页岩气输送用转角弯头内腐蚀减薄原因分析

目的针对某页岩气输送平台用转角弯头发生严重内腐蚀减薄的问题开展原因分析,明确腐蚀类型及机理,指导防腐处理,提高转角弯头的服役安全性。方法以页岩气输送用转角弯头为研究对象,针对转角弯头内腐蚀减薄行为开展基础研究,通过宏观观察及尺寸测量分析内腐蚀的腐蚀形貌及分布,并进行理化检测、微观观察、物相分析,探究腐蚀产物,综合分析转角弯头内腐蚀减薄的原因。结果宏观分析发现,转角弯头内壁外弧侧与中性区过渡区域有壁厚发生突变而产生的腐蚀台阶,最大壁厚减薄率达63.4%。电子显微形貌与金相分析表明,弯头内壁的腐蚀坑呈纵深发展,逐层剥离,腐蚀产物疏松、形貌多样,且可观察到细菌形貌。腐蚀产物的能谱及XRD分析发现,管体内壁的腐蚀产物主要是Fe S、Fe2O3、Fe CO3等,内腐蚀可能与CO2、H2S、SRB等有关。结论弯头腐蚀减薄是硫酸盐还原菌(SRB)-CO2腐蚀协同作用的结果,SRB的存在对CO2腐蚀起催化作用。此外,Cl-对腐蚀产物膜的破坏和弯头外弧侧的冲刷加速了腐蚀作用。建议确定SRB细菌来源,以便有效投放杀菌剂,同时对管线内壁定期进行清理,避免菌落长期附着于管体内壁。此外,建议添加多级气液分离装置,严格控制气相中的含水量。     

油田产出水的腐蚀及防护研究

本文在对长庆油田的靖北、吴旗、油房庄和大水坑区块采油装置发生腐蚀原因分析的基础上,开展了产出水的缓蚀和杀菌试验研究。结果表明,引起井下管柱及集输管线腐蚀的因素主要有产出水矿化度高、H2S和SRB含量高、部分水质溶解氧超标以及井下存在CO2伴生气和不均匀结垢;优选的CI-2缓蚀剂具有较好的缓蚀效果,加量为50mg/L时,可使产出水的腐蚀速度由0.125mm/a降至0.012mm/a,缓蚀率达90%以上;经杀菌剂筛选,BI-2和BI-3对SRB、TGB具有较好的杀菌效果,为了防止产生抗药性,采用BI-2和BI-3交替加药。     

Bacterial degradation of naphtha and its influence on corrosion

The degradation problem of naphtha arises since hydrocarbon acts as an excellent food source for a wide variety of microorganisms. Microbial activity leads to unacceptable level of turbidity, corrosion of pipeline and souring of stored product. In the present study, biodegradation of naphtha in the storage tank and its influence on corrosion was studied. The corrosion studies were carried out by gravimetric method. Uniform corrosion was observed from the weight loss coupons in naphtha (0.024 mm/yr) whereas in presence of naphtha with water, blisters (1.2052 mm/yr) were noticed. The naphtha degradation by microbes was characterized by Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy (NMR). IR study reveals the formation of primary alcohol during degradation process. It was found that microbes degrade (CH₂CH₂)_n to RCH₃. Iron bacteria, manganese oxidizing bacteria, acid producers, and heterotrophic bacteria were enumerated and identified in the pipeline. SRB could not be noticed. Since water stratifies in the pipeline, the naphtha-degraded product may adsorb on pipeline, which would enhance the rate of microbial corrosion. On the basis of degradation and corrosion data, a hypothesis for microbial corrosion has been proposed.     

Effect of flow velocity on pipeline steel corrosion behaviour in H2S/CO2 environment with sulphur deposition

The effect of element sulphur on the performance of corrosion inhibitor in H₂S/CO₂ gas field solution was investigated at different velocities. The morphology and composition of corrosion products were characterised by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) methods. The results indicated that L360 QS steel surface suffered from sulphur-induced pitting corrosion at a low velocity due to insufficient sulphur-carrying fluid power. At high flow velocities, the steel surface is likely to be suffered high fluid power which can remove the inhibitor film and corrosion scales by the mechanical erosion effect. The sulphur corrosion mechanism model and the flow-induced corrosion model due to the high wall shear force have been proposed in the study. This work suggested that the gas production rate should be controlled at an acceptable level to guarantee the service safety of pipeline system.     

