Materials, which are intended to be used to safely, are often the source of hazards. The source may grow probabilistically into the hazards. Thus, the risk associated with materials has yet not been discussed quantitatively.
In the present paper, the hidden risks associated with materials which lead to failure accidents, are extracted and analyzed quantitatively, using data base and case study analyses of failure accidents.
Data bases and case studies of failure accidents have been shown to be useful in extracting hidden risk factors associated with materials. Hidden risks associated with materials are classified herein into three categories: material-intrinsic-risk, material-induced-risk and material-shared-risk. Finally, quantitative analysis of the hidden risk associated with materials is discussed.

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Recently, risk-based engineering has become of major interest in the field of maintenance of mechanical structures. Actually, the technique has not been introduced into Japan rigorously. In this paper, the details that the risk-based engineering has become of major interest together with the background unique to Japan are described. This paper summarizes the fundamentals of risk-based engineering and will help the person who begins learning this field.

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Fossil fuel power generation is now supplying about 60% of the electric power consumed in Japan, while the accumulated operation time of approximately 80% of fossil power plants in service is more than the 100000 hour-life anticipated in their design. Furthermore, the maintenance of these aged plants is forcing simplification in order to reduce electric charges under the present severe competitive conditions in the electric power industry. In the future, therefore, it will be essential to improve the safety and reliability of aged fossil fuel plants with the application of risk-based approaches. Furthermore, to avoid the risk of accidents, it is also very important to build a database of the knowledge and wisdom learned from past accidents. The knowledge and wisdom that has been acquired must then be adequately disseminated from this database. This paper reviews typical accidents in boilers and steam turbines experienced in the U.S. and Japan, and describes the knowledge and techniques learned from these accidents. Finally, future issues for the favorable maintenance of fossil power plants in Japan are proposed.

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Fossil power plays an important role in the supply of electric power as well as nuclear power. However, the accumulated operating time of most fossil power plants now exceeds 100000 hours, which is the designed life of high-temperature components. In addition to the problem of aging of fossil power plants, costs need to be reduced maintaining supply reliability. This paper describes current maintenance and diagnosis techniques used for aged fossil power plants, and the RBI/RBM method as a new maintenance method that reduces cost while maintaining reliability. Remaining issues to be resolved for applying RBI/RBM are also discussed.

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A risk-based maintenance (RBM) technique has been generated to optimize inspection and maintenance plans for fossil-fired power plants which will be deregulated in Japan. In the present study, technological advances and problems are considered that have resulted from the application of the RBM to actual boiler plants with operating times exceeding 100,000 hours. Risk is defined as the product of the likelihood of damage in plant components by the consequence due to failure of the components or system. The present study found that the RBM is a useful decision tool for determining inspection priority, mitigation of undesirable risk, extension of the inspection period, and other improvements in maintenance practice. At the same time, serious potential problems are brought out.

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Reliability analyses were conducted on field inspection data of steam turbines and creep data of turbine rotor materials to show how risk-based maintenance was introduced into the life assessment and maintenance of steam turbine plants. The cumulative hazard function method was applied to the field events requiring recovery actions, in order to obtain unreliability functions of operation hours or start cycles. The rotor bowing phenomena were investigated as the typical examples of creep deformation. The event tree and unreliability functions were obtained for those phenomena. Moreover, a unified unreliability function was obtained by substituting operation hours to time fraction t⁄t_r, where, t_r was time to rupture. As the time to rupture was expressed by the function of stress, temperature and Vickers hardness, this unified unreliability function could be used for various machine and material heats. Unreliability functions were also obtained from the statistical analysis of creep rupture data, especially using the normalization of stress by hardness. The risk functions were derived from the sum of unreliability functions multiplied by recovery costs along the event tree. Maintenance intervals could be determined based on cost analyses among risk costs, preventive maintenance costs and operational benefits. This procedure was proved to be effective for economical and reliable operation & maintenance for steam turbine plants.

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The chemical industries, which deal with hazardous or high-pressure flammable materials, have been continuing process safety management programs for a long period. But the determinant base approaches to process safety are not always effective because of the variety of causes of incidents.
In recent years, chemical industries have been introducing the risk based management methods to fields of the process safety, the instrumentation and the maintenance of chemical plants. It is recognized that the risk based methods are effective to reduce both risk and cost at same time. Quick review of the risk based idea of process safety, safety instrumentation system and maintenance are presented.

