微弧氧化工艺及封孔处理对镁合金耐蚀性能的影响

为寻求在低成本下获得高性能镁合金防护膜的方法,采用直流低压微弧氧化工艺,在硅酸盐体系中添加抑弧剂抑弧以获得均匀的膜层,并对随后获得的微弧氧化陶瓷膜进行封闭处理.通过形貌分析及腐蚀析氢的方法研究了膜层的耐蚀性能及腐蚀特征,结果表明:在低电流密度下适当延长微弧氧化时间,可获得更为致密的陶瓷膜层,抗腐蚀性能更好.碳酸盐封孔处理可使膜层的致密层变厚,并进一步强化膜层的致密度;能保证基体完全不受腐蚀的时间显著延长,并在较长时间内使膜层的抗腐蚀性能明显提高.     

高参数发电机组腐蚀的原因及其防范措施

在某600MW发电机组大修过程中,发现汽轮机低压缸的叶片和隔板发生了腐蚀.从腐蚀形貌,腐蚀产物成分和工作情况等不同方面进行了分析,发现该汽轮机产生腐蚀的原因为氯离子腐蚀,并提出了相应的防范措施.     

6063铝合金阳极氧化膜腐蚀行为研究

分别对6063铝合金原样与硫酸直流阳极氧化法处理样品样进行铜加速盐雾腐蚀,考查时间对腐蚀样品形貌、元素分布及电化学腐蚀行为的影响,利用质量损失法对腐蚀动力学进行分析.结果表明:腐蚀时间延长,腐蚀电流增大,原样表面腐蚀产物明显增多;阳极氧化处理后改善6063铝合金的抗腐蚀性,阳极氧化样的抗腐蚀性能在盐雾条件下提高2.2倍,在暴露环境下可提高4.5倍.     

辽宁土壤腐蚀性研究

采用自然埋藏和室内加速试验方法，结合土壤理化性质、腐蚀微生物、气象等自然条件分析对辽宁地区土壤进行腐蚀性调查和腐蚀规律性研究。对所得结果用统计分析，灰色系统和模式识别等数学方法进行数学处理。将所得结果对本地区土壤进行腐蚀性分级，最后绘制成腐蚀图。     

影响热水锅炉腐蚀的主要因素及水质判定指标

用极化曲线法研究了影响热水锅炉水质腐蚀性的主要因素。根据《均匀腐蚀的十极标准》验证了大连港务局房产公司四工区热水锅炉的补给水和循环水对钢的腐蚀速度均小于０．５ｍｍ／ａ，中属于可用级的，同时也提出了热水锅炉水质腐蚀吕质腐蚀的判定指标，具有一定的实际意义。     

油气田集输管线点腐蚀试验与评级研究

采用点腐蚀测深仪观察联合站内原油处理系统、天然气处理系统和污水处理系统管道腐蚀监测挂片的点腐蚀坑形貌,测量和采集点腐蚀坑相关数据,并对点腐蚀程度进行评级,分析不同腐蚀监测环境对点腐蚀坑的影响。结果表明：油、气、水处理系统管道腐蚀挂片在平均腐蚀都为轻度的范围内,点腐蚀程度逐步加重,通过点蚀评级和孔蚀系数的深入研究,为合理评价腐蚀监测挂片的腐蚀程度,对介质腐蚀性进行有效监测提供科学的技术支撑。     

X70管线钢激光热辐射渗铝处理后抗盐雾腐蚀行为（英文）

利用激光热辐射对X70管线钢表面进行渗铝处理,通过SEM观察了渗铝层表面和界面形貌,并对其结合界面的化学元素进行了EDS线能谱分析。对盐雾腐蚀后界面化学元素进行了EDS面能谱分析,用XRD分析了盐雾腐蚀前后渗铝层表面的物相,研究了渗铝层对X70管线钢抗盐雾腐蚀性能的影响。结果表明,激光热辐射渗铝处理后X70管线钢表层为氧化铝层,化学元素在表面和界面分布均匀,无富集现象,在结合界面处相互渗透,形成冶金结合形式;盐雾腐蚀后原始试样表面点蚀严重,形成全面腐蚀;渗铝处理后试样表面生成致密的Al2O3保护膜,阻止了腐蚀性介质Cl-离子和基体活性Fe的接触,提高了X70管线钢抗盐雾腐蚀能力。     

