Microbial consortium influence upon steel corrosion rate, using polarisation resistance and electrochemical noise techniques

The microbiologically influenced corrosion (MIC) is a process, which affects the oil industry, particularly the hydrocarbons extraction, transport and storage. MIC evaluation has been normally based upon microbiological tests, and just a few references mention alternating methods, such as the electrochemical techniques, which can be used as criteria for their evaluation.In this work, two different electrochemical laboratory techniques, polarisation resistance and electrochemical noise were used, in order to determine the corrosion behaviour of a microbial consortium, obtained from a gas transporting pipeline, located in the southeast of Mexico.The bacteria population growth was found to be different for sessile and plancktonic microorganisms. Moreover, long incubation times were required to reach the maximum concentration of sessile bacteria.The electrochemical techniques used in this study exhibited a similar tendency on the corrosion rate behaviour with time, and values above 0.3 mm year⁻¹ were observed at the end of the experiments.The experiments were complemented with surface analysis. Scanning electron microscope observation of APIXL52 steel coupons, exposed to the consortium action, revealed bacteria presence, as well as a damaged steel surface. A type of localized corrosion was observed on the metal surface, and it was associated to the bacteria effect.     

The influence of microstructure on the corrosion rate of various carbon steels

This paper presents a fundamental study of the influence of carbon steel microstructure on the corrosion rate. Subsequently, the corrosion performance of various grades of carbon steels were evaluated in stirred autoclaves under elevated carbon dioxide and temperature conditions. Corrosion and penetration rates were determined via mass loss and optical microscopy, respectively. It was found that the corrosion rate of carbon steel line pipe is influenced by microstructure. More specifically, a relationship between localized corrosion susceptibility and the presence of pearlite bands in the steel microstructure was found. However, no correlation was evident between minor elemental concentrations (i.e., Ni, Cr, Mo) and corrosion resistance. It has been proposed that the corrosion stability of the various microstructures may arise from variations in the distribution of carbon bearing phases within the steel. In the banded ferrite/pearlite structure, the carbon-bearing phase (pearlite) is distributed in layers whereas in the other structures the carbon-bearing phases are much more evenly distributed. This study reports on the corrosion resistance of carbon steels in relation to their chemical and physical properties.     

碳钢试片实海电化学检测与腐蚀规律的相关性

引言 由于海水腐蚀的严重性和复杂性,材料在海洋环境中的腐蚀数据积累及试验研究一直受到各国的重视.美国ASTM曾委托LaQue腐蚀试验中心开展了全球14个海水腐蚀站点的材料腐蚀试验[1],为评价世界范围内海水的腐蚀性提供了依据.     

Corrosion behaviour of innovative stainless steels in mortar

The main problem of the building sector is the limited durability of reinforcing concrete structures under highly aggressive environments due to the corrosion of reinforcements. In order to demonstrate that stainless steels are the adequate solution to avoid corrosion of reinforced concrete structures by contained chlorides, the corrosion behaviour of AISI 304 and AISI 316L stainless steels in mortar with two chloride doses is compared with the corrosion behaviour of three new stainless steels of low Ni content and reduced cost, and with the traditional carbon steel. The lowest chloride contamination (2% Cl⁻) has been used in this research to provoke corrosion in an active state of reinforcing carbon steel, whereas the highest one (5% Cl⁻) exceeds all expected levels found in the natural environment, including sea water. The new stainless steels remain in the passive state in mortar specimens with both chloride contents.     

Electrochemical investigation of the corrosion behavior of chromium-modified carbon steels in water

Electrochemical measurements were performed on four steels with different chromium (Cr) contents in simulated CANDU reactor coolant at room temperature to investigate the influence of chromium content on the corrosion behavior of the steels. The addition of chromium to carbon steel can promote passivation. The passive film significantly decreases the corrosion rate, and thus improves the corrosion resistance of the steels as chromium content is increased. Repassivation kinetic experiments indicate that there is a more rapid repassivation rate and a more stable passive film on steels containing a higher concentration of chromium. The slip-oxidation model was used to calculate the crack growth rate (CGR) on the steels. The 304L stainless steel has the highest CGR with an increase in potential of the steels studied. Chromium modification of steels can improve the resistance to corrosion. However, its influence on cracking and crack growth must be taken into consideration. The 2.5%Cr-1%Mo steel gave the best overall results when considering both the corrosion and the cracking behavior of the steels studied.     

