Under-deposit Corrosion Research Articles

Study on the Relationship Between Humidity and Under-Deposit Corrosion in High Strength Medium Manganese Steel

Study on the Relationship Between Humidity and Under-Deposit Corrosion in High Strength Medium Manganese Steel

Penetration of imidazoline derivatives through deposited scale for inhibiting the under-deposit corrosion of pipeline steel

Effective penetration of corrosion inhibitors through deposits is vital for controlling under-deposit corrosion (UDC) in oil/gas production. Herein, the penetration of three imidazoline derivatives across a CaCO3-based scale in CO2-saturated brine was examined, along with the resulting protection effect on mild steel. Real-time spectral monitoring revealed the correlation between inhibitor structures and penetration ability, with a maximum permeability of 24.1 %. Imidazoline's affinity with water, indicated by coordination number, significantly influenced the penetration. The intrinsic efficacy of imidazoline derivatives determined actual UDC inhibition efficiency, reaching a maximum of 92.33 %, under conditions of sufficient penetration.

Corrosion Inhibition Properties of Corrosion Inhibitors to under-Deposit Corrosion of X65 Steel in CO2 Corrosion Conditions.

Under-deposit corrosion is widely present in the pipelines of oil and gas production, causing significant corrosion damage. In this paper, a novel electrochemical cathodic-polarization method was carried out to accelerate the formation of CaCO3 scale on a X65 steel surface in a simulated solution containing scaling ions. Subsequently, pre-scaled X65 steel was placed in a high temperature and pressure autoclave to conduct corrosion weight-loss experiments and in situ electrochemical measurements. The study mainly compared the corrosion inhibition behavior of four quaternary ammonium salt corrosion inhibitors, pyridinium quaternary salt (BPC), quinolinium quaternary salt (BQC), 8-hydroxyquinolinium quaternary salt (BHQ) and pyridinium (1-chloromethyl naphthalene) quaternary salt (1-CPN), in a simulated oilfield scale under corrosive conditions. The results of the weight-loss experiments demonstrated that the inhibition efficiencies of the corrosion inhibitors from high to low were as follows: 1-CPN < BHQ < BQC < BPC. The in situ electrochemical measurements showed that the immersion time and type of corrosion inhibitor had a pronounced influence on the corrosion and corrosion inhibition behavior of X65 steel with CaCO3 coating. It was also proved using both EIS and PC that 1-CPN shows the best inhibition performance in all. Lastly, the inhibition mechanism of corrosion inhibitors at under-deposit conditions was analyzed via a surface morphology observation of SEM.

Electrochemical study on under-deposit corrosion evolution of oil pipelines

In the development of oil and gas fields, due to the sand, calcium, and magnesium ions in the produced liquid, the under-deposit corrosion formed by deposition during the transportation process has become one of the key factors of pipeline failure. Therefore, aiming at the problem of CaCO3 under-deposit corrosion in CO2-flooded oil pipelines, this paper studied the influence of deposit thickness change on metal corrosion based on electrochemical experiments, image characterization, and corrosion product analysis. The results showed that the corrosion process of the deposit layer can be divided into three stages. (1) The deposit layer promoted the movement of the electrolyte and then enhanced the corrosion rate of the matrix, leading to the increase of the size and maximum pit depth of the matrix, which was manifested as a rapid negative shift of the open circuit potential. (2) The deposit layer played a certain physical shielding role, leading to the size and maximum pit depth of the pit decreasing, and the number of pits increasing, at which the open circuit potential basically remained unchanged. (3) The deposit layer can play an effective physical shielding role, and the oxygen concentration corrosion inside and outside the deposit layer made the number of pits increase sharply, which was manifested as a slow negative shift of open circuit potential. The deposit layer mainly affected the cathode reaction process of the corrosion process. With the increase of the deposit thickness, the metal corrosion intensified with an increasing corrosion current density.

