Corrosive Sulfur Research Articles

Corrosion mechanism for local enrichment of acids and copper ions in copper-insulating paper contacts leading to the acceleration of copper sulfide formation induced by dibenzyl disulfide

Local enrichment of acids and copper ions in copper-insulating paper accelerates sulfur corrosion.

Inhibition effectiveness and depletion characteristic of Irgamet 39 in transformer oil

Recently, a large amount of power transformer dielectric failures caused by the copper sulfide (Cu 2 S) contaminant are reported, which is a semi-conductive black solid material produced by the reaction of DBDS additive and copper under certain temperatures. Irgamet 39 is used as metal passivator in transformer oil that can delay the corrosion process in laboratory investigations, which forms a protective layer on the copper surface to prevent the harmful reactions between the corrosive sulfur and copper. However, the inhibition effectiveness of Irgamet 39 on mildly corroded copper surface and its depletion characteristic are still not clear. Herein, corroded copper was treated with Irgamet 39 under different aging conditions, suggesting Irgamet 39 could dramatically improve the properties of copper strips as determined by EDX analysis. Evaluation of the stability of impermeable layer under continuous ageing processes suggests that maintenance of specific concentration of metal passivator is critical for the stability of protective layer. In addition, the depletion characteristic of Irgamet 39 was investigated under different ageing conditions with variables like temperature, copper, insulating paper and atmosphere factor. It indicates that oxygen plays an important role in consumption of the metal passivator.

Heat-Mass Exchange in the Separating Filter of Fuel System for the Gas Turbine Plant of Gas-Compressor Unit

The removal of mechanical impurities and drop moisture from the cycle air contributes to an increased reliable operation of the gas turbine plant of gas-compressor unit. Many scientific papers discuss the issues related to the air purification and little attention is paid to the preparation of fuel gas for the combustion. The presence of gas condensate and water drops in the fuel gas results in an increased irregularity of temperature field in the combustion chamber, the deposit formation in the burners, the erosion wear of blade row and the acceleration of erosion processes. A reliable operation of the gas turbine plant of gas-compressor unit requires preventing liquid hydrocarbons and water drops from entering the combustion chamber. A separating filter was developed for gas-compressor units installed in underground gas storages, whose operating conditions differ by an increased content of mechanical particles. The development of this filter is based on the experimental investigations of processes that occur in the heat-exchange element. This unit combines the principles of mechanical purification and heat exchange that allows us to produce fuel gas of appropriate quality. Pilot full-scale tests showed that the use of separating filter for the fuel preparation system of gas turbine plant prevents not only heavy hydrocarbon compounds and mechanical impurities, but also sulfur from getting into the combustion chamber. Thanks to this we manage to get rid of the sulfur corrosion of the equipment, which is caused by liquid hydrocarbon drops that get into the combustion chamber of gas turbine plant.

Evaluation of kaolin clay as natural material for transformer oil treatment to reduce the impact of ageing on copper strip

Copper sulfide formation is one of the possible corrosion mechanisms involving the corrosive sulfur of copper. EDX scans of copper strip before and after immersing in aged transformer oils containing sulfur without copper passivator at 100°C for 3h indicated that copper sulfide was formed on the copper strip surface. The reclaimed oil by using kaolin clay reduced the sulfur content of all tested aged oils reducing the corrosion on copper strips in all samples investigated. In every case studied, the oil after reclamation by kaolin clay showed no sign at all of corrosive sulfur on the surface of copper strips. Nevertheless the atomic absorption analysis of copper ions in oil samples showed that the dissolution of copper was increased with increasing the sulfur content in the oil at different times of immersed copper strip in the oil.

Assessment of paper-oil insulation under copper corrosion using polarization and depolarization current measurements

This paper discusses the effect of temperature on polarization and depolarization current measurements on paper oil insulation system. The influence of copper sulphide formed due to corrosive sulphur in mineral oil, on the changes in polarization and depolarization current at different temperatures are considered. A significant increase in the magnitude of polarization and depolarization currents due to deposits of copper sulphide on paper layers is observed. The conductivity of paper insulation increases significantly with increase in temperature. The increase in current is attributed to thermally active conducting particles of copper sulphide. The Debye model parameters of equivalent circuit under copper corrosion have been computed and a model for failure due to copper sulphide is explained using the data on polarization and depolarization currents.

