Corrosion failure of marine steel in sea‐mud containing sulfate reducing bacteria

The corrosion failure behavior of marine steel is affected by stress, which exists in offshore structures at sea‐mud region. The sulfate reducing bacteria (SRB) in the sea‐mud made the steel more sensitive to stress corrosion cracking (SCC) and weaken the corrosion fatigue endurance. In this paper, a kind of natural sea‐mud containing SRB was collected. Both SCC tests by slow strain rate technique and corrosion fatigue tests were performed on a kind of selected steel in sea‐mud with and without SRB at corrosion and cathodic potentials. After this, the electrochemical response of static and cyclic stress of the specimen with and without cracks in sea‐mud was analyzed in order to explain the failure mechanism. Hydrogen permeation tests were also performed in the sea‐mud at corrosion and cathodic potentials. It is concluded that the effect of SRB on environment sensitive fracture maybe explained as the consequences of the acceleration of SRB on corrosion rate and hydrogen entry into the metal.     

海洋结构用钢在海泥中的氢渗透行为

采用改进的Devnathan-Stachurski双电解池技术研究了管线钢API X56在海泥中的氢渗透行为.研究表明,海泥中SRB的一个生长周期可分为4个生长阶段:快速生长阶段,平稳生长阶段,衰亡阶段和残余阶段.在一个生长周期内自腐蚀电位下氢渗透电流密度曲线和SRB在海泥中的生长曲线相对应,活性SRB能够促进X56钢在海泥中的氢渗透;在阴极极化条件下,海泥中的SRB对氢渗透的促进作用显著.     

Effects of SRB on cathodic protection of Q235 steel in soils

The effects of sulfate reducing bacteria (SRB) on cathodic protection (CP) of the Q235 steel in the soils have been studied by bacterial analyses, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) and energy‐dispersive X‐ray analysis (EDX). The results showed that the pH value of the soil around the steel gradually increased, the number of SRB and the corrosion rate of the steel decreased, and the CP efficiency increased with the increasing of applied cathodic potential. At the cathodic polarization potential of ?1050 mV, SRB still survived in the soils. At the same potential, the CP efficiency in the soil without SRB was higher than that with SRB, and the corrosion rate of the steel in the soil with SRB was much higher than that without SRB. The cathodic current density applied for the steel in the soil with SRB was bigger than that without SRB at the same cathodic potential.     

Hydrogen uptake by structural steels at cathodic protection in sea water inoculated with sulfate reducing bacteria

The effect of sulfate reducing bacteria (SRB) on the hydrogen permeation rate through ferrite‐pearlite and sorbite steels of quite similar chemical composition was studied using a specially designed facility. Tests were carried out in synthetic sea water, sterile or inoculated with bacteria, at potentials corresponding to cathodic protection (? 800 mV to ? 1400 mV_NCE). Cathodic polarization within the studied potential range did not stop the metabolism of SRB. Presence of SRB was found to increase the hydrogen permeation rate, to form S^2? ions, to increase the polarization current, to modify the impedance spectrum and to change the appearance of cathodic deposits in comparison with sterile conditions. The promoting effect of SRB on the hydrogen uptake was concluded to be the result of the increase in polarization current due to the formation of the less protective layer of cathodic deposits on the steel surface, the presence of S^2? ions and the possible decrease in pH. Despite the similar tendencies, the effect of SRB on hydrogen uptake was more pronounced in the case of sorbite steel. The bacteria action can cause hydrogen deterioration of steel at potentials, recognized as safe ones at cathodic protection.     

含硫酸盐还原菌土壤中阴极保护对Q235钢腐蚀的影响

利用交流阻抗测试技术、扫描电镜及表面能谱、微生物分析等方法，研究了阴极保护对土壤中Q235钢硫酸盐还原菌腐蚀的影响.30天的实验结果表明，在相同的阴极极化电位下，有菌土壤中Q235钢所需要的阴极极化电流密度均大于灭菌土壤，有菌土壤中Q235钢的平均腐蚀速率均大于灭菌土壤.随着阴极极化电位负移的增大，有菌及灭菌土壤中Q235钢试件周围土壤逐渐呈碱性，有菌土壤中Q235钢试件周围土壤中硫酸盐还原菌数量逐渐减少，当阴极极化电位为-1050 mV时，Q235钢试件周围土壤中硫酸盐还原菌仍能够存活.     

