基于缩比模型理论的船舶外加电流阴极保护系统水线下表面电位的研究

采用缩比模型理论建立船舶外加电流阴极保护系统,研究船体表面电位分布的影响因素之间关系。结果表明,单区阴极保护系统辅助阳极位置决定船体表面电位曲线的形状,参比电极影响曲线电位值的大小;增加阳极数量能够优化电位分布,降低曲线电位的波动。试验证明,基于缩比模型理论的船舶表面电位测量方法是一种方便、有效的测量手段,为进一步优化外加电流阴极保护系统提供新的研究途径。     

船体外加电流阴极保护系统设计与应用

本文以船体外加电流阴极保护系统设计与应用案例,详细讲解了系统参数计算、布置要求、调试方法及相关注意事项。外加电流阴极保护系统运行后,船体保护电位符合设计和实际使用要求,达到了阴极保护效果,可以有效预防船体腐蚀,延长船舶使用寿命。     

影响舰船外加电流阴极保护电位因素分析及仿真

舰船都会使用外加电流阴极保护的方法进行船体防腐保护,保护电位是进行外加电流阴极保护方法的核心参数,如何设定保护电位的数值将会决定舰船的防腐效果。文章首先建立舰艇外加电流阴极保护电位计算模型,然后从阳极与被保护体的距离,腐蚀介质电阻率变化对电流分布的影响,涂层对电位电流分布影响三个方面讨论影响外加电流阴极保护电位的因素。通过仿真,确定了以上因素如何影响外加电流阴极保护电位,为合理设计外加电流阴极保护电位参数提供了理论依据。     

交流干扰影响下的最小阴极保护电位

通过模拟试验装置,采用恒电位和恒电流极化试验研究了交流干扰影响下埋地管道阴极保护系统的破坏机理,探究新的确定阴极保护电位的方法。结果表明,可以根据保护电流密度曲线的趋势制定新的阴极保护准则。根据试验结果确定了0～100A·m-2干扰电流密度范围内的最小阴极保护电位限值公式。     

船体压载舱牺牲阳极阴极保护的数值模拟

数值模拟计算技术是研究牺牲阳极阴极保护效果的有效手段,采用边界元数值模拟分析软件对船体压载舱牺牲阳极阴极保护进行了数值模拟分析。结果表明,根据常规牺牲阳极设计,常规数值计算压载舱内表面电位范围稍宽(即-800~-1 100mV,相对Ag/AgCl参比电极,下同),通过调整牺牲阳极位置,表面保护电位范围收窄(即-890~-1 110mV),保护效果变好。     

介质和阴极保护电位对12CrNi3MoV钢长短疲劳裂纹扩展行为的影响

<正> 一、前言 船体钢在海水中的腐蚀疲劳是船舶结构破坏的主要形式。设计舰船壳体阴极保护系统时通常着眼于防腐蚀效果,并不考虑对船体结构强度的影响。已有的研究资料指出,阴极保护可提高光滑试佯的腐蚀疲劳强度,但对疲劳裂纹扩展速率影响的看法存在分岐。有人认为,阴极保护加速疲劳裂纹扩展;也有人认为,在一定条件下阴极保护会阻碍疲劳裂纹扩展。本工作在实验室条件下研究介质和阴极保护电位对长、短疲劳裂纹扩展行为的影响。 二、材料及试验方法 试材采用调质态12CrNi3MoV钢,化学成份见表1,机械性能见表2。     

某大型站场强制电流阴极保护失效的原因

某大型站场阴极保护系统运行一段时间后,阴极保护电位合格率发生大幅度的下降.从现场恒电位仪输出参数、土壤电阻率、预包装高硅铸铁阳极表面形貌和阳极接地电阻等方面对该阴极保护失效的原因进行了分析.结果 表明:阳极埋设处土壤较为干燥,土壤电阻率较高,阳极表面的致密氧化物和土壤中的碎石增加了阳极与土壤接触电阻,导致整个系统的回路...     

钢质贮罐底板外侧阴极保护时的电位分布

钢质贮罐底板外侧阴极保护时的电位分布往往不均匀。本文用有限元法计算了几种情况下的电位分布和电流分布规律,并在此基础上讨论了多种因素对电位分布的影响,包括土壤的电阻率、贮罐底板外侧表面状态、阳极的数量和分布以及极化量等。这些结果可以解释罐底阴极保护的特征。这个计算方法可用于贮罐底板外侧阴极保护系统的设计。     

X80钢在河南伊川境内土壤模拟溶液中的阴极保护电位

利用电化学阻抗谱和阴极极化曲线两种方法,研究了X80钢在"西气东输二线"沿线河南伊川土壤模拟溶液中的阴极保护电位,并对两种结果进行了对比.结果表明:这两种方法均可以确定阴极保护极限电位,且具有较好的一致性.通过拟合电荷传递电阻与电位关系曲线,得到X80钢的阴极保护极限保护电位为-1007～-753 m V;通过阴极极化...     

