Korrosionsschutz in Rohren durch Betonauskleidungen

Corrosion protection in pipelines by concrete linings Cast iron and steel pipes of various diameters may be protected against corrosion by internal linings of cement mortar. This lining results in addition in an improvement of the mechanical properties of the composit. Within 28 days the mortar cures to compressive strength between 700 to 1000 kg/cm² and tensile flex strength exceeding 100 kg/cm²; even when the metal tube is damaged a high pressure resistance is maintained. Adhesion between lining and metal improves with time: green cement is rather porous, so that water may penetrate to the metal; calcium hydroxide from the cement and ferric hydrates formed on the metal surface are incorporated in the concrete so that good adhesion results. Sulfate-resistant special grades have shown to be resistant in waste water containing up to 3000 mg/l sulfate and having pH-values down to 4,5 for short times.     

Einflußeiner Verzinkung auf die Korrosion von mit Zementmörtel beschichtetem Stahl in NaCl-Lösung

Effect of galvanizing on the corrosion of steel in concrete immersed in NaCl solution Galvanized or pickled steel sheet specimens were embedded in portland cement mortar of various water cement ratios and curing conditions and then wholly or partially immersed in 0.5 M NaCl solution for 1 to 5 yrs. Free corrosion potentials and electrical resistances have been measured. Immersion conditions and the presence of zinc have a significant effect on the corrosion resistance of the embedded steel sheets. The potentials of the wholly immersed specimens are very negative. Thus, these specimens cannot act as cathodes in corrosion cells, and the steel sheets within the mortar do not corrode. The partially immersed specimens, on the other hand, show very noble potentials. Also in the case of galvanized steel sheets the potentials are shifted to the same positive values in the course of exposure time. Thus, all these specimens can act as cathodes in corrosion cells. Localized corrosion generally occurs at the water/air line. In the case of pickled specimens the mortar is cracked due to growing corrosion products. In the case of galvanized steels the corrosion is retarded significantly. The test results are discussed in detail with respect to practical problems of cell formation, internal and external protection of pipes as well as the corrosion resistance of reinforced concrete.     

20#钢和球墨铸铁材质燃气管道的土壤腐蚀行为比较研究

采用正交试验设计方法，以含水量、孔隙度、pH值等9种影响因素作为试验因素进行土壤腐蚀模拟试验，对20#钢和球墨铸铁的腐蚀形貌和腐蚀产物进行比较分析，探讨其腐蚀行为和腐蚀机理。分析表明：在相同环境下球墨铸铁比20#钢更容易腐蚀，它们的土壤腐蚀环境因素重要度排序呈现较大的差异，但两者对Cl^-都比较敏感，在20#钢的腐蚀产物中检出了球墨铸铁腐蚀产物中没有的磷酸铁族物质Fe₂PO₅。含碳量少、含有抗腐蚀元素Cr、腐蚀产物中含有抗腐蚀作用的磷酸铁族物质以及晶界少是20#钢比球墨铸铁耐腐蚀性好的主要原因。     

Der Einfluß von Neutralsalzen auf das Korrosionsverhalten unlegierter Eisen-Werkstoffe in gut gepufferten Trinkwässern

The influence of increased neutral salt content on the corrosion behaviour of non-alloyed steel in well buffered drinking waters The influence of higher neutral salt contents in well buffered drinking water on the corrosion behaviour of unalloyed steel pipes is described in this paper. The tests were mainly performed by differential methods to measure corrosion rate and iron uptake rate. It could be shown, that higher contents in chloride and sulphate increase corrosion and even more iron uptake rate. Nitrates have no measurable effect. Additionally, it could be shown, that an increase in neutral salts leads to increased local corrosion. Further research in this field by using drinking waters with low buffer capacity will be performed and reported later on.     

Untersuchung des chemischen und elektrochemischen Verhaltens von zementmörtelausgekleideten Stahlrohren in kohlensäurehaltigen Wässern

Investigation of electrochemical element formation by crevices of different width in cement lined steel tubes The author describes an experimental setup for the investigation of the attack of water with aggressive carbonic acid on the cement lining of steel tubes. In equilibrium waters crevices in the cement are covered by protective layers; in aggressive waters, however, there is a critical crevice width (probably 2 mm), which must not be exceeded without the danger of corrosion. When dissolved calcareous constituents aer replaced by iron oxide in the mortar the resistance of the cement is increased.     

