Selektive Korrosion von Kupfer-Zink-Legierungen

Selective corrosion of copper-zinc-alloys Starting from recent ideas on the mechanism of corrosion the most important parameters – with respect to materials properties and water chemistry – of dezincation, pitting and intercrystalline corrosion of CuZn alloys are explained. Dezincation is increased if the alloy contains β-phase (duplex brass). Within certain limits of chloride and sulphate content dezincation of these materials can be prevented by an increased hydrogencarbonate concentration of the medium. At pure α-brass dezincation is preceded by local cestruction of the natural protection layer. Intercrystalline corrosion occurs preferentially at α-brass if the material contains precipitations at the grain boundaries. Intercrystalline attack is favoured by higher temperatures, coarse-grained microstructure, higher contents of the alloying elements arsenic and phosphorus as well as from the water-side by ammonia and the activity of aeration elements.     

Einfluß steigender Phosphat-Silikatgehalte auf die Loch- und Kontaktkorrosion verzinkter Stahlrohre sowie die Korrosion von Kupfer in Warmwasser-Mischinstallationen aus beiden Werkstoffen

Influence of increasing phosphate/silikate contents on the pitting and general corrosion of galvanized steel tubing and the corrosion of copper in warm water mixed installation systems In hot tap water (65°C) the influence of a mixture of phosphate/silicate inhibitor on the general, the pitting and the galvanic corrosion of galvanized steel tubes and the general corrosion of copper in mixed installations of both metals was investigated. Increasing concentration of inhibitors decreases the general corrosion rate of galvanized steel and copper. A worth mentioning reduction of pitting and galvanic corrosion of steel could be reached only with high concentrations of 5 mg/l P₂O₅ and 30 mg/l SiO₂. Galvannealed tubes are much more sensitive to pitting corrosion than galvanized ones. Referring to this they could not be inhibited.     

Über den Einfluß des Sauerstoffgehaltes,des pH all und der Strömungsgeschwindigkeit auf die Korrosion feuerverzinkter und unverzinkter unlegierter Stahlrohre in Trinkwasser

Influence of oxygen content, pH and flow velocity under corrosion of hot-dip galvanized and bare piping of unalloyed steel in potable water Sections and weighed ring specimens from galvanized and nongalvanized tubes had been exposed to flowing tap water with different flow rates and oxygen concentrations of 0.01–4 mg/l at pH 7.2 and 8.0 for 3.5 ys. Specimens taken at different testing times had been investigated with respect to data of protective layers, corrosion manifestation and weight loss. The corrosion rate is nearly constant in the first weeks (initial corrosion), later it follows a power law (stationary corrosion). These two phases of corrosion are determined by the testing parameters differently. Thus, results from short-time experiments of some weeks cannot inform on the stationary behaviour. In oxygen free tap water remarkable corrosion occurs due to the acids H₂CO₃ and HCO₃^?. The corrosion resistance is supported by high oxygen content, high pH, flow rate and by galvanizing.     

Korrosionsbeständigkeit von Verbindungen von Rohren aus nichtrostenden Stählen in Wässern

Corrosion of joints for stainless steel tubes in water The most important commonly used joining techniques for stainless steel tubes which are used for the transport of water and gases are welding and brazing. With corrosion attack by dry gases, both connections are resistant against corrosion. However, in water and aqueous condensates limits of application exist with regard to the corrosion resistance. The corrosion resistance of weld connections with stainless steel tubes is diminished by

• – annealing colours (oxide films) and scale layers in the weld area;
• – changes in the microstructure adjacent to the welds (sensitization of the stainless steel material);
• – surface finish of weld seams after welding;
• – welding faults resulting from bad handling and workmanship.