X70钢在盐碱土环境下的腐蚀研究

研究了X70钢在天津大港油田的3个不同地点的腐蚀情况，对现场3种盐碱土土壤环境进行了调查和腐蚀性研究， 通过电化学方法测定腐蚀速率，应用XRD技术分析了腐蚀产物，应用SEM观察腐蚀形貌.结果表明X70钢的腐蚀程度主要取决于3种土壤中的氯离子和硫酸根离子的浓度.      

Salt Spray Corrosion Resistance of Aluminized Coatings on X70 Pipeline Steel by Laser Thermal Radiation

利用激光热辐射对X70管线钢表面进行渗铝处理,通过SEM观察了渗铝层表面和界面形貌,并对其结合界面的化学元素进行了EDS线能谱分析。对盐雾腐蚀后界面化学元素进行了EDS面能谱分析,用XRD分析了盐雾腐蚀前后渗铝层表面的物相,研究了渗铝层对X70管线钢抗盐雾腐蚀性能的影响。结果表明,激光热辐射渗铝处理后X70管线钢表层为氧化铝层,化学元素在表面和界面分布均匀,无富集现象,在结合界面处相互渗透,形成冶金结合形式;盐雾腐蚀后原始试样表面点蚀严重,形成全面腐蚀;渗铝处理后试样表面生成致密的Al2O3保护膜,阻止了腐蚀性介质Cl-离子和基体活性Fe的接触,提高了X70管线钢抗盐雾腐蚀能力。     

EDTA-CuNa2对医用镁合金微弧氧化膜性能的影响

目的 在镁合金表面生成一层含铜氧化膜,以提高镁合金的耐蚀性和抗菌性.方法 利用微弧氧化技术在镁合金表面生成含铜氧化膜,用SEM、EDS和电化学工作站研究含铜电解质浓度对镁合金氧化膜的表面形貌、成分和耐蚀性的影响,及含铜氧化膜的腐蚀机理.结果 随着EDTA-CuNa2浓度的增加,一方面,更多的Cu/Mg构成微电偶腐蚀电池,加速镁合金的腐蚀;另一方面,析出的Cu覆盖在镁合金基体表面对镁合金起着保护作用,同时由于Cu的电位更正,促使镁合金的腐蚀电位正移,降低镁合金腐蚀倾向.EDTA离子是一种腐蚀性介质,0.01 mol/L EDTA–的腐蚀性比3.5％NaCl略强.随着EDTA-CuNa2浓度的增加,溶液中含有更多的EDTA离子和Cu离子,导致镁合金基体的腐蚀电流增大,耐蚀性降低.镁合金在含EDTA-CuNa2的电解质中氧化时,由于EDTA离子和Cu离子共同对镁合金腐蚀导致Cu离子难以参与成膜.EDTA离子和铜离子对镁合金均具有腐蚀作用,所以限制了铜离子进入氧化膜中.结论 随着EDTA-CuNa2浓度的增加,氧化膜中的铜元素含量缓慢增加,氧化膜的腐蚀电位正移,腐蚀电流密度变化不大.     