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An offshore structure is not able to avoid the encounter of the severe storm always, because of the characteristic of the purpose which is to stay at the specified sea area for the operation. This paper describes the design method for typical offshore structure briefly, then explains the some accidents of the offshore drilling rig, and finally presents the fundamental idea about the safety issue based on the investigation of the specific technical problems related to the causes of accidents.
Many rigs for Arab, Mexico, Canada and North sea were constructed at Japanese shipbuilding yards between the 1970’s and the 1980’s followings the world wide rig construction boom. As Japan has a few rigs and a little information about the accidents of the offshore drilling rigs, according to the Lloyd’s lists and some reports related accidents, the accidents of the offshore structures occur often as compared with ships and the scale of the accidents is often beggar than normal ship. Norwegian semi-submersible accommodation platform “Alexander L. Kielland” collapsed and capsized due to fatigue failure at the weld part of the brace at North sea oil field in March 1980.
123 lost their lives by this accident. Also jack up rig “Dan Prince” sank in Araskan waters during wet towing in October 1980. These impact the later design philosophy to establish the residual stability requirements and structural redundancy evaluation requirement for the offshore structures.

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Propagating shear fracture is unique to natural gas transmission pipelines. It can propagate in extremely long distance such as several hundreds or thousands meters. Reproductive experiments for the fracture were introduced and interactive simulation between the gas decompression and the crack propagation were carried out in several cases. The simulation can predict the crack propagation and arrest in the pipelines under any design conditions in which pressure, ambient temperature, gas compositions for transmission, and material properties such as the grade, sizes and toughness of the large diameter pipes used for the pipelines. Samples for the standardization of the toughness of the pipes used were proposed and the important role of the standardization for preventing large scale failure in the pipelines was discussed.

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The Shinkansen Line has experienced no serious car-accidents since its operation start in 1964. Why has the Shinkansen Line been able to keep such a good safety performance? This paper intends to clarify the background and the reasons why those miracles became possible—when, what kinds of risks and what kinds of actions the staff of the Japanese National Railways took in, who participated in the development of the Tokaido Shinkansen railway-axles in 1950s∼1960s as a designer, an investigator, a maintenance engineer, an inspector, or a top executive in technology. I discovered all the staff had been dedicated to their duties and their actions were prudent enough in general. As a result their behaviors have reduced the riskiness of their works objectively. But the most of the staff were not so much sensitive to risk itself as a few technical top executives of JNR. For example when the inspectors first found unexpected micro cracks on the 20% running axles in 1965, the top executives adapted a new management system in 1966 based on those inspections, which contained a systematic long-range R&D plan of high-quality railway-axles as well as an effective risk management for micro cracks.

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To establish the risk-based material engineering, survey of basic concepts on social risk is inevitable. The present study first surveyed the concept of “social risk” based on the basic literatures in the area of STS (Science and Technology Studies). Social rationality is considered as the concept to legitimate the decision making for public problems that even scientists and engineers cannot provide the right answers. Consensus conference, Focus goups, and Science shops are introduced as social devices to construct social rationality for selecting/evaluating the engineering for future society. These concepts and devices are important for construct the future of risk-based material engineering.

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Engineering is a sort of professional works. But, in contrast to such typical professions as medical doctors and lawyers, engineers are special in that their prime objects are artifacts rather than persons. In doing their business, doctors and lawyers inevitably engage in direct, personal relations with their clients. On the other, engineers design some artifacts, which serve as media, through which they indirectly engage with other persons like users.
In the light of this indirectness, it seems natural that ‘do the right design’ or ‘ensure safety’ is engineers’ counterpart of the central norm for doctors; ‘do not harm’.
To ensure safety, it is not enough for engineers to behave and cope with their colleagues in scientifically, or technologically adequate manners. Appropriate social institutions are also in need to ensure safety. In the case of traffic safety, required institutions include traffic light system, emergency hospital system and even insurance system.
So the good design of these social institutions or systems is essential for the fulfillment of the engineers’ ethical norm. The freedom of engineers i.e. that of research and development (R & D) is an important factor for the good design.
From the view stated above, I discuss the following three institutions; the law of product liability, function standard, and the exemption from responsibility.
The last of them relates the matters of accidents investigations. And the information or knowledge acquired is the central point of engineering knowledge.