Hydrogen permeation measurements in natural sea environment

The specially designed, fully equipped, and computerized devices for the underwater long‐term measurements have been used to study the hydrogen permeation rate through the structural steels under natural sea water conditions. By applying constant cathodic potentials, the polarization current and the hydrogen permeation rate were recorded. The temperature and the concentration of S^?2 ions in sea water were also measured. After the tests, the concentration of residual hydrogen in samples and the chemistry of the membrane surface were analyzed. The obtained permeation data were compared with the S^?2 content in sea water and with the chemistry and appearance of formed deposits. The effect of SRB on the hydrogen permeation through structural steels is dependent on the site of the sample placing and on the sea water temperature. At a lower water temperature, the low hydrogen absorption was measured due to a lower activity of SRB. The highest hydrogen uptake accompanied by the highest content of S in corrosion and cathodic deposits was observed for membranes situated on the sea bed. The electric field of cathodically protected wall did not affect the hydrogen absorption. The hydrogen uptake recorded under the natural sea conditions can be higher than that measured in the laboratory tests, which should be taken into account while servicing marine constructions, especially embedded ones.     

Electrochemical corrosion behavior of X80 pipeline steel in a near‐neutral pH solution

In this work, the electrochemical corrosion behavior of X80 pipeline steel was investigated in a near‐neutral pH solution using electrochemical impedance spectroscopy (EIC) and photo‐electrochemical (PEC) measurements as well as X‐ray photo‐electron spectroscopy (XPS) technique. The effects of hydrogen‐charging and stress were considered. The results show that the steel is in an active dissolution state, and a layer of corrosion product is formed and deposited on the electrode surface, which is subjected to further oxidation to form ferric oxide and hydroxide. Photo‐illumination enhances anodic dissolution of the steel when it is under anodic polarization due to destroying of the corrosion product film. When the steel is under cathodic polarization, the cathodic current density decreases upon laser illumination due to the photo‐oxidation of hydrogen atoms generated during cathodic reactions, which behaves as an anodic reaction to offset the cathodic current density. Hydrogen‐charging and stress decrease the corrosion resistance of the steel and enhance the dissolution rate of the steel.     

The effect of cathodic polarization on the corrosion behavior of X65 steel in seawater containing sulfate-reducing bacteria

Sulfate-reducing bacteria (SRB) are one of the main reasons for the accelerated corrosion of steel. Cathodic polarization has been reported as an effective and economic method against marine corrosion, including microbiologically induced corrosion. However, the interaction between cathodic polarization and microbial activity has not been well defined. In this study, a fluorine-doped tin oxide electrode is used to study the effect of cathodic current on SRB cells. Fluorescence microscopy results clearly show that the attachment degree of SRB is dependent on the electric quantity and current intensity. The large electric quantity and high cathodic current (400 mA/m² × 30 h) can effectively inhibit bacterial attachment and subsequent biofilm formation. Furthermore, the effect of cathodic potential on the corrosion behavior of X65 steel in the presence of SRB is systematically investigated. Results show that the impressed charges, the increase of pH, and the formation of calcareous deposits on the electrode surface at the cathodic potential of −1,050 mV/SCE inhibit the attachment of SRB. In turn, the presence of SRB also interferes with the electrochemical reactions that occur during the polarization process, thus increasing the cathodic current. The interaction between SRB-induced corrosion and the process of preventing corrosion by various cathodic potentials is discussed.     