SwRK-Versuche und Rißeinleitungsuntersuchungen am neuentwickelten Duplexstahl X 3 CrMnNiMoN 25 6 4 im Vergleich zum bekannten ferritisch-austenitischen Stahl X 2 CrNiMoN 22 5

Investigation into corrosion fatigue and crack initiation with the newly developed duplex steel X 3 CrMnNiMoN 25 6 4 by comparison with the known ferritic-austenitic steel X 2 CrNiMoN 22 5 The majority of low pressure steam turbine damages are caused by corrosion fatigue. This kind of damage occurs primarily in the Wilson-zone of steam turbine machines. In spite of careful feed water washing there is still a build-up of damaging chloride-containing water impurities on the turbine blades. During the last twenty years the standard material X 20 Cr 13 often was and is still used for industrial turbine applications, although the corrosion fatigue resistance was insufficient concerning the increasing operation conditions of moder steam turbine machines. Modifications of the chemical composition of the steel and further material development did not reach a satisfying corrosion fatigue resistance till today. Recent investigations of duplex stainless-steels, especially the steel X 3 CrMnNiMoN 25 6 4 (A905; austenite/ferrite = 50/50) show both a good corrosion behaviour and a sufficient strength of this type of steels. In the present investigations the dependence on the corrosion fatigue limit on the pH-value, chloride concentration, temperature and the behaviour of corrosion cracking (crack initiation) is evaluated.     

Enhanced Droplet Erosion Resistance of Laser Treated Nano Structured TWAS and Plasma Ion Nitro-Carburized Coatings for High Rating Steam Turbine Components

This article deals with surface modification of twin wire arc sprayed (TWAS) and plasma ion nitro-carburized X10CrNiMoV1222 steel using high power diode laser (HPDL) to overcome water droplet erosion occurring in low pressure steam turbine (LPST) bypass valves and LPST moving blades used in high rating conventional, critical, and super critical thermal power plants. The materials commonly used for high rating steam turbines blading are X10CrNiMoV1222 steel and Ti6Al4V titanium alloy. The HPDL surface treatment on TWAS coated X10CrNiMoV1222 steel as well as on plasma ion nitro-carburized steel has improved water droplet resistance manifolds. This may be due to combination of increased hardness and toughness as well as the formation of fine grained structure due to rapid heating and cooling rates associated with the laser surface treatment. The water droplet erosion test results along with their damage mechanism are reported in this article.     

Boiler materials for ultra-supercritical coal power plants—Steamside oxidation

The corrosion behavior of tubing materials carrying steam at high temperature is of great concern to fossil power plant operators. This is due to the fact that the oxide films formed on the steam side can lead to major failures and consequently to reduced plant availability. The wall loss of the pressure boundary caused by oxidation can increase the hoop stresses and cause premature creep failures; second, the increased insulation of the tubes due to the low thermal conductivity of the oxide film can lead to increased metal temperature, thereby exacerbating the fireside corrosion as well as creep problems. The third concern is that thicker oxides may spall more easily when the plant is cooled down. On restart, the spalled material may lodge somewhere in the system with the potential for causing tube blockages, or it may be swept out with the working fluid and enter the steam turbine causing erosion damage to the turbine nozzles and blades. Failures of tubing and turbine components by these mechanisms have been widely reported in the United States. In view of the importance of the steamside oxidation, a major study of the phenomenon is being carried out as part of a major national program sponsored by the U.S. Department of Energy and the Ohio Coal Development Office. As a prelude to the experimental work, a literature survey was performed to document the state of the art. Results of the review are reported here.     

About the Authors

Abstract

A case history is presented relating to corrosion of boiler plant which provides clear examples of the problems that can arise with inadequate attention to water treatment. Failures were observed in various components of the steam circuit of a urea plant: superheater tubes; stainless steel pipelines; expansion bellows carrying steam at 3·5 MPa pressure; the plugs and seats of steam admission valves; bolts and studs and the heads of Allen screws in reversing segments of the turbine; and the turbine rotor disc. All the components that failed were using steam from the steam generation plant. Investigation revealed that carryover of boiler chemicals in the steam had resulted in buildups of alkalinity and chlorides, leading to stress corrosion cracking.     

