氯离子对球墨铸铁管土壤腐蚀影响机理研究

基于埋片加速腐蚀试验,采用电化学阻抗谱测量和微观分析技术,研究了氯离子(Cl~-)对球墨铸铁腐蚀规律、腐蚀层结构以及腐蚀产物的影响。主要结论如下:(1)球墨铸铁主要发生局部腐蚀,且随Cl~-含量的增加,腐蚀速率增大,出现严重腐蚀坑;其腐蚀坑深与腐蚀时间成幂函数关系,当Cl~-含量高于0.515%时,局部腐蚀情况尤为严重。(2)球墨铸铁腐蚀经历点蚀诱导期、点蚀发展期和稳定腐蚀期3个阶段;在前两个阶段电荷传递为腐蚀速率控制步骤,第三个阶段转变为氧的扩散控制。(3)腐蚀产物主要为铁的氧化物和羟基氧化物;高Cl~-环境下产生的β-Fe OOH和铁的羟基氯化物均能加速球墨铸铁的电化学腐蚀。     

Influence of soil structures on corrosion performance of floating-DC transit systems

The production of stray currents by DC-transit systems leads to the corrosion of nearby buried metallic structures, such as pipelines and cable sheaths. The paper details the corrosion performance of a DC transit system with a floating return rail, for a number of different soil-resistivity structures: uniform, horizontal and vertical-layer models. This builds on previous work carried out in homogenous soils. It is shown that a variation in soil type along the route of a transit system can lead to high local leakage-current densities on buried metallic structures, increasing their vulnerability to corrosion damage.     

Strong exploration of a cast iron pipe failure model

A physical probabilistic failure model for buried cast iron pipes is described, which is based on the fracture mechanics of the pipe failure process. Such a model is useful in the asset management of buried pipelines. The model is then applied within a Monte-Carlo simulation framework after adding stochasticity to input variables. Historical failure rates are calculated based on a database of 81,595 pipes and their recorded failures, and model parameters are chosen to provide the best fit between historical and predicted failure rates. This provides an estimated corrosion rate distribution, which agrees well with experimental results. The first model design was chosen in a deliberate simplistic fashion in order to allow for further strong exploration of model assumptions. Therefore, first runs of the initial model resulted in a poor quantitative and qualitative fit in regards to failure rates. However, by exploring natural additional assumptions such as relating to stochastic loads, a number of assumptions were chosen which improved the model to a stage where an acceptable fit was achieved. The model bridges the gap between micro- and macro-level, and this is the novelty in the approach. In this model, data can be used both from the macro-level in terms of failure rates, as well as from the micro-level such as in terms of corrosion rates.     

The shielding effect of wild type iron reducing bacterial flora on the corrosion of linepipe steel

Microbiologically influenced corrosion (MIC) by microbes capable of iron reduction (iron reducing bacteria (IRB)) on API 5L ×52 carbon steel coupons was investigated. A wild type of IRB was isolated and cultivated from a water sample collected from a sour oil well located in Louisiana, USA. 16S rRNA gene sequence analysis indicated that the mixed bacterial consortium contained two phylotypes close to members of the Proteobacteria (Shewanella oneidensis sp.) and Firmicutes (Brevibacillus sp.). The corrosion behavior of carbon steel coupons exposed to different media, with and without these microbes, was characterized by open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and polarization resistance (R_p), and a corrosion mechanism has been proposed. The biofilm and pit morphology that developed with time were characterized using field emission scanning electron microscopy (FESEM). Interestingly, surface morphology and electrochemical evaluations confirmed that IRB metabolic activities and resulting biofilms inhibit the corrosion process. The maximum corrosion rate in the biotic system was 4 mpy, while it was 20 mpy in the abiotic solution. Minor isolated pits were revealed in the biotic system, whereas extensive general pitting was found in the abiotic system. Elemental analysis and corrosion product structures were characterized by energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). XRD confirmed the formation of a significant amount of iron oxide compounds that include iron, Hematite (Fe₂O₃), Magnetite (Fe₃O₄) and iron (II) hydroxide Fe(OH)₂ on the steel surface exposed to a biotic system.     