Development of measures to improve technologies of energy recovery from gaseous wastes of oil shale processing

Prospects of the use of oil shale are associated with its thermal processing for the production of liquid fuel, shale oil. Gaseous by-products, such as low-calorie generator gas with a calorific value up to 4.3MJ/m3 or semicoke gas with a calorific value up to 56.57 MJ/m3, are generated depending on the oil shale processing method. The main methods of energy recovery from these gases are either their cofiring with oil shale in power boilers or firing only under gaseous conditions in reconstructed or specially designed for this fuel boilers. The possible use of gaseous products of oil shale processing in gas-turbine or gas-piston units is also considered. Experiments on the cofiring of oil shale gas and its gaseous processing products have been carried out on boilers BKZ-75-39FSl in Kohtla-Jarve and on the boiler TP-101 of the Estonian power plant. The test results have shown that, in the case of cofiring, the concentration of sulfur oxides in exhaust gases does not exceed the level of existing values in the case of oil shale firing. The low-temperature corrosion rate does not change as compared to the firing of only oil shale, and, therefore, operation conditions of boiler back-end surfaces do not worsen. When implementing measures to reduce the generation of NO x , especially of flue gas recirculation, it has been possible to reduce the emissions of nitrogen oxides in the whole boiler. The operation experience of the reconstructed boilers BKZ-75-39FSl after their transfer to the firing of only gaseous products of oil shale processing is summarized. Concentrations of nitrogen and sulfur oxides in the combustion products of semicoke and generator gases are measured. Technical solutions that made it possible to minimize the damage to air heater pipes associated with the low-temperature sulfur corrosion are proposed and implemented. The technological measures for burners of new boilers that made it possible to burn gaseous products of oil shale processing with low emissions of nitrogen oxides are developed.

Inhibition method for the degradation of oil–paper insulation and corrosive sulphur in a transformer using adsorption treatment

This study investigated the inhibitory effects of adsorption treatment on the degradation of oil–paper insulation and corrosive sulphur in oil. A thermal ageing experiment at 130°C was conducted using five different adsorbents to adsorb some impurities in oil on the 15th day of a 30 day ageing test, the related characteristics of oil–paper insulation before and after the adsorption treatment were measured and analysed. Meanwhile, a thermal ageing experiment at 150°C was also conducted before using five different adsorbents to adsorb dibenzyl disulphide (DBDS) in oil, energy dispersive X-ray was used to evaluate the degree of the corrosion of windings. The result indicates that adsorption treatment is an effective method to inhibit the degradation of oil–paper insulation. A molecular sieve, silica gel and activated alumina can effectively improve the performance of oil–paper insulation. By contrast, the antioxidant (2, 6-di-tert-butyl-p-cresol) can be also adsorbed by adsorbents, which accelerate the ageing degradation of the insulating oil. On the other hand, the adsorbents can adsorb DBDS in oil, but cannot remove all DBDS. The effect achieved from silica gel is especially significant, which not only effectively improves the performance of oil–paper insulation but also adsorbs DBDS in oil.

Marine Slow-Speed Diesel Engine Diagnosis with View to Cylinder Oil Specification

The possibility of marine slow-speed diesel engine cylinder-piston group diagnosis with view to the specification of waste oil taken from the under-piston space has been discussed. The specifics of using high-base cylinder oils in marine slow-speed diesel engines to prevent sulfur corrosion of the cylinders have been described. Typical challenges, arising in the process of using oils for lubricating the cylinder-piston group and ways to overcome such challenges have been specified. Empirical data that allowed for determining the optimum cylinder oil consumption and ensuring minimum wear diesel engine cylinder bushings have been provided. The experiments that were carried out in sea ship conditions are proved by findings of an oil analysis at a third-party onshore research laboratory.