Corrosion of carbon steel influenced by anaerobic biofilm in natural seawater

The bacteria in the anaerobic biofilm on rusted carbon steel immersed in natural seawater were characterized by culturing and molecular biology techniques. Two types of anaerobic bacterium, sulfate-reducing bacteria (SRB) Desulfovibrio caledoniensis and iron-reducing bacteria Clostridium sp. uncultured were found. The compositions of the rust layer were also analyzed and we found that iron oxide and sulfate green rust were the major components. To investigate the corrosion mechanisms, electrochemical impedance spectra was obtained based on the isolated sulfate-reducing bacteria and mixed bacteria cultured from rust layer in laboratory culture conditions. We found that single species produced iron sulfide and accelerated corrosion, but mixed species produced sulfate green rust and inhibited corrosion. The anaerobic corrosion mechanism of steel was proposed and its environmental significance was discussed.     

Threshold chloride concentration for stainless steels activation in concrete pore solutions

The threshold chloride concentration for stainless steels activation in concrete environments depends not only on chemical composition of the steel and on pH level of concrete pore solution but is also considerably affected by the superficial state of the steel. The presence of scales leads to significant decrease of corrosion resistance. This study evaluates the corrosion resistance of various stainless steels exposed to pore solutions of fresh concrete by means of electrochemical methods. All tested materials with bare surface, except for martensitic chromium steel FeCr12, proved to be completely resistant to fresh concrete pore solution containing chlorides. If the surface is scaled, the identically high resistance cannot be expected even for the most alloyed stainless steels.     

In situ corrosion study of stainless steels in an MSF desalting plant

The corrosion resistance of different stainless steel grades have been studied as regards localized attack under service conditions. Test racks with welded samples with artificially applied crevices were inserted in three different flash chambers. Materials used for splash plates, brine piping and. condenser tubes were also tested.Beinge a pilot plant, various process conditions were tested. Hence, the materials have been exposed to different corrosive conditions, including stagnant seawater during shut-down periods.The results show that stainless steels of type 316L and higher alloyed exhibit good corrosion resistance, even in brine at high temperature viz pipes from the brine heater.     

The influence of Desulfovibrio vulgaris on the efficiency of imidazoline as a corrosion inhibitor on low-carbon steel in seawater

The action of Desulfovibrio vulgaris (Dv) during a corrosion process has been reported in literature, but the influence of imidazoline in the formation of biofilms is not clear, as well as the effect of bacteria on the efficiency of the corrosion inhibitors. The aim of this work is to determine the behavior of bacteria in the presence of imidazoline. Therefore, the growth of Dv, isolated and characterized from a morphological point of view, was monitored during 21 days, during which synthetic seawater was used as the culture medium, according to the ASTM D665-98 standard. Electrochemical noise (EN) was employed to establish the corrosion type generated by the microorganism on an AISI 1018 steel cylinder. The attack was observed using scanning electron microscopy (SEM). In order to evaluate the efficiency of the corrosion inhibitor, Tafel extrapolation was used; the optimum concentration of the inhibitor was used in the presence of sulphate-reducing bacteria (SRB). In general, two forms of corrosion were observed: localized corrosion (in the LAG phase) and mixed corrosion (in the LOG phase).     

Corrosion behaviour of new stainless steels reinforcing bars embedded in concrete

The activities concerned with the evaluation, repair and restoration of structures are estimated to amount to 35% of the total volume of the work in the building sector and this continues to increase. The corrosion of rebars in the reinforced concrete structures (RCS) is the main reason for their degradation, so the use of reinforcing stainless steels seems to be one of the possible solutions with most probabilities of solving this problem. In this work, in order to demonstrate the advantages of using reinforcing stainless steels, the corrosion behaviour of AISI 304 and 316 reinforcements embedded in concrete slabs (C35/45 and C60/70 concrete) with two chloride contents are compared with three low-cost and low-Ni austenoferritic stainless steels and with the conventional carbon steel. The lower chloride contamination selected in this research, was enough to cause the corrosion in the active state of the carbon steel reinforcements, whereas the highest one exceeded the expected contamination in the natural environments, including sea media. The metallic materials remaining in the passive state can be considered, from the point of view of corrosion resistance, adequate as reinforcements in the RCS.     