TRIZ理论在提高石油钻井平台涂料耐腐蚀性方面的应用

目的 提高石油钻井平台防腐涂料的耐腐蚀性,减少由于石油钻井平台防腐涂层失效造成的经济损失。方法 本文以石油钻井平台漆装系统为研究对象对其进行系统分析,并基于TRIZ理论(Teoriya Reshenivya Izobreatatelskikh Zadatch, TRIZ, 译为发明问题解决理论)中的功能分析、因果分析、裁剪、九屏幕法、物理矛盾等工具对石油钻井平台漆装系统中涂料的组成成分进行创新设计。结果 本文共得到了12个方案,通过初步分析选用了其中的5个方案构成解决问题的最优方案:首先在聚氨酯面漆中加入共轭结构的邻羟基苯甲酸甲酯,同时加入对苯醌自由离子捕捉剂,捕捉二氧化钛分子因吸收紫外线产生的自由基,防止面漆老化。此外还在面漆中加入OTS-SiO2超疏水材料,阻止微生物附着。然后将环氧树脂中间漆中的不锈钢鳞片由不导电的玻璃鳞片替换。最后在底漆中加入弹性材料(微米级橡胶粒子),改善涂层易剥落的问题。结论 该研究成果为提高防腐涂料的耐蚀性和环保性提供了参考。     

铁－氧联合监测仪（Ⅱ型）的研制

铁－氧联合监测仪是用于油田注水的、自动化程度高的在线监测仪表。铁离子的测量采用程序分析法；溶氧的测量采用薄膜式极谱型氧电极。可进行连续或定时监测，自动打印结果。在研制中，重点解决了比色计微型化、电磁阀的耐化学腐蚀、单片机的软件开发和硬件设计以及软、硬件的抗干扰等问题。针对油田注水的特点，仪器还设计了微型加热装置。     

Premature Failure of Ductile Iron Pump Impeller in Cooling Tower System

The root cause of corrosion of a pump impeller in a cooling water system is investigated. The impeller material was made of ductile cast iron. The pump failure was encountered after eight months of operation. A detailed visual examination, microstructure examination, and water analysis were carried out to ascertain the probable cause of failure. Finally, the obtained results infer that the solid-particle containing fluid flow was responsible for erosion–corrosion in the impeller failure.     

Effect of Sulfate-reducing Bacteria on Corrosion Behavior of Mild Steel in Sea Mud

Microbiologically influenced corrosion （MIC） is very severe corrosion for constructions buried under sea mud environment. Therefore it is of great importance to carry out the investigation of the corrosion behavior of marine steel in sea mud. In this paper, the effect of sulfate-reducing bacteria （SRB） on corrosion behavior of mild steel in sea mud was studied by weight loss, dual-compartment cell, electronic probe microanalysis （EPMA）, transmission electron microscopy （TEM） combined with energy dispersive X-ray analysis （EDX） and electrochemical impedance spectroscopy （EIS）. The results showed that corrosion rate and galvanic current were influenced by the metabolic activity of SRB. In the environment of sea mud containing SRB, the original corrosion products, ferric （oxyhydr） oxide, transformed to iron sulfide. With the excess of the dissolved H2S, the composition of the protective layer formed of FeS transformed to FeS2 or other non-stoichiometric polysulphide, which changed the state of the former layer and accelerated the corrosion process.     

The application of knowledge-based systems to corrosion management

A rule-based method of representation of an expert system has been used to formalize corrosion management applications. Essential variables were represented by a series of IF-THEN rules. The application of an integrated database and an expert system provides an interrogative and advisory process which would facilitate decision making. The method is illustrated by reference to two corrosion management applications: (1) during the construction of oil, gas and water pipelines and (2) oilfield corrosion troubleshooting. Potential costs and other benefits are elucidated.     