弹塑性应力作用下X80管线钢的菌致开裂行为

目的 揭示硫酸盐还原菌（SRB）在管线钢表面裂纹萌生中的作用。方法 采用恒载荷实验装置施加弹性和塑性应力,通过XPS和EDS分析产物成分,利用SEM观察微生物膜形态、管线钢腐蚀形貌,研究弹性和塑性应力作用下管线钢的微生物致裂裂纹萌生和扩展行为。结果 弹性和塑性应力对SRB生长无明显影响。不管是在弹性应力还是塑性应力作用下,SRB生理活动均改变了腐蚀产物的结构,增加了腐蚀产物的硫含量,提高了管线钢局部腐蚀敏感性。与弹性应力作用相比,塑性应力和SRB协同作用对管线钢微裂纹萌生和扩展的影响更大。塑性应力作用下,灭菌和接菌环境中管线钢表面均产生了微裂纹分叉。结论 弹性应力和塑性应力均促进了管线钢的微生物腐蚀过程。塑性应力作用下管线钢菌致开裂更加剧烈,裂纹扩展过程与SRB生理活动有关。     

Microbial Corrosion in Linepipe Steel Under the Influence of a Sulfate-Reducing Consortium Isolated from an Oil Field

This work investigates microbiologically influenced corrosion of API 5L X52 linepipe steel by a sulfate-reducing bacteria (SRB) consortium. The SRB consortium used in this study was cultivated from a sour oil well in Louisiana, USA. 16S rRNA gene sequence analysis indicated that the mixed bacterial consortium contained three phylotypes: members of Proteobacteria (Desulfomicrobium sp.), Firmicutes (Clostridium sp.), and Bacteroidetes (Anaerophaga sp.). The biofilm and the pits that developed with time were characterized using field emission scanning electron microscopy (FE-SEM). In addition, electrochemical impedance spectroscopy (EIS), linear polarization resistance (LPR) and open circuit potential (OCP) were used to analyze the corrosion behavior. Through circuit modeling, EIS results were used to interpret the physicoelectric interactions between the electrode, biofilm and solution interfaces. The results confirmed that extensive localized corrosion activity of SRB is due to a formed biofilm in conjunction with a porous iron sulfide layer on the metal surface. X-ray diffraction (XRD) revealed semiconductive corrosion products predominantly composed of a mixture of siderite (FeCO₃), iron sulfide (Fe _x S _y ), and iron (III) oxide-hydroxide (FeOOH) constituents in the corrosion products for the system exposed to the SRB consortium.     

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.     

某天然气管道内腐蚀原因及防控措施

目的分析某天然气管线典型管段的腐蚀特性,明确管线的腐蚀原因及机理。方法采用扫描电镜对管道内壁不同方位的腐蚀形貌进行表面和截面微观观察。采用X射线衍射和EDS方法进行成分定量分析。结合天然气管道输送天然气成分、清管记录等服役状况进行天然气管线的内腐蚀特性研究。结果 CO_2腐蚀是造成该天然气管道内腐蚀的主要原因,管段12点钟方向腐蚀坑深度约为0.18 mm,3点钟和6点钟方向腐蚀坑深度均约为0.1 mm,腐蚀产物以Fe_2O_3和FeCO_3为主,6点钟方位的腐蚀产物厚度最大,3点钟方位的腐蚀产物厚度最小,3点钟和6点钟方位的腐蚀产物主要以Fe、O、C为主,12点钟方位的腐蚀产物含有S元素,同时可能存在细菌腐蚀。SiO_2是管线内残余的污泥本身所含,该管道在投入工作前可能已经发生了腐蚀。针对性地提出了相关腐蚀防控措施,采取措施后换管频率降低了56%。结论天然气管线存在的内腐蚀多为局部腐蚀,运行过程中应尽可能地避免腐蚀的发生,及时采取相应的防控措施,以免造成不必要的损失。     