Type and extent of corrosion damage occurring on weld connections with decreased corrosion resistance depend on the composition of the water and condensates, mainly on their chloride content. Typical examples for the causes of degraded corrosion resistance of weld connections, and possible types of corrosion attack, namely pitting, crevice corrosion, and stress corrosion cracking and their mechanisms are described. Furthermore, measures are shown by which the corrosion resistance of weld connections with stainless steel tubes can be increased. Joints of stainless steel tubes by hard soldering with capillary fittings are endangered by knife line attack at the phase boundary between the stainless steel and solder (interfacial corrosion). Knife line attack means in this context the loss of adhesion between steel and hard solder. The severity of the corrosion risk, in particular the incubation time until the occurrence of the corrosion damage, depends on the water quality, mainly on chloride concentration, and pH. The press fitting with non-metallic gasket is a relatively new joining system, and it is used in the cold and warm water domestic installation. This joining technique is described. For domestic water distribution, an installation system with tubes and press fittings made of steel grade AISI 316 SS has been developed. This system is resistant to corrosion attack in potable water of usual composition, and it is already applied in-service in a considerable extent. Other joining systems are stainless steel weld fittings, threaded screw fittings, and compression couplings with cutting or clamping rings. They are used mainly in industrial installations.     

Untersuchungen über den interkristallinen Kongrenzenangriff von austenitischen Mangan-Chrom-Stählen durch Wasser und wäßrige Lösungen

Research on intercrystalline grain boundary corrosion of austenitic manganesechrome steels caused by water and aqueous salt solutions Stressed bar specimens of welded and tempered austenitic manganesechrome steel such as as X 40 MnCr 18 and X 22 MnCrNi 885, exposed to sea water, tap water or destilled water, are liable to suffer intercrystalline stress corrosion cracking. The occurrence of intercrystalline corrosion is not necessarily dependent on mechanical tensil stress. In particular, even unstressed specimens exposed to tap or distilled water are liable to show marked intercrystalline corrosion. Additional tensile stress merely has the effect of speeding up the inter-crystalline corrosion. The cause for the intercrystalline corrosion must be seen in the segregation of chrome-rich carbids at the grain boundaries and the consequent reduction in the chrome content within the grain boundary zone. It is possible to prove the segregation of a chrome-rich carbide of the structure M₇C₃ at the grain boundaries of steel X 40 MnCr 18, and the aggregation of a chrome-rich carbide of the structure M₂₃C₆ at the grain boundaries of steel X 22 MnCrNi 885. Through contact with zinc, it is possible to obtain a complete corrosion protection with the manganese-chrome steels investigated. A short circuit with passive austenitic chrome-nickel steels increases the general or selective corrosion rate through anodic polarisation. By adding chromate to the sea water, the corrosion rate is retarded. In tap water, an addition of chromate result in complete corrosion protection.     

热水器不锈钢内胆孔蚀原因的研究

根据国内热水器不锈钢内胆孔蚀多发地区水质分析报告,研究了自来水的稳定性、Cl-、NaClO含量以及温度对不锈钢孔蚀趋势的影响,并从不锈钢内胆材质以及加工工艺分析了孔蚀集中发生在焊缝附近的原因.实验证明热水器不锈钢内胆孔蚀是不锈钢成分和组织结构与特殊腐蚀介质、温度等因素共同作用的结果.     

SUS304不锈钢在浓缩自来水中的点蚀敏感性

采用极化曲线研究了SUS304不锈钢在不同温度浓缩不同倍率的自来水中的点蚀敏感性,比较了含不同浓度氯化钠的去离子水和自来水对不锈钢耐点蚀性能的影响。结果显示,随自来水温度和浓缩倍率的提高,不锈钢的点蚀敏感性增大;与自来水相比,在去离子水中氯离子对不锈钢点蚀敏感性的影响更显著。     