Study on the inhibition mechanism of corrosion under inert deposit-covered X65 steel by three corrosion inhibitors

In order to solve the problem of under-deposit corrosion caused by typical inert minerals in oil and gas fields, three corrosion inhibitors with small molecular weight thiourea (TU), oil-soluble alkyl imidazoline (IM) and water-soluble thiourea imidazoline (TAI) were selected. The corrosion inhibition effect and mechanism of the them under SiO2 and CaCO3 deposit were studied by surface analysis, electrochemical analysis and theoretical calculations. The results show that TU, IM and TAI can adsorb on the metal surface through the deposits, and the corrosion inhibition efficiency is η(TAI) > η(TU) > η(IM). TU and TAI are mixed corrosion inhibitors that inhibit both the cathode and the anode reactions, and the thiourea group in TU and TAI can form coordination chemical bonds with the empty d orbital of iron atoms as electron-rich regions. Due to hydrophobic groups, the adsorption film formed by TAI on the metal surface is denser. However, it is difficult for IM to form a continuous protective corrosion inhibitor film under the two deposits, so it shows poor corrosion inhibition performance.

A Bayesian network‐based susceptibility assessment model for oil and gas pipelines suffering under‐deposit corrosion

AbstractOil and gas pipelines are exposed to harsh operating conditions that facilitate their susceptibility to complex corrosion mechanisms. This affects their integrity and results in failure with associated consequences. Capturing these complex corrosion phenomena requires a robust approach. This study proposes the application of a dynamic probabilistic model to capture the key influential factors that contribute to the complex under‐deposit corrosion (UDC) mechanism in oil and gas pipelines. The Bayesian network model assesses the pipeline's susceptibility (degradation rate) to the UDC, capturing parametric dependencies. The predicted corrosion rates are input data for the corrosion propagation prediction. Three semi‐empirical corrosion propagation models are used for a comparative assessment to establish the degree of susceptibility given the prevalent influential factors and model parameters. The proposed approach is tested on an offshore pipeline, and the degree of impact of the key influential parameters is predicted. The result shows a percentage increase in the degradation rate by 18.7%, 33.2%, 35.8%, and 63.4%, respectively, for the various interaction scenarios. The present approach offers an adaptive and robust technique that would provide an early warning guide on the rate of pipeline degradation to aid integrity management for offshore assets suffering from deposit corrosion.

Effect of coexistence of sulfate reducing bacteria and nitrate reducing bacteria on the under-deposit corrosion of carbon steel

The effect of sulfate reducing bacteria (SRB) and nitrate reducing bacteria (NRB) on under-deposit corrosion (UDC) of carbon steel is studied by weight loss tests, electrochemical measurements and surface analysis. The results show that SRB-induced UDC is significantly inhibited by NRB. This inhibition is attributed to the accumulation of NRB in deposits suppressing the growth of SRB, as revealed by the analysis of total accumulation number of bacteria and the characterization of bacteria-formed micro-holes indicating localized accumulation of bacteria in deposits. The suppressed SRB growth in deposits is discussed based on the NRB-induced biologically competitive exclusion and metabolite inhibition mechanisms.

Understanding of ammonium salts under-deposit corrosion: Electrochemical and AIMD investigations

In-situ electrochemical experiments and ab initio molecular dynamics (AIMD) simulations are combined to investigate the under-deposit corrosion and hygroscopicity of ammonium salts on SAE 1020 steel interdigital electrodes. The findings indicate that the hygroscopicity of ammonium salts influences the evolution of the interface and the accumulation of the product film. The corresponding simulations reveal that the hydrolysis of NH4+ leads to the generation of a proton transfer chain, resulting in an elevation of H+ concentration. This hydrolysis behavior is effectively catalyzed on the Fe(1 0 0) surface, promoting the occurrence of anodic adsorption and cathodic hydrogen evolution reaction, thereby inducing corrosion.

