Corrosive Sulfur Research Articles

Integrating Flow Field Dynamics and Chemical Atmosphere Predictions for Enhanced Sulfur Corrosion Risk Assessment in Power Boilers.

In this work, we attempt to explain the phenomenon of sulfur corrosion of power boiler water walls under the conditions of large fluctuations in carbon monoxide concentrations. To assess the conditions required for corrosion formation, a criterion based on the chemical and flow field parameters of the flue gas is proposed. The formulated sulfur corrosion criterion is based on the mixture fraction variance and the turbulence time scale. Numerical modeling of coal combustion in a 250 MW power boiler is performed using ANSYS. Two cases of combustion in a boiler are analyzed, with the first simulating the boiler operated using classic high-swirl burners and the second one accounting for boiler operation with modified low-swirl burners. Calculations of pulverized coal combustion are performed using the standard k-ε turbulence model and the combustion described by the mixture fraction. The simulation results reveal that the low-swirl burner is characterized by higher values of the mixture fraction variance and a higher frequency of fluctuation of the velocity field, which is strongly related to an increased corrosion rate. The study outcomes show the validity of using the criterion of the mixture fraction variance and velocity field fluctuations to determine the areas at risk of sulfur corrosion.

First-Principles Study of Sulfur Corrosion Mechanism at Carbon Steel Grain Boundaries

First-Principles Study of Sulfur Corrosion Mechanism at Carbon Steel Grain Boundaries

Kinetic investigation of sulfur corrosion: First principles calculations

The expressions of two important kinetic parameters (chemical activation energy of electrode reaction and absolute potential of equilibrium state) that determine the reaction rate during the anodic dissolution reaction are derived from the thermodynamic and kinetic relationships of the anodic dissolution reaction, the relationship between absolute potential and current density in the anode dissolution process is constructed. Under the framework of first principles, the calculation model of the electrochemical corrosion anodic dissolution reaction is proposed. Density functional theory study of the process of dissolving Fe atoms from the surface of Fe(111) alloy models in vacuum and explicit water molecules. The addition of water molecules and sulfur atoms promotes charge transfer during dissolution and increases the corrosion rate, while water molecules reduce the work function, while S goes increases the work function. Through the corrosion current density model of activation energy, the role of alloy dissolution kinetics with different alloys added was explored. The analysis shows that the addition of Mn and Cr can greatly reduce the anodic corrosion rate and increase the corrosion resistance of Fe.

Influences of Sulfur-Containing Components on the Key Phases of FeS Spontaneous Combustion Dynamics

ABSTRACT In petroleum storage tanks, sulfur-containing crude oil continues to corrode equipment, generating sulfur corrosion products such as FeS. These products exhibit rapid exothermic reactions upon contact with air, thereby increasing the risk of fires and explosions. Additionally, sulfur monomers precipitated from sulfur or other compounds present in crude oil can adhere to FeS, consequently altering its spontaneous combustion characteristics. To explore the impact of associated sulfur content on the spontaneous combustion characteristics of FeS during its formation, this research synthesized FeS and its sulfur mixtures with sulfur concentrations of 5%, 10%, 15%, and 20%. These mixtures were prepared using a liquid-phase method, which involved the synthesis of self-made active FeS followed by the addition of different sulfur components. Differences in the spontaneous combustion characteristics of the five groups of samples were investigated in stages by simultaneous thermal analysis. The trends of the characteristic parameters of spontaneous combustion of FeS with different percentages of sulfur-containing components were analyzed. Finally, the apparent activation energy values of FeS with FeS and its associated sulfur were calculated by using thermodynamic analysis in the room-temperature spontaneous combustion stage (RT-75℃) and high temperature combustion stage (160–250℃). The findings indicate that the presence of sulfur components enhances the reactivity of FeS, yet reduces its oxygen absorption saturation threshold, thus advancing the oxygen absorption endpoint and facilitating entry into the high-temperature combustion stage. Moreover, FeS and its associated sulfur exhibit prolonged sustained combustion times when the sulfur component percentage is below 10%, favorably influencing the combustion behavior of FeS. As the percentage of sulfur component increases (from 10% to 20%), the combustion duration temperature rises from 60°C to 95°C. Additionally, an increase in the percentage of sulfur component (from 10% to 20%) leads to a higher combustion temperature. The activation energies of the five samples were determined using the Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS) kinetic methods. During the room temperature spontaneous combustion stage, the activation energy increases from 65.05 kJ/mol to 112.44 kJ/mol as the percentage of sulfur component rises from 0% to 20%. During the high temperature combustion stage, the activation energy increased from 108.32 kJ/mol to 214.49 kJ/mol with the increase in the percentage of sulfur component. FeS and its associated sulfur necessitate energy to propel the process due to heat absorption from the melting of sulfur monomers. As the reaction progresses into the high temperature stage, the required activation energy escalates accordingly.

