基于改进BP神经网络优化的管道腐蚀速率预测模型研究

目的构造金属管道腐蚀速率预测模型,预测管道的使用寿命。方法分析了二氧化碳(CO2)和硫化氢(H2S)对金属管道的腐蚀过程,给出了管道腐蚀的化学反应方程式。引用了BP神经网络构造金属管道腐蚀速率的数学模型,采用了改进粒子群算法对预测模型进行优化。以45号金属管道为例,借助于Matlab软件对管道腐蚀速率进行仿真验证,并与实验测量数据进行对比和分析。结果金属管道腐蚀速率随着CO2或H2S压强的增大而逐渐增大,仿真结果显示CO2和H2S的最大腐蚀速率分别为7.20×10-5 mm/h和5.76×10-5mm/h,而实验测量结果显示CO2和H2S的最大腐蚀速率分别为7.14×10-5 mm/h和5.65×10-5 mm/h,采用改进BP神经网络预测模型所产生的相对误差在5%以内。结论金属管道在不同压强条件下,采用改进BP神经网络预测模型能够近似地预测其腐蚀速率,为金属管道的更换提供了参考依据。     

对45#钢管道的缝隙腐蚀模拟研究

目的预测埋地金属管道缝隙表面电位分布和腐蚀速度。方法造金属管道缝隙腐蚀的几何模型,对腐蚀管道采取阴极保护,推导腐蚀管道的电化学反应动力方程式。对几何仿真模型的初始条件及边界条件进行约束,采用MATLAB软件对阴极保护电位分布规律和表面缝隙腐蚀速度的几何模型进行了仿真,并且与实验测量结果进行对比,得出了仿真结果与实验结果的相对误差。结果采用阴极保护金属管道表面缝隙腐蚀的底部仿真电位随时间的增加而反向增大,在极化时间50 h内最大电位为-8.6 V。采用阴极保护金属管道表面缝隙腐蚀的仿真电位随缝隙深度的增加而反向减小,在距离缝隙表面10 cm内最小值为-0.78 V。采用阴极保护金属管道表面缝隙的仿真腐蚀速度随时间的增加而逐渐减小,在前5年内腐蚀速度最小值达到0.334 mm/a。同时,电位分布和腐蚀速度的仿真值与实验测量值的相对误差在5%以内,误差较小。结论采用矩形缝隙模型可以近似预测阴极保护的电位分布和缝隙表面腐蚀速度,从而降低了金属管道腐蚀速度,避免了金属管道发生灾难性的事故。     

金属管道在CO_2/H_2S环境中的腐蚀行为

金属管道因油气输送介质中含有CO_2与H_2S而遭受严重腐蚀,尤其是点蚀,导致其过早失效、油气水泄漏,增加了安全隐患与环境污染风险。对金属管道在含CO_2、H_2S环境中的腐蚀行为进行概述,论述了CO_2与H_2S共存体系中竞争协同效应与二者分压比的划分,探讨了CO_2、H_2S以及CO_2/H_2S腐蚀机理、腐蚀产物类型以及环境对管道腐蚀速率的影响。结果表明,温度、CO_2分压、H_2S分压以及Cl-浓度均对金属管道的腐蚀产生较大的影响,而CO_2/H_2S分压比对CO_2/H_2S腐蚀起决定性作用。最后,对金属管道的CO_2/H_2S腐蚀研究进行展望,以期为油气输送管道的防护措施制定提供参考。     

基于FSM无损检测的金属管道均匀腐蚀剩余寿命预测

目的预测均匀腐蚀下金属管道的剩余寿命。方法研究API579中对金属管道剩余寿命预测的方法,具体分析方法中存在的缺陷。采用场指纹法(FSM)对直径为750 mm、壁厚为10 mm的金属管道的腐蚀情况进行实时检测。检测时随机选择15个不同的位置,每隔3个月检测一次,通过检测各个位置电极对之间电压值的变化量计算出管壁厚度的变化值。结果根据对实验数据的分析,随着时间推移,金属管道壁厚值逐渐减小,且减小的速率越来越快。腐蚀速率与运输介质、含氧量、金属管道材料、运输介质中的杂质有着密切关系,全面分析实验数据可以得到金属管道腐蚀速率的规律。加入腐蚀速率影响因素的影响因子K,运用数理统计的方法探索性地提出了一种均匀腐蚀下金属管道剩余寿命Rlife预测的数学模型。结论在工程实际中,可以运用数理统计的方法对大量实时数据及运行过程中已经记录的数据进行分析,从而找到金属管道在特定环境下的腐蚀规律,再通过该数学模型可对均匀腐蚀的金属管道进行寿命预测。     

