Book Reviews

Abstract

The corrosion of types 310S and 410 stainless steels in forming gas containing 1%H₂S or 1%H₂S/1%HCl has been studied at 600°C. In the conditions chosen, sulphide scales formed on both materials and significant differences in corrosion rate and depth of attack were observed. Thermogravimetric results showed that for both materials there was an initial transient period of rapid sulphidation after which linear or parabolic kinetics were observed. Type 310S and 410 both developed non-adherent, multi-layered sulphide corrosion products. Scanning electron microscopy, energy dispersive X-ray analysis and X-ray diffraction were used to examine the structure and composition of these sulphide scales. The differences in corrosion morphology are in agreement with the variations in the thermogravimetric experiments. Mechanistic corrosion models are being developed.     

Degradation of heat exchanger materials under biomass co-firing conditions

Abstract

Co-firing biomass in conventional pulverised coal fired power stations offers a means to rapidly introduce renewable and CO₂ neutral biomass fuels into the power generation market. Existing coalfired power stations are both much larger and more efficient than current designs of new biomass combustion systems, so feeding a few percent of biomass feed into an existing large coal fired station will give more biomass derived power than a new dedicated biomass station. Co-firing levels started at ～2% biomass, but this has increased to ～5–10% biomass, with higher levels of biomass co-firing being investigated, although supply of biomass becomes an issue with increasing co-firing levels. The lower levels of biomass co-firing (up to ～5%) can be achieved with relatively minor modifications to existing plants, so avoiding the large capital costs and risks of building new biomass-only fired power systems. However higher levels of co-firing are more difficult to achieve, requiring dedicated biomass supply systems and burners. For existing coal-fired power stations, the co-firing of biomass causes some practical problems, e.g.: the control of co-firing two fuels; changes to bottom/fly ash chemistry; changes to deposition (fouling and slagging) within the boiler; reduced reliability of key high temperature components (e.g. heat exchangers) due to increased corrosion problems relative to those experienced with coal alone.

This paper reports the results of assessments carried out to evaluate the potential operating conditions of heat exchangers in combustion systems with biomass (wood or straw) and coal cofiring, as well as laboratory corrosion tests that have been carried out to give an initial assessment of potential effects of biomass-co-firing.

The corrosion tests have been carried out using the deposit recoat method in controlled atmosphere furnaces. A series of 1000 hour tests have been carried out at typical superheater and evaporator metal temperatures using simulated deposit compositions and gaseous environments (selected on the basis of plant experience and potential fuel compositions). Five materials were exposed in these tests: 1Cr steel, T22 steel, X20CrMoV121, TP347HFG and alloy 625. In order to produce statistically valid data on the actual metal loss from the materials, the performance of the materials in these tests was determined from dimensional metrology before and after exposure. For each material, these data have been used to determine the sensitivity of the corrosion damage to changes in the exposure conditions (e.g. deposit composition, gas composition) thereby producing initial models of the corrosion performance of the materials. The corrosion data and model outputs have been compared with data available from power plants operating on coal, straw or wood fuels.     

当量加速腐蚀条件下7B04-T6高强度铝合金疲劳裂纹扩展规律研究

基于编制的机场环境加速试验谱,针对关键结构高强度铝合金件进行当量腐蚀试验,在实验室条件下成功地模拟和再现了服役环境条件的腐蚀损伤,借助复型法观测得到了腐蚀损伤的演化规律;通过预腐蚀疲劳试验和疲劳断口扫描电镜定量分析,得到了裂纹长度a与循环次数N数据集,分析了裂纹扩展速率da/d N与应力强度因子幅值ΔK的对应关系,定量表征了不同程度腐蚀损伤对疲劳裂纹扩展行为的影响规律.结果表明,在腐蚀初期,疲劳裂纹扩展过程中有经典的小裂纹扩展阶段;随着腐蚀损伤的加重,小裂纹行为不明显;腐蚀损伤越严重,疲劳裂纹扩展速率越快,结构抗疲劳性能显著退化.     

