X65 steel on SRB corrosion in oilfield produced water. Streptomyces and SRB had a competitive growth relationship. The Streptomyces metabolites affected the number and activity of SRB and had good corrosion inhibiting properties. The formation and development of SRB biofilm was inhibited. Mixed bacteria inhibited anodic dissolution of X65 steel and slowed down the electrochemical reaction rate. The film layer on the sample was denser, and the average and localized corrosion rates caused by SRB were significantly suppressed.

Probing pipe flow impact corrosion monitoring effectiveness under corrosion monitor coupons conditions

To reduce the corrosion failure frequency of oil and gas pipelines, corrosion monitoring coupons are often used to evaluate the internal corrosion status of pipelines. However, the local flow field varies after the installation of the coupons, so the monitoring corrosion rate is different from that of the pipe wall. To evaluate the effectiveness of corrosion coupons monitoring, a lab-scale flow loop system was used to carry out flow corrosion experiments to obtain the local corrosion rates of corrosion monitoring coupons and pipe wall, respectively. Combined with the characterization of corrosion products and multiphase flow, a mechanism model of corrosion monitoring effectiveness was established. It was clear that the deviation of corrosion monitoring rate was related to the flow rate, shear force and turbulent kinetic energy. The accumulation of corrosion media and the detachment of corrosion product films resulted in variation in the morphology and the monitoring effectiveness.

Microstructural Understanding of Flow Accelerated Corrosion of SA106B Carbon Steel in High-Temperature Water with Different Flow Velocities.

All light or heavy water reactors fabricated with carbon steels suffer from flow-accelerated corrosion (FAC). The FAC degradation of SA106B with different flow velocities was investigated in terms of microstructure. As flow velocity increased, the major corrosion type changed from general corrosion to localized corrosion. Severe localized corrosion occurred in the pearlite zone, which can be the prior location for generating pits. After normalizing, the improvement in microstructure homogeneity reduced the oxidation kinetics and lowered cracking sensitivity, causing a decrease in FAC rates of 33.28%, 22.47%, 22.15%, and 17.53% at flow velocity of 0 m/s, 1.63 m/s, 2.99 m/s, and 4.34 m/s, respectively. Additionally, localized corrosion tendency was decreased by reducing the micro-galvanic effect and tensile stresses in oxide film. The maximum localized corrosion rate decreased by 21.7%, 13.5%, 13.8%, and 25.4% at flow velocity of 0 m/s, 1.63 m/s, 2.99 m/s, and 4.34 m/s, respectively.

Localized Corrosion Mechanism of Q125 Casing Steel in Residual Acid Solution during Oil Reservoir Acidizing

This paper aims to investigate the localized corrosion mechanism of Q125 casing steel in residual acid solution with Mannich base type inhibitors during oil reservoir acidizing process. The corrosion behavior of Q125 casing steel in fresh acid (20% HCl) and residual acid solution (pH 1.0 and pH 3.0 HCl) with and without 3-(4-chlorophenylimino)-1-(piperidine-1-ylmethyl) indolin-2-one (Mannich base type, Mb) inhibitor was studied by electrochemical test, weight loss, and surface analysis. The morphology and composition of corrosion products were analyzed by SEM/EDS and XPS; the local corrosion rate of casing steel with or without inhibitor was obtained by 3D profilometry. It was determined that the inhibitor had higher inhibition efficiency in fresh acid conditions than in residual acid conditions. Under the condition of residual acid, the decrease in inhibitor molecular coverage on the substrate surface promotes the occurrence of local corrosion. Pitting corrosion was detected in the residual acid solution containing Mannich base inhibitor, which may be related to the fact that FeCO3 hinders the adsorption of inhibitor molecules on the substrate surface.

Metallurgical investigation of early failure of heater pipes in a gas complex

An early corrosion failure of the piping system of a gas heater was reported by a gas complex company. Local corrosion rates of 0.90 and 0.66 mm/year were observed in the heater piping system. An investigation including visual examination, macrostructure, microstructure (SEM, EDS and XRD), thickness gauging, chemical analysis, and mechanical testing, was performed. The results showed that corrosion damage occurred on the external surface of the pipes. Corrosion occurred at the cold sides of the pipes and elbows. The corrosion pattern is broad and shallow pitting. Some elbows showed an early stage of carbide spheroidization and pearlite decomposition. The EDS microanalysis revealed that the level of sulfur, chlorine, and nitrogen was substantially high in the rust samples. The XRD of the corrosion products showed that the main oxyhydroxide was Akaganeite. The analysis of results showed that the flue gas dew point corrosion was the mechanism of damage, and the root cause was the operation of the heater at low temperatures and the frequent outings of service, combined with evident material drawbacks including low levels of Si, Cu, Ni, Cr, and Mo. These elements should be at their maximum allowable limits of the SA 105 and SA 106 to improve the corrosion resistance of the steel piping components.