铬系白口铸铁在液-固两相流中冲刷腐蚀的交互作用

用失重法和电化学法研究铬系白口铸铁在液－固两相液中冲刷腐蚀的交互作用，结果表明：（1）提高白口铸铁铬含量，不仅可以明显减小冲刷腐蚀交互作用失重率，而且显著降低冲刷腐蚀总失重率；（2）纯腐蚀失重率接近纯冲刷失重率的20倍，冲刷腐蚀交互作用失重率约占总失重率的70％，因此在本实验条件下，铬系白口铸铁的失效机理是以腐蚀加速冲刷为主要特征。     

汽轮机末级叶片纳米涂层抗水蚀性能研究

采用高压脉冲水射流试验装置对不锈钢、司太立合金及CNx／TiN纳米复合涂层的性能进行测试，并采用扫描电镜对材料的失效破坏形貌及机理进行了分析。结果表明，纳米涂层具有优异的抗水蚀性能，可以作为汽轮机末级叶片抗水蚀用涂层。     

Stress corrosion cracking of steam turbine disc steel--measurement of the crack-tip potential

In situ measurements have been made of the crack-tip potential in a fatigue-precracked compact tension specimen of a 3% NiCrMoV steam turbine disc steel immersed in simulated steam condensate environments at 90 °C. Despite high corrosion potentials of 0.1 V saturated calomel electrode (SCE) the extent of crack-tip anodic polarisation was very constrained, a limiting potential of about −0.61 V SCE being attained. Surprisingly, adding chloride up to 1500 ppb, or separately sulphate at 406 ppb, had no impact on the tip potential and its variation with corrosion potential, compared with pure water. Increasing the pH of initially neutral pure water also had no significant effect.     

Stress Corrosion Cracking of Turbine Disc and Rotor Alloys

Abstract

Investigations have been carried out to examine the stress corrosion behaviour of some medium strength low alloy steels in high purity wet steam and water. The alloys involved are used for the manufacture of steam turbine discs and rotors.

Stress corrosion cracking occurred in both 3% CrMo and 31/2% NiCrMoV steels. Crack growth rates were measured, after exposure in on-site rigs, for periods up to 20,000 h. The effects of applied stress, stress intensity, and strength level were studied in addition to microstructure. The possible role of certain non-metallic incluszons upon the cracking process is highlighted, as is the presence of chromium.     

Nitridation of grate in a biomass‐fired boiler

After a straw‐fired power plant in Denmark had been in operation for 16 years with 93,815 hr operation, there was a need for overlay welding repair of the grate due to a decrease in wall thickness from erosion/corrosion. The grate consisted of 15Mo3 (Werkstoff nr. 1.5415) tubes where water/steam flows through, which were welded together with fins, and where one side faced the combustion zone coming into contact with the fuel (the side that required weld overlay). The water/steam temperature was 320°C and the surface metal temperature was estimated to be 350°C. However, there were difficulties when trying to overlay weld the grate as the weld pool was unstable. The microhardness measurements on cross‐sections of the tubes revealed a higher hardness of the tube facing the combustion zone compared to opposite the combustion zone. In addition, there was higher hardness adjacent to the combustion side than the steam/water side. Analysis of etched cross‐sections with light optical and scanning electron microscopy revealed the presence of acicular structures at the convex surface. Further analysis has been conducted with X‐ray diffraction and a LECO nitrogen analyser indicating the presence of iron nitrides. Reasons for their evolution and implications for the repair welding are discussed.     

Stress corrosion cracking of a low alloy steel in high purity steam

The catastrophic failure of a steam turbine at Hinkley Point “A” Nuclear Power Station resulted from stress corrosion cracking of the discs on the low pressure (L.P.) turbine rotor. This paper describes investigations carried out within the South Western Region of the C.E.G.B. to determine the mechanism and the environment responsible for cracking.The results show that stress corrosion cracks can be initiated and propagated during normal turbine operation and furthermore they suggest that cracking is due to the action of wet, high purity steam on stressed metal. The chemical quality of the steam was found to be very high, the impurities were well within the normal range associated with power plant operation.The results are in agreement with the recent findings of more widespread cracking at Hinkley Point and elsewhere. It is considered that as the steam is inherently aggressive then the measures currently being taken by C.E.G.B., i.e. the removal of the highly stressed keyways, limiting steam access to regions of high stress and the use of improved alloys, should prevent further failures of this type.