Surface treatments for controlling corrosion rate of biodegradable Mg and Mg-based alloy implants

Abstract

Due to their excellent biodegradability characteristics, Mg and Mg-based alloys have become an emerging material in biomedical implants, notably for repair of bone as well as coronary arterial stents. However, the main problem with Mg-based alloys is their rapid corrosion in aggressive environments such as human bodily fluids. Previously, many approaches such as control of alloying materials, composition and surface treatments, have been attempted to regulate the corrosion rate. This article presents a comprehensive review of recent research focusing on surface treatment techniques utilised to control the corrosion rate and surface integrity of Mg-based alloys in both in vitro and in vivo environments. Surface treatments generally involve the controlled deposition of thin film coatings using various coating processes, and mechanical surfacing such as machining, deep rolling or low plasticity burnishing. The aim is to either make a protective thin layer of a material or to change the micro-structure and mechanical properties at the surface and sub-surface levels, which will prevent rapid corrosion and thus delay the degradation of the alloys. We have organised the review of past works on coatings by categorising the coatings into two classes—conversion and deposition coatings—while works on mechanical treatments are reviewed based on the tool-based processes which affect the sub-surface microstructure and mechanical properties of the material. Various types of coatings and their processing techniques under two classes of coating and mechanical treatment approaches have been analysed and discussed to investigate their impact on the corrosion performance, biomechanical integrity, biocompatibility and cell viability. Potential challenges and future directions in designing and developing the improved biodegradable Mg/Mg-based alloy implants were addressed and discussed. The literature reveals that no solutions are yet complete and hence new and innovative approaches are required to leverage the benefit of Mg-based alloys. Hybrid treatments combining innovative biomimetic coating and mechanical processing would be regarded as a potentially promising way to tackle the corrosion problem. Synergetic cutting-burnishing integrated with cryogenic cooling may be another encouraging approach in this regard. More studies focusing on rigorous testing, evaluation and characterisation are needed to assess the efficacy of the methods.     

Boiler corrosion and monitoring

Abstract

Results of a collaborative effort to investigate and develop solutions for key material issues affecting the performance of large-scale coal-fired boilers operating at advanced conditions is presented. Advanced conditions include advanced steam temperatures, oxyfuel firing, and co-firing biomass materials. A series of laboratory experimental results are presented on fireside corrosion in environments representing air-, and oxy-fired conditions, and with coal and/or biomass as the fuel. The effects of fluctuating reducing atmospheres and heat flux effects were examined. A variety of boiler corrosion probes and sensors were developed and tested. The probes measured corrosion by section loss and the sensors by electrochemical techniques including electrochemical noise. The probes were tested in coal and waste-to-energy boilers. Correlations between section loss probes and electrochemical noise sensors allow for real-time corrosion rate measurements to be made that allow for changes in boiler operations to be tracked in terms of corrosion effects.     

海军装备腐蚀仿真技术现状、挑战和展望

海军装备腐蚀防护能够降低装备维护成本,减小腐蚀对装备安全和战备的影响。自然环境试验、实验室加速试验、模拟仿真试验是材料与装备腐蚀及其规律研究及预测的3个最主要的手段,由于模拟仿真试验具有成本低、时间短、可应用于复杂系统等优势,越来越受到人们的青睐。国外已经发展了有限微分法、有限差分法、有限元法、边界元法等数值方法,建立了多种类型的腐蚀数据库。我国也开展了数十年自然环境腐蚀数据积累工作,已经在导弹、飞机、舰船等方面开展了腐蚀仿真研究,但是目前装备腐蚀仿真技术发展还缺乏全局规划和评价体系,仿真精度和可靠度有待提高。未来装备腐蚀仿真研究应该加强数据积累和相关规范、标准的建立,朝着全寿期、全尺寸、互操作性、可信性、重用性及大数据挖掘等趋势发展。     

Challenging gold based filler metals for uses in medicine

Abstract

Research has been carried out to investigate new soldering materials and technologies for the medical field. The two soldering techniques, which have been considered, are diffusion and active soldering. In order to satisfy the most important medical requirement, the biocompatibility, gold based solders and soldering systems have been studied. According to the Directive 2002/95/EC of the European Parliament, lead as well as cadmium, hexavalent chromium and mercury have not been alloyed in the developed solders. The examined soldering systems enable joining similar and dissimilar materials, which is essential in the field of hybrid microsystems engineering. Furthermore, the achieved low process temperatures reduce the incidence of damage and thermally induced stresses in the components being joined.     