Localised corrosion failure of an L245N pipeline in a CO2–O2–Cl− environment

ABSTRACT Multicomponent thermal fluid flooding has become a widely used and very effective heavy-oil recovery technology, but the harsh CO2–O2–Cl− environment can lead to serious corrosion perforation failure of the pipeline. Therefore, the influence of O2 content and main controlling factors on corrosion perforation were investigated through a weight-loss experiment, corrosion defect test, characterization and grey correlation method. The results showed that, with the increase in O2 content, the general corrosion rate and localized corrosion rate increased. The uneven protection performance of the product after the addition of O2 was found to be the key cause of localized corrosion. In addition, the synergistic effect of O2–Cl− promoted the lateral and longitudinal expansion of pits. The results of the grey correlation showed that the temperature (30–120 °C) had a greater impact on localized corrosion compared with the content of O2 (0–0.045 MPa) and Cl− (0–16,000 mg/L).

Corrosion Behavior of Petroleum Pipeline Steel in the Sulfur Ion Enriched Solution with Quinoline

Localized corrosion is a serious, hazardous destroyer of steel petroleum pipelines meant for long-time use. However, previous studies on localized corrosion primarily focused on local corrosion morphology and corrosion rate of bulk metals because detecting the corrosion state of occlusive metals is difficult. Herein, we employ a simulating occluded battery unit to disclose the local corrosion behavior of the steel petroleum pipeline (N80 steel) in an occlusive S2–-enriched solution. After simulating localized corrosion in the S2–- containing corrosion solution using the occluded battery unit, the occlusive solution was acidified and the migration amount of S2– to the occluded area increased. Despite the increase of S2– concentration, the addition of quinoline corrosion inhibitor (0.8 wt%) still effectively impedes the corrosion of the occluded metal. Moderately raising the environmental temperature can stimulate the activity of the inhibitor and promote the inhibition effect. The quinoline corrosion inhibitor displays the maximum inhibition rate at an elevated temperature of 50°C. Meanwhile, a maximum over the temperature of 60°C-70°C will likely accelerate the failure of the inhibitor.

Under-deposit microbial corrosion of X65 pipeline steel in the simulated shale gas production environment

The synergistic effect of sand deposit and sulfate-reducing bacteria on the X65 pipeline steel was investigated in the simulated shale gas production environment, by means of weight loss tests, EIS, SEM and EDS. The results indicated that the coexistence of sand deposit and sulfate reducing bacteria (SRB) resulted in 63% reduction in uniform corrosion, but 183% increase in localized corrosion rate. The EIS results revealed that the formation of biofilm altered the protectiveness of the surface mixed layer and showed a trend related to the bacterial growth curve. The mixed layer was also clarified from the cross-section morphology and EDS analysis. This mixed layer may hinder the diffusion of substances to the deposit/steel interface, thus creating a microenvironment at the deposit/steel interface that promotes localized corrosion.

Probing and evaluating non-uniform corrosion behavior of pipe weldment using an array of coupled multi-ring form electrical resistance sensor

A novel corrosion system defined as coupled multi-ring form sensor array (CMRSA) was designed and fabricated to study the non-uniform corrosion performances of pipe weldment immersed in the CO2 saturated solution of different pH. The macro-cell currents flowing among heterogeneous welding areas, i.e. base metal (BM), heat affected zone (HAZ), and welding metal (WM), and the micro-cell corrosion inside of each welding area were explored. In conjunction with electrochemical measurements and surface characterization, it is found that all the welding areas would suffer active corrosion in the pH = 4 solution. While the HAZ suffered severe localized corrosion due to the local defects of the corrosion product film in the pH = 6.6 solution. Based on the dispersion interval analysis of the localized corrosion rate, the pipeline corrosion risk caused by the non-uniformity of circumferential corrosion could be estimated.