Korrosionsschutzmaßnahmen bei erdverlegten Rohrleitungen und ihre Überwachung

Measures for corrosion protection of buried pipelines and their control Corrosion protection of buried pipelines involves a combination of proper coating and electrochemical protective measures. The cathodic protection is based on the potential dependence of corrosion rates of steel in water. The theory is easy to understand. But problems in service arise with respect to questions on current distribution as well as the control by pipe-to-soil potential measurements. Proper coating is an essential requirement for an adequate current distribution. In the neighbourhood of large holidays disturbances of the current distribution can occur which can go undetected by normal potential control in steps of 1 to 2 km depending on the soil conditions. For a better control the intensive measuring technique was employed. By this method pipe-to-soil potentials and potential gradients for both “on” and “off” conditions of the polarisation current are measured in steps of 5 m. The values are evaluated through a computer assisted programme. Pipe sections with large holidays and with insufficient polarisation can thus be detected. In special cases that are characterized by high cell currents caused by contact with foreign structures or by stray currents from foreign dc sources it is difficult to measure IR-free potentials. In this case external measuring probes are installed which simulate holidays of the object to be protected. The potential of these probes can be measured without IR-drops with the aid of capillaries. The probes inform on proper cathodic protection, provided the holidays of the object to be protected are smaller than the testing area of the probe. With the aid of the intensive measuring technique as well as the application of the measuring probes it is possible to control the total object to be protected. But in the case of very high ac densities difficulties cannot be excluded. Diversion of these current is a protective measure. Questions occur as to possible corrosion danger beneath disbonded coatings and the occurrence of stress corrosion cracking. Experiments have shown that corrosion resistance is not restricted provided the construction and the service conditions of the pipeline comply with the standards.     

掺杂镍对镁合金表面冷喷涂锌基涂层性能的影响

目的研究镍添加对冷喷涂锌基涂层耐蚀性的影响,为镁合金提供有效的防护涂层。方法采用低压冷喷涂技术在镁合金基体表面分别制备锌基和锌/镍基复合涂层,通过微观观察、摩擦磨损实验、电化学极化法和电化学阻抗谱测试及全浸泡腐蚀试验,研究镁合金表面冷喷涂涂层的结构、摩擦磨损行为和耐蚀性。结果镁合金表面冷喷涂锌基涂层后,其硬度和耐磨性得到显著提高,掺镍后的锌/镍基涂层具有更高的硬度和耐磨性。锌基和锌/镍基涂层均能为镁合金提供腐蚀防护,锌/镍基涂层比锌基涂层具有更好的耐蚀性。相对镁合金来说,锌基涂层和锌/镍基涂层的自腐蚀电位分别正移了260 mV和560 mV;长期腐蚀后锌/镍基涂层形成了更致密的腐蚀产物膜,腐蚀电阻显著高于锌基涂层。结论冷喷涂锌基和锌/镍复合涂层均能对镁合金提供防护作用,掺杂镍后的锌/镍基复合涂层具有更高的硬度、耐磨性和耐蚀性。     

Encapsulated cerium nitrate inhibitors to provide high-performance anti-corrosion sol–gel coatings on mild steel

A rapid cure silane sol–gel coating containing encapsulated corrosion inhibitors that can be applied to a mild steel substrate to form a crack-free coating has been developed. The benefit of this system is that it appears to emulate the protection mechanism found with traditional chrome (VI) based systems, but without the environmental disadvantages, namely that it is non-toxic and non-carcinogenic. The high corrosion resistance performance of this coating is derived from the combination of the hydrophobic nature of the sol–gel coating and the presence of the encapsulated rare earth corrosion inhibitor which can be released at defects within the coating resulting in cerium hydroxide precipitation which hinders the reduction reaction at cathodic sites. The proposed mechanism for this protection is based upon an evaluation of the barrier properties of the coating using electrochemical impedance spectroscopy and long-term immersion/salt spray tests.     

Korrosionsverhalten von Hybridschichtsystemen

Corrosion behaviour of hybrid coating systems Potentiodynamic methods were used to investigate the corrosion protection value of various hybrid coating systems. Combinations of galvanic chromium and electroless nickel interlayers with titanium nitride and chromium nitride coatings produced by sputterion-plating method were tested. Anodic polarization curves show that corrosion resistance is strongly connected with the microdefects present in the coatings. The coating system consisting of chromium nitride with electroless nickel as an interlayer exhibits excellent corrosion resistance properties in 1N H₂SO₄ solution. The reason for this behaviour is presented and discussed in detail.     