Effects of Leptothrix discophora on the potential behavior of stainless steel

Biofilm formation and electrochemical behavior of stainless steel have been studied in well water, in tap water and in water taken from fire extinguishing system. Some of the waters have been modified by adding manganese ions as well as in some cases acetate and yeast extract as a nutrient. Manganese oxidizing bacteria Leptothrix discophora has been used in these studies. To eliminate crevices in the specimen holder and to simulate reasonably well the conditions in fire‐extinguishing systems where the water is stagnant most of the time, a tape test arrangement with very slow flowing rate has been used in most of these studies. Also specimens with heat tint areas produced by heating inductively a small section of the specimen under flowing argon shielding gas were used in these studies. The results of these tape tests show that manganese oxidizing bacteria are able to increase the potential of both the base material (stainless steel UNS S30400) and of specimens with heat tint areas in well water, in tap water and in water taken from fire extinguishing system. Manganese oxidizing bacteria are also able to increase the cathodic reaction and thus enhance the initiation of corrosion. However, the increase of potential is not alone enough to start the corrosion. In these tests corrosion was initiated only in the specimens with heat tint areas in one of the waters taken from fire extinguishing system. No corrosion was detected in the specimens exposed to the well water or to the tap water used in these tests.     

Immersion corrosion tests on metal‐salt hydrate pairs used for latent heat storage in the 48 to 58°C temperature range

Efficient energy storage is one of the biggest problems facing alternative energy technologies. In whatever form the energy is stored, an alternative energy system usually requires a storage buffer between carrying energy input and the varying energy demand regime at the output end of the system. A method of energy storage is the use of the latent heat from Phase Change Materials (PCMs), for example salt hydrates. In this paper we tested the corrosion resistance of five commercial metals (aluminum, brass, copper, steel and stainless steel) in contact with two salt hydrates, commonly used as PCM, with a melting temperature in the range of 48 to 58°C (sodium acetate trihydrate and sodium thiosulfate pentahydrate) in experiments with a duration up to 70 days. The results demonstrated that brass and copper should be avoided when sodium acetate trihydrate is used in long term applications, but aluminum, steel and stainless steel can be used without problem. When the salt hydrate used is sodium thiosulfate pentahydrate, brass and copper should not be used in any case, aluminum and stainless steel can be used, and steel in contact with graphite should be monitored because corrosion could appear after some time of use.     

Untersuchungen zum Korrosions- und Verschleißverhalten von hartstoffverstärkten „Duplexstahl“-Schutzschichten

Investigations on corrosion and wear behaviour of duplex stainless steel coatings reinforced with hardening components This paper is dealing with corrosion and wear resistance results of protective duplex stainless steel coatings (X2CrNiMoN25-10-4) made by two-powder-plasma weld surfacing with additional hardening components Cr₂C₃ and WC-WC₂. First the developing of a process technique was important which allows an exact addition of hardening components and an as low as possible dissolution of carbides. The microstructure did not show the typical ferritic-austenitic structure. The wear and corrosion resistance in sulphuric acid is very good and reveals the high quality of the protective coatings. However the corrosion resistance in synthetic sea water is considerable reduced. Low grain size and pre-heat temperatures of 100 °C have a positive influence on the corrosion resistance.     

Erosion and Corrosion Behavior of Laser Cladded Stainless Steels with Tungsten Carbide

Laser cladding of tungsten carbide (WC) on stainless steels 13Cr-4Ni and AISI 304 substrates has been performed using high power diode laser. The cladded stainless steels were characterized for microstructural changes, hardness, solid particle erosion resistance and corrosion behavior. Resistance of the clad to solid particle erosion was evaluated using alumina particles according to ASTM G76 and corrosion behavior was studied by employing the anodic polarization and open circuit potential measurement in 3.5% NaCl solution and tap water. The hardness of laser cladded AISI 304 and 13Cr-4Ni stainless steel was increased up to 815 and 725Hv_100?g, respectively. The erosion resistance of the modified surface was improved significantly such that the erosion rate of cladded AISI 304 (at 114?W/mm²) was observed ~0.74?mg/cm²/h as compared to ~1.16 and 0.97?mg/cm²/h for untreated AISI 304 and 13Cr-4Ni, respectively. Laser cladding of both the stainless steels, however, reduced the corrosion resistance in both NaCl and tap water.     