Effect of the grain boundary character distribution on the sulfur corrosion behaviour and mechanisms of copper windings under different high temperatures

AbstractAs a typical failure phenomenon in transformers, sulfur corrosion has garnered significant attention in the field of high‐voltage engineering. Grain boundary character distribution (GBCD) copper windings have been introduced to enhance sulfur corrosion resistance by slowing down intergranular corrosion. In this study, the sulfur corrosion behaviour and mechanisms of the GBCD copper windings under various temperatures were experimentally and theoretically studied. Results show that GBCD can enhance the corrosion resistance of copper in liquid environments. With the increase in temperatures, the insulating properties of oil and papers in traditional copper windings experience notable degradation, while GBCD copper windings show more stable insulating behaviours. In addition, modelling of grain boundary energy indicates that the grain boundary structure of GBCD copper windings has a lower average interface energy of 0.170 eV/Å2. Calculations of reaction thermodynamics show that GBCD copper windings possess a higher failure temperature (135.2°C) and inhibition degree (activation energy) of the sulfur corrosion (32,557.62 J/mol), revealing the stability and enhanced sulfur corrosion resistance at elevated temperatures.

Predicting the Ageing Time of Thin Film Sacrificial Copper Strip Sensors Over a Wide Range of DBDS Concentrations

Catastrophic transformer failures are often attributed to corrosive sulphur-related faults. However, the existing challenge lies in the absence of practical, real-time monitoring techniques for sulphur corrosion, especially on-site. Previous studies have proposed the use of thin film sacrificial copper strip sensors as a promising solution to address this issue. Yet, their effectiveness in detecting corrosive by-products resulting from varying concentrations of DBDS breakdown remains unexplored. To bridge this knowledge gap, this study introduces an alternative technique that utilizes MATLAB software for linear interpolation and extrapolation. The findings demonstrate the capability of this technique to predict the ageing time of thin film sacrificial copper strip sensors when exposed to corrosive by-products derived from DBDS breakdown across a broad concentration range. This research aims to provide a valuable contribution towards enabling effective monitoring of sulphur corrosion and enhancing transformer maintenance practices.

100 Years of Corrosion Testing—Is It Time to Move beyond the ASTM D130? The Wire Corrosion and Conductive Deposit Tests

<div>The ASTM D130 was first issued in 1922 as a tentative standard for the detection of corrosive sulfur in gasoline. A clean copper strip was immersed in a sample of gasoline for three hours at 50°C with any corrosion or discoloration taken to indicate the presence of corrosive sulfur. Since that time, the method has undergone many revisions and has been applied to many petroleum products. Today, the ASTM D130 standard is the leading method used to determine the corrosiveness of various fuels, lubricants, and other hydrocarbon-based solutions to copper. The end-of-test strips are ranked using the ASTM Copper Strip Corrosion Standard Adjunct, a colored reproduction of copper strips characteristic of various degrees of sulfur-induced tarnish and corrosion, first introduced in 1954. This pragmatic approach to assessing potential corrosion concerns with copper hardware has served various industries well for a century.</div> <div>Driveline lubricants have always been required to protect hardware, and transmission fluid specifications have always included a version of the copper corrosion strip test to assure this. In conventional transmissions, copper and its alloys are present in the form of mechanical parts such as bushings, bearings, and washers. Corrosion of these parts, while detrimental, does not typically result in immediate failure. However, the incorporation of electronics and electric motors has resulted in new failure modes which can have immediate and devastating consequences. Designing a lubricant to protect new electrified hardware requires an understanding of corrosion that occurs under actual operating temperatures, as well as potential damage from corrosion products. While the ASTM D130 provides general insight regarding the susceptibility of the hardware to corrode, the information is typically gleaned at elevated temperatures, and no information is gathered about the impact of corrosion products. The ASTM D130 is simply not sufficiently specific to adequately assess the risk of these new failure modes that may occur within electric drive units (EDUs). Newer methods, in particular, the wire corrosion test (WCT) and conductive deposit test (CDT), have been created to fill these gaps.</div> <div>In this article, we provide the history of the creation and evolution of the ASTM D130 standard, which is important in understanding both its significance and limitations. We then assess the corrosion characteristics of five lubricants using both the ASTM D130 strip method and the WCT method. We contrast these results, which demonstrate the greater understanding gleaned from the WCT. We then assess the five lubricants with the CDT, which provides insight into whether the corrosion products might endanger the system. We conclude that both the WCT and CDT are needed to provide a holistic understanding of corrosion in electrified hardware necessary to minimize the risk of corrosion-related failure modes. We anticipate that the WCT and CDT will establish themselves in original equipment manufacturer (OEM) specifications over the next decade and will provide a useful assurance of lubricant performance in corrosion, especially for hybrid (HEVs) and electric vehicles (EVs).</div>