Corrosion at the Steel–Medium Interface

Corrosion on the interface between a metal alloy, such as steel, and a wet, permeable non-metallic medium is of considerable practical interest. Examples include the interface between steel and water, the atmosphere or concrete, as for steel reinforcement bars; between metal and soil, as for buried cast iron or steel pipes; deposits of some type, as in under-deposit corrosion; and the interface with insulation, protective coatings, or macro- or micro-biological agents. In all cases, corrosion initiation depends on the characteristics of the interfacial zone, both of the metal and the medium, and the spatial variability. For (near-)homogeneous semi-infinite media with good interfacial contact, the pitting, crevices and general corrosion of the metal will be largely controlled by the metal (micro-)characteristics, including its inclusions, imperfections and surface roughness. In other cases, these may be overshadowed by the macro-characteristics of the medium and the degree of interfacial contact, possibly with severe resulting corrosion. Where the build-up of corrosion products can occur at the interface, they will dominate longer-term corrosion and govern the long-term corrosion rate. For media of finite thickness, diffusion issues and material deterioration may also be involved. The practical implications are outlined. It is argued that with the presence of a suitable medium, it is possible to achieve negligible long-term corrosion but only if certain practical actions are taken.

Assessing underdeposit corrosion inhibitor performance for carbon steel in CO2/Sulfide environment

Under deposit corrosion (UDC) that occurs due to the deposition of solid particles, like iron sulfide or organic solids, and CO2 corrosion, cause disasters for pipelines and fluid-handling apparatus. This research investigated the impact of mineral deposits, like iron disulfide, iron sulfide, and sand, on the inhibition performance of the commercial UDC inhibitor in sulfated CO2-saturated brine solution at 60 °C and 1000 rpm flow rates for different immersion times. The deposit characteristics, type, and coverage technique on the steel (full/partial) were explored. The surface morphology, elemental analysis, and particle size of deposits in the absence and presence of the inhibitor were analyzed. The inhibitive effect at different inhibitor concentrations and the corrosion rates of steel in the absence and presence of the deposits were calculated from the fitting process of the electrochemical impedance spectroscopy (EIS) results. The utilized UDC inhibitor has the highest efficiency (about 95 %) at a concentration of 400 ppm. The FeS, FeS2 and SiO2 deposits in the presence of the inhibitor offered a 77.5 %, 94.5 % and 94.6 % inhibition efficiency after 6h of immersion time, resulting in about 77.5 %, 25.6 % and 60.1 % increase in their efficiencies before the addition of the inhibitor. Therefore, the inhibitor can effectively inhibit the UDC triggered by FeS and SiO2 deposits in an aqueous environment containing sulfated CO2. However, it is unavailable in the steel underneath the FeS2 deposit to inhibit corrosion. EDX and XPS analyses confirm the success of the inhibitor movement through deposits and its adsorption on steels.

Electrochemical Study on the Macro-Cell Corrosion of Pipeline Steel Partially Covered by Different Kinds of Mineral Deposits.

This study presents the impact of mineral deposits (SiO2, Al2O3, and CaCO3) on the corrosion behavior of X65 pipeline steel in CO2-containing brine solution with low pH. The study investigates the initiation and propagation of under deposit corrosion (UDC) using a wire beam electrode (WBE) partially covered by different mineral deposit layers, in conjunction with electrochemical measurements and surface characterization. The results indicate that the corrosion behavior varies, depending on the characteristics of the deposit. During the test period, the Al2O3-covered steel acted as the main anode with more negative potential, while the bare steel acted as the cathode. The SiO2-covered steel acted as the cathode with more positive potential and a localized FeCO3 layer formed beneath the silica mineral. The CaCO3-covered steel initially acted as an anode with a more negative potential but transformed into the cathode at the end of the test. Additionally, shallow and small pits were observed beneath the deposits with the depth in the sequence Al2O3 > SiO2 > CaCO3.