A review of factors controlling the gas turbine hot section environment and their influence on hot salt corrosion test methods

Environmental and operational factors that influence the formation and deposition of corrosive species on hot section components in gas turbine engines are reviewed. In addition to air and fuel impurities, combustion gas chemistry, velocity, pressure and temperature are identified as key operational factors affecting the formation and deposition of Na₂SO₄ salt (the primary corrosive species) when trace amounts of sodium and sulphur are entrained into combustors. Test methods for ranking the resistance of different materials to hot salt corrosion are reviewed and compared in terms of the type of damage they produce. The methods considered range from a simple furnace or crucible test to burner rig and engine tests. It is shown that high velocity burner rigs, running at atmospheric pressure, allow all the relevant operational factors to be simulated, and they produce realistic hot corrosion damage similar to that observed on engine parts in service.     

Materials behavior in the Nuon Power IGCC Plant in Buggenum

Abstract

Since 2001 the Willem–Alexander IGCC in Buggenum has been owned by Nuon, one of the largest energy and water companies in the Netherlands. After a short introduction into Nuon, an overview of recent plant performance figures and future plans with Green Power (biomass co gasification) is given.

Over the past 48,500 operating hours completed at the plant several types of material failures have been encountered. In general terms it can be concluded that no cases of intrinsic material degradation have been seen. Failures have been attributed to imperfections in the ability to adhere in all details to the applicable design rules and conditions. Examples of damage as a result of erosion, corrosion and thermal cycling are discussed.     

Development of peening technique using recirculating shot accelerated by water jet

Abstract

The present paper demonstrates the development of a peening technique using recirculating shot accelerated by a water jet that can be used as a risk free treatment in power and chemical plants. Although it is important to increase the reliability of structural materials used in large scale structures, such as power and chemical plants, it is hazardous to treat these structures by general shot peening (SP) techniques because of the risk of sparks and dust explosions. In the present study, an SP technique using a water jet to accelerate shot has been developed, and the conditions under which it is used have been optimised in terms of nozzle geometry, standoff distance and amount of shot. In order to demonstrate the effect of SP, austenitic stainless steel Japan Industries Standards SUS316L was peened and evaluated in terms of its residual stress, fatigue strength and resistance to stress corrosion cracking.     

Investigations of corrosion resistance of Fe-, Ni- and Co-based hardfacings

In the present paper, the potential of surface coatings to increase corrosion of internal combustion engine valves is discussed. The corrosion tests were carried out to study in simulated engine chamber environment the performance of Ni-, Co- and Fe-based materials used for plasma deposition. Hot corrosion tests were performed in air, sulphur dioxide containing atmosphere and in molten synthetic ash. The crucible-sorting test was used to simulate deposits on valve seats from residual fuel combustion which are responsible for rapid corrosion due to the presence of molten phase. The new alloys containing Ni and Co can be potentially applied as valve hardfacings.     

硫酸盐环境中CFRP约束劣化混凝土柱的力学性能

为研究碳纤维增强树脂复合材料(CFRP)加固经硫酸盐腐蚀劣化后混凝土柱的力学性能,构建CFRP约束劣化混凝土的力学模型,采用CFRP约束普通混凝土后腐蚀和CFRP约束劣化混凝土两种工况进行试验,在试验研究基础上,引入损伤率及强度保持率作为损伤的量化指标,建立两者之间的关系;通过对CFRP约束混凝土强度及应变规律的回归分析,建立适用于硫酸盐环境下CFRP约束劣化混凝土的极限强度、应变模型及应力-应变关系模型。结果表明:随侵蚀时间增长,两种工况下CFRP约束混凝土极限强度和应变的变化规律及劣化速度均不同。预劣化的混凝土柱虽然进行了表面处理,但内部已经存在损伤,在侵蚀环境中采用CFRP加固混凝土柱时,应该考虑混凝土初始损伤的影响。      

