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The EU project SmartResilience aims to develop methods for practical assessment of the resilience of smart critical infrastructures (SCIs) in urban environments. The paper will describe an approach applied in the case of the energy supply system of the city of Helsinki, Finland. One selected scenario involves a cold winter period challenging the supply and performance of the city district heating network that provides heating for most buildings of the city. A fire in an underground fuel storage initiates an escalating chain of events to reduce production capacity first in the adjacent plant and then in another heating plant of the network. Simultaneous extended period of high demand during the cold spell will trigger regional cooling in the district heating network, so that elderly and other vulnerable citizens may need to be relocated for safeguarding when they cannot rely on their own back-up alternatives. The scenario implies cascading involvement of city infrastructures and actors beyond the energy supply system. The details will affect the essential aspects, phases and indicators of functionality and resilience, and the effort to improve or optimize resilience. The tools developed for the project have helped to describe, visualize and quantify resilience for these purposes. The results and implications are discussed from the point of view of other plausible threats from extreme weather events or interdependencies in the evolving regional and European energy systems.

Risk-based inspection and maintenance can help to achieve safe and economically viable plant operation by justifying and prioritizing actions, choices and schedules according to the associated risk. To manage the risk, the implemented inspections and maintenance actions aim to limit the probability of failure and its uncertainty. Failure statistics of similar components operating in similar environments may provide fair estimates of the probability of failure, but biased or lacking comparable statistics may require adjustment through additional measurements or expert information. In parallel, inspection and monitoring data can more directly help in assessing the evolution of probability of failure. Presented example is a tubular heat exchanger, with inspection and failure criteria considered for a full life cycle that included multiple inspections by the same inspecting party and equipment. Uneven distribution of in-service wall loss without changes in mechanisms or local loss rates nevertheless required a change of inspection strategy during the life cycle.

In this annual report of the project “Experimentally verified model based predictions for integrity of copper overpack” (PRECO2017) the status of the experimental and modelling activities and results has been summarised up to the end of January 2018. The testing program and related activities have been continued and partly modified to support the assessment and verification of the long term integrity of the protective copper (Cu-OFP) overpack of the canister. To consider more discontinuous uniaxial behaviour, creep tests with stepwise increasing load and stress dips were conducted, and the results were compared with those from normal constant load creep testing. In general, the transients especially from stepwise increase in loading can consume a part of the deformation capacity and shorten creep (or creep-fatigue) life. The relaxation testing programme has continued with cyclic relaxation tests. The relaxation testing aims at developing a relaxation model for the FE calculation. It is expected that with the relaxation model the stress and strain distributions will be different when compared to the FE results with a traditional creep model only. The results of continuing multiaxial (notched bar) creep testing program suggest notch weakening, or life reduction by tensile multiaxiality. The 10.000h testing of a CT specimen from the modified welding (FSW) process with argon protective atmosphere is complete and the specimen is going to be investigated by metallography to study the behaviour of the oxide particles.

The share of energy produced from renewable resources is rapidly growing. Future conventional power plants will increasingly shift from base-load to more fluctuating load-follow operation, to balance the supply and demand in the grid. This will mean more frequent and faster load changes, decreasing minimum loads and more start-ups and shutdowns than assumed in design. The resulting challenges can be severe for effective operation aiming to avoid excessive cost from increased rate of damage to the plant equipment and from increased emissions at part-load and transient operation. At the same time, fuel feedstocks are increasingly diverse, containing e.g. different types of biomass and low rank coals, allowing the use of local resources and reduced dependence on imported fuels. The fuel changes may not be directly visible in operational parameters, but fouling and corrosion tend to increase material wastage and risk of tube leakage, operational problems and unplanned shutdowns. The future roles of thermal power plants will also frame the economic conditions of their survival. This paper aims to describe the challenges and possible solutions for successful operation of flexible power plants.

The performance of materials in critical high temperature components of power and process plants is one of the major technical reasons limiting both the component life and process efficiency. New structural materials can be attractive in principle, but it has been challenging to simultaneously achieve good mechanical strength, oxidation resistance and cost-effective composition in the candidate alloys. The optimal material solutions for a given component depend on multiple factors, but one typical limiting factor is the waterside oxidation resistance at highest operating temperatures and pressures that extend to the supercritical (SC) or even ultra-supercritical (USC) range. To facilitate development of improved alloys for the new demanding applications, the methods of materials modelling can be useful to explore the effects of new ranges of chemical composition and fabrication routes. In the current paper oxidation modelling based on the concept of Cr and Ni equivalents is presented and applied to long term operation of superheaters made of nominally similar 11%Cr steel. The model quantifies the impact of the alloying elements on steam side oxidation to facilitate prediction of the oxide growth according to the alloy composition. The model can be used to predict the effect of variation of particular alloying elements, to explore the effects of alloying modification on performance for alloy development, and for life prediction when life is limited by water/steam side oxidation. The model prediction shows generally good agreement with the observed oxide layer thickness and also with prediction from conventional parabolic expressions when available for the alloy.

The paper highlights the practical aspects of new EU project SmartResilience and its application in Finland. The basic idea of the project is that modern critical infrastructures are becoming increasingly "smarter" (e.g. cities). Making the infrastructures "smarter" usually means making them smarter in normal operation and use, but it has to be checked if these smart critical infrastructures (SCIs) will behave equally "smartly" and be "smartly resilient" also when exposed to extreme threats, such as extreme weather disasters or, e.g., terrorist attacks. Similarly, the question is, if making existing infrastructure "smarter" is achieved by making it more complex, would it also make it more vulnerable? Would this affect resilience of an SCI as its ability to anticipate, prepare for, adapt and withstand, respond to, and recover? These questions are tackled by the project, which plans answer these questions in several steps: by (#1) identifying existing indicators suitable for assessing resilience of SCIs; (#2) identifying new "smart" resilience indicators (RIs) - including those from Big Data; (#3) developing a new advanced resilience assessment methodology based on smart RIs ("resilience indicators cube", including the resilience matrix); (#4) developing the interactive "SCI Dashboard" tool; and (#5) applying the methodology/tools in eight case studies, integrated under one virtual, smart-city-like, European case study. One of these case studies will take place in Finland, dealing with modern systems of energy supply.

Recurring waterwall leaks have been observed in a coal-fired boiler