油气管道SRB腐蚀研究新进展

由硫酸盐还原菌(SRB)引发的腐蚀是造成管道材料破坏和失效的重要原因,研究微生物腐蚀机制和防控措施具有重要的科学意义和经济价值.首先通过介绍国内外油气管道微生物腐蚀的失效案例,说明SRB对油气管道破坏的严重性.接着介绍了管道表面微生物膜的微观形成过程和结构特点,梳理了微生物膜作用下管材发生局部腐蚀的机理,主要对当前较为流行的微生物电化学腐蚀(EMIC)理论和管道微生物腐蚀预测模型做了深入探讨.综合考虑管道运行实际工况,结合模拟试验结果,进一步阐述了管线钢即使处于正常阴极保护条件下,由于受SRB生命代谢活动的影响,管道表面Fe中的电子通过细菌的新陈代谢作用直接获取,从而导致管材依然发生局部腐蚀甚至更为严重.而焊缝及其附近热影响区是管道发生腐蚀穿孔的薄弱区.最后全面总结了油气管道工业中抗SRB腐蚀防护前沿的理念和方法,分析了当前各种防护技术在实际应用中的不足,对微生物腐蚀如何更有效地防治提供了富有价值的参考,为管道工程SRB腐蚀防护技术的未来发展指明了方向.     

Microbiologically influenced corrosion of underground pipelines under the disbonded coatings

The microbiologically influenced corrosion (MIC) of underground pipeline was identified. Corrosion was typically found under the disbonded area of girth welds coating where cathodic protection (CP) current could not penetrate. Sulfate reducing bacteria (SRB) and fermentative acid producing bacteria (APB) were confirmed as the microbes involved in the corrosion process. This corrosion occurred despite the fact that the CP level was well below the criteria of -850 mV (Cu/CuS0₄). Detailed field surveys and laboratory analysis revealed the presence of high numbers of microbes at these sites, metallurgical and mineralogical fingerprints of MIC. The results indicate that the synergistic effects of disbonding, the ineffective input of CP current under the disbonded coatings, and environments favorable to bacterial growth were the corrosion mechanism.     

某集气站埋地管道腐蚀失效原因分析

对某集气站埋地管道的失效管段进行了宏观检查、腐蚀产物分析、管道材质与金相分析等,并开展了管道内部气/液两相流动计算和腐蚀模拟实验,综合分析了埋地管段腐蚀失效原因及腐蚀机理。结果表明：埋地管道的水样中存在大量的SRB,铁细菌和腐生菌,管道内流态为层流,管道底部5~7点钟部位发生了严重小孔腐蚀。细菌腐蚀和垢下腐蚀是导致管道腐蚀穿孔的主要原因,水中的Cl^-加速了腐蚀穿孔的发生。     

Model for microbiologically influenced corrosion potential assessment for the oil and gas industry

Corrosion is one of the major causes of failure in onshore and offshore oil and gas operations. Microbiologically influenced corrosion (MIC) is inherently more complex to predict, detect and measure because, for instance, the presence of biofilm and/or bacterial products is not sufficient to indicate active microbiological corrosion. The major challenge for current MIC models is to correlate factors that influence corrosion (i.e. chemical, physical, biological and molecular variables) with the potential of having MIC. Previous work has proposed the potential for MIC as a simple product of multiple factors, without fully considering the synergy or the interference among the factors. The present work proposes a network-based approach to analyse and predict MIC potential considering the complex interactions among a total of 60 influencing factors and 20 screening parameters. The proposed model has the ability to capture the complex interdependences and the synergic interactions of the factors used to assess MIC potential and uses an object-oriented approach based on a Bayesian Network. The model has been tested and verified using real data from a pipeline leakage incident that was a result of MIC. The proposed model constitutes a significant step in deepening the understanding of when MIC occurs and its predictability.