The Impact of Trisodium Phosphate on Chloride-Driven Under Deposit Corrosion in Steam Generators

Carbon or low alloy steel tubes in steam generators (or boilers) are potentially vulnerable to under deposit corrosion (UDC), arising from the formation of porous magnetite deposits on the waterside heat-transfer surfaces. Beneath these deposits, “wick-boiling” causes a concentration of contaminants (such as chlorides), which eventually leads to rapid corrosion. In this work, the corrosion of carbon steel has been investigated in hot acid chloride solutions that simulate the concentrated local environments formed during UDC. Trisodium phosphate (TSP) is sometimes dosed into boilers for pH control. This work has shown that TSP addition such that the phosphate concentration equals the chloride concentration dramatically reduces the corrosion rate in these simulated environments from &amp;gt;20 mm/y to &amp;lt;0.1 mm/y. Additionally, a model of wick-boiling beneath deposits has been used to analyze the concentration of chlorides and phosphates during the initiation stages of UDC, suggesting that dosing of only 100 ppb of TSP into bulk boiler water should be sufficient to increase the critical deposit thickness (required for UDC) by &amp;gt;100 µm across a wide range of operational scenarios.

Dynamic Bayesian network model to study under-deposit corrosion

Dynamic Bayesian network model to study under-deposit corrosion

THERMAL-POWER-PLANT CONDENSER-TUBE CORROSION ANALYSIS

The thermal-power-plant condenser tubes, conducting cooling seawater, experienced frequent leakages, prompting the hereby presented failure analysis. Visual inspection of the corroded/ruptured tube segments revealed that localized corrosion may be linked to seawater sediments and thick layers of corrosion products at the tube water side. Sediments were found along the tube bottom and thick corrosion products were found adjacent to the point of contact between the baffle plates and the exterior tube walls. Underdeposit corrosion, accelerated due to sulphate-reducing bacteria, was diagnosed based on the excess sulphur found at the pit bottom using EDX, the FT-IR spectrum indicating the presence of biofilm and SEM determining the featuring corrosion products based on the biofilm. It was proposed that the corrosion initiating deposits were linked to the condenser shutdown and startup periods. Results showed that pitting corrosion occurred under the influence of biofilm microorganisms tolerant to copper. The main goal of this research was achieved by defining a systematic procedure for avoiding a shutdown of the thermal power plant.

Role of Fe oxide in the underdeposit corrosion of pipeline steel in oilfield produced water containing SRB

AbstractThe corrosion behavior of C20 pipeline steel was studied under Fe oxide and sand deposits in oilfield produced water containing sulfate‐reducing bacteria (SRB) via electrochemical techniques and surface analyses. A galvanic current of about 2 μAcm−2 was detected when the Fe oxide deposited sample and the bare steel were coupled in zero resistance ammeter (ZRA) mode, with the former being the anodic member of the couple. The Fe oxide deposited steel recorded severe localized corrosion after 14 days of testing in the SRB inoculated oilfield produced water. Corrosion severity decreased on the sand‐deposited steel, with general corrosion as the dominant morphology of surface attack. The development of product film was a vital factor in steel corrosion under the Fe oxide deposit.

A Bayesian approach to assess under-deposit corrosion in oil and gas pipelines

Under-deposit corrosion (UDC) and microbiologically influenced corrosion under deposits (UD-MIC) have increasingly been identified as severe forms of localized corrosion threatening the integrity of pipelines. This work utilizes a knowledge-based, semi-quantitative Bayesian approach to capture UDC and UD-MIC susceptibility and severity. This article proposed a Bayesian Network framework to study susceptibility to UDC and UDC corrosion rate. The effective corrosion rate is introduced as a measure to combine the susceptibility and corrosion rate. This measure could identify high-risk locations by assessing the probable corrosion rate while highlighting the pipeline's vulnerability to deposit settlement. Four case studies of pipeline failures due to UDC illustrate the framework's validity. A case study for a sweet gas pipeline is adapted to explore the model's robustness in assessing cases with low probabilities of UDC occurrence. The gas pipeline data, the corrosion key performance indicators spanning six years, general information on the pipeline, and the Bayesian network are made publicly available through a repository.