Der Einfluß unterschiedlicher Nitratgehalte auf das Korrosionsverhalten von verzinkten Stahlrohren

The influence of different nitrate contents of drinking water on the corrosion behaviour of galvanized steel pipes At the water works Biblis and Alsbach of Südhessische Gas und Wasser AG, Darmstadt, field tests were performed over a period of 2 1/2 years to describe the influence of different nitrate contents in drinking water and the corrosion behaviour of different qualities of galvanized steel pipes. The results obtained showed, that weight loss and corrosion rate measurements give no information on this subject. Optical inspection and flushing tests could prove, that selective corrosion occurred in the water with higher nitrate content. Galvannealed pipes showed local corrosion attack after a certain exposition time in water with higher nitrate content, depending on flow velocity. Air blown galvanized pipes and galvannealed pipes in water with higher nitrate content additionally produce „Zinkgeriesel”︁ during flushing. The selective corrosion attack also takes place to a very small extent in galvanized steel pipes, where quality is in accordance to the German Standard DIN 2444.     

Chloride-induced steel corrosion in alkali-activated fly ash mortar: Increased propensity for corrosion initiation at defects

Chloride contents at the steel–mortar interface that initiate steel corrosion were determined for carbon steel in alkali-activated fly ash mortar for three different exposure conditions: exposure to 1 M NaCl solution; leaching in deionized water and then exposure to 1 M NaCl solution; and leaching in deionized water, aging in air at 20°C and natural CO₂ concentration, and then exposure to 1 M NaCl solution. For comparison, a Portland cement mortar, exposed to 1 M NaCl solution, was studied. The median values of the corrosion-initiating chloride contents (average over the full length of the rebar) in the alkali-activated fly ash mortar varied between 0.35 and 1.05 wt% Cl with respect to binder, consistently lower than what was obtained for the Portland cement mortar, but with no clear trend regarding the exposure conditions. For most of the alkali-activated fly ash mortar specimens, preferential corrosion at the connection between the working electrode and the external measurement setup was observed, while preferential corrosion did not occur for the Portland cement mortar. Scanning electron microscopy and auxiliary experiments in synthetic solutions indicated that this behavior was caused by inhomogeneities at the steel–mortar interface in the alkali-activated mortar, likely due to its peculiar rheological properties in the fresh state.     

Corrosion behaviour of steel in mortar with wood biomass ash

The present study investigates the influence of partial cement substitution with biomass ash on the corrosion behaviour of steel embedded in the mortar. To evaluate this influence, corrosion parameters of steel in mortar exposed to tap water and 3.5 wt% NaCl solution were monitored over a period of 50 days. The electrochemical cell consisted of a steel plate as a working electrode, covered with a layer of mortar that was exposed to the testing solution. Open-circuit potential and linear polarisation were used to monitor changes in corrosion behaviour, whereas electrical impedance spectroscopy was used to evaluate the conductivity of the matrix. Additional to corrosion parameters, the chloride migration coefficient was tested after 28 days. On the basis of the results, it was observed that mortars with biomass ash provide equal or better protection for embedded steel, compared with the reference mortar. Mortars that performed slightly better than the reference mortar and other mortars were prepared with ashes with a higher amount of pozzolanic oxides.     

滨海盐土中典型供水管材腐蚀机理的土壤加速腐蚀研究

基于土壤加速腐蚀实验,采用失重法和电化学测试手段研究了滨海盐土中球墨铸铁、灰口铸铁和碳钢3种典型供水管材的腐蚀规律、腐蚀层结构变化以及腐蚀的阴阳极反应动力学过程。结果表明：3种材质在滨海盐土中的腐蚀行为规律一致。腐蚀主要分为点蚀诱导期、点蚀发展期和稳定腐蚀期3各阶段;腐蚀初期和中期主要受电荷传递控制,且随着腐蚀的进行,电荷传递电阻快速上升;腐蚀稳定期,氧的扩散成为了腐蚀的控制步骤。3种材质腐蚀的极化曲线均出现明显的阴极扩散和阳极活化双重控制的现象,其中阴极扩散控制作用更为明显。     

Schweißnaht-Korrosion an verzinkten Stahlrohren der Trinkwasser-Installation

Corrosion of welds in galvanized steel tubes of drinking water supplies Stellungnahme des DVGW-Fachausschusses „Innenkorrosion Wasser”︁ During the last years corrosion damages in welded galvanized steel tubes of drinking water supplies could be observed frequently. Because of its shape this corrosion is called grooving corrosion. It appears also in film forming water and is caused by segregations in ingots of strip steel used for fabrication of tubes. This corrosion only occurs in ERW pipes welded without aftertreatment mostly with sulphur contents of more than 0.008%. Grooving corrosion could be prevented by metallurgical techniques, which way however is expensive and difficult to realize. Therefore the DVGW is first requested to cancel the Register No. for those tubes which are susceptible to grooving corrosion. The susceptibility to grooving corrosion can be tested by pickling in hydrochloric acid.     