Effects of anaerobe in sea bottom sediment on the corrosion of carbon steel

The in‐situ study of steel corrosion in sea bottom sediment (SBS) was carried out by Transplanting Burying Plate method (TBP method). It was found that the corrosion rate of steel in the sea bottom sediment with sulfate reducing bacteria (SRB) could be as high as ten times of that in sea bottom sediment without SRB. The experiments in simulated sea bottom sediments with different SRB contents by artificial culturing showed that the electrochemical behavior of steel in the sea bottom sediment with SRB was different from that without SRB. SRB altered the polarization behavior of steel significantly. The environment was acidified due to the activity of SRB and the corrosion of steel was accelerated. The corrosion of carbon steel in sea bottom sediment is anaerobic corrosion, and the main factor is anaerobe. There are SRB commonly in SBS, and the amount of SRB decreases along with the depth of sediment. Because of the asymmetry and variation of sea bottom sediment, the most dangerous corrosion breakage of steel in SBS is local corrosion caused by SRB. So the main countermeasure of corrosion protection of sea bottom steel facilities should be controlling of the corrosion caused by anaerobe.     

Effect of cathodic polarization and sulfate reducing bacteria on mechanical properties of different steels in synthetic sea water

At the slow strain rate tensile tests done using the specially designed facility, the decrease in the elongation to fracture, reduction of area, fracture energy and no effect on the strength have been stated for the low alloy ferrite‐pearlite and sorbite steels, polarized in synthetic sea water at potentials corresponding to the cathodic protection (? 800 to ? 1400 mV_SCE). Presence of SRB promotes the plasticity loss, being especially pronounced at potentials ? 1100 to ? 1200 mV_SCE. At higher cathodic polarization, the plasticity estimated in inoculated and in sterile water equalizes. The effects have been correlated with the contents of absorbed and of permeable hydrogen. The promotion of hydrogen charging and the plasticity loss by SRB at the low and medium applied cathodic polarization has been accounted for the observed production of S^?2 ions and inhibition of deposit formation. The negligible effect of SRB at the high cathodic polarization has been suggested to be a result of the suppression the SRB growth due to the high alkalization of the near surface solution. The same amount of hydrogen produces the less detrimental effect on the sorbite than on the ferrite‐pearlite steel. However, at the similar cathodic polarization, the sorbite steel absorbs the highest amount of hydrogen and reveals the most pronounced degradation. Cathodic protection of constructions subjected to the action of SRB in the sea water should provide the conditions, under which no fragment of marine construction could be polarized by potential corresponding to the maximum degradation of the plastic properties of steels (? 1100 to ? 1200 mV_SCE).     

X65碳钢在模拟油田采出水中的阴极保护研究

采用极化曲线、恒电位阴极极化和失重法,并结合SEM,EDS和XRD分析产物的形貌、成分和结构,研究了不同保护电位下X65碳钢的保护效果和机制。结果表明:该环境中,自腐蚀条件下的X65碳钢发生严重腐蚀,失重速率大,坑蚀严重;-800~-1000 mV的保护电位对X65碳钢的腐蚀均有明显抑制效果;-800 mV阴极保护电位下X65碳钢表面无良好的钙质沉积层形成,-900 mV下表面能生成牢固致密的钙质沉积层,有效降低保护电流密度,-1000 mV下沉积层容易因析氢反应而鼓泡脱落;相比于海洋环境,X65碳钢在油田采出水中的析氢电位偏正,沉积层中不含Mg(OH)2。     

Determination of biocorrosion of low alloy steel by sulfate‐reducing Desulfotomaculum sp. isolated from crude oil field

In this study corrosion behavior of low alloy steel, in the presence of anaerobic sulfate‐reducing Desulfotomaculum sp. which was isolated from an oil production well, was investigated. In order to determine corrosion rates and mechanisms, mass loss measurements and electrochemical polarization studies were performed without and with bacteria in the culture medium. Scanning electron microscopic observations and energy dispersive X‐ray spectra (EDS) analysis were made on steel coupons. The effect of iron concentration on corrosion behavior was determined by Tafel extrapolation method. In a sterile culture medium, as the FeSO₄ · 7H₂O concentration increased, corrosion potential (E_cor) values shifted towards more anodic potentials and corrosion current density (I_cor) values increased considerably. After inoculation of sulfate‐reducing bacteria (SRB), E_cor shifted towards cathodic values. I_cor values increased with increasing incubation time for 10 and 100 mg/L concentrations of FeSO₄ · 7H₂O. Results have shown that the corrosion activity changed due to several factors such as bacterial metabolites, ferrous sulfide, hydrogen sulfide, iron phosphide, and cathodic depolarization effect.     