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.     

THE RELATIONSHIP BETWEEN PITTING SUSCEPTIBILITY AND INCLUSIONS IN CARBON STEELS IN ARTIFICIAL SEAWATER

1. IlltroductionMany studies have been conducted on the pitting of steels[1]. Actually3 pitting ofcarbon steels is less typical than that of stainless steels, and for the former the pits arewider and more shallow. For the pitting of carbon steels and the effect of inclusions on thepitting, there are some previous investigations. Wranglen[2] found a correlation betweensusceptibility to localized corrosion and the ratio of active to inactive sulfides; and onlyactive sulfide was believed to act a…     

The delamination of polymeric coatings from steel Part 3: Effect of the oxygen partial pressure on the delamination reaction and current distribution at the metal/polymer interface

In the third part of this paper, it is shown that oxygen reduction plays the central role in the delamination process. The oxygen partial pressure controls the potential of the local cathode at the metal/polymer interface and potential changes, which are measured after change of the oxygen activity, allow us to determine the local diffusion coefficient of oxygen in the polymer. The delamination is caused by reaction products, like radicals, which are formed during the oxygen reduction at the metal/polymer interface. However, the reaction rate of the oxygen reduction for the simple non-pigmented polymer under investigation is determined by the ohmic potential drop between the defect and the delamination frontier. This potential drop is given by the difference of the open circuit potential at the defect and the intact interface (which results from the surface treatment, such as phosphating) and the ionic conductivity between both sites. Both are confirmed by a direct measurement of the distribution of the galvanic current along the metal/polymer interface.     

An investigation of the electropolymerization of terthiophene in boron fluoride–ethyl ether

Various potentials have been used to oxidize terthiophene in boron fluoride–ethyl ether (BFEE), the final products are then studied by the surface-reflection IR and UV–Vis spectra. When a potential is controlled in the region of 0.7–0.8 V which is slightly higher than that of monomer oxidation, a regularly ,′-linked polymer is obtained which has an average chain length of about 21 thiophene rings and an absorption peak of 482 nm at its neutral state. An oxidation potential higher than 0.8 V is found to lead to the occurrence of mislinkage, while an oxidation potential lower than 0.7 V only produces oligomers. The polyterthiophene prepared by control of the oxidation potential has further been cycled in BFEE to check its electrochemical stability. Comparing with the polymers from thiophene and bithiophene, the thin polyterthiophene film adhering onto a stainless-steel electrode exhibits a better cycling behaviour.     

Monitoring of blistering of organic coatings by a contact-free measurement

A new technique is presented, which is able to detect corroding parts of a metal surface below technical polymercoatings. The technique (vibrating reference electrode) is based on the observation, that the local corrosion potential – which in turn is given by the rates of the anodic and cathodic partial reactions of the corrosion process– is quite different for an intact and for a delaminated metal/polymer interface. In this paper two different coatings are analysed, which are used in technical flue gas desulfurisation (FGD) plants. It is shown, that the different stability of the two coatings can clearly be elucidated by mapping the corrosion potential of the surface in a humid atmosphere.     

Electrochemical behavior of surface films formed on Fe in chromate solutions

The stability of passive films formed on Fe in K₂Cr₂O₇ solutions during exposure at open-circuit potential or by potential cycling is studied in a chromate-free solution. The electrochemical behavior of chromate-passivated Fe is investigated with cyclic voltammetry combined with LASER light reflectance measurements which allow an in situ determination of the thickness of the iron oxide film. The electrochemical behavior of chromate-passivated Fe in chromate-free solutions strongly depends on passivation treatment. Passivation of iron by immersion at open-circuit in chromate solution leads to a passive film, in which both Fe and Cr species dissolve almost independently of the presence of the other one: Fe oxide by reductive dissolution and Cr oxide by oxidative dissolution in the corresponding potential regions. Passivation of iron by potential cycling in chromate solutions leads to much less loss of the otherwise soluble oxidized chromate and reduced ferrous species in subsequent electrochemical experiments (trapping in a protective film). Concerning the dissolution behavior, the film formed on iron by cycling in chromate solution behaves similarly as the passive film on Fe-17Cr alloy. However, the remnant passive film after reductive or oxidative dissolution on the Fe-Cr alloy is of truely protective nature as compared to the films formed on iron in chromate solutions, which show only a small contribution to the potential drop.     