A framework for the prediction and management of environmental cracking problems

The complexity of engineering systems is growing steadily with the introduction of advanced materials and modern protective methods. This increasing technical complexity is paralleled by an increasing awareness of the risks, hazards and liabilities related to the operation of engineering systems. Environmental cracking (EC) is, in the context of lifetime prediction, one of the most important forms of damage because of its insidious and catastrophic character. EC and particularly stress corrosion cracking (SCC) can affect a wide variety of metals and alloys exposed to specific environments. After briefly reviewing some of the tests and simple models used to evaluate and represent the susceptibility of materials to SCC, this paper proposes the adoption of a top-down approach, used in the aircraft industry for the development of its maintenance programmes, as an information model for the integration of lifetime data. Such an approach can provide the ability to accommodate different sources of information into a single information system while keeping the specific details in a managerial context.     

Effect of environment on corrosion characteristics of newly developed DMR-1700 structural steel

Abstract

The corrosion resistance of any metallic material depends on the environment to which it is exposed. DMR-1700 steel is a material for structural applications that has been recently developed at Defence Metallurgical Research Laboratory by changing the chemistry of alloying elements. Therefore, a detailed understanding of its corrosion characteristics under different environmental conditions is essential. In the present paper, we report the results of a systematic corrosion study that was carried out on the new steel to determine the effect of the environment on the protective nature of the oxide scale that forms on its surface under different environmental conditions. Furthermore, the oxide scale as well as the resistance to pitting and crevice corrosion were studied in various environments. The surface morphologies of the corroded steels were observed under a scanning electron microscope (SEM) to determine the nature of the corrosion. On the basis of studies by different techniques, DMR-1700 steel is recommended for the manufacture of components used in various systems in conjunction with the application of an appropriate protective coating to improve its resistivity to corrosion.     

Performance evaluation of repair systems under varying exposure conditions

This paper reports results of a study conducted to assess the performance of commonly utilized repair systems when exposed to some selected exposure conditions, such as marine, belowground, fire, acid, and sulfur fumes. The performance of the selected repair systems was assessed by exposing large-sized repaired concrete specimens to the selected exposure conditions in addition to thermal variations. After the completion of the exposure, the repaired specimens were visually examined for damage to the surface coating and presence of rust stains, salt scaling, etc. The bond of the coating with the substrate was evaluated and then the specimens were crushed to retrieve reinforcing steel bars that were examined for the extent of corrosion, if any. The data developed in this study were utilized to recommend repair systems suitable for the selected exposure conditions.     

Materials Selection for a Finite Life Time

Classical methods for materials selection only poorly account for the need of incorporating time into the design requirements. Corrosion, fatigue, wear and creep are phenomena that can lead to an accumulation of damage with time, ultimately causing failure. The first step in dealing with this is an evaluation of the potential risk for delayed damage followed by a qualitative ranking of the possible candidates. Beyond this point, both quantitative estimates and design rules have to be used to make the appropriate selection. Examples involving corrosion and creep will illustrate the possibility of and the need for under the form of.     

Corrosion behaviour of four high temperature engineering materials exposed to landfill gas engine flue gas