Microbiologically influenced corrosion of X60 carbon steel in CO2‐saturated oilfield flooding water

The corrosion behavior of X60 carbon steel in CO₂‐saturated oilfield flooding water inoculated with sulfate‐reducing bacteria (SRB) was investigated using polarization curves and electrochemical impedance spectroscopy (EIS). With the propagation of SRB in the flooding water, the pH values of flooding water increased quickly in the initial 2 days and remained relatively steady during the later stage. Polarization curves showed that the corrosion current density decreased during the first 10 days due to the protection of corrosion products and SRB‐biofilms, and then increased possibly due to the partial detachment of the corrosion products and the biofilms. EIS analysis also showed that the charge transfer resistance increased initially and then decreased with exposure time. In the beginning of corrosion, the anodic dissolution of X60 steel was dominated by CO₂. After the formation of SRB‐biofilms, part of FeCO₃ corrosion products was converted to incompact FeS precipitates by SRB bio‐mineralization. Thus, the dispersed iron sulfide in SRB‐biofilms and X60 steel base may constitute a galvanic couple, accelerating the localized corrosion of the steel base in the flooding water.     

A3钢在海泥中的腐蚀行为

对A3钢在模拟海泥环境中进行了埋片试验和电化学试验,以研究海底管道在含硫酸盐还原菌(SRB)海泥中的腐蚀行为.结果表明,A3钢在砂泥中的腐蚀速率明显高于在海砂中的腐蚀速率,随温度的升高,A3钢在海砂中的腐蚀速率升高;且随温度的升高、SRB和SO42-含量的增加,A3钢在砂泥中的腐蚀速率随之升高;在无菌海泥中A3钢的腐蚀速率随温度升高而增大,主要是由于作为阴极去极化剂的氧的扩散速度随温度升高而增大;在有菌海泥中SO42-能参与阴极去极化而加速A3钢的腐蚀.     

pH值对海水中TMCP X80钢氢脆敏感性影响

采用氢渗透实验法、动电位极化法研究TMCP X80管线钢在不同pH值海水中的氢渗透行为,结合扫描电镜 (SEM) 观察研究显微组织及氢渗透行为对氢脆敏感性的影响。结果表明,随着海水pH值的减小,析氢电位发生正移。天然海水和酸性海水中氢扩散系数随着极化电位负移而增加;极化电流密度越大,氢扩散系数和氢浓度越大。在负于析氢电位时,显微形貌显示出明显的蚀坑和氢鼓泡,酸性海水中更严重。随着海水pH值的减小及外加阴极极化电位负移,氢扩散到材料内部的量更大;充氢电流密度增加也促进氢的扩散,X80钢氢脆敏感性增加。     

Einfluß sulfatreduzierender Bakterien auf den kathodischen Korrosionsschutz

Influence of sulfate-reducing bacteria on cathodic protection Sulfate-reducing bacteria (SRB) are frequently encountered at coating defects of cathodically protected pipes buried in soil. In laboratory experiments the corrosion behaviour of steel St 37 was studied at potentials in the range of ?0.5 V > U_Cu/CuSo4 > ?1.27 V and at the open circuit potential in the presence of a mixed culture containing SRB. For simulation of real conditions the experiments were performed on steel samples in sand columns through which a glucose-containing mineral salts solution was continuously pumped. On the basis of the corrosion rates determined an immediate corrosion risk was not evident for a homogeneous mixed electrode even at the open circuit potential. There was only an increase in protective current demand compared to sterile conditions. Hydrogen permeation through the low-alloy steel was slightly higher in the presence of SRB-containing mixed cultures than under sterile and H₂S-free conditions. The observed permeation current densities indicated that at potentials of U_Cu/CuSo4 < ?0.85 V hydrogen-induced corrosion damage was not to be expected under sulfate-reducing conditions.     