Q235上电弧喷涂Zn55Al涂层在3.5wt%溶液中的腐蚀行为研究

本文使用电弧喷涂通过包套挤压+拉拔的方法制备的Zn55Al伪合金丝材成功的在Q235钢上喷涂出了Zn55Al涂层。通过扫描电镜和微区XRD研究了Zn55Al 伪合金丝材的显微结构。通过浸泡腐蚀实验和电化学方法研究了Zn55Al涂层、Zn15Al涂层和 Al涂层的腐蚀行为,并对比了三种涂层之间的差异。结果表明Zn55Al伪合金丝材由纯锌和纯铝组成,在整个成型过程中没有产生合金化。Zn55Al涂层由层片状的富锌相和富铝相组成。经过20天的浸泡实验,Zn55Al涂层形成了一层致密的钝化膜,比其他两种涂层有更好的耐腐蚀性。Zn55Al涂层的自腐蚀电位大约是-1.25v,高于Zn15Al涂层低于纯Al涂层和Q235基体.电偶腐蚀实验表明,Zn55Al涂层比Zn15Al涂层具有更好的点虎穴保护作用。这些结果说明Zn55Al涂层具有更好的耐腐蚀性和可以给Q235基体提供更强的电化学保护.本文也讨论了Zn55Al涂层的的腐蚀机理。     

Effect of fluxing chemical: An option for Zn-5wt.%Al alloy coating on wire surface by single hot dip process

The corrosion of wire is one of the primary causes for premature failure. The ideal way to overcome this problem is to provide corrosion protection right at the time of manufacturing. It is well established fact that Zn-5 wt.% Al alloy coating on steel surface provides much better protection against corrosion than the conventional pure Zn coating. Conventional fluxing operation is done on wire surface using zinc and ammonium chloride mixture before dipping in molten zinc bath. Galvanization bath temperature of about 415 °C for Zn-5 wt.% Al alloy coating on wire surface develops black spots of AlCl₃ when conventional flux is used. Double dip process is being followed for Zn alloy coating on wire surface due to non availability of suitable flux. An effort has been made to develop a suitable flux to obtain Zn-5 wt.% Al alloy coating on wire surface by single hot dip process. A salt mixture (containing zinc, ammonium, sodium, potassium, cobalt and lead chloride) was formulated based on the decomposition temperature of individual chloride salts. Differential thermal and thermo gravimetric analysis indicate the temperatures for complete decomposition of conventional and formulated flux are 445 and 410 °C, respectively. The lower decomposition temperature of formulated flux is ensured black spot free Zn-5 wt.% Al alloy coating. Alloy coated wire consists of alternative layers of zinc rich and aluminium rich phases. The performance of alloy coated wires has been evaluated by salt spray and Tafel tests. The alloy coated wire shows around 4 times improvement of corrosion performance against aggressive chloride environment compared to pure zinc coated wire. This can be attributed to the fact that aluminium rich phase prevents dissolution of zinc rich phase.     

Tests und Erfahrungen über den Korrosionsschutz durch Anstrichsysteme auf Siliconharzbasis unter besonderer Berücksichtigung von Temperaturwechselbeanspruchung

Testing of, and experience with, corrosion protection through coating systems on silicon resin basis, with special reference to stresses caused by temperature fluctuations. The paper reports on the development of aluminium-pigmented silicon resin coatings which hace temperature endurance strength of at least 600°C and can be exposed to temperature fluctations from 600°C to 0°C without suffering damage. A special advantage of these systems consists in the use of the same recipe for primer and finishing coat and in the fact that the coating provides a complete corrosion protection even without stoving. The systems have been throughly tried out both in realistic tests, which are described in detail, and in actual practice. After more than one year's successful experience with the coating applied to the doors of the drying kilns of a brickworks, under strong exposure to drying gases containing SO₂, these coatings are expected to have to life of at least five years.     

Corrosion protection of sintered metal parts by coating deposition. Part II: Corrosion and electrochemical characterization

Coated sintered steel parts were subjected to corrosion resistance tests and electrochemical characterization. A wide range of industrially produced coatings, covering all the main proposed treatments, were analysed. Conventional corrosion tests were employed to compare corrosion resistance, whereas electrochemical test methods were used with the aim of giving a better understanding of the mechanisms which control corrosion processes and the corrosion rate. In particular, electrochemical impedance spectroscopy showed to be very helpful in allowing the monitoring of corrosion behaviour as a function of testing time, without introducing significant electrical perturbation on the examined system. The experimental results of this study showed that sintered steel protection by coating is possible if the process is very well controlled, however, defects in the coating can always be present due to the substrate porosity. With this fact in mind the use of sacrificial coatings is recommendable due to the possibility of a cathodic protection corresponding to coating defects.     