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To establish a safe society, it is necessary to secure the safety of products and systems and improve their reliability. However, it is impossible to produce perfectly safe products and systems. Recognizing the existence of these risks, consumers or users must select and use products and systems according to their own choices. The preparation of information and data concerning such risks will help users to know whether they are acceptable or not. For coping with such a risky society, engineering and technology based on consideration for risk are expected to progress. A study was conducted on this subject from the standpoint of material research, and the development of a materials risk information platform was commenced in 2001. This report describes the details of this platform development, the contents of the research, and the expected results.

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“Risk-based design”, “risk-based manufacturing”, and “risk-based maintenance” are increasingly being applied to the area of mechanical equipment. These are very useful concepts and methods for plant management, etc.; however, when the risks associated with mechanical equipment are examined from the viewpoint of materials, it is often difficult to obtain risk information for use as a basis for study. One reason is that most materials-related databases tend to be built separately for individual fields of study, and are limited to digitized numerical data. As an approach to solving this problem, our team began in the middle of 2001 an investigation of the feasibility of setting up a platform system for material risk information. This project was cooperated in and supported by the National Institute for Material Science. The concept of this system is a portal site to be used via the Internet, designed to collect information related to material risk from a distributed network environment and to provide it to users. “Life test data on materials”, “information on problems or accidents attributable to materials”, “standard information”, “information related to various evaluations”, “other risk information” etc., comprise the material risk information used. This paper gives an overview of our platform system for collecting information on materials-related risks and the overall project plan.

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The effect of minor alloying elements on the heat-to-heat variation in creep rupture time has been investigated for the nine heats of 18Cr-8Ni austenitic stainless steel (JIS SUS 304 HTB) at temperatures between 600 and 700°C for the periods from 30 to 1.8×10⁵ h.
The heat-to-heat variation in creep rupture time at first increases more than one order of magnitude then reduces and again increases with decreasing stress and increasing test duration. The first increase in heat-to-heat variation with increasing test duration, which is more pronounced at a lower temperature of 600°C, is caused by precipitation strengthening due to very fine Nb-carbides having a size of 10 nm or less. The precipitation strengthening due to Nb-carbides becomes disappeared by about 10⁵ h at 650°C, because of their agglomeration during creep. This causes the reduction of heat-to-heat variation. The second increase in heat-to-heat variation at long times is more pronounced at higher temperature of 700°C and at long times above 10⁴ h, but it does not appear at 600°C for the duration up to 10⁵ h. The available nitrogen concentration, defined as the concentration of nitrogen free from AlN and TiN, clearly explains the second heat-to-heat variation. Accelerated void formation in a heat containing high Al also decreases the creep strength at long times. It is concluded that the present results improve the reliability of remaining life estimation for respective heats of SUS 304 HTB steel and hence reduce materials risk.

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To evaluate material risk caused by human-error, fatigue properties of Ti-5Al-2.5Sn ELI alloys and the effects of surface roughness and notches on the properties have been investigated at cryogenic temperatures. Specimens with surface roughness changed by plural SiC papers (Grade #600, #100) and notched specimens were prepared (Kt=1.5, 3). The S-N curves shifted to higher stress level with a decrease of the test temperature. Regarding the effect of surface roughness, the fatigue strength of the Grade #100-surface-roughness specimens was a little lower than those of Grade #600-surface-roughness specimens. Fatigue crack initiation sites of each surface roughness specimen at 4 K were found in the specimen interior. Using root area analysis, which is the size of the crack propagation plane as a shape parameter, the fatigue strength depends on the \sqrtarea size. In notched specimens, the fatigue strength of the Kt=3 specimen were lower than those of the Kt=1.5 notched specimens. Although fatigue crack initiation sites of the Kt=3 notched specimen were at the notch root, those of the Kt=1.5 notched specimen were in the specimen interior.
Fatigue properties of surface roughness and notched specimens at cryogenic temperatures were expected to be more improved when the grain size of the materials was minimized, i.e., fatigue crack initiation sites were minimized.