Entstehung und Aufbau farbiger schichten auf rostfreiem stahl: I. Verfärbungen beim Kochen von Nahrungsmitteln

Formation and structure of coloured layers on stainless steel: I. Discolorations by cooking of food Upon cooking of vegetables and other food coloured layers can be formed on stainless steel. By cooking tests, AES-studies of the formed layers and by electrochemical experiments the formation of these layers was simulated and their structure was elucidated. By the process of oxygen corrosion OH^? ions are formed near the surface of the steel, precipitation of Mg(OH)² is caused which is bound to the surface together with silicates and phosphates. The layer is 100 to 200 Å thick and appears coloured by built-in ions of the alloy metals. The ions needed for formation of the layers, Mg²⁺, SiO₃^2? and PO₄^3?, all are present in tap water, thus the formation of such layers can occur always upon cooking and is only intensified by substances from the food (phosphates). The use of steels which are more corrosion-resistant or the precipitation or complex formation of the above mentioned ions or the exclusion of oxygen during cooking would prohibit the layer formation. However, such measures are hardly feasible and they are even unnecessary since the described process is harmless concerning hygienic aspects.     

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。     

Ein Beitrag zum Korrosionsverhalten von austenitischem 17-12-2 CrNiMoTi-Stahl in siedenden Essigsäurelösungen - Betriebserfahrungen und Laborversuche

A contribution concerning the corrosion behaviour of austenitic 17-12-2 CrNiMoTi stainless steel in boiling acetic acid solutions - Service experience and laboratory tests Service experience of acetic acid processing industry shows that X 6 CrNiMoTi 17-12-2 stainless steel (similar to AISI type 316 Ti) can be used as construction material for handling concentrated boiling acid without facing corrosion problems if, in the medium, dissolved oxygen and small amounts of water are present, and if chloride ions are virtually absent. In laboratory tests performed on X 6 CrNiMoTi 17-12-2 stainless steel in acetic acid of 118°C containing variable extents of impurities, the steel exhibited passive behaviour in cases where the chloride ion concentration was less than 1 ppm and, at the same time, water amounts to some few tenths of a percent. The exact value of the water content necessary to achieve passivity depends on the concentration of formic acid the presence of which, at least in traces, is unavoidable. In anhydrous acetic acid, the steel corrodes in its active state, and dissolved oxygen increases the corrodes in its active state, and dissolved oxygen increases the corrosion rate. If chloride ion concentration is 1 ppm or higher the otherwise passive steel undergoes localized corrosion and the attack mostly follows crystallographic orientations. In aerated boiling mixtures of acetic acid and anhydride, the steel is boiling mixtures of acetic acid and acetic anhydride, the steel is severely corroded until the portion of anhydride reaches 70%. Beyond this, corrosion rate steeply decreases. Practically no corrosion could be found in 97% acetic anhydride.     

低比例甲醇汽油对金属的腐蚀研究

目的减轻甲醇汽油的腐蚀性。方法以汽车油路系统常用的紫铜、黄铜、钢、铁、铝等金属材质为研究对象,采用金属试片的腐蚀度和颜色变化相结合的方法,分析判断甲醇汽油的腐蚀性,通过考察不同金属试片在不同含量甲醇汽油、含水甲醇汽油以及添加缓蚀剂甲醇汽油中的腐蚀情况,分析甲醇汽油腐蚀的主要原因,并根据缓蚀机理筛选缓蚀剂。结果低比例甲醇汽油对不同金属材质都有明显的腐蚀作用,与93#汽油相比,加入5%(体积分数)的甲醇就能使紫铜、黄铜、钢、铝的腐蚀度增加一倍以上。少量水分可加剧甲醇汽油的腐蚀,但当水含量达到一定程度时,腐蚀度减小。缓蚀剂B对铜系金属材质的腐蚀有较好的抑制作用,缓蚀剂C对铁片腐蚀有较好的抑制作用,复配缓蚀剂H对所选金属材质都有良好的缓蚀效果,可使紫铜、黄铜、铁和铝的缓蚀率分别减小82.1%、81.5%、85.3%和89.5%。结论复配的缓蚀剂能够有效地减缓甲醇汽油对金属的腐蚀。     