Cathodic protection monitoring of buried carbon steel pipeline: measurement and interpretation of instant-off potential

The criterion used to verify the cathodic protection condition of a structure is based on structure-to-electrolyte potential measurement, which can include an ohmic drop contribution. Among the available techniques, the use of potential probes with internal reference electrode and of corrosion coupons with a so-called soil-access tube represents the most appropriate way to measure the IR-free potential, eliminating the ohmic drop contribution. An alternative is represented by on-off technique if equalising, galvanic or stray currents are not present. Laboratory tests have been carried out in soil-simulating solution on cathodically protected carbon steel in order to evaluate the effectiveness of off-potential for the assessment of cathodic protection. Instant-off potential is not reliable in overprotection condition; moreover, the accuracy of the measurement is strongly influenced by the presence of external current as galvanic or equalising currents. The effect of low-pass filter in the data acquisition system on the potential reading is discussed.     

Microscopic study for the behavior of grain boundary using molecular dynamics

In this study, MD simulations have been performed to observe the behavior of a grain boundary in an a-Fe plate under 2-dimensional loading. In MD simulation, the acceleration of every molecule can be achieved from the potential energy and the force interacting between each molecule, and the integration of the motion equation by using the Verlet method gives the displacement of each molecule. Initially, four α-Fe rectangular plates which have different misorientation angles of grain boundary were modeled by using the Johnson potential and Morse potential. We compared the potential energy of the grain boundary system with that of the perfect structure model, which does not have a grain boundary inside. Also, we could obtain the width of the grain boundary by investigating the local potential energy distribution. The tensile loading for each grain boundary model at room temperature was applied and the behavior of the grain boundary was studied. From this study it was clarified that when the Johnson potential is used, the obvious fracture mechanism occurs along the grain boundary. With the Morse potential, the diffusion of the grain boundary appears instead of the grain boundary fracture.     

Attaining the Steady State of the Nitriding Potential after a Change of NH3 Atmosphere Flow Rate during the Gas Nitriding Process

In single and multi-stage nitriding processes, each stage is characterized by the following parameters:temperature and time, type and composition of incoming atmosphere, as well as the set value of the nitriding potential. In the case of an atmosphere composed of raw ammonia and dissociated ammonia (NH3-NH3diss), the set value of the nitriding potential can be achieved by a change of the incoming atmosphere make-up, while in the case of atmospheres comprising NH3 and NH3 - N2 - by a change of the atmosphere flow rate. The time needed to reach a stabilized state, after the initiation of a change in the atmosphere gas mix can be assessed relatively easily. The problem is much more complex if we want to predict the time of reaching a new stabilized state following a change in atmosphere flow rate. The time of reaching stabilized state is, in this case, a complex function of the flow rate of the atmosphere which forces the potential change, and of temperature. This problem, in the case of the NH3 type atmosphere, is the subject of investigation in this work. Factors are discussed, affecting the rate at which stabilized state is reached by the system after the introduction of a disturbance, necessary to attain the required nitriding potential.     

Pit growth behaviour of aluminium under galvanostatic control

The pit growth process on (1 0 0) aluminium under anodic pulse current in a mixed solution of 1 M HCl and 0.1 M H₂SO₄ at 30 °C has been evaluated using potential transient measurements and pit size distributions obtained by scanning electron microscopy. Sustained pit growth is observed for all pits during the initial anodic potential rise before reaching a steady-state etch potential, whereas a substantial fraction of the pits passivate at the steady-state etch potential. The pit growth rate during the initial potential rise is 3.4 μm s⁻¹, which is similar to that at the steady-state etch potential. The growth rates of active pits are potential-independent.     

Anodic behavior of hafnium in water-alcohol solutions of sodium chloride

High-rate anodic dissolution of hafnium in water-isopropanol-glycerin chloride solutions is studied in relation to the alcohol concentration and electrolyte temperature by voltammetric, chronoamperometric, and photoelectric measurements. The dissolution mechanism varies with increasing potential: upon reaching a potential of 0.4 to 0.5 V, the diffusion control of the process is replaced by kinetic one. It is supposed that the anodic behavior of hafnium is determined by the properties of surface nonstoichiometric semiconducting films, which are present on the metal under all studied conditions.