氢渗透传感器及其在海洋腐蚀环境中的应用

目的探究电化学氢渗透传感器在海洋腐蚀环境中的适用性以及相应腐蚀环境下高强度钢的氢渗透行为。方法设计和制作系列氢渗透传感器,将氢渗透传感器置于海洋大气腐蚀环境、模拟浪花飞溅区腐蚀环境和模拟海洋潮差区腐蚀环境,通过电化学氢渗透技术反映自然腐蚀条件下由腐蚀导致的氢向AISI 4135高强钢材料的渗透情况。结合各腐蚀环境下影响材料腐蚀速率的因素,分析各腐蚀环境下氢产生的机理。结果海洋大气腐蚀环境下由腐蚀引起的材料的氢渗透电流密度处在一个较小的数量级,氢渗透电流的大小与大气的绝对湿度呈正比例关系;模拟浪花飞溅区腐蚀环境下,氢渗透电流的大小与模拟浪花飞溅效应的海水喷淋间隔时间相关,相较于海水喷淋间隔为1min条件下的氢渗透电流密度,喷淋间隔为10min条件下的氢渗透电流密度的最大值更大。处于模拟海洋潮差区腐蚀的材料的氢渗透电流呈现周期性波动,并且前期氢渗透电流的波动幅值较大,而后趋于稳定。结论电化学氢渗透传感器在检测大气腐蚀环境和模拟浪花飞溅、模拟海洋潮差环境下由腐蚀引起的氢渗透电流的应用中,展现了良好的稳定性和可靠性,表明了相应试验海洋腐蚀环境下氢渗透电流的特点,不同腐蚀环境下材料的氢渗透行为差异较大。     

EFFECT OF SULFATE–REDUCING BACTERIA ON THE PITTING CORROSION BEHAVIOR OF 18–8 STAINLESS STEEL

利用原子力显微镜(AFM)和电化学方法研究了海水中硫酸盐还原菌(SRB)对18--8不锈钢(18--8SS)点蚀过程的影响. AFM探测显示, 微观蚀孔的生长速率在含SRB介质中明显高于在灭菌介质中. 阳极循环极化结果表明, SRB的代谢产物显著降低了18--8SS的点蚀电位和再钝化电位; 而且在含SRB介质中, 18--8SS在短时间内就能被活化, 表明SRB的代谢活动极大地促进了钝化层的破坏过程. 阴极极化曲线表明, 含SRB介质中单质硫或多态硫的还原是促使点蚀生长的主要因素, 其阴极还原电流密度可以达到很高的数值(>10 μA/cm²).     

Hydrogen absorption resulting from the simulated pitting corrosion of carbon-manganese steels

Hydrogen permeation measurements were performed on membranes of BS4360 Grade 50D C-Mn steel in the quenched and tempered condition. The rates of hydrogen absorption resulting from exposure to FeCl₂ solutions in a simulated corrosion pit were measured and found to be lower than those occurring in artificial sea water at applied potentials in the range commonly used for cathodic protection. A progressive decrease in the hydrogen permeation flux was recorded during simulated pitting and was attributed to the formation of a partially protective film of magnetite on the steel surface. At cathodic applied potentials iron plating was observed on the membranes. It is suggested that a similar process occurs in the cathodic protection of steel containing real corrosion pits and leads to a lowering of the Fe²⁺ ion concentration within the pits and a decrease in the aggressiveness of the local environment.     

Influence of the sulphate reducing bacteria on API‐X70 steel corrosion

The corrosion behaviour of API X70 immersed in a specific medium with a strain of thermophilic sulphate reducing bacteria (SRB) was analysed. Anaerobic corrosion test was carry out for 32 days at 50 °C. During the exposure time, pH, sulphate (SO) and hydrogen sulphide (H₂S) concentration were measured. Corrosion potential, linear polarization resistance and potentiodynamic polarization curve were used in order to get the influence of the SRB in the corrosion phenomenon. Scanning electron microscopy was used to determine corrosion morphology. Results show that the SRB activity influenced the overall corrosion process. The anodic branches in the polarization curves show a passivity feature, whereas, the cathodic branches were not affected. A localized corrosion attack was found.