Einfluß korrosiver Medien auf die Lebensdauer hartgelöteter Verbindungen (Teil I)

Influence of corrosive media on the life of brazed materials (part I) Brazings made of austenitic stainless steel (German designation X 5 CrNi 18 9) and the silver base brazing materials (Nos. 4003, 5009 and 5603) were studied in tap water and sulfuric acid (5%). The parameters studied were the influence of the medium on the mechanical properties and on the structure of the brazed systems. The results were obtained electrochemically (potentiokinetic current potential and potential/time curves) and by metallographic investigation. The analysis were carried out with the aid of the electromicro probe. The tests have revealed that the systems brazed with the Zn containing materials (No. 4003 and 5009) are more of heavily corroded than those made with the zinc free materials (No. 5603). The attack is localized in the first case at the mixed crystals the brass type which adhere to the steel surface; this attack then gives rise to a loss of continuity. The brazings made with the braze No. 5603 are characterized by mechanical resistance superior to that of the base material. According to the results of the electrochemical investigation the breakthrough potential of these brazings is considerably more positive than that of the two others. The attack is different in the two test media: in tap water there is preferential attack of the braze while sulfuric acid preferentially attack of the base material.     

储热式热水器不锈钢水箱腐蚀漏水原因分析

采用材料显微分析方法,对某品牌储热式热水器的水箱漏水原因进行了分析.结果表明:厂家采用的304不锈钢储热式热水器水箱在使用过程中位于搭接焊处发生了严重的腐蚀深沟导致了漏水,其主要原因是搭接焊方式形成了狭窄的缝隙,造成了缝隙内的介质处于滞流状态,使得与腐蚀有关的物质迁移困难从而引起了缝隙腐蚀.同时,当缝隙内溶液中的氧耗竭...     

Sicherung von Schraubenverbindungen aus nichtrostenden Stählen

Securing screws of stainless steels The author emphasizes the importance of screwed connections in technology and discusses the conclusions which must be drawn from existing standards with respect to the utilization of stainless steel screws. Examples are shown to demonstrate the corrosion resistance of such connections (tests in sea water, 3% NaCl, tap water, salt spray) giving prominence to the problems resulting from the use of spring elements (crevice corrosion danger).     

Erosion und Korrosion of metallischer Werkstoffe in feststoffhaltigen Wässern

Erosion and corrosion of metallic materials in particle containing aqueous solutions The combined effect and mutual influence, respectively, of erosion and corrosion of metallic materials in particle containing flows was investigated. Materials under investigation are carbon steel of different hardness levels, ferritic chromium steel, austenitic stainless steel and brass. Corrosive medium was deionized water, acid (pH 4.5), alkaline (pH 10) and chloride (3% NaCl) solution. Quartz particles were used as abrasive at various particle concentrations, grain sizes and flow velocities. For comparison, tests were performed with pure water and under conditions of idle corrosion. Mechanical or corrosive influences dominate depending on material and test conditions, in some cases, synergistic effects of both mechanisms cause an increased mass loss.     

“原位观察”下的水龙头激光焊接头腐蚀性能分析

采用低耗能激光焊新工艺制造水龙头薄壳,替代传统高污染、高耗能的整体铸造工艺,对304、310 s不锈钢激光焊接头进行沸腾硫酸-硫酸铁及室温浸蚀对比腐蚀研究.在设定的腐蚀时间内,采用“原位观察”腐蚀过程焊缝及熔合区微观组织变化.结果表明,310 s比304耐腐蚀性更好,随腐蚀时间加长,接头熔合区晶粒晶界未明显加宽,焊缝断口微观特征主要为韧窝,证明其未发生晶间腐蚀.焊缝金属成分分析表明焊缝中心晶粒与母材相近,腐蚀沟Cr元素降至20.81%高于12%,保证其耐腐蚀性能.