涂层剥离条件下X70管线钢的应力腐蚀裂纹萌生行为

通过循环载荷实验,研究了管道涂层剥离条件下,阴极保护电位对X70管线钢在近中性pH值溶液(NS4溶液)中应力腐蚀裂纹萌生的影响.利用SEM观察了距涂层剥离口不同距离处的应力腐蚀裂纹的萌生情况.结果表明,外加-850 mV阴极保护电位时,剥离涂层下样品表面裂纹的萌生程度随距离涂层开裂口长度的增加而逐渐减轻;外加-1000 mV阴极保护电位时,剥离涂层下样品表面裂纹的萌生程度随距离涂层开裂口长度的增加而稍有增加,但缝隙内各个位置的裂纹萌生程度低于-850 mV极化电位下缝隙内部相应位置的裂纹萌生程度;涂层的剥离降低了阴极保护的效果,要达到涂层完整时的阴极保护效果,则需要使阴极保护电位适当负移.     

杂散电流干扰和阴极保护作用下碳钢腐蚀规律研究

目的探讨杂散电流和阴极保护二者共同作用对碳钢腐蚀的影响。方法在碳钢管表面手工涂刷涂层并制造小块破损点,研究Q235碳钢在涂层破损后,受单纯直流杂散电流干扰、单纯阴极保护以及二者共同作用时随时间变化的电化学交流阻抗图谱(EIS),通过图谱信息以及图谱数据拟合进行分析。结果所有条件下,Bode图低频阻抗和Nyquist图容抗弧半径都随时间延长而逐渐增加。通过图谱和数据拟合发现,单纯杂散电流条件下,杂散电流越大,电化学阻抗越小,浸泡15天时,20 m A杂散电流条件下的极化电阻达到200 m A条件下的4倍。阴极保护对杂散电流腐蚀具有防护作用,无论是单独施加阴保,还是杂散+阴保共同作用,-1000 m V(vs.CSE)与-850 m V(vs.CSE)横向对比,总是-1000 m V条件下的极化电阻更高。一定程度上,阴保电位越负,极化电阻越大,保护效果越好。结论在一定范围内,不论是单独施加,还是共同作用,总是杂散电流越小,阴极保护电位越负,对碳钢的保护效果越好,腐蚀程度越轻。利用电化学交流阻抗技术监测管道腐蚀状况是可行的。     

破损涂层下管线钢的交流电干扰腐蚀行为

构建了带破损点的剥离涂层管道腐蚀模拟实验装置,采用微电极技术研究交流干扰X80管线钢破损/剥离涂层下局部腐蚀行为及规律。结果表明:交流电干扰使涂层破损管线钢电位负向偏移;随交流电密度增大,X80钢的阳极溶解速率增大,腐蚀形态由均匀腐蚀逐渐向局部腐蚀转变;破损点处管线钢发生严重腐蚀,剥离区腐蚀程度稍有减缓;但施加100 A/m~2交流电时,剥离区深处X80钢表面仍出现了较严重的点蚀坑。从交流干扰的整流效应、阳极反应不可逆性及交流电对钢/环境界面双电层结构影响等角度讨论了交流电干扰对涂层破损下管线钢腐蚀行为的影响。     

剥离涂层下的极化——常规阴极保护与脉冲阴极保护的比较

钢管线上的涂层剥离会产生屏蔽现象，从而导致各种腐蚀问题。由于阴极保护受钢体表面和剥离涂层之间形成的高电阻所限，常规阴极保护不能达到控制腐蚀的目的。本试验研究的目的就是应用脉冲阴极保护改进剥离层下阴极保护电流的分布，更有效地进行腐蚀控制。分别采用常规阴极保护和脉冲阴极保护对剥离涂层下的试件进行极化试验，通过计算求出每个系统的电流量、电位分配、极化电位、pH值范围和工作效率，结果表明，一定的脉冲信号肯定能延长剥离处达到保护电位的距离。     