Beschichtungssysteme für Verbindungselemente in Kontakt mit Leichtmetallen

Coating systems for joining elements in contact with light metals Galvanic corrosion of light metal alloys can only be avoided, if the steel fasteners are given an electrochemically compatible protection or if the corrosion circuit is interrupted by electric insulating layers. Current density vs. potential curves of chromated zinc alloy coatings show, that by means of zinc nickel coatings a largely electrochemical adaption to the equilibrium potential of quenchaged aluminium alloys of the type AlMgSi is possible. On the other hand, the equilibrium potentials of chromated systems based on ZnFe, ZnCo respectively, are too low to avoid galvanic corrosion on aluminium. In practicerelated corrosion tests on joining elements, this result was confirmed. Besides this, zinc- and aluminium-bearing sintersystems, galvanic tin depositions as well as ternary mechanical coatings based on ZnSnAl have been proved to be compatible with AlMgSi-type alloys. For coating systems in contact with magnesium a satisfactory protection against galvanic corrosion can be achieved effectively with insulating top coats. The results with suitable duplex systems are presented and recommendations for practical applications are derived.     

Korrosionsschaden durch Elementbildung – Fallbeispiel aus dem Stahlwasserbau

Corrosion damage by element formation – example from hydraulic steel structures Hydraulic steel structures with huge costs of investments generally are protected against corrosive deterioration. Usually the protection is guaranteed by application of a coating system based on polymeres. Additional application of priming coats can raise the efficiency. Research on a weir plant in this work however show, that even protection by a high performed coating system does not necessarely lead to a prevention of corrosion. Immediately there are no hints of a general denial of the applicated coating systems or any causal influence by the immersion medium (river water). The weir plant is constructed by high alloyed steel in combination with carbon steel, partly welded one to another. Thereby the premises of corrosion by galvanic elements are given: an electronic conductivity through the phase boundary of the different types of steel as well as an ionic conductivity by the immersion medium. Delaminations of the coating of the weir gate can be explained by that as well the anodic iron desolution (pitting corrosion) of the carbon steel. Even a renovation of the coating system by an inclusion of the alloyed steel did not stop the corrosion as a whole. An essential improvement of the protection efficiency finally was reached by the installation of a cathodic protection system with sacrificial anodes. With the help of Ohm's and Faraday's law the rate of iron desolution on the one side and the consumption of sacrificial material on the other side can be estimated.     

核电站消防水稳压罐腐蚀分析及处理

稳压罐是核电站用于盛装消防用水,在火灾事故时可以迅速响应,协助完成灭火动作。核电站消防水稳压罐定期检查时,发现稳压罐内部涂层失效,多处腐蚀严重,腐蚀产物附着在罐壁,检查罐底出口阀门及管道同样存在严重腐蚀情况。分析结果表明,发生腐蚀的主要原因为涂层破坏,基体腐蚀均存在闭塞电池腐蚀过程,但各具特点,在实际维护分析中应各有侧重。建议采取更换阀门、修补稳压罐腐蚀坑、重新整体涂刷防腐涂层的方案,防止发生稳压罐腐蚀穿孔,保证消防系统的正常运行。     

A room temperature cured sol–gel anticorrosion pre-treatment for Al 2024-T3 alloys

The inherent reactivity of the Al–Cu alloys is such that their use for structural, marine, and aerospace components and structures would not be possible without prior application of a corrosion protection system. Historically these corrosion protection systems have been based upon the use of chemicals containing Cr(VI) compounds. Organic–inorganic hybrid silane coatings are of increasing interest in industry due to their potential application for the replacement of current toxic hexavalent chromate based treatments. In the present study, a hybrid epoxy–silica–alumina coating with or without doped cerium nitrate has been prepared using a sol–gel method. The hybrid coatings were applied by a dip-technique to an Al–Cu alloy, Al 2024-T3, and subsequently cured at room temperature. The anticorrosion properties of the coatings within 3.5% NaCl were studied using electrochemical impedance spectroscopy (EIS), and conventional DC polarisation. An exfoliation test method involving immersion in a solution of 4 M NaCl, 0.5 M KNO₃ and 0.1 M HNO₃ was also used. The cerium nitrate doped sol–gel coating exhibited excellent anticorrosion properties providing an adherent protection film on the Al 2024-T3 substrate. The resistance to corrosion of the sol–gel coating was also evaluated by analysing the morphology of the coating before and after corrosion testing using scanning electron microscopy.     