Analysis of the failure mechanism of a blast furnace tuyere sleeve with protective coating

The tuyere sleeve plays a crucial role in blast furnaces, enduring a harsh working environment that frequently leads to substantial damage. One approach to extend the service life of tuyere sleeve is to prepare a Ni-based alloy protective layer on its surface. However, there is a lack of experimental information concerning the failure of these protective coatings after real-world use. Therefore, in this study, the failure of a blast furnace tuyere sleeve with protective layer was investigated. Characterizations were performed on both the “original” and failed protective layers, as well as the scale layer. The “original” protective layer exhibits two main issues: excessive copper dilution (＞40%) and significant Ni-Cr enrichment at the interface, which may be attributed to inadequate preparation techniques. The failed protective layer surface is covered with molten slag and iron, and there is a crack running almost completely through the coating. Both oxidation reaction and sulfur corrosion are important factors contributing to the accelerated failure of the coating. Moreover, it is suggested that the compositional inhomogeneity of the protective layer of the tuyere sleeve leads to local stress concentration within the coating, which is an internal cause for thermal fatigue crack formation. Additionally, it can be inferred that the molten slag and iron falling onto the protective layer surface under abnormal furnace conditions not only accelerates crack initiation and propagation but also directly melts the coating material or causes interface reactions, leading to the failure of the protective layer.

New insight into the pyrophoricity and mechanism of ironic sulfide from synergistic effect of FeS and FeS2

The pyrophoricity of ironic sulfide of sulfur corrosion products in oil tanks is a critical safety and environment concern that may trigger fire and explosion accidents. This paper focused on mixtures of FeS with FeS2 and aimed to systematically investigate their influence on the pyrophoricity of ironic sulfide. The results showed that the mixtures’ oxidation spontaneous combustion processes are generally similar, including low-temperature heating, oxidation decomposition, and burning-out stages. The more unstable molecular configuration and uneven surface morphology of FeS made it more prone to spontaneous combustion than FeS2. As the proportion of FeS2 in the sample increased, it absorbed the energy used to activate FeS during the early stages of oxidation and decomposition, causing the sample’s activation energy to increase and its pyrophoricity to weaken. When the proportion of FeS2 reached a certain level, the reaction may produce a large amount of elemental sulfur, which further oxidized and released heat, thus promoting the sample’s pyrophoricity. The study results suggest that the oxidation process of ironic sulfide involved a spontaneous, multistage exothermic reaction and produced intermediate products such as elemental sulfur, leading to a synergistic effect that influenced the reaction process.

Study on the performance and sulfur tolerance mechanism of Pd/beta zeolite in catalytic combustion of toluene

Based on the method of quantitative pyrolysis of ammonium sulfate, sulfur tolerance of Pd/beta zeolite in catalytic conversion of toluene was explored in this paper. Changes in pore structure, valence, acidity, oxidation, and adsorption/desorption behavior were investigated in detail through XRD, N2 adsorption, HRTEM-EDS, XPS, H2-TPR, and NH3-TPD before and after sulfur poisoning. The results proved the structural stability of Pd/beta zeolite in the process of sulfur poisoning. Combined with FT-IR and ICP characterization results, the possible sulfur poisoning process and the intrinsic sulfur tolerance mechanism of Pd/beta zeolite were revealed: Active PdO/Pd reacted with sulfur species to produce inactive PdSO4 was regarded as a major cause of partial deactivation of Pd/beta zeolite. AlO4 units in beta zeolite were likely to combine with sulfur species to obtain Al2(SO4)3 and generate more acidic sites, and SiO4 units in beta zeolite were structurally stable enough to resist sulfur corrosion, guaranteeing the stability of the catalyst. The catalyst catalytic performance was not seriously affected after deep sulfur poisoning, exhibiting good resistance to sulfur poisoning.