Theoretical and experimental study of galvanic coupling effects between carbon steel and stainless steels

The use of stainless steel in high corrosion risk areas represents a viable option for reducing the life-cycle cost and extending the service life of concrete structures. However, the possible galvanic corrosion between it and carbon steel continues to be a concern. In this article, the galvanic coupling behaviours of carbon steel and three different stainless steels were investigated in simulated pore solutions and concrete specimens. The results showed that the oxygen reduction reaction was much lower on stainless steel than on passive carbon steel, leading to a lower galvanic coupling current between stainless steel and corroding carbon steel than that between passive and corroding carbon steels. However, rust contamination of stainless steel was found to increase galvanic coupling corrosion on carbon steel.     

Effects of sulfate-reducing bacteria on the corrosion behavior of carbon steel

The influences of the growing process of sulfate-reducing bacteria (SRB) in seawater system on the medium state and corrosion behavior of carbon steel were studied by detecting solution state parameters and using corrosion electrochemical methods. The growing process of SRB in the seawater shows the three stages of growing, death and residual phases. The solution state parameters of the concentration of sulfide, the pH value and the redox potential changed during the three stages of the SRB growing process. And the corrosion rate of D36 carbon steel was accelerated during the growing phase and stable during the death and residual phases. The results indicate that the medium state and the corrosion rate of the steel do not depend on the number of active SRB, but depend on the accumulation of the metabolism products of SRB.     

Successful use of special stainless steels in nitrogen-based fertilizer plants

The modern urea plants are using a stripping process to reduce the energy consumption. The potential, very severe corrosion problems have been mastered by special grades and strict process control. The different grades are reviewed. After more than 20 years operation the results are very satisfying. In ammonia plants, an often forgotten corrosion problem is found in the heat exchangers. After about 3–6 years failures caused by chloride continuing cooling water may appear on carbon steel or low alloyed austenitic stainless steels. Corrosion mechanism is reviewed. Duplex stainless steels has been used with success and the properties are presented. An example of life-cycle cost shows that duplex stainless steel is an inexpensive way to solve chloride related corrosion problems. Condensation and evaporation of nitric acid in heat exchangers in nitric acid plants cause severe corrosion on conventional stainless steel grades. Low impurity in combination with high chromium content has proved to result in stainless steel with improved corrosion resistance.     

奥氏体钢盐雾腐蚀研究

本文采用盐雾腐蚀方法评价奥氏体钢的抗盐雾腐蚀性能,利用金相、XRD对材料的组织进行了分析,对该材料在盐雾环境中的腐蚀形态进行了观测,结果表明该材料在盐雾环境中的腐蚀形态以点蚀为主,并提出在盐雾环境中使用该材料的热处理方法,以提高该材料的耐盐雾腐蚀性能.     

Corrosion behaviour of some stainless steels in chlorinated Gulf seawater

The corrosion resistance of conventional and high alloy stainless steels (specifically 316L, 317L, 904L, duplex 2205, 3127hMO, 1925hMO, 254SMO, 654SMO and Remanit-4565) was determined electrochemically in chlorinated and unchlorinated Arabian Gulf Seawater at 25 and 50 °C. The stainless steels 316L and 317L were used as reference alloys. The electrochemical potentiodynamic cyclic polarization method was used to determine the passive film break down potential (E _b), protection potential (E _prot) and maximum current attained on scan reversal (I _max). It was found that at 25 °C in chlorinated and unchlorinated seawater and at 50 °C in unchlorinated seawater, stainless steels 316L and 317L have poor resistance to corrosion, Stainless steels 904L and duplex 2205 at 25 °C in chlorinated and unchlorinated seawater showed good resistance to corrosion but at 50 °C these steels failed to resist. The high alloy stainless steels such as 3127hMO, 1925hMO, 254SMO, 654SMO and Remanit-4565 showed better corrosion resistance under all the test conditions.     

生物基聚丁内酰胺在开放水体中的降解行为

探讨了生物基聚丁内酰胺在上海周边不同开放水体中的降解行为,对材料的失重率、黏均分子质量、表面形貌和力学性能等进行测试.结果表明:聚丁内酰胺在不同水体中均可发生本体降解,40 d内在海水中黏均分子质量降低可超过50％,并随水体盐度、浸泡时间的增加而进一步降低.水体中的微生物及潮汐带来的机械力加剧了表面腐蚀,使样品破坏.材...     