Study of surface roughness and corrosion performance of Ni/Zn–Fe and Zn–Fe/Ni compositionally modulated multilayer coatings

Compositionally modulated multilayer coatings consisting alternative layers of nickel and zinc–iron alloy were electroplated using dual bath technique. The coating's surface morphology was studied using a scanning electron microscope. The effects of coatings configuration, i.e., order and the number of layers on the coatings surface roughness was investigated. It was observed that as the number of layers increases in the different Ni/Zn–Fe CMM coatings, 2 and 4-layer Zn–Fe/Ni CMM coatings the final surface roughness is decreased due to the lower grain growth of zinc–iron individual layers. The coatings corrosion protection performance was evaluated using Tafel extrapolation, anodic polarization and salt spray tests. The results of corrosion study showed that all Ni/Zn–Fe and Zn–Fe/Ni CMM coatings, except the 8-layer Zn–Fe/Ni coating, had a better corrosion protection performance compared to the single layer zinc–iron alloy coating or nickel coating.     

Corrosion resistance of painted zinc alloy coated steels

Organic coating in combination with sacrificial metal coating is the most popular method of protecting steel strips against atmospheric corrosion. Experiences over the years have proven that such duplex coating systems are best suited for the coil industry for the long term corrosion protection of steel. The excellent corrosion resistance of such systems has been attributed to the synergy between the cathodic protection provided by the sacrificial coating of zinc alloys and the combined barrier resistance of the metal and organic coatings. Traditionally continuously hot dip zinc-coated steels are used for such applications. However, off late the quest for further extending the longevity of the coil coatings has led to the replacement of the zinc coating with a host of other hot dip zinc–aluminium alloy coatings such as Galvalume^®, Galfan^®, ZAM^®, SuperDyma^®, etc. Each of these metal coatings has its own unique metallurgical features in terms of flexibility, bonding, microstructure and electrochemical characteristics which may significantly influence the performance of the organic coatings applied over it. This paper looks into the various aspects of these features of the hot dip coatings on the corrosion performance of the pre-painted steel strips. For simplicity only polyester paint system, the work horse of the coil industry, is considered.     

粘结钕铁硼磁体阴极电泳工艺研究

粘结NdFeB磁体极易被腐蚀,因而需要涂层保护.本文研究了粘结NdFeB磁体的阴极电泳工艺,主要是电泳电压,电泳时间,电泳时漆液温度以及涂层烘烤固化对涂层抗蚀性的影响.研究发现用合适的工艺参数所获得的涂层能够显著提高粘结NdFeB磁体的抗蚀性能.     

镁合金表面防腐蚀超疏水涂层制备研究进展

镁合金是一种有发展前途的绿色工程金属材料，但其较差的抗腐蚀性能限制了它的大规模应用。对镁合金表面进行超疏水处理，能够极大地提高镁合金的耐腐蚀性能。当超疏水试样浸泡在腐蚀溶液中时，该结构将在腐蚀介质中形成固-气-液界面层，减少镁合金表面与腐蚀介质之间的接触面积，从而降低腐蚀速度。超疏水表面需要满足微纳米结构和低表面能2个必要条件。可以采用二步法或一步法在镁合金表面制备超疏水表面，详细介绍了在镁合金表面构造微纳米结构的方法，包括激光处理、机加工、化学刻蚀、化学镀、电化学沉积、阳极氧化、微弧氧化、水热合成和喷涂等方法。超疏水表面一旦受到机械损伤，微纳米结构无法满足条件，超疏水表面的“气垫效应”消失，腐蚀介质就会直接与微纳米结构接触，因此需要保证构建的微纳米粗糙结构对镁基体具有良好的保护作用并具有自愈功能。通过制备复合涂层，提高下层微纳米结构的自愈合性能，上层涂层的超疏水性与下层涂层的良好物理屏障能力的协同效应可以改善涂层的长久耐腐蚀性能。综述了在镁合金上制备具有良好耐腐蚀性能的复合超疏水表面的方法，并对镁合金超疏水表面防护技术的研究方向进行了展望。     