Elemental sulfur corrosion of nickel-based alloy 825 in CO2–H2S-containing environment at high temperature and high pressure

The elemental sulfur corrosion resistance and corrosion mechanisms of nickel-based alloy 825 at high temperature and high pressure are still missing. This work investigates the elemental sulfur corrosion of nickel-based alloy 825 in CO2–H2S-containing environment at high temperature and high pressure using weight loss measurement, surface characterization and in-situ electrochemical techniques including electrochemical noise, electrochemical impedance spectroscopy as well as polarization curves. The results show that in the absence of elemental sulfur nickel-based alloy 825 hardly corrodes in the environment containing 0.5 MPa CO2 and 1.6 MPa H2S at 100 °C, since the passive film on the substrate could offer an enough protective performance. However, with the increasing elemental sulfur content, the corrosion of nickel-based alloy 825 becomes more and more obvious. Under the condition of full coverage of elemental sulfur, the uniform corrosion rate of the specimen can be as high as 0.327 mm/y. Moreover, under such a condition, serious localized corrosion could also be observed on the specimen surface. Based on results of electrochemical measurement and surface analysis, it is considered that underneath the elemental sulfur deposit the formation of a strong acidic environment generated from the hydrolysis of elemental sulfur largely destroys the passive film, leading to serious corrosion. Therefore, nickel-based alloy 825 used in high sulfur-containing environment should pay close attention to safety risk from elemental sulfur corrosion. The results of this work could provide a reference for the material selection in high sulfur natural gas field.

Modelling the Mechanism of Sulphur Evolution in the Coal Combustion Process: The Effect of Sulphur–Nitrogen Interactions and Excess Air Coefficients

The efficient use of coal resources and the safe operation of coal-fired boilers are hindered by high-temperature corrosion caused by corrosive sulphur components. To predict the impact of sulphur–nitrogen interactions on sulphur’s evolution and its mechanism of action, a conventional sulphur component evolution model (uS–N) and an improved sulphur component evolution model (S–N) that considers sulphur–nitrogen interactions were proposed in the present study. The models were built using OpenFOAM–v8 software for the coal combustion process, and the generation of SO2, H2S, COS, and CS2 was simulated and analysed under different air excess coefficients. The simulations were conducted to analyse the patterns of SO2, H2S, COS, and CS2 generation at different air excess factors. The results show that, compared with the uS–N condition, the simulated values of coal combustion products (SO2, H2S, COS, and CS2) under the S–N condition were closer to the experimental values, and the errors of different sulphur components at the furnace exit were all less than 5%. As such, the S–N model can more accurately predict the evolution of sulphur components. In the simulation range, when the air excess factor increased from 0.7 to 0.9, the production rate of SO2 increased, while the production rates of corrosive sulphur components H2S, COS, and CS2 decreased significantly by 41.3%, 34.8%, and 53.8%, respectively. Further, the mechanism of the effect of sulphur–nitrogen interactions on the generation rates of different components was revealed at different air excess coefficients. Here, the effect of sulphur–nitrogen interactions on SO2 and COS was found to be more significant at smaller air excess coefficients, and the effect of sulphur–nitrogen interactions on H2S and CS2 was more significant at larger air excess coefficients. The present study can provide a theoretical basis for predicting the evolution of sulphur components during coal combustion and improving the high-temperature corrosion problems caused by such a process.

Isotherm, Thermodynamic and Kinetic Studies of Elemental Sulfur Removal from Mineral Insulating Oils Using Highly Selective Adsorbent.

Elemental sulfur (S8) is a corrosive sulfur compound which was found to be extremely reactive to silver, causing intensive silver sulfide (Ag2S) deposition on on-load tap changer (OLTC) contacts in power transformers. A highly selective adsorbent (HSA), called Tesla'Ssorb, for the removal of S8 from mineral insulating oils was prepared from raw material (RM) using the novel procedure. In this study, the adsorption properties of HSA for the removal of S8 from the oil were determined. RM and HSA were characterized using various techniques, such as field-emission scanning electron microscopy (FESEM), energy-dispersive X-ray (EDX), and X-ray diffraction (XRD). The performance of HSA was determined by adsorption equilibrium, thermodynamic, and kinetic study through batch experiments, at various temperatures and initial concentrations of S8. The obtained results were analyzed by Langmuir and Freundlich adsorption isotherms and it was found that equilibrium data were fitted better with the Langmuir isotherm model. The maximum adsorption capacity was 4.84 mg of S8/g of HSA at 353 K. Thermodynamic parameters, such as enthalpy (ΔH°), Gibbs free energy (ΔG°), and entropy (ΔS°), were calculated and it was found that the sorption process was spontaneous (ΔG° < 0) and endothermic in nature (ΔH° > 0). It was found that the adsorption of S8 follows pseudo-second-order kinetic model, and the activation energy indicated the activated chemisorption process.