Abstract

Four engineering materials commonly used in high-temperature applications were exposed to landfill gas engine flue gas for 25 days at 411°C. The flue gas was composed mostly of nitrogen and oxygen, although some carbon monoxide and hydrocarbons were detected together with low concentrations of hydrogen chloride gas and sulphur oxides. Hydrogen fluoride was not analysed, but, due to the nature of the fuel, may have been present at low levels. The materials tested were a carbon steel, a low alloy steel, a 12%Cr stainless steel and an austenitic stainless steel. Thin, protective films were formed on the 12%Cr and austenitic stainless steels, however, the corrosion products formed on carbon and low-alloy steels consisted of several layers, the outermost of which were extremely friable and non-adherent, especially on cooling from the flue gas working temperature. The maximum corrosion rate obtained was 70 μm yr^–1 for carbon steel, which may be acceptable for a number of flue gas applications. The exposed coupons were examined using conventional techniques such as X-ray diffraction (XRD), optical microscopy (OM) and scanning electron microscopy (SEM). The predominant scale formation mechanism controlling the corrosion appeared to be simple oxidation type reactions, however, the influence of HCl, as evidenced by the presence of akaganeite (β-FeO(OH)), was hypothesised. A model describing the corrosion mechanism is proposed in order to provide an improved life prediction capability for such flue gas environments.     

TEM investigations of intergranular stress corrosion cracking in austenitic alloys in PWR environmental conditions

Abstract

Analytical transmission microscopy has been used to investigate the initiation of stress corrosion cracking in Inconel 600 subjected to constant load testing under simulated pressured water reactor primary water conditions. The observations revealed that intergranular attack proceeded by the development of a zone of polycrystalline chromia along the boundary plane intersecting either the free surface or a blunted, open crack in contact with the free surface. Ni-rich metal particles were interspersed within the chromia. Conversely, open cracks were filled with nanocrystalline NiO and large compound particles of spinel and NiO, indicating a difference in potential between closed, attacked boundaries and open cracks. Open cracks appeared to have initiated by fracture of the chromia zones, such fracture being strongly dependent on boundary geometry with respect to loading direction. The observations suggest that stress corrosion crack initiation and propagation is dependent on diffusion of oxygen through the porous oxides. Dislocations and stress could enhance diffusion as chromia was observed along slip planes at the arrested tips of blunt cracks.     

Erosion–corrosion of preoxidised Incoloy 800H in fluidised bed environments: effects of temperature,velocity, and exposure time

Abstract

The effects of preoxidation as a potential protective measure for alloys exposed to erosion–corrosion have been evaluated for Incoloy 800H in laboratory simulated fluidised bed conditions. The performance of the specimens after exposure to such environments was estimated from weight change data, electron microscopy, and X-ray diffraction patterns. The results showed that, in ‘corrosion dominated’ conditions, i.e. at relatively high temperatures and low velocities, preoxidation was successful in reducing the erosion–corrosion of the underlying alloy. However, when the velocity was increased and the temperature decreased, preoxidation afforded only some short term protection to the alloy. In these more ‘erosion–corrosion dominated’ regimes, preoxidation delayed the incubation period for erosion–corrosion of the alloy, but, once the scale was removed, the erosion–corrosion rates were similar to those of the non-preoxidised alloys. The effects of temperature, velocity, and exposure time are discussed for the preoxidised and non-preoxidised alloys. Comparisons are made between the results of the present and other erosion–corrosion studies, to explain the distinctive pattern of alloy wastage in these environments.

MST/1432     

Construction of erosion–corrosion maps for erosion in aqueous slurries

Abstract

Although much research has been carried out on the erosion of materials in aqueous slurries, little attention has been given to defining transitions between erosion regimes in such environments. This is despite the large amount of work that has been carried out in this area in ‘dry’ high temperature corrosion environments. Defining transitions between regimes permits distinction between erosion and corrosion dominated behaviour, which can be an aid to materials selection and to process monitoring in such conditions. This paper describes the basis of a relatively simple theoretical method for evaluating the transitions between erosion and aqueous corrosion regimes. Models for solid particle erosion at normal impact are combined with those for aqueous corrosion to define regimes of damage in corrosion conditions varying from dissolution to passivation. This permits the construction of the erosion–aqueous corrosion map where the transitions between the regimes are shown as a function of erosion and aqueous corrosion variables. The rationale for the regimes suggested is discussed on the basis of research on erosion maps in oxidising conditions. The boundaries on the maps are compared with experimental data. Other issues addressed in this study include using the erosion–corrosion map to identify favourable and adverse operating conditions in addition to identifying the mechanism of damage.

MST/3543