Application of molecular probe to investigate surface structure of metal passivator on copper

Copper sulfide (Cu 2 S) contaminant is semi-conductive. Its formation and migration to insulating paper and oil caused insulation breakdown. Addition of benzotriazole derivatives as metal passivator slows down the corrosion process, as the metal passivator produces a protective layer on the copper surface, which prevents the reaction between corrosive sulfur and copper. But the surface structure of this impermeable film is still unknown. Herein we reported our investigation on the orientation of metal-passivator complex on copper surface by means of molecular probe. Ageing experimental study with different steric and electronic groups in benzotriazole skeleton indicated that the second position of the molecule was sensitive to steric effect, suggesting end-on orientation preferable. Subsequently, SEM-EDX revealed the relative amount of copper sulfide on copper surface. Moreover, FTIR represented the characteristic wavenumber of C=O, C=N moiety and benzene skeleton of passivator-copper complex. XPS analysis delivered the organic elemental composition of the protective layer.

Formation of Corrosive Sulfur with Dibenzyl Disulfide in Fluid-Filled Transformers

The formation of corrosive sulfur as a result of the addition of dibenzyl disulfide (DBDS) to transformer oils has been investigated. Corrosive sulfur in a transformer affects all aspects of its insulation and conductive components by deposition of Cu2S. Previous studies have suggested that the formation of Cu2S was initiated by a DBDS–Cu complex. This work shows an alternate pathway via thiolate formation for the deposition of corrosive sulfur on copper conductors. The open circuit potential results showed no reduction of DBDS onto copper surfaces, but the degradation products of DBDS, which include dibenzyl sulfide and benzyl mercaptan, were both found to adsorb on copper surfaces, forming a copper thiolate. The formation of copper thiolates was also demonstrated by a heterogeneous reaction of CuO and benzyl mercaptan. Thermal degradation of the thiolate eventually produced copper sulfide Cu7.2S4 as identified by X-ray diffraction analysis.

Electrochemical noise monitoring of sulphur corrosion for nickel alloy 718

Sulphur corrosion for nickel alloy 718 was monitored by electrochemical noise under high temperature. Cross-recurrence quantification analysis (CRQA) on potential and current noise signals was used to characterise the stable coupling interaction between them. Diagnosis criterion for stable pitting started was proposed based on the CRQA parameter determinism per cent trajectory. The proposed method displayed accurate and robust characteristics compared to the common localisation index.

Maximum acceptable concentrations of dbds, sulphur mercaptan and optimal concentration of passivators for safe and prolonged operation of power transformers

The study presents the results of experimental investigation of finding out the maximum acceptable concentrations of DBDS, sulfur mercaptan, and optimal concentration of passivator for safe and prolonged operation of power transformers in the local environmental conditions of Saudi Arabia. For experimental investigation of optimal concentrations of DBDS and sulfur mercaptan, new oil free of sulfur compounds was acquired. Four specimens of this were spiked with different concentrations of DBDS and another four with free sulfur mercaptan RSH concentrations. The covered conductor deposition (CCD) tests were performed in accordance with IEC 62535 method on all the specimens. Next, to study the effect of passivator concentrations and temperatures on corrosive sulfur formation, 10 specimens from new oil were spiked with different concentrations of BTA and Irgamet 39. Copper strips were immersed in these specimens and the vials containing the oil and the copper strips were subjected to different temperature from 50 to 150°C for 24 hours in the oven. The experimental results indicated that the concentration of DBDS should always be <4 ppm and sulfur mercaptan < 1 ppm in the new oils before putting in to the service. Based on the effectiveness of the passivators, BTA was found to be effective with 50 ppm concentration at 150°C compared to Irgamet 39 which was effective only with 150 ppm concentration.

エンジンルームに実装される筐体構造電子部品の硫黄腐食における加速試験方法の提案

エンジンルームに実装される筐体構造電子部品の硫黄腐食における加速試験方法の提案

Removal of corrosive sulfur from insulating oil with adsorption method

Corrosive sulfur has been found in numerous mineral insulating oils. Adsorption is a promising method to remove the corrosive sulfur in insulating oil. In this paper, three types of adsorbents, CeY, CuY, and AgY, were prepared with liquid-phase ion exchange. The adsorbents were characterized by X-ray fluorescence, X-ray photoelectron spectroscopy, BET analysis, thermo-gravimetric/differential scanning calorimetry and X-ray diffraction. The results showed that active ions, Ce, Cu, and Ag, had highly decentralized into the lattice location of zeolites and occupied the cationic position. The adsorbents achieved good adsorption effect toward dibenzyl disulfide and dodecyl mercaptan through π complexation of Cu, Ag, and Ce cations in zeolites with sulfide.