Multiple Sulfur Corrosion Simulation on the Oil–Paper Insulation System Under Synergistic Electric and Thermal Fields

Sulfur corrosion in transformers results in insulation deterioration failures. Therefore, in this study, multiple sulfur corrosion was simulated on the oil–paper insulation system. The mechanical properties and hydrogen bond of the insulating paper as well as the mean square displacement and shear viscosity of the insulating oil were investigated under different combinations of electric and thermal fields. The electric field could promote the degradation of the elastic modulus of cellulose. The influence of the AC electric field on the modulus is not as obvious as that of the DC electric field. Temperature has a significant effect on the modulus parameters. With the increase in the temperature, the elastic modulus decreases considerably. The radial distribution function of the model was also investigated. Cellulose can easily form intramolecular hydrogen bonds under AC electric fields. Furthermore, intermolecular hydrogen bonds are easily formed under a DC electric field. The shear viscosity of insulating oil decreases with the increase in the temperature. The presence of the electric field could increase shear viscosity. The results of the study can provide some reference for the microscopic mechanism of multiple corrosive sulfides and investigate effective protection techniques against sulfur corrosion.

Spontaneous Combustion Characteristic Stages of Active FeS and Its Inhibition Effect by Gas-Phase Passivation

ABSTRACT To explore the spontaneous combustion characteristic stages of active ferrous sulfide (FeS) and its inhibition effect by gas-phase passivation. Active FeS samples were prepared and then the spontaneous combustion characteristics of active FeS and commercial FeS samples were compared. The active FeS spontaneous combustion process was divided into several characteristic stages from the perspective of spontaneous combustion kinetics. Furthermore, the inhibition effect of gas-phase passivation on the characteristic stages and the kinetics and thermal effects of active FeS spontaneous combustion process were investigated to further reveal the inhibition mechanism. The results indicate that spontaneous combustion process of active FeS is divided into the room temperature (RT) spontaneous combustion, oxygen-adsorption-induced weight gain, high-temperature combustion and burnout stages, while the spontaneous combustion process of commercial FeS excludes the RT spontaneous combustion stage. Active FeS presents greatly advanced characteristic stages, stronger spontaneous combustion reactivity and more intense reaction in the RT spontaneous combustion and high-temperature combustion stages, which agrees more with the sulfur corrosion products under actual on-site working conditions. The spontaneous combustion tendency of passivated FeS weakens gradually with the increase of passivation time until it loses its RT spontaneous combustion reactivity after 6 h passivation. After the oxide film formed on the surface of passivated FeS is destroyed, its high-temperature combustion reaction becomes relatively intense. The activation energy of passivated FeS in the spontaneous combustion reaction is much higher than that of active FeS, and their activation energies both soar with the deepening of passivation, indicating that the gas-phase passivation technology can effectively inhibit the FeS spontaneous combustion process. The gas-phase passivation time must be maintained for over 6 h despite the weakening inhibitory effect of passivation treatment on the FeS spontaneous combustion process.

Characterization of the Sulfur Corrosion of Paper-Wrapped Windings in the Terahertz Range

Dibenzyl disulfide (DBDS) in mineral insulating oil reacts with the copper wires of windings in the oil-immersed power equipment, thereby decreasing oil-paper insulation properties and even transformer faults. Existing methods applied to detect sulfur corrosion depend mainly on visual observation, which is destructive to the windings. A laboratory study on the characterization of sulfur corrosion in paper-wrapped windings based on reflection terahertz (THz) time-domain spectrum (TDS) is introduced. Test results demonstrate that copper sulfide (Cu2S), a typical corrosion product, shows a significant absorption and scattering in the THz range. Neither the thickness nor the status of insulating paper nor the oxides on the surface of copper conductor greatly influence corrosion detection. The 2-D image of the corrosion morphology of the winding is obtained by <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${X} - {Y}$ </tex-math></inline-formula> horizontal scanning, and the corrosion degree (CD) of the winding is characterized based on reflection THz-TDS.