埋地管线剥离覆盖层下阴极保护的有效性

由微小缝隙模拟管线剥离覆盖层（涂层）下的局部电化学环境，用微电极技术测量了缝隙内局部电位及pH的分布，研究了缝口阴极保护电位、剥离区几何形状、溶液电导率等因素对剥离区内部局部环境及阴极保护水平的影响。结果表明，剥离区内电位降（电位梯度）主要集中在破损口附近，而剥离区深处接近自然腐蚀状态；剥离区内有效保护距离随缝口保护电位负移而增加，但缝口过保护并不能有效提高剥离区保护效果。阴极保护可使剥离区局部电化学环境pH升高、电导率增大。     

干湿交替土壤环境中剥离涂层管线钢阴极保护有效性

基于长输管线三层聚乙烯(3PE)防腐层失粘剥离的现场调查情况,构建剥离防腐层下管道腐蚀模拟实验装置,研究干湿交替工况剥离防腐层下管道的阴极保护电流和电位分布、阴极保护有效距离及屏蔽区管线的腐蚀行为。结果表明,带破损点涂层剥离区内阴极保护电位梯度和保护电流主要集中在破损点区域,而缝隙深处管体处于自腐蚀状态;随干湿循环次数的增多,破损点至缝隙内45 mm处稳定后的局部电位逐渐负移;剥离间隙1 mm情况下,有效保护距离仅数厘米。     

剥离涂层下管线钢腐蚀研究进展

综述了在有阴极保护的条件时剥离涂层下缝隙内电位电流的分布和化学环境的变化、阴极保护防止缝隙腐蚀的机理、微生物腐蚀的机理以及前人提出的关于剥离涂层下微生物腐蚀与阴极保护相互作用的规律，并展望了对于解决剥离涂层下微生物腐蚀难题需进一步的实验研究.     

阴极保护电位对破损环氧涂层阴极剥离的影响

采用电化学阻抗技术(EIS),并结合SEM,EDS和XRD研究了室温、静态模拟海水中不同保护电位对海洋平台研制钢在模拟海水中防腐涂料与阴极保护联合作用效果以及对破损环氧防腐涂层的阴极剥离机理。结果表明:在本实验选择的保护电位中,随着电位的负移,涂层剥离面积逐渐增大。-750 mV (vs SCE,下同)保护电位对于破损涂层的金属基体欠保护。-1050 mV电位极化下发生严重的析氢现象,破坏了钙质沉积层的完整性,界面碱化程度较大,涂层剥离面积最大;-850和-950 mV保护电位均能抑制破损处金属的腐蚀;-950 mV保护电位下生成的CaCO_3和Mg(OH)_2钙质沉积层完整致密,保护效果最佳。     

阴极极化条件下X70钢的缝隙腐蚀行为

采用矩形缝隙装置,测量了模拟剥离涂层下不同位置X70钢的电位、溶液pH值及氧含量随时间的变化曲线．研究了外加阴极极化电位、涂层破损尺寸和缝隙厚度对X70钢在Nu2SO4溶液中的缝隙腐蚀行为的影响．结果表明,缝隙内氧气迅速耗尽并使溶液pH值升高,氧耗尽与外加阴极极化电位无关．随着缝口阴极极化程度加大,缝隙内各点电位负移,有效保护距离增加．溶液介质电位（IR）降集中在缝口．极化程度过高会导致氢气的析出．减小缝隙厚度和破损点尺寸使缝隙内极化程度降低．     

结合WBE与EIS技术研究环氧涂层下碳钢与铜合金在海水中的电偶腐蚀

目的 研究环氧涂层下碳钢与铜合金在海水中的电偶腐蚀行为及涂层整体和局部区域的劣化过程。方法 使用丝束电极（WBE）技术和电化学阻抗谱（EIS）技术研究丝束电极表面的电流密度分布和涂层阻抗谱演化,同时对比分析碳钢区域与铜合金区域涂层的阻抗谱特征。结果 阳极电流峰首先出现在碳钢局部区域,而电流密度较大的阴极电流峰主要集中出现在铜合金区域的边缘。当浸泡至122 h时,铜合金区域的涂层阻抗明显低于碳钢区域的涂层阻抗,且EIS响应出现了Warburg扩散阻抗特征。在浸泡456 h后,单根钢电极发生由阴极向阳极的极性转换。结论 涂层下碳钢与铜合金在海水中发生电偶腐蚀时,铜合金作为阴极被保护,但铜合金区域的涂层在阴极剥离的作用下加速劣化。在涂层劣化过程中,碳钢区域的涂层缺陷处成为腐蚀反应的阳极区,而主要的阴极区位于铜合金的边缘区域,这与溶解氧的“竞争效应”有关。由于涂层发生阴极剥离现象使得基底金属被腐蚀,从而导致涂层下单根钢电极的电流发生由阴极向阳极的极性转换。     