2205双相不锈钢在不同Cl~-含量的饱和H_2S/CO_2溶液中的腐蚀行为

采用全面腐蚀实验及SEM,EDS等表面分析技术研究了2205双相不锈钢在不同Cl-含量的饱和H2S/CO2溶液中腐蚀速率、腐蚀形态以及腐蚀表面膜层成分,并建立腐蚀过程机制模型。结果表明:随着温度与Cl-浓度的变化,腐蚀速率发生变化的转折点在Cl-浓度为(57-100)×10-6时,p H=4时,Cl-为170×10-6,温度50℃时的腐蚀速率最大,p H=6时,Cl-为170×10-6,温度80℃时的腐蚀速率最大,其最大腐蚀速率不超过0.004 mm/a;腐蚀表面形成较为致密的钝化膜,随着温度与氯离子浓度的升高,表面出现3~5μm的不稳定点蚀核。     

恒定的pH值和Fe~(2+)浓度下X65碳钢的CO_2腐蚀行为

在初始pH值为5.80和初始Fe~(2+)浓度为20 mg/L的条件下,采用离子交换树脂调节腐蚀过程中的pH值和Fe~(2+)浓度,使p H值和Fe~(2+)浓度在整个腐蚀过程中保持恒定。采用开路电位测试、线性极化技术、扫描电镜等手段研究了X65钢的CO_2腐蚀行为,并与非恒定条件(腐蚀过程中不调节pH值和Fe~(2+)浓度)下X65钢的CO_2腐蚀行为进行了对比。结果表明,在非恒定的pH值和Fe~(2+)浓度下,X65钢的腐蚀速率在120 h后迅速下降,220 h后腐蚀速率约为0.5 mm/a,样品表面的FeCO3膜完整且致密。在恒定的pH值和Fe~(2+)浓度下,X65钢的腐蚀速率在160 h后才开始缓慢下降,220 h后腐蚀速率仍高达4.5 mm/a,样品表面FeCO3膜的裂纹较多,且与基体之间存在明显间隙。因此,在密闭容器中维持相对恒定的pH值和Fe~(2+)浓度对获得与油气田现场一致的CO_2腐蚀行为规律十分重要。     

含CO2油气管道内腐蚀模拟及剩余寿命预测

目的通过对含CO_2油气管道的内腐蚀状况进行仿真和实验研究,得出管道的内腐蚀规律和剩余使用寿命。方法以渤西海域某一管道的实际工况为基础,采用OLGA软件并选择De Waard95模型对CO_2腐蚀速率的影响因素进行仿真分析。采用失重实验研究了温度和CO_2分压对X52级管道钢腐蚀速率的影响,在仿真数据的基础上对腐蚀管道的剩余寿命进行预测。结果仿真结果表明,管道沿线的温度、压力、持液率、流型及pH值对CO_2腐蚀程度的影响都很大。实验发现,CO_2腐蚀速率随温度的升高呈先增后降的趋势,且在温度为333 K时达到最大值,为0.22 mm/a。随着CO_2分压的升高,腐蚀速率呈上升趋势,最大值为0.24 mm/a。结论随着管道高程和里程的不同,不同因素对CO_2腐蚀有不同程度的影响,管道入口段的腐蚀速率最大,仿真和实验结果对管道的内腐蚀防护和剩余寿命预测有一定的参考价值。     