Evolution of oxygen reduction current and biofilm on stainless steels cathodically polarised in natural aerated seawater

The aim of a series of works recently performed at ISMAR was to provide new useful information for a better understanding of the mechanisms by which bacteria settlement causes corrosion on Stainless Steels (SS) and similar active-passive alloys exposed to seawater. In this work, the evolutions of cathodic current, bacteria population, and electronic structure of the passive layer were investigated on SS samples polarised at fixed potentials during their exposure to natural seawater. It was found that, during the first phase of biofilm growth, cathodic current increase is proportional to the number of settled bacteria at each fixed potential. However, the proportionality factor between settled bacteria and cathodic current depends on imposed potential. In particular, the proportionality factor strongly decreases when the potential is increased above a critical value close to −150 mV Ag/AgCl. This effect seems to be correlated with the electronic structure of the passive layer. Indeed, the outer part of the passive layer on tested SS was found to behave like a conductor at potentials more active than −150 mV Ag/AgCl, and like an n-type semiconductor at more noble potentials.     

不锈钢和低碳钢在高浓度相变储能溶液体系中的腐蚀行为

文章研究了10号钢、20号钢、314和316L不锈钢在高浓度三水醋酸钠和饱和硫酸铵铝两种相变储能溶液体系中的腐蚀行为,采用PS-268B电化学工作站测试四种钢材在这两种体系中的极化曲线。实验结果表明,316L不锈钢在高浓度醋酸钠溶液体系中耐蚀性能最好,自腐蚀电流密度为6.89×10-5 A·cm-2,与20号钢(0.855 A·cm-2)相比,少了四个数量级。316L不锈钢在饱和硫酸铵铝溶液体系中耐蚀性能最好,自腐蚀电流密度为0.025 A·cm-2,仅为20号钢(0.133 A·cm-2)的五分之一。对钢种进行归纳,综合比较,不锈钢在两种溶液中的耐蚀性能比低碳钢优异。     

Galvanic corrosion in the systems titanium/316 L stainless steel/Al brass in Arabian Gulf water

The present study aims to further the understanding of the galvanic corrosion behaviour of the two systems: titanium/Al brass and 316L stainless steel (st.st)/Al brass in Arabian Gulf water. The study involves the measuring of the open circuit potentials (OCP) of coupons of three metals in seawater at temperatures between 25°C and 65°C. When steady values are attained, the coupons are short-circuited and the couple potentials are followed as functions of time. Corrosion currents are simultaneously recorded. The OCP behaviour of each element depends on the prevailing experimental conditions. With Ti in stagnant and stirred solutions at all temperatures, the OCP shifts towards positive values denoting film formation, repair and thickening. Stainless steel in stagnant seawater at low temperatures undergoes pitting corrosion. At high temperatures the metal is protected by a film of CaCO₃, whereas in stirred solutions the metal escapes pitting. Peculiar behaviour is recorded, when together with the steel, a coupon of uncoupled Al brass is immersed in the same solution. This arrangement seems to protect against pitting attack. The OCP behaviour of Al brass in low-temperature seawater suggests film destruction and dissolution. Coupling of Ti or stainless steel to Al brass produces initial potentials near those of the base metal. At advanced times partial protection due to the electrochemical formation of CaCO₃ takes place. This affects the magnitude of corrosion currents which decrease also with a rise in temperature. These conditions are supported by the results of measurements carried out in synthetic seawater free from HCO₃ and Ca²⁺ ions. Because of the large difference between the free corrosion potentials of titanium and stainless steel, on the one hand, and of Al brass on the other, severe corrosion of the latter can occur. The intensity of attack can be greatly reduced when the oxygen content of the brine is reduced. The same can be achieved through the appropriate manipulation of the naturally forming CaCO₃ film.     

Corrosion behaviour of low-nickel austenitic stainless steels reinforcements: A comparative study in simulated pore solutions

The use of austenitic stainless steel reinforcements is one of the most reliable methods to assure the durability of reinforced concrete structures exposed to aggressive environments, but the initial cost of the material often limits its use in practice. Nickel is one of the alloying elements that raise most the cost of the stainless steels reinforcements. In this work the corrosion resistance of low-Ni 204Cu reinforcements is compared with that of more traditional austenitic stainless steels such as 304, 304L, 316, 316L and 316Ti. Polarization tests were carried out in simulated carbonated and non-carbonated pore solutions with different chloride concentrations. Results prove the very good corrosion behaviour of 204Cu stainless steel in carbonated media and in non-carbonated, chloride contaminated media. The corrosion resistance of low-Ni type 204Cu is only meaningfully lower than that of more traditional austenitic stainless steels in very highly aggressive solutions.