The anoxic corrosion behaviour of carbon steel in anoxic alkaline environments simulating a Swiss L/ILW repository environment

The Swiss waste management programme foresees that low- and intermediate-level radioactive waste will be disposed of in a deep geological repository constructed in Opalinus Clay. Gas generation is expected in the repository due to the decomposition of organic materials and the corrosion of metals, with carbon steel being the primary source. The corrosion behaviour of mild steel under anoxic conditions has been studied over the course of several years to better understand the long-term hydrogen evolution profile under anticipated repository conditions. Steel, either bare or encased within mortar, was tested in water vapour or immersed in electrolytes representative of aged cement waters at 50°C. The corrosion rate was measured indirectly through the hydrogen analysis using a solid-state probe. The hydrogen evolution behaviour of grout was also monitored to more accurately determine the hydrogen generating from the corrosion of the embedded steel. For steel in water vapour or in alkaline environments, embedded in cementitious material or immersed in simulated aged cement pore water, corrosion rates were invariably <1 nm/year after several years of analysis.     

滨海电厂水系统碳钢管道的腐蚀控制

针对某滨海电厂海水及海水反渗透产水管道的腐蚀现象,采用失重法、扫描电镜、X射线衍射及电化学测试,对比研究了碳钢在其中的腐蚀差异。结果表明:在海水中锈层抑制氧的传递,对碳钢起保护作用;在反渗透产水中锈层起大阴极作用,加速基体腐蚀。实际工程中,海水反渗透产水比海水对碳钢管道更具侵蚀性。重新矿化反渗透产水是降低其腐蚀性的有效方法;另外,可考虑采用更耐蚀的不锈钢、碳钢衬塑管等作为管材。     

混凝土中钢筋点蚀的电化学噪声特性研究

    采用Sym4小波分析氯离子环境下砂浆中碳钢电化学噪声的电流波动及电压波动信号,通过提取信号的小波能量,得到了信号的能量分布曲线.结果表明,电化学噪声的小波能量是点蚀监测信号解析的重要特征参数,根据能量分布曲线的变化可以判定点蚀的发生.     

Korrosionsgefährdung von Rohrleitungen aus unlegiertem Stahl durch Elementbildung

Corrosion of domestic installation of unalloyed steel by cell formation The corrosion protection effect of alkaline lime or cement mortar substances on steel parts, for example on the outer surface of a pipe, is a result of passivation occurring under these environmental conditions. The availability of water as an electrolytic solution is a precondition for the establishment of a galvanic cell with the steel surface, that is not covered with mortar, as anode. Environmental factors leading to the destruction of the passive layer are also an other cause of damage. Preventive and protection methods according to DIN 50 929 Part 2 are discussed.     

Felduntersuchungen mit feuerverzinkten Stahlrohren – Auswertung von Langzeit-Daten

Field corrosion tests on hot dip galvanized steel pipes – Assessment of long term data The degree of metal loss and its time dependence of hot dip galvanized steel pipes in flowing waters were correlated with the water parameters. A good correlation was observed with CO₂ concentration of the water. The higher the initial corrosion rate the higher is in many cases the decrease in corrosion rate with time. This is explained in terms of increased iron oxide content in the protective layers formed after the dissolution of a significant amount of zinc layer. Except phosphates the other water parameters (chlorides, sulphates, nitrates and TOC) do not exhibit any influence. The favourable influence of the iron oxide rich protective layers on the corrosion rate may get lost in waters very rich in carbon dioxide.     