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Newly developed β⁺-γ coincidence positron lifetime spectroscopy was applied to analysis of fatigue damage aiming at non-destructive evaluation of fatigue stored in type 316 stainless steel which is mostly used in primary water line of pressurized water reactor. Stress-controlled fatigue specimens and strain-controlled fatigue specimens were prepared and relations between fatigue life and positron lifetime were investigated. Mean positron lifetime increases with the fatigue life monotonically in both fatigue test modes. In the strain-controlled mode, mean positron lifetime increases faster at early stage than that in the stress-controlled mode; however, it converges to the same value at the end of the fatigue life in both conditions. Component analysis of positron lifetime spectra revealed that main defects are dislocations and their density increases with fatigue life to a critical value. With this non-destructive evaluation method, the fatigue damage can be analyzed precisely without destruction of the sample.

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In order to detect persistent slip bands (PSBs) which can be nucleus of fatigue cracks, surfaces of fatigued copper single crystals were observed using electron channeling contrast imaging (ECCI) method. The ECCI method enables us to observe dislocation structure existing near the surface of bulk crystal, nondestructively. The copper single crystals having [2\bar31], [001] and [\bar111] tensile axes were cyclically deformed at a constant plastic shear strain amplitude of 2×10⁻³. After the fatigue tests, the ECCI observations of the crystal surfaces were performed with a field-emission scanning electron microscope. When the [2\bar31] single crystals were fatigued until 1500 cycles, band-like images along a primary slip plane were detected by the ECCI method. It was found at high-magnification observation that the band-like image was composed from ladder-like structure. Because this structure is identical to the PSB which has been observed with transmission electron microscope (TEM), it can be concluded that the band-like images of the ECCI observation were the PSBs which were formed near crystal surface. The ECC images of the fatigued single crystals having [001] and [\bar111] axes revealed linear and wavy structures lying perpendicular to tensile axis, respectively. These structures were also analogues to the observations which have been conducted using the TEM.

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We investigated the nitriding process and the microstructure of the alloyed layer between foreign metals under composite arc spraying using two different wire materials, Ti and the paired metal (Mo, Ni, Cu and Al). The Ti element in the composite coatings (Ti-Mo, Ti-Ni, Ti-Cu and Ti-Al) was of TiN and/or TiN_0.3, and the oxide or nitride of the paired metal was not found in the coatings. An intermetallic compound (Ti₂Al) in the Ti-Al coating was detected in the XRD pattern, but none was detected in the other coatings. It is considered that the reaction of Ti with foreign metal occurs only in the solidification process at the moment of droplet impact. The composite coatings were of very dense packing, and had the diffusion layer in the interface region between the foreign metals. The solute element, Ti in the composite coating Ti-Mo, reacted with nitrogen to form many micrograins of TiN_0.3 within molten Mo during thermal spraying. In the other coatings (Ti-Ni, To-Cu and Ti-Al), eutectics were mainly identified, and the Ti nitride in the alloyed layer between foreign metals was only TiN_0.3. In addition, the intermetallic compounds, which were not detected in the XRD pattern, were identified in the TEM observation.

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We developed a two-step stir, mix, and quenching (SMQ) process to produce an Al-Cr-Cu alloy slurry with a high volume fraction of fine primary intermetallic crystals. In this process, we used a hypoeutectic Al-Cu alloy melt for the first melt and a hyperperitectic Al-Cr alloy melt with a higher liquidus temperature for the second and third melts. In the first step of the process, we stir-cast the first melt in a vessel to produce a semi-solid slurry containing aluminum solid solution (α-phase), and then mixed the second melt into the slurry. The hypoeutectic Al-Cu alloy slurry acted as a coolant, whose apparent heat capacity is enhanced by the latent heat of fusion of α-phase. The second melt was thus rapidly quenched, precipitating numerous primary intermetallic crystals when it contacted the slurry. In the second step of the process, we cooled the mixed alloy slurry while agitating it until it crystallized a certain quantity of α-phase, and then quenched the third melt into the slurry. An Al-6.7 mass%Cr-1.8 mass%Cu alloy slurry produced by this process was centrifugally cast to produce a tubular casting with thin, flange-like part. In the major portion of the tubular casting, fine primary intermetallic crystals were uniformly distributed. The average size of the primary crystals was 15±2 (μm), and their volume fraction was 0.22±0.05.