钢铁材料电镀镉的研究现状

钢铁材料广泛地应用于诸多工业领域中,但其表面耐蚀性差,发生于材料表面的腐蚀会导致材料失效。镉与空气接触时会迅速氧化并形成致密的保护性氧化膜,因此表面镀镉可以有效地提高钢铁材料表面的耐蚀性。从电镀镉技术的具体应用出发,综述了用于钢铁表面防护的电镀镉技术和用于表面修复的电刷镀镉技术的应用现状。镀镉层作为阳极保护层,实现了对钢铁材料的防护。在镀液中添加钛盐后,形成的镉钛镀层比单纯的镀镉层具有更优异的耐蚀性和更好的低氢脆性。电刷镀镉作为一种特种镀镉技术,可用作镀镉局部破损件的补镀和修复。针对电镀镉废水对环境和人体的高危害,简要阐述了化学法、物理化学法、生物法三种电镀镉废水的处理方法,且微生物法具有良好的发展前景。最后,展望了钢铁材料电镀镉技术的相关研究思路和方法。     

Schwingungsrißkorrosion feuerverzinkter Schweißverbindungen im bauteilähnlichen Maßstab bei wechselnden Korrosionsbedingungen in chloridhaltigem Medium

Corrosion fatigue of hot-galvanized component-like welded joints in chloride medium at changing corrosion conditions The project was focussed on the investigation of the fatigue behaviour of welded specimens of hot-galvanized plate material of steel RSt 37-2, St 52-3 and St 70-2 as frequently used in steel constructions which were mended by thermal zinc-spraying in the fillet area and tested at changing corrosion conditions. In addition, the fatigue behaviour of welded specimens with additional PVC coating of both non-galvanized and galvanized types at changing corrosion reaction was also investigated. The established findings can be summarized as follows:

• – At constant amplitude loading, hot-galvanized precludes very markedly the drop in endurance which would occur under corrosion. By contrast, an increase of fatigue strength in the corrosive medium due to galvanizing is only conditionally discoverable at variable amplitude loading. In regard to the protection against corrosion, welding of hot-galvanized parts brings an improvement at variable amplitude loading only if a given thickness of the zinc coating depending on the material is not exceeded. Too thick coating results in the formation of pores at the subsequent welding and reduces the fatigue strength in spite of the later zinc-spraying.
• – The structural steels RSt 37-2 and St 52-3 in hot-galvanized state are better suitable for welding than the more notch- and corrosion-sensitive St 70-2.
• – Soldering brittleness could not be established as cause of the failure.
• – The application of PVC protective layers secures high rates of increase or the fatigue for the non-galvanized specimens.

     

原位微锻造冷喷涂制备高致密铝基涂层及耐腐蚀性能

目的提出一种基于原位微锻造冷喷涂制备高致密度金属沉积体的新方法,旨在为镁合金腐蚀防护提供一种低成本的涂层制备方法。方法通过在Al喷涂粉末中混入20%～60%(体积分数)的大粒径喷丸颗粒,借助其在喷涂过程中对已沉积Al涂层的原位微锻造效应,实现Al涂层制备中的实时致密化,研究了原位微锻造强度对涂层显微组织及耐腐蚀性能的影响规律。采用SEM分析了涂层的显微结构,采用电化学测试及长期浸泡试验测试了涂层的耐腐蚀性能。结果随着微锻造强度的提高,金属沉积体的致密度逐渐增加,当混合粉末中的喷丸颗粒含量高于40%时,可获得孔隙率低于0.3%的高致密度Al涂层。电化学测试及长达1000 h的Na Cl溶液浸泡腐蚀结果显示,高致密度Al涂层包覆后的镁合金表现出与冶金块材铝相当的耐腐蚀性能,比无保护镁合金腐蚀速率降低两个数量级以上;在1000h的盐雾腐蚀后,涂层与基材界面无腐蚀产物生成,表明涂层可完全对腐蚀介质进行物理隔绝。同时,致密铝涂层表面形成了微米级的钝化膜,可进一步提高耐腐蚀性能。结论通过原位微锻造辅助冷喷涂技术,可在较低的气体温度和气体压力条件下在镁合金表面获得完全致密的Al腐蚀防护涂层。该技术还有望用于诸如高导热、高导电涂层的制备,金属构件修复及增材制造等其他对金属沉积体有致密度要求的领域。     

CORROSION PROTECTION OF Al CATHODES IN ZINC ELECTROLYSIS

1.IntroductionAlthoughthecomputerizedpredictionofalloyphasediagramsbythermodynamicmethodhasmadegreatachievements,thelackofthermodynamicdataisoneoftheobstaclesforthecomputationofalloyphasediagrams.Manymethodsforcomputerizedalloyphasediagramshavebeenproposedinordertoovercometheobstacle.Forexample,thereareHume--Rotherytheory[']forsolidsolutiollofbinaryalloysystemandMiedema'stwoparameters.oded2](Ark*,A.;/sa)forthethermodynamicpropertyestimationofalloysystems.Che.[3--5]hajsappliedatomicparameter-…