管道3PE涂层的阴极剥离性能研究

分析探讨了管道3PE涂层阴极剥离的机理和产生条件,试验研究了不同温度、时间下极化电位等因素对3PE涂层等的阴极剥离性能的影响规律.结果表明,在一定的条件下,极化电位的变化对3PE涂层的阴极剥离性能影响不大。     

饮用水水质对缺陷涂层腐蚀行为的影响

目的研究带缺陷环氧富锌涂层在不同水质的饮用水模拟溶液中的腐蚀机理,为饮用水输水管内壁涂层的选用提供建议。方法采用电化学阻抗谱(EIS)研究涂层浸泡过程中的电化学行为,分别采用扫描电子显微镜(SEM)、EDS能谱仪和拉曼光谱对腐蚀产物的形貌和成分进行分析。结果在含Ca2+较多的溶液中,缺陷处形成了致密的水垢,并在水垢附近形成了双层锈结构;在含Ca2+较少的溶液中,垢的生长受到限制,缺陷处布满黄锈,并且起泡现象严重。结论涂层在硬度较小的溶液中具有更好的抗渗性;而在硬度较大的溶液中更容易形成粗大而紧密堆积的碳酸钙柱状晶,覆盖在缺陷处形成水垢,阻碍涂层的阴极剥离和阴极起泡过程。对于输送软水的饮用水管道,内壁涂层的防划伤是关键;对于输送硬水的饮用水管道,内壁涂层的抗渗能力是关键。     

Effect of cathodic protection on corrosion of pipeline steel under disbonded coating

In this work, a test rig was developed to study the effect of cathodic protection (CP) on corrosion of X70 pipeline steel in the crevice area under disbonded coating through the measurements of local potential, solution pH and dissolved oxygen concentration. Results demonstrated that, in the early stage of corrosion of steel, CP cannot reach the crevice bottom to protect steel from corrosion due to the geometrical limitation. Corrosion of steel occurs preferentially inside crevice due to a separation of anodic and cathodic reaction with the depletion of dissolved oxygen in the crevice solution. The main role of CP in mitigation of sequential corrosion of steel in crevice under disbonded coating is to enhance the local solution alkalinity. With the increase of distance from the open holiday, a high cathodic polarization is required to achieve appropriate CP level at crevice bottom. A potential difference always exists between the open holiday area and inside crevice, reducing the CP effectiveness.     

硅烷偶联剂处理对富锌涂层行为的影响

 采用测量涂层的腐蚀电位和电化学阻抗谱(EIS)等方法研究了硅烷偶联剂处理(钢铁表面的硅烷偶联剂预处理和富锌漆中掺入硅烷偶联剂)对富锌涂层在3.5mass%NaCl溶液中腐蚀行为的影响.结果表明，两种硅烷处理方式均明显延长了富锌涂层的阴极保护期.钢铁表面硅烷处理减弱了无机富锌涂层的阴极保护作用.      

Electrochemical Characteristics in Seawater for Cold Thermal Spray-Coated Al-Mg Alloy Layer

For corrosion protection of carbon steel in a marine environment,cold arc thermal spray coating was applied to the surface with Al and Al-Mg alloy wires.The surface hardness of Al and Al-Mg thermal spray coatings increased with Mg content.And the various electrochemical experiments were carried out to evaluate corrosion damage characteristics of the thermal spray coating layers.The Al and Al-Mg thermal spray coating layers presented negative potentials compared to carbon steel in corrosion potential measurements.And an anodic polarization experiment revealed a tendency of activation polarization with no passivation.Furthermore,the corrosion damage of the thermal spray coating layer in galvanostatic experiment was observed mainly at the defect area,and the Al-3Mg thermal spray coating layer presented less surface damages than others.In addition,the Al-3Mg thermal spray coating layer showed the lowest corrosion rate while having a sufficient driving voltage for cathodic corrosion protection.Therefore,it is an optimal thermal spray material for sacrificial anode.     