Effects of Thiophene Degradation on the Corrosiveness of Oil and the Properties of Oil–Paper Insulation in the Oil-Immersed Transformers

As a non-corrosive inactive sulfur, thiophene is one of the most common sulfides in mineral oil, which are retained in oil and used for improving the oxidation stability of the oil. However, thiophene may be decomposed and form low-molecular sulfide with strong corrosiveness because of rapid energy accumulation under operating conditions of the oil-immersed power transformer. Thus, this study explored the effect of thiophene degradation on the corrosiveness and properties of insulating oil under thermal and electrical aging conditions, including a case investigation of sulfur corrosion of a 500-kV electric reactor and the accelerated aging experiments of oil–paper insulation. The results showed that the degradation and pyrolysis of thiophene depend on energy accumulation induced by thermal and electric fields in the oil-immersed transformers. Under the premise of thiophene without degradation and transformation, thiophene can still delay the deterioration of insulating oil due to its high oxidation resistance. The continuous energy accumulation induced by thermal and electric fields may cause the molecular chains of thiophene molecules to break and form some corrosive low-molecular sulfides, thereby resulting in the increase of the corrosiveness of oil, the decrease of the properties of oil–paper, and posing a huge corrosion threat to the oil-immersed transformer.

Permeating hydrogen generated from the elemental sulfur corrosion of low carbon steel

Permeating hydrogen generated from the elemental sulfur corrosion of low carbon steel was investigated using a double cell system and its effect on the mechanical properties of steel was also discussed. Results show that elemental sulfur corrosion of low carbon steel is accompanied by significant hydrogen permeation, e.g., permeating hydrogen current reaches 12.3 μA/cm2 in CO2-containing environment at 80 °C. The hydrogen permeation process are greatly affected by the structure and composition of the corrosion product, the environmental temperature and gas composition. This permeating hydrogen enhances the brittleness of the low carbon steel and tends to cause hydrogen-induced cracking.

Gas production mechanism of Irgamet 39 and its long‐term corrosion resistance

AbstractThe phenomenon of transformer failure caused by oil‐sulphur corrosion of oil₋paper insulation system has always been concerned by scholars. Irgamet 39 is the most used metal passivator for inhibiting sulphur corrosion. However, Irgamet 39 causes abnormal dissolved gas in oil during the process of exerting anti‐corrosion effect. Herein, the gas production mechanism of Irgamet 39 and its long‐term corrosion resistance were investigated. Compared with other metal passivators, the Irgamet 39 produces more dissolved gases in oil, especially H2, CO and CO2. The main sources of free radicals in the gas production process are from the branched chains of the Irgamet 39 structure (−CH2N(C8H17)2 and −CH3). Furthermore, the ageing products of insulating paper and oil promote the cleavage of the chain in the Irgamet 39 molecule, which then causes Irgamet 39 to generate more dissolved gases. Irgamet 39 exhibits excellent long‐term corrosion inhibition properties,while it also leads to abnormal gases in the oil, which can affect the interpretation of the dissolved gas analysis data and thus interfere with the diagnosis. This work provides useful information for the practical application of Irgamet 39 and helps electrical workers make reasonable predictions for transformer problems.

Sulfur Corrosion Mechanism in Power Transformers and Its Detection Techniques: A Review

Monitoring the progression of sulfur corrosion in insulating oils, particularly mineral oils, gives valuable information on the general health of the power transformers, thus preventing the possibility of catastrophic failures. The sulfur corrosion mechanism in insulating oils remains unclear although it is believed that this phenomenon is initiated by the presence of corrosive by-products of dibenzyl disulfide (DBDS) (i.e., mercaptans and elemental sulfur). A number of models have been developed that explain the chemical reactions, formation, and deposition of copper sulfide in power transformers. Irrespective of the sulfur corrosion mechanism, monitoring the progression of sulfur corrosion in power transformers is crucial before effective countermeasures can be implemented. The capability and limitations of standard and non-standard corrosion test methods based on the quality of the insulating oils and paper insulations are extensively reviewed in this article. This sets out the ultimate goal of searching for a reliable and quantifiable online condition monitoring tool to track the progression of sulfur corrosion in transformer insulating oils in real-time and facilitate timely remedial intervention.