Investigation of Stainless Steel Corrosion in Ultrahigh-Purity Water and Steam Systems by Surface Analytical Techniques

Stainless steel pipes with different degrees of rouging and a Teflon^®-coated rupture disc with severe corrosion were thoroughly investigated by combining multiple surface analytical techniques. The surface roughness and iron oxide layer thickness increase with increasing rouge severity, and the chromium oxide layer coexists with the iron oxide layer in samples with various degrees of rouging. Unlike the rouging observed for stainless steel pipes, the fast degradation of the rupture disc was caused by a crevice corrosion environment created by perforations in the protective Teflon coating. This failure analysis clearly shows the highly corrosive nature of ultrapure water used in the manufacture of pharmaceutical products, and demonstrates some of the unexpected corrosion mechanisms that can be encountered in these environments.     

Messung der Kupfer-Ionenkonzentration in Stagnationswässern aus kupfergelöteten Plattenwärmeübertragern

Measuring of the copper concentration in drinking water stagnating in copper brazed plate heat exchangers A whole lot of corrosion damage occurred in galvanized steel pipes used in hot water supply systems, showing copper-induced pitting corrosion. The damage were obviously caused by copperions which migrated from the braze of the heat exchangers into the water. Some tests were carried out to determine the copper-concentrations entering the stagnating water.     

Die Messung der Aufeisenung im Trinkwasser – Ein neues Verfahren zur Beurteilung von Deckschichten in schwarzen Stahlrohren

Measurement of iron-pickup by potable water – A new method for the assessment of surface layers in black steel piping Red water in drinking water distribution systems causes problems for the water companies because of the consumers pretension to get drinking water of high quality. The corrosion products in the water are normally iron compounds, which arise from the corrosion process and diffuse through the surface layer into the aqueous phase. With the proposed method, the increase of the iron concentration in the water and parallel the corrosion rate, by the determination of the differential oxygen demand, is measured. This allows to make direct statements with regard to the protective qualities of the surface layer.     

Study and characterization by acoustic emission and electrochemical measurements of concrete deterioration caused by reinforcement steel corrosion

The durability of reinforced concrete structures becomes a matter of concern, due primarily to the increase of damage by the corrosion of steel reinforcements. This corrosion is not only related to the composition and to the procedure of concrete manufacturing (water/cement, sand/cement, etc.), but also to the aggressive agents as chlorides, carbon dioxide, etc. present in the surrounding medium (Cl⁻, CO₂, etc.). It is well known that the first kind of rebar corrosion (chloride) is more detrimental and that this process contains three basic components: chloride diffusion, electrochemical corrosion and concrete fracture. Therefore the early detection of possible degradation of structures by means of non-destructive testing is essential in order to ensure the functionality of these structures.

This paper presents the results of an experimental investigation on the use of acoustic emission during the corrosion of steel rebars embedded in mortar and immersed in sodium chloride solution. The process of corrosion is accelerated by various imposed potentials and is followed by acoustic emission coupled to electrochemical techniques. The experimental results show that electrochemical techniques can evaluate the corrosive character of the medium used. The acoustic emission showed an activity characteristic of the corrosion initiation phase and the corrosion propagation phase. Thus, it was significantly possible to highlight the acoustic signature of the concrete damage related to the porosity of the mortar and to chloride concentration. The results also show a perfect correlation between the evolution of the acoustic activity and the current of corrosion density.     

金属材料在模拟地热水环境中的腐蚀与结垢特性

目的地热水的腐蚀和结垢是地热资源开发利用的核心问题,研究几种常见金属材料在地热水中的腐蚀和结垢规律,为地热资源开发利用提供理论依据。方法通过扫描电子显微镜,X射线衍射仪、动态挂片试验、极化和交流阻抗测试等方法,对比研究紫铜、304不锈钢和20#碳钢在模拟地热水溶液中的腐蚀和结垢情况。结果 3种金属材料表面的结垢产物均为Ca CO3,20#碳钢表面的Ca CO3均为方解石相,304不锈钢和紫铜表面的Ca CO3包含方解石相和少量文石相,304不锈钢表面的Ca CO3分布较紫铜疏松,且含垢量较小。20#碳钢表面腐蚀产物的内层主要是黑色的Fe3O4,外层主要是黄色的Fe2O3;紫铜表面的腐蚀产物主要是铜的氧化物;304不锈钢表面无腐蚀产物。浸泡期间,304不锈钢未发生腐蚀且腐蚀电流密度最小;紫铜的整体耐蚀性能不及304不锈钢,但耐点蚀性能最佳;20#碳钢腐蚀严重,腐蚀电流密度较大。结论在模拟地热水溶液中,304不锈钢拥有比紫铜和20#碳钢更好的耐腐蚀性能和阻垢性能。