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A new synthetic process of composite material, reactive infiltration technique, in which both combustion synthesis and spontaneous infiltration are combined, was investigated. In this research, fabrication of TiC/Al composites was attempted by the in situ synthesis of TiC particles and the subsequent spontaneous infiltration of molten aluminum. The combustion synthesis of Ti-C-Al system is triggered by a reaction between titanium and aluminum at around 933 K, which is the melting point of aluminum. In the powder blend containing the optimum amount of aluminum, (Ti:C:Al=1:0.95:0.8-1.2), the synthesized Al-Ti intermetallics melted by their heat of reaction, and TiC particles were synthesized successfully. Heating the optimum powder blend with the aluminum ingot, the TiC particle reinforced Al composite was fabricated at low temperature during a short range of time.

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Commercially pure aluminum alloy (A1050) with an ultra-fine grain size was produced by a friction stir process (FSP). The influences of a tool rotation speed on the temperature profile, microstructure and mechanical properties of a friction stir processed (FSPed) zone were also experimentally investigated. FSP was carried out at tool rotation speeds of 560∼1840 min⁻¹. Although the maximum temperature in the FSPed zone increased almost linearly with the tool rotation speed, it was lower than the melting point of the starting material in every condition. The cooling rate of the FSPed zone increased from about 341 to 1473°C·min⁻¹ with the tool rotation speed. In the FSPed zone, a dislocation density was very low and fine equiaxed grains were observed. This grain size increased with the tool rotation speed. It seems that these fine grains resulted from the inhibition of the growth of recrystallized grain, which was formed in the FSPed zone, by the high cooling rate after FSP. It is noteworthy that, for 560 min⁻¹, the grain size decreased to even the submicron level with only a ‘single pass’ of FSP. Although, for 560 min⁻¹, the average hardness of the FSPed zone increased up to about 37% as compared with the unprocessed zone, it decreased with the increase in the tool rotation speed. The tensile specimens, which were processed at 560, 980 and 1350 min⁻¹, were fractured in the unprocessed zone. This result confirms that the tensile strength of the FSPed zone increased with the decrease in its grain size. From these results, it is concluded that FSP is very effective in producing ultra-fine grained materials with excellent mechanical properties. In addition, it is possible to control mechanical properties by varying the maximum temperature and grain size of the FSPed zone with the tool rotation speed.

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In order to encapsulate cobalt nanoparticles into an organic polymer micro-capsule, cobalt and PET (polyethylene terephthalate) polymer have been co-deposited using a PVD technique.
When the incident beams of cobalt and the polymer were perpendicular to the substrate, cobalt nanoparticles were deposited into two layers of polymer thin film. The surface layer contained cobalt particles 10-15 nm in diameter, and the bottom layer contained cobalt particles of just several nm in diameter. The film showed the perpendicular magnetic anisotropy caused by the preferred orientation of the cobalt nanoparticles. The degree of the preferred orientation in structure decreased with an increase in the temperature of the substrate.
When the incident angle of the polymer beam was 80°, the polymer made a scaly deposit on the substrate, and the cobalt nanoparticles deposited were concentrated into scaly polymer deposits. Those scaly particles grew in a direction normal to the substrate. However, the width of the scaly particle grew in a direction normal to the incident plane of the polymer beam. Hcp-Co nanoparticles 3-7 nm in diameter were dispersed uniformly in each composite particle.
The conditions for encapsulating cobalt nanoparticles into micro-polymer capsules were as following: the incident angle of the polymer was 80° and the substrate temperature was 30°C.