List of acronyms: APB: acid producing bacteria; Aw: water activity; BN: Bayesian network; MIC: microbiologically influenced corrosion; MMMs: molecular microbiological methods; NRB: nitrate-reducing bacteria; OOBN: object-oriented Bayesian network; PWRI: produced water re-injection; SPs: screening parameters; SRB: sulphate-reducing bacteria; SRPs: sulphate-reducing prokaryotes; TDSs: total dissolved solids     

Pitting corrosion of titanium by a freshwater strain of sulphate reducing bacteria (Desulfovibrio vulgaris)

Pitting corrosion of titanium (ASTM Grade 2) was investigated by exposing coupons (2.0 × 1.5 cm) to a semi-continuous culture of sulphate reducing bacteria (SRB) strain Desulfovibrio vulgaris. The coupons were exposed to the SRB culture for 90 days along with a control set in uninoculated medium. During the course of the experiment sulphide was estimated at intervals of 4 days and the concentrations ranged from 0.2 to 0.4 mM in the bulk medium. Epifluorescence microscopy revealed extensive colonization by the SRB and the cell count ranged from 10⁴ to 10⁵ cells cm⁻². Optical microscopy revealed the presence of two types of pits; large hemispherical pits of ∼2 mm diameter and many micropits. Pitting was not observed in control coupons exposed to SRB free medium. SEM and CSLM pictures showed the corroded titanium surface with several micropits, along with typical rod shaped SRB cells in the pitted regions. EDAX analysis revealed peaks for Ti, O, N, C, Fe and P in the pitted region. XPS data showed clear peaks for titanium sulphur (three states) and phosphorous. The study reveals that at room temperature and in the presence of 0.2-0.4 mM of sulphide, as well as the putative phosphine, SRB can promote pitting corrosion of titanium by formation of titanium sulphide.     

X70管线钢在大庆土壤环境中微生物腐蚀行为研究

采用极化曲线、电化学阻抗谱技术和SEM、EDS、XRD分析方法研究了X70管线钢在含硫酸盐还原菌(SRB)的大庆土壤模拟溶液中的微生物腐蚀行为。结果表明,SRB在大庆土壤环境模拟溶液中生长周期分为对数生长期、衰减期和死亡期3个阶段。SRB的新陈代谢对大庆土壤环境产生显著影响:pH值在SRB生长的前2 d降低,然后呈逐渐上升趋势。氧化还原电位在SRB对数生长期降低,在衰减期和死亡期呈增加趋势。溶液电导率在SRB的对数生长期时增加,在衰减期和死亡期呈整体减小趋势。在SRB对数生长期,游离的SRB利用其新陈代谢产物H将硫酸盐还原成硫化物,促进了点蚀的发生;在SRB衰减期,腐蚀产物成团簇状,膜层致密,减缓腐蚀;在SRB死亡期,生物膜脱落,腐蚀产物膜有明显裂纹出现,形成微观腐蚀电池,导致X70管线钢的腐蚀加剧。X70管线钢在SRB的大庆土壤中腐蚀产物为FeS和Fe3O4。     

X70管线钢在硫酸盐还原菌作用下的应力腐蚀开裂行为

目的油气管输中X70钢的应力腐蚀开裂问题日趋严重,而且土壤环境中微生物腐蚀现象备受关注,因此拟通过实验室模拟土壤环境下X70管线钢的腐蚀,获得高强度管线钢在硫酸盐还原菌作用下的应力腐蚀开裂规律。方法采用自制的应力电化学测试装置,通过慢应变速率拉伸试验(SSRT)对材料的应力腐蚀敏感性进行分析,利用交流阻抗以及扫描电镜(SEM)对断口形貌以及生物膜的成分进行研究。结果当应变速率为5×10~(-7)s~(-1)时,无菌模拟溶液中试样的应力腐蚀敏感性远大于含SRB模拟溶液中试样的应力腐蚀敏感性,SRB的存在对X70管线钢应力腐蚀起到很大程度的促进作用。当应变速率为1×10~(-6)s~(-1)时,SRB对于X70管线钢应力腐蚀敏感性的影响较小,断裂主要由力学因素主导,SRB起辅助作用。结论 X70管线钢在沈阳土壤模拟溶液中具有一定的应力腐蚀敏感性。SRB对于X70管线钢在沈阳土壤模拟溶液中的应力腐蚀起到一定程度的促进作用。     

Specification of sulfate reducing bacteria biofilms accumulation effects on corrosion initiation