Laboratory validation of method of solvent extraction for removal of sulphur compounds from mineral oil

The presence of corrosive sulphur compounds in mineral oil is a serious problem affecting the life of transformers. There are several techniques available to remove corrosive sulphur and among them the method of solvent extraction is useful for complete removal of sulphur compounds. In this investigation, laboratory experiments were carried out to validate method of solvent extraction for removal of sulphur compounds like Dibenzyl disulphide and Mercaptan sulphur from mineral oil. The optimum oil to solvent ratio, solvent to co-solvent ratio are investigated and discussed. Efficiency of method of solvent extraction for removal of sulphur compounds is demonstrated on a laboratory scale and further improvements to properties of mineral oil is proposed by the use of conventional reclamation techniques.

Unique antioxidant and sulfur corrosion retardant properties of transformer oil blended with turmerone extract

One of the most detrimental effects associated with transformer insulating materials (paper and oil) and copper windings is the corrosive action of certain sulfur components found in transformer oil. Consequently, transformer oil is typically blended with both antioxidant and anti-corrosive agents in an attempt to prolong ageing effects and hinder copper sulfide deposition respectively. This study focusses on the effect antioxidants have on corrosive sulfur deposition on copper metal surfaces. To this end transformer oil was blended with a natural extract from turmeric powder and tested for its ability to act as an antioxidant and to retard copper sulfide deposition. The efficacy of this blended oil was compared with that of oil blended with either of two commonly used antioxidants, namely, 2,6-di-tert-butyl- 4-methylphenol or 2,6-di-tert-butylphenol. Tests for corrosive sulfur showed that for the turmerone oil blend there was a substantial delay in the onset of copper sulfide deposition on the surface of copper metal. Open circuit potential studies showed that the turmerone fraction that was blended into the transformer oil was adsorbed onto the copper surface. This unique property was not observed for the other two antioxidants in this study and can account for the retardation of copper sulfide deposition. In addition, the turmerone-virgin oil blend did not alter the thermal stability of the Kraft insulation paper in direct contact with the oil. The performance of the turmerone oil blend as a dual antioxidant and retardant of copper sulfide deposition renders it eminently suitable for extending the lifetime of insulation in fluid-filled transformers.

High-Temperature Reliability of Copper Wire-Bonded Packages Encapsulated with Mold Compounds Containing Sulfur Compounds

Cu wire-bonded (CuWB) packaging is more susceptible to corrosion than traditional inert gold wires. CuWB reliability greatly depends on the compatibility of Cu wire with the surrounding encapsulating mold compound as this matrix can provide a corrosive environment leading to reliability issues. Many mold compounds contain specific components, which are sulfur-based compounds. Since the reliability testing of an encapsulated packaged device involves thermal treatments, such as the high-temperature storage life (HTSL) test, there is a concern that corrosive sulfur compounds can be produced at high temperatures (e.g., 150°C and 175°C), endangering CuWB reliability. This article describes detection methods of sulfur compounds produced from mold compounds, if any, at high temperatures such as 175°C and CuWB die package reliability with mold compounds containing sulfur compounds. The dynamic headspace concentration-gas chromatography-mass spectroscopy analysis technique was used to test liberation of gaseous and volatile sulfur compounds from mold compounds at temperatures 25°C, 150°C, 175°C, and 200°C. No gaseous sulfur compounds were detected by chromatographic methods within the time period of the experiments. To determine sulfur-containing anionic species present in the mold compound matrix, such as sulfide, sulfite, sulfate, and thiosulfate, ionic compounds were extracted to water and analyzed by ion chromatography. Upon analysis, the only sulfur-bearing anion found in the samples was sulfate. Thermally treated mold compounds for 2,000 h at 150°C and for 1,000 h at 175°C were also extracted and analyzed to determine possible decomposition of sulfur compounds due to the thermal aging process. Corrosion due to sulfur compounds and reliability of CuWB was evaluated by HTSL for 2,000 h at temperatures of 150°C and 175°C with devices packaged with mold compounds containing sulfur compounds. CuWB ball bond-Al interface and Cu stitch bond integrity were evaluated by focused ion beam-scanning electron microscopy with energy-dispersive x-ray spectroscopic analysis and wire pull and ball shear testing of CuWB ball bonds. No reliability issues due to sulfur compounds were found with mold compounds containing sulfates up to ∼45 ppm.