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Vanadium-based alloys are usually produced by alumino-thermic reduction of V₂O₅. In order to use it in hydrogen storage alloys, contained impurities such as aluminum and oxygen have to be removed by electron beam purification, increasing the alloy cost by one-order. In this work, we have developed an electro-slag remelting purification method for removing the impurities with low cost. In this electro-slag remelting process, a crude vanadium consumable electrode made by alumino-thermic reduction and flux of CaF₂-CaO-Al₂O₃ are used. By applying high current, the vanadium electrode is partially melted, the contained impurity such as aluminum oxide is removed to the flux and a purified molten metal is dropped to bottom.
Removal ratio of the aluminum oxide is in proportional to the CaO content in the flux. Then, remained oxygen in the metal is removed by remelting with rare-earth metal as a reducing agent. The alloy prepared by this process shows the same hydrogen storage capacity as that prepared using high purity metal. The electro-slag remelting purification method is suitable for mass production with reasonable cost.

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Nano-sized processing is reported to realize distinctive features in physical properties. We found a remarkable microwave absorption property caused by the increase of permeability and permittivity when nanogranulating ferromagnetic metals (Fe) and high electrical resistance ceramics (SiO₂) in the frequency range of GHz. In this paper, we report the microwave absorption properties is effected by the dispersion state of Si-oxides in Fe-SiO₂ nanogranular powder and the improvement of the microwave absorption properties by nanocompositing Fe and SiO₂ is caused by the diffusion between Fe nanocrystal grains and amorphous Si-oxides in MA process.

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The transformation behavior of near equiatomic NiTi alloys were precisely measured by a four-probe potentiometric method in order to investigate the effects of the repetition of the transformation with thermal cycling. Complete and incomplete thermal cycles induce an anomalous increase in electrical resistivity which is attributed to formation of the R-phase. The incomplete thermal cycle is effective in the formation of the R-phase in comparison with the complete thermal cycle. The behavior of the transformation to the R-phase with thermal cycles depends on the composition and it is more difficult to induce and stabilize the R-phase by thermal cycling in NiTi with higher M_s. The characteristics on the effects of the thermal cycles are the shift of the M_s to the low-temperature side and the stabilization of the R-phase, which are taken to be attributable to the accumulation of transformation-induced defects. The precise measurement of the electrical resistivity proved helpful in order to detect the trace of the R-phase and characterize the effects of the thermal cycles.

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The electrochemical characteristics and corrosion behavior of Niiro-colored Cu, colored by a traditional Japanese craft technique, have been investigated. The specimens are colored in a solution containing CuSO₄, artificial malachite powder and alum. The oxidation potential of Niiro-colored Cu is higher than that of untreated Cu, indicating that the corrosion resistance of Niiro-colored Cu is higher than that of untreated Cu. Although the reaction electron number of untreated Cu is approximately two, the number of Niiro-colored Cu is unity in 2-8 pH solutions. The Niiro-colored Cu surface consists of double layers chemically. The thin upper layer is a copper(II) oxide such as CuO and the underlayer is a copper(I) oxide such as Cu₂O. Niiro-colored Cu shows good corrosion resistance when the specimens are exposed at 353 K in 90%RH atmosphere. The oxidation potential of Niiro-colored Cu in a solution containing Cl⁻ of 8.3 pH is higher than that of untreated Cu.

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In order to improve the alkaline corrosion resistance of anodized aluminum, silicon oxide coating film was formed on an anodic oxide film by the sol-gel process using the sol solution, to which a tetraethoxysilane and a multiple alcohol having different vapor pressures were added. The composite films consisted of a porous layer of anodic oxide film filled with silicon oxide and a silicon oxide coating layer deposited thereon. The alkaline duration time of composite films was increased as the repetition number of dip-coating was carried out untill five dip-coating, and the alkaline duration time of composite film prepared by five dip-coatings was about 1.6 times that of the anodic oxide film after the boil sealing. According to the changes of the internal pressure in the vacuum chamber and evacuation time, the amount of exhaust gas from composite film was clearly less than that of the anodic oxide film after the steam sealing and was approximately similar to that of the anodic oxide film before the steam sealing. From the mass spectrometric analysis of exhaust gas, hydrocarbon and water were mainly detected in the exhaust gas from the composite film. The water amount contained in each film was also decreased in the order of the sol-gel composite film<the anodic oxide film before the steam sealing<the anodic oxide film after the steam sealing.

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