The accumulation process of sulfate reducing bacteria (SRB) biofilms established in anaerobic stagnant batch bioreactors on the surface of carbon steel and the nutrient transport and corrosion products distribution in it were characterized by X‐ray Photoelectron Spectroscopy (XPS). In addition, the corrosion occurrence and development of carbon steel under SRB biofilm was investigated by Electrochemical Impedance Spectroscopy (EIS) in‐situ. The results show that the thickness of SRB biofilms increases exponentially with time in the beginning and after 14 days reaches a maximum. From then on, the accumulation rate decreases to zero. In mature biofilms, SRB dispersed throughout the biofilm. In the inner layer near the substrate, due to the high sulfate‐reducing activity of SRB, corrosion products such S^2?, H₂S and organic acid are present, which lead to corrosion occurrence and development. In the outer layer of the biofilm SRB can also reduce the SO^2?₄ to SO^2?₃ and S₂O^2?₃. This metabolism process enhances the Fe²⁺ transfer from the inner to the outer side. The activity of SRB in the biofilm plays a key role in the initial corrosion process.     

天然气管道环焊缝缺陷部位的腐蚀沉淀机理

为了深入分析天然气管道的“梗阻”现象,采用金相法和能谱仪对靖边某气田典型的有大量沉积物管道进行了焊缝和沉积物结构及成分分析.结果表明,焊缝缺陷处的腐蚀和沉淀机理为管内发生CO₂腐蚀、缝隙腐蚀和H₂S腐蚀,产生了氧化物、氯化物和硫化物等腐蚀产物.随着腐蚀产物的逐渐堆积,其阻隔了管子材料与腐蚀性介质,使得腐蚀速率减慢,沉积物转为以粉尘为主.沉积物堆积到一定高度时,天然气的流向改变,管道顶部的腐蚀变为冲刷腐蚀,腐蚀速率加快,管道壁厚严重减薄,危害管道的正常安全运行.     

二氧化碳对X60钢微生物腐蚀行为影响

利用失重法和扫描电镜研究了CO₂与嗜热SRB共存条件下X60钢在海底污泥和污水中的腐蚀行为.结果表明:CO₂饱和条件下,随着温度的升高,污泥和污水中腐蚀速率均增加,且含SRB的污泥和污水中X60钢的腐蚀速率均大于不含SRB的腐蚀速率,SEM观察表明,X60钢遭受的破坏以点蚀为主;随着CO₂分压的增大,X60钢的腐蚀速率增大,且污泥中腐蚀速率大于污水中腐蚀速率.     

铁细菌对L245钢腐蚀行为的影响研究

采用挂片、电化学实验和SEM等手段研究了L245钢在含有铁细菌(FB)的页岩气压裂产出水中的腐蚀行为。结果表明:有、无FB压裂产出水都会对L245钢造成腐蚀,但失重分析和极化曲线分析都证明FB的存在促进了L245钢的腐蚀;电化学阻抗拟合结果表明,在不含FB的页岩气压裂产出水中,L245钢的腐蚀速率在前5 d逐渐增大,后快速减小。在含有FB的页岩气压裂产出水中,L245钢的腐蚀速率先减小,至8 d后逐渐增大。SEM分析结果表明,两种体系生成了不同的腐蚀产物膜。     

H2S和CO2分压及Cl-浓度对L360QCS钢腐蚀行为的影响

通过高温高压反应釜模拟普光气田集输环境,研究H2S和CO2分压及Cl-浓度对普光气田用集输管线钢L360QCS钢腐蚀行为的影响。采用失重法测试腐蚀速率,用四点弯曲法进行应力腐蚀试验,结合宏观形貌观察和扫描电镜(SEM)微观观察及能谱(EDS)分析,进行了综合研究。在H2S和CO2分压比固定的情况下,随着H2S压力升高,腐蚀速率先降后升。压力较低时,L360QCS应力腐蚀试样表面均出现不同程度的氢鼓泡,当压力升高时,氢鼓泡减少或者消失。腐蚀速率随着Cl-浓度的升高而增大,达到临界值后,腐蚀速率随着Cl-浓度的升高而降低;在低浓度条件下,Cl-浓度的增加会促进点蚀的发生,进而诱发裂纹的产生;而当Cl-浓度增加到临界值时,腐蚀产物的沉积可以抑制点蚀的生成,从而使材料的应力腐蚀开裂敏感性降低。