Effect of electric field at 150 &amp;#x000B0;C on the formation of corrosive sulfur in mineral transformer oil

The effect of the application of 12 kV at 150 °C on the formation of corrosive mineral copper sulfide in mineral transformer oil was investigated. It is considered that the presence of sulfur corrosion causes failures in operating windings transformers above 35 kV. Research trials on mineral transformer oils were performed at 150 °C without an electric field, and also at 150 °C in electric field based on the norms for the detection of corrosive sulfur established by ASTM D-1275 and IEC 62535. The effect of the applied electric field on the process of corrosive sulfur formation was determined. Varying amounts of copper sulfide were found, both on bare Cu electrodes and Cu electrodes covered with Kraft paper, pure Cu formation was also found in the oil. Copper sulfide was quantified using the X-ray dispersion technique with a scanning electron microscope, with EDX.SEM E., and chemical methods are used to determine the quantity of Cu in the oil after the test.

Effects of metal salt addition on odor and process stability during the anaerobic digestion of municipal waste sludge

Anaerobic digestion (AD) is an effective way to recover energy and nutrients from organic waste; however, several issues including the solubilization of bound nutrients and the production of corrosive, highly odorous and toxic volatile sulfur compounds (VSCs) in AD biogas can limit its wider adoption. This study explored the effects of adding two different doses of ferric chloride, aluminum sulfate and magnesium hydroxide directly to the feed of complete mix semi-continuously fed mesophilic ADs on eight of the most odorous VSCs in AD biogas at three different organic loading rates (OLR). Ferric chloride was shown to be extremely effective in reducing VSCs by up to 87%, aluminum sulfate had the opposite effect and increased VSC levels by up to 920%, while magnesium hydroxide was not shown to have any significant impact. Ferric chloride, aluminum sulfate and magnesium hydroxide were effective in reducing the concentration of orthophosphate in AD effluent although both levels of alum addition caused digester failure at elevated OLRs. Extensive foaming was observed within the magnesium hydroxide dosed digesters, particularly at higher doses and high OLRs. Certain metal salt additions may be a valuable tool in overcoming barriers to AD and to meet regulatory targets.

Space Charge Behavior in Paper Insulation Induced by Copper Sulfide in High-Voltage Direct Current Power Transformers

The main insulation system in high-voltage direct current (HVDC) transformer consists of oil-paper insulation. The formation of space charge in insulation paper is crucial for the dielectric strength. Unfortunately, space charge behavior changes because of the corrosive sulfur substance in oil. This paper presents the space charge behavior in insulation paper induced by copper sulfide generated by corrosive sulfur in insulation oil. Thermal aging tests of paper-wrapped copper strip called the pigtail model were conducted at 130 °C in laboratory. Scanning electron microscopy (SEM) was used to observe the surface of copper and paper. Pulse electroacoustic (PEA) and thermally stimulated current (TSC) methods were used to obtain the space charge behavior in paper. Results showed that both maximum and total amount of space charge increased for the insulation paper contaminated by semi-conductor chemical substance copper sulfide. The space charge decay rate of contaminated paper was significantly enhanced after the polarization voltage was removed. The TSC results revealed that copper sulfide increased the trap density and lowered the shallow trap energy levels. These results contributed to charge transportation by de-trapping and trapping processes. This improved charge transportation could be the main reason for the decreased breakdown voltage of paper insulation material.