Internal localized corrosion of X65-grade crude oil pipeline caused by the synergy of deposits and microorganisms

A case study of an X65-grade crude oil pipeline suffering from severe internal localized corrosion after short-time service was presented. The causes were analyzed via thickness measurement, microbial analysis, SEM, EDS, and XRD analysis. The results showed that a large number of corrosion pits were distributed in the area of 4–8 o'clock at the bottom of the pipeline, and severe localized wall thickness reduction was observed. Around the corrosion pits, extremely thick (∼3 mm) and complex products/deposits can be seen at the edge of the pit, while relatively thinner ones can be seen at the bottom of the pit. In addition, a large amount of SRB was detected in the pigging solids and products/deposits scarped from the inner pipe. Based on the results, the under-deposit microbial corrosion was proposed as the leading cause for the significant localized corrosion of the pipeline in a short-term service.

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.

Rapid Pitting of Copper Tube from Deposits of Cathodic Manganese in Hot Water Systems: Mechanism and Effects of Water Chemistry

A large building with water frequently above 65°C experienced at least 300 leaks in a hot water recirculating line. The leaks were unusual, as they occurred along the very top of horizontal pipes that were heavily coated with iron and manganese sediment on the bottom half of the pipe. This etiology of the leaks is inconsistent with under-deposit corrosion but consistent with a previously hypothesized mechanism of chemistry-related hot water pitting. We verify this mechanism for the first time by: (1) developing a macrocell setup to test the proposed anodic and cathodic reaction and (2) determining how water chemistry can promote or inhibit this form of nonuniform corrosion. The macrocell demonstrated that copper or stainless steel coated with manganese oxides were highly cathodic relative to an anodic exposed copper surface. Pitting current densities as high as 200 µA/cm2 were found in the worst-case conditions at pH 8.2 in waters with a high ratio of sulfate to bicarbonate. High levels of silica inhibited pitting corrosion currents, but orthophosphate inhibitors did not. No iron oxide coatings tested in this work had cathodic tendencies.

Effect of deposit chemistry on microbial community structure and activity: Implications for under-deposit microbial corrosion.

The deposition of solid particles carried by production fluids from oil and gas companies in horizontal surfaces of different assets has shown to cause severe localised corrosion. Sand, one of the most common deposits in the energy sector pipelines, is frequently mixed with crude, oil, asphaltenes, corrosion inhibitors, and other organic compounds. For this reason, they might favour the metabolic activity of native microbial communities. This study aimed to determine the impact of sand-deposit chemical composition on the microbial community structure and functional attributes of a multispecies consortium recovered from an oilfield and the resulting risk of under-deposit microbial corrosion of carbon steel. Sand deposits recovered from an oil pipeline were used in their raw form and compared against the same deposits exposed to heat treatment to remove organic compounds. A four-week immersion test in a bioreactor filled with synthetic produced water and a two-centimeter layer of sand was set up to assess corrosion and microbial community changes. The raw untreated deposit from the field containing hydrocarbons and treatment chemicals resulted in a more diverse microbial community than its treated counterpart. Moreover, biofilms developed in the raw sand deposit exhibited higher metabolic rates, with functional profile analysis indicating a predominance of genes associated with xenobiotics degradation. Uniform and localized corrosion were more severe in the raw sand deposit compared to the treated sand. The complex chemical composition of the untreated sand might have represented an additional source of energy and nutrients to the microbial consortium, favoring the development of different microbial genera and species. The higher corrosion rate obtained under the untreated sand suggests that MIC occurred due to syntrophic relationships between sulphate reducers or thiosulphate reducers and fermenters identified in the consortium.