EFFECT OF CATHODIC PROTECTION ON FRACTURE BEHAVIOUR OF LOWALLOY STEELS IN SEAWATER

Fracture behaviour of low-alloy steels AIST4340,HY100,Welten60,AISIA537 and A131 inartificial seawater under static,cyclic loading and at cathodic protection potential has beeninvestigated by using the techniques of fracture mechanics, electrochemistry andelectronfractography.The results reveal that at hydrogen evolution potentials(cathodic pro-tection potential)the critical yield strength required for the occurrance of SCC decreasesfrom 985 at corrosion potential(E_c)to 872 MPa.The effect of cathodic protection on crackpropagation of corrosion fatigue(CF)is not simple,it is closely related to the yield strengthof steels and their SCC behaviour.For the steels with high yield strength,cathodic protectionpromotes(da/dN)_Ⅱ evidently,and reduces △K_(th) value.The(da/dN)-△K curves dis-play a plateau at the third stage of CF for steels with medium or low yield strength.It is men-tioned that the cathodic protection potential for oceaneering constructures should be control-led at top level of the protective range.It seems reasonable that the strength of steel foroceaneeing use might be increased by 200 or 300 MPa.     

Role of dissolved oxygen diffusion in coating defect protection by emeraldine base

The corrosion protection of emeraldine base (EB) on mild steel in the artificial defect exposed to 1 wt% NaCl solution was studied using in situ optical microscope and scanning electron microscopy (SEM). The EB coating displayed good corrosion protection on the exposed bare steel, which was difficult to understand by traditional anodic protection mechanism or inhibitory protection mechanism, or cathodic protection mechanism, since steel usually cannot be passivated in brine, and EB coating cannot release inhibitory anions to protect exposed bare steel, and further, the galvanic coupling measurement demonstrates that EB cannot provide cathodic protection to exposed bare steel. The importance of dissolved oxygen diffusion caused by EB in corrosion protection was disclosed in this paper, a related protection model was therefore proposed, which was qualitatively verified by corresponding electrochemical measurements.     

阴极极化对LY12CZ铝合金腐蚀疲劳寿命的影响

在LY12CZ铝合金腐蚀疲劳寿命曲线的基础上,研究了不同阴极电位下有无涂层试件在3．5％NaCl溶液中腐蚀疲劳寿命的变化规律．记录了一定阴极电位下阴极电流的变化情况．并通过对腐蚀疲劳断裂微观形貌的观察、分析,探讨了阴极极化对有无涂层保护的LY12CZ铝合金腐蚀疲劳寿命影响机理．对于无涂层试样,一定范围内的阴极电位会抑制阳极反应,明显提高腐蚀疲劳寿命,但当阴极电位达到一定值时(-1400mV以上),发生铝合金的阴极腐蚀,使腐蚀疲劳寿命显著降低．对于有涂层试样,由于涂层的保护,一定电位值范围的阴极保护作用并不显著,阴极电位超过一定值,涂层阻碍抑制了阴极腐蚀作用,试样腐蚀疲劳寿命较无涂层试样有显著提高。     

Effect of porosity of phosphate coating on corrosion resistance of galvanized and phosphated steels Part II: Evaluation of corrosion resistance

The effect of porosity of phosphate coatings on the corrosion resistance of ungalvanized (UG), electrogalvanized, and hot dip galvanized steels is evaluated in this study. The corrosion resistance of phosphatized and painted steel is related to the integrity and continuity of phosphate and paint layers, and pores in the phosphate layer affect the corrosion resistance of material. The porosity of the phosphate coating was evaluated by using the cathodic polarization electrochemical test. To evaluate the corrosion resistance of the phosphatized and painted steels, they were submitted to accelerated corrosion tests. As was expected, the creepback from the scribe increased with the increase in porosity. This behavior was evident for UG steel, but less evident for galvanized steels due to cathodic protection and/or barrier effect of the zinc coating.