CO2输送管道腐蚀研究进展

在碳捕获、利用与封存(CCUS)的研究中,CO_2管输中的腐蚀控制尤为重要。在CO_2管道腐蚀研究成果的基础上,归纳了CO_2输送管道的腐蚀速率、机理、过程及主要控制措施。研究显示H2O是产生腐蚀的主要因素,输送过程中水含量的均值不应超过0.038%(体积分数)。当存在SO2及O2时,管道的腐蚀速率将达到4.0 mm/a;当存在NO2时,管道的腐蚀速率将达到12 mm/a。O2含量较低时加速腐蚀,当O2含量大于0.057%(体积分数)时出现钝化现象,且腐蚀速率小于0.01 mm/a。CO_2腐蚀产物中的表层是Fe CO3等轴晶粒,中间为棒状晶粒且充满孔洞,最内层为致密的Fe CO3晶粒。形成过程为:钢材基体在最初溶解阶段形成Fe3C架构,Fe CO3晶粒沉积在表面,然后CO_22-和HCO3-向内扩散并与钢基体反应形成中间层和内层。工程中采用抗腐蚀管材、涂镀层管材、加注缓蚀剂以及阴极保护等措施克服腐蚀影响。     

埋地钢质管道强制电流阴极联合保护研究

目的验证阴极保护系统在保护目标管道的同时对临近管道造成的杂散电流腐蚀,对比柔性阳极与阳极地床在保护管道的过程中产生的杂散电流污染情况,确定同沟铺设的不同管道联合保护方案。方法通过同一排流设备对相同区域的不同管线进行统一保护,阴极保护系统中的接地装置作为唯一的阳极,多条埋地管线作为电化学电池的阴极实现保护。结果阳极地床产生的杂散电流干扰明显强于柔性阳极材料;排流保护中,两条20 m埋地金属管道达到排流保护的范围时,柔性阳极的排流电压为1.2~1.52 V,远小于碳钢阳极地床的3.5~15 V,能够有效减少防护过程中电能的使用。结论同一阴极系统同时对多条金属管道或金属构筑物进行排流保护的措施可行。     

油管钢在模拟超临界CO2中耐蚀特性的研究

目的研究普通碳钢P110、3Cr、普通马氏体不锈钢13Cr和超级马氏体不锈钢HP2-13Cr钢在某油井超临界CO_2环境中的耐蚀特性。方法模拟该高温高压高含CO_2且含Cl–油井的腐蚀环境,采用高温高压反应釜对上述四种油管钢进行挂片实验,借助高精度天平、扫描电子显微镜(SEM)、能量色散X射线能谱(EDS)从平均腐蚀速率、清理腐蚀产物后试样的表观特征、腐蚀产物的表面形貌和化学成分及腐蚀机制方面分析其抗均匀腐蚀与抗点蚀特性。结果在CO_2分压达12 MPa,110℃,Cl–质量浓度为16 542 mg/L的典型环境,P110,3Cr油管钢的平均腐蚀速率分别为5.625,2.992 mm/a;13Cr为0.155 mm/a,有点蚀发生,HP2-13Cr则为0.003 mm/a,且为均匀腐蚀,HP2-13Cr能满足模拟腐蚀环境的使用要求。结论在上述超临界CO_2环境,碳钢P110与3Cr在基体表面不存在Cr的富集,耐蚀性差;马氏体不锈钢13Cr和超级马氏体不锈钢HP2-13Cr因基体表面能生成致密的钝化膜,则表现出相对优良的耐蚀性,但两者的合金元素Ni,Mo含量不同,造成了对两者抗均匀腐蚀与抗点蚀性能的显著差异。     

Oxidation behaviour of some nickel base alloys in carbon dioxide at 900–1000°

Abstract

The oxidation behaviour of three nickel base alloys, EPE 16, Nimonic 75 and Hastelloy X, has been studied in 1 atm of CO₂ at 900°, and in the case of Hastelloy X at 1000°, for a maximum exposure period of 8000 h. Weight gain data were obtained and changes in the subsurface of the metal were examined. The structure of the metal could be altered up to a maximum depth of 200 μ by void formation, internal oxidation and decarburisation. Hastelloy X was the most resistant alloy and an aluminised coating greatly increased the resistance of EPE 16. With the exception of one batch of Nimonic 75, the addition of 5–10% of CO to the gas did not influence the behaviour. The decarburisation of the surface of Nimonic 75 in 3 × 10^-3 atm of CO₂ was studied at 900° using the radioactive tracer ¹⁴C. Carbon was transferred both to the gas phase by the reaction CO₂ + C (in the metal) → 2CO, and to the centre of the specimen. After the initial oxidation, the rate of carbon transfer to the gas was approximately 6 × 10^-3 μg/cm² h decreasing to 3 × 10^-3 μg/cm² h at the end of the 1900 h exposure. Over half the carbon removed from the surface diffused into the centre of the specimen. This diffusion has been attributed to chromium depletion at the surface to form a chromium-rich oxide, being primarily responsible for the decomposition of the chromium carbide phase in the metal.     