Fouling and corrosion of bed nozzles in a bubbling fluidized-bed power boiler

An inspection of the floor in a bubbling fluidized-bed power boiler during a planned shutdown revealed significant corrosion of the type 310H stainless steel (UNS S31009) bed nozzles. One severely corroded bed nozzle was removed, along with samples of the deposit encasing the surface of the bed nozzle, for a subsequent failure analysis. The deposit covering the external (fireside) surface of the bed nozzle was almost entirely sodium and potassium chlorides, which covered a thick layer of corrosion product on the bed nozzle surface. The corrosion product was predominantly oxides of chromium, nickel, and iron. Chlorides were also found interspersed through the layer of corrosion product. It is concluded that the fireside corrosion was predominantly caused by chlorine-containing compounds (active oxidation). Overheating induced by the fouling, particularly within the air holes, is believed to be a major factor influencing corrosion.     

Boiler Stack Economizer Tube Failure

A metallurgical evaluation was performed to investigate the failure of a type 304 stainless steel tube from a boiler stack economizer. The tube had three distinct degradation mechanisms: pitting corrosion, chloride stress corrosion cracking, and fatigue fracture. The primary failure mechanism for the tube was fatigue fracture, but the other mechanisms may have eventually caused a tube failure in the absence of fatigue. This paper details the visual, SEM/EDS, and metallographic examinations used to determine that these failure mechanisms were each present in the same tube.     

冷喷涂颗粒在铸铁和Q235钢表面沉积过程的数值分析

核废料储存装置需长久埋于地下,其材料(包括低碳钢、Cu、Ti、镍基合金及不锈钢等)的防腐设计至关重要。以铸铁和Q235钢的防腐蚀为出发点,采用有限元方法,分析了冷喷涂制备铸铁表面铜涂层和Q235钢表面不锈钢涂层的沉积特性。结果表明,颗粒的速度越大,其扁平程度越高,基板上凹坑深度越深;最大塑性变形、最大应力以及最大温度分布位置为粒子与基板的接触部位,温度分布与塑性应变分布一致;撞击过程中,能量在粒子和基板间发生转移与转化。     

Failure assessment of crude oil preheating tubes in mono ethylene glycol–water mixture solution

Aqueous solutions of glycol are commonly used in many applications as heat transfer media. In this study, failure analysis and the leakage of oil tubes in a crude oil pre-heater of a desalting plant were assessed. Crude oil pre-heater (furnace) is a type of heat exchanger in which heat is transferred to oil tubes via ethylene glycol solution in order to increase its temperature for further processing. With the increase of temperature, the viscosity of the oil plus water mixture inside the tubes is reduced and desalting is facilitated. Reports show that, these tubes facing external corrosion in the form of smooth cavities finally lead to leakage. These tubes are made from ASTM A106 Gr B steel. The failure assessment of tubes was carried out by performing various chemical and metallurgical tests. Corrosion coupons were also immersed in ethylene glycol fluid at different places inside the furnace. The investigation revealed that degradation of ethylene glycol forming organic acids (acetic acid, carbonic acid, and formic acid), as the consequent reduction of the pH, take place progressively, being responsible for carbon steel acidic corrosion and eventually to the failure of pre-heating tubes. An action was taken to examine different pH stabilizers for mono ethylene glycol solution. The results obtained by polarization curves showed that, by using stabilizer EN231 at pH = 10.5, corrosion rate reduces to a minimum.     

Probabilistic risk analysis of corrosion associated failures in cast iron water mains

This paper proposes a method using probabilistic risk analysis for application to corrosion associated failures in grey cast iron water mains. External corrosion reduces the capacity of the pipeline to resist stresses. When external stresses exceed the residual ultimate strength, pipe breakage becomes imminent, and the overall reliability of a water distribution network is reduced. Modelling stresses and external corrosion acting on a pipe involves uncertainties inherent in the mechanistic/statistical models and their input parameters. Monte Carlo (MC) simulations were used to perform the probabilistic analysis. The reduction in the factor of safety (FOS) of water mains over time was computed, with a failure defined as a situation in which FOS becomes smaller than 1. The MC simulations yielded an empirical probability density function of time to failure, to which a lognormal distribution was fitted leading to the derivation of a failure hazard function. A sensitivity analysis revealed that the contribution of corrosion parameters to the variability of time to failure was more significant than the combined contributions of all other parameters. Areas where more research is needed are identified.     

地铁的杂散电流腐蚀与防治

由直流动力运输系统产生的大地漏泄电流会造成地铁设施或附近公用设施管线和其它埋地结构物的腐蚀。解决这种杂散电流腐蚀的问题有很大的社会意义和经济意义。本文论述地铁杂散电流腐蚀的原理，介绍地铁系统中杂散电流腐蚀的状况、监测和防治地铁杂散电流腐蚀的方法。     

基于IPSO-GEV优化的腐蚀油气管道剩余寿命预测

针对埋地管道腐蚀的随机性及极值类型选择不当而引起的拟合误差等问题,构建了基于IPSO(免疫粒子群优化算法)-GEV(广义极值分布)优化的油气管道最大腐蚀深度预测模型。首先,采用GEV分布拟合极值数据,利用1PSO优化GEV分布函数的参数并确定极值分布类型,以此确定整条管道的最大腐蚀深度;然后,建立基于可靠性理论的腐蚀裕量模型,来预测管道的剩余寿命;最后,以国内两条腐蚀管道为例验证模型的预测精度。实例结果表明:经IPSO-GEV优化的管道最大腐蚀深度预测模型不受限于数据的具体分布,且预测模型的预测精度较高,管道的剩余寿命预测合理。     

燃气电厂内埋地钢质输气管道腐蚀整改设计

根据埋地燃气管道腐蚀检测结果,对燃气电厂内埋地钢质输气管道腐蚀原因进行了分析。对腐蚀后的管道壁厚进行了强度复核,提出了无遗漏的管道壁厚检测方法,根据管道壁厚检测结果提出管体修复要求,同时对修复后管道进行防腐蚀层修复设计,并重新对埋地管道进行了阴极保护系统设计。     

The abrasive corrosion behavior of plasma-nitrided alloy steels in chloride environments

Both corrosion and abrasive corrosion behavior of plama-nitrided type 304 and 410 stainless steels and 4140 low alloy steel were investigated in 3% NaCl solution (pH = 6.8) by electrochemical corrosion measurements. Surface morphology and alloying elements after corrosion and abrasion corrosion tests were examined by scanning electron microscopy and energy dispersive analysis of X-rays. The results indicated that the plasma-nitrided SAE 4140 steel containing -(Fe,Cr)_{2 – 3}N and -(Fe,Cr)₄N surface nitrides which produce a thick and dense protective layer exhibited a significant decrease of corrosion currents by inhibition of the anodic dissolution of iron, whereas the plasma-nitrided type 304 and 410 stainless steels containing the segregation of chromium nitride CrN exhibited a extensive pitting corrosion by acceleration of the anodic dissolution of iron. It is concluded that the susceptibility to pitting is consistent with the degree of chromium segregation, and decreases as follows: 304 stainless steel > 410 stainless steel > 4140 steel. Also, the results of abrasive corrosion testing for the plasma-nitrided alloys are strongly related to the subtleties of the nitrided microstructures resulting in a pitting and spalling type of abrasive corrosion of type 304 and 410 stainless steels, and excellent abrasive corrosion resistance for SAE 4140 steel.     

某输油管道腐蚀穿孔原因

某油田在巡线过程中发现输油管道有泄漏现象,通过宏观分析、化学成分分析、金相检验和腐蚀产物分析等方法,结合服役工况,对输油管道腐蚀穿孔的原因进行了分析。结果表明:环焊缝防腐补口的密封失效而导致的外层腐蚀是输油管道腐蚀穿孔的主要原因,同时土壤中的Cl^-加速了腐蚀穿孔的发生。     

Corrosion of steel structures in sea-bed sediment

Seabed sediment (SBS) is a special soil that is covered by seawater. With the developments in marine oil exploitation and engineering, more and more steel structures have been buried in SBS. SBS corrosion has now become a serious problem in marine environment and an important issue in corrosion science. In this paper, approach in the field of SBS corrosion is reviewed. Electrochemical and microbial corrosion factors, corrosion mechanism, measurement of metal corrosion rate, corrosion evaluation and prediction of corrosion are also discussed here.