等离子堆焊Q235电解打壳锤头的组织和性能

采用等离子堆焊技术在Q235铝电解打壳锤头表面堆焊F40合金粉末熔覆层。利用扫描电镜、能谱仪和显微硬度计等分析等离子堆焊层的微观组织、微区成分和硬度分布。利用磨擦磨损仪对试样进行耐磨性测试,通过恒电位法评估堆焊层和基体的耐蚀性能。结果表明,堆焊层与基体形成了良好的冶金结合,堆焊层为典型的柱状晶组织。等离子堆焊层平均显微硬度为444HV0.1,为基体的2倍;耐磨性为基体的1.6倍;腐蚀速率Rcorr为3.524×10-4 mm/a,为基体的1/(4.2×104)。等离子堆焊后Q235钢材料的耐磨性、硬度和耐腐蚀性均有显著提高,有望提高电解铝打壳锤头的耐磨耐蚀性能。     

A study of 4-carboxyphenylboronic acid as a corrosion inhibitor for steel in carbon dioxide containing environments

4-Carboxyphenylboronic acid (CPBA) has been found to be an efficient carbon dioxide (CO₂) corrosion inhibitor for steel in aqueous media. The results indicate that the addition of CPBA to CO₂ containing sodium chloride solutions at a low concentration is able to retard corrosion anodic reactions, reduce corrosion current densities, increase charge transfer and total resistances, resulting in more uniform and smoother steel surfaces. These effects are attributed to the formation of a barrier layer on steel surface, which provides metal surface protection. The inhibitor was also found to mitigate corrosion by promoting random distribution of minor anodes.     

3Cr低合金钢焊接接头腐蚀膜对基体的保护作用

利用扫描电镜分析3Cr低合金管线钢高频电阻焊接头微观组织,采用高温高压反应釜和电化学阻抗测试技术对焊接接头的CO₂腐蚀行为进行研究. 3Cr低合金钢高频电阻焊焊缝和母材的化学成分一致,组织均为铁素体+珠光体,且焊缝组织更加细小、均匀. 失重试验结果表明,焊接接头的腐蚀速率比母材小0.28 mm/年. 电化学阻抗测试结果表明,浸泡时间48和168 h后,焊缝表面腐蚀膜电阻均大于母材,焊缝腐蚀膜对基体的保护性均好于母材. 这是由于焊缝组织分布均匀细小,表面腐蚀膜均比母材均匀和致密. 浸泡48 h时焊缝表面为双层膜结构,母材为单层膜;浸泡168 h时焊缝和母材表面均为单层膜结构.     

Numerical modeling of stray current corrosion of ductile iron pipe induced by foreign cathodic protection system

Stray current corrosion phenomena of ductile iron pipe (DIP) located in the vicinity of cathodically protected steel pipe was assessed using the boundary element method. When all joints in DIP were electrically connected, the maximum corrosion rate was 0.005 mm/y. However, when the joints were isolated, the corrosion rate increased due to the jumping effect of stray current at isolated joints, which resulted in the increase of maximum corrosion rate to 0.87 mm/y at the isolated point. Moreover, the electrical bonding between the DIP and steel pipe could not act effectively but showed an adverse effect of collecting more cathodic protection (CP) currents into the DIP, which eventually jumped out into the soil and resulted in larger amount of stray current corrosion. Therefore it is desirable to apply control methods from the design and construction stage, which include the increase of anodebed and the pipe distance, electrical connection of DIP joints, installation of sacrificial anode at isolated joints, or the application of CP on DIP, etc.     

Microstructure and corrosion resistance of tantalum after nitrogen ion implantation

This paper investigates the effect of nitrogen ion implantation on surface structure as well as resistance against tantalum corrosion. Bulk Ta surface was implanted with 30?keV nitrogen ions at a temperature of 100°C with doses between 1?×?10¹⁷ and 1?×?10¹⁸?ions/cm². The implanted samples were characterised by atomic force microscopy, X-ray diffraction analyses and the corrosion test to identify structural, compositional and electrochemical changes at various doses. The experimental results indicate the formation of hexagonal tantalum nitride (TaN_0.43), in addition to the fact that by increasing the ion dose, nitrogen atoms occupy more interstitial spaces in the target crystal, a case which can significantly improve corrosion resistance. The maximum extent in the improvement of the micro hardness was 75% and the reduction in the corrosion current was 83%. According to scanning electronic microscopy and corrosion results, in the dose of 1?×?10¹⁸?ions/cm² the highest corrosion resistance was received against the H₂SO₄ corroding media.     

The effects of crosshead speed and temperature on the stress corrosion cracking of Cu-30% Zn alloy in ammoniacal solution

Stress corrosion cracking (s.c.c. of Cu-30% Zn alloy in Mattsson's solution (0.05 mol/l CuSO₄ + 0.5 mol/l (NH₄)₂SO₄, pH 7.2) was investigated as a function of temperature (298 K–323 K) and crosshead speed (10^?5 mm/min to 1 mm/min). Crack propagation behaviour in a crosshead speed of 10^?4 mm/min at 298 K was also studied. All tests were carried out using a slow strain rate technique. Cracks occurred intergranularly under all experimental conditions used. At high crosshead speeds (5 × 10^?3 mm/min to 1 mm/min) the susceptibility to s.c.c. increased with increasing temperature. At slow crosshead speeds, however, an inverse effect of temperature on the susceptibility was revealed. Constant crack velocities were obtained in both specimens with or without surface coating, and the velocity in the coated specimen was lower than that in the uncoated specimen by one order of magnitude. Scanning electron microscopic examination revealed that ahead of intergranular cracks small corrosion pits were formed along grain boundaries.Based on the above experimental results, the mechanism of intergranular s.c.c. of Cu-30%Zn alloy was discussed by considering the growth rate of microcrack formed along grain boundary and the corrosion rate (or repassivation rate) of the microcrack.     

2-hydroxyethilammonium oleate protic ionic liquid as corrosion inhibitor for aluminum in neutral medium

Protic ionic liquid (PIL) 2-hydroxyethylammonium oleate (2HEAOl) proved to be a good lubricant for aluminum-forming processes. However, with the aim of keeping the formed component integrity, it is interesting that the same substance employed during forming does not need to be removed and works out as corrosion inhibitor. Then, the aim of this study was to test the performance of 2HEAOl as corrosion inhibitor for aluminum in neutral 0.5 mol/L NaCl medium by electrochemical characterization. Results showed that the concentration of 5 × 10⁻⁴ mol/L was a suitable concentration to promote corrosion inhibition until 72 h at the high chloride concentration studied. The PIL worked out as mixed-type organic corrosion inhibitor, as it promoted the diminution of the oxygen reduction reaction rate and, in consequence, the pit initiation by its adsorption on the metal surface.     

Novel laser surface treatment approach to suppress sensitisation in modified type 316(N) stainless steel weld metal

Abstract

Welded components are subjected to solution annealing heat treatment for achieving full stress relief and restoration of mechanical properties and corrosion resistance. During such heat treatments, optimum cooling rate has to be selected because very slow cooling rate will result in sensitisation and susceptibility to intergranular corrosion whereas fast cooling will result in reintroduction of residual stress. For 316 LN stainless steel which is welded using modified E316-15 electrodes (0·045–0·055%C), critical cooling rate above which there is no risk of sensitisation is 75 K h^?1. This paper presents a novel laser surface treatment which suppresses sensitisation in weld metal, even at a slower cooling rate of 65 K h^?1. Experiments involving laser surface melting were carried out with 150 W average power pulsed Nd:YAG laser and 10 kW CO₂ laser, in both continuous wave and pulse modulated (100 Hz) modes. Best results were obtained when surface melting was performed with high frequency pulse modulated CO₂ laser beam. The processed weld metal remained unsensitised after solution annealing followed by slower rate of cooling at 65 K h^?1. Numerical simulation study was performed with ANSYS 7·0 software to understand the physical reason behind the difference in sensitisation behaviour of CO₂ laser melted specimens under continuous wave and high frequency pulse modulated conditions and the predictions were validated using results of electron backscattered diffraction studies. Weld metal specimens treated with high frequency pulse modulated CO₂ laser clearly showed evolution of fine grains near the fusion boundary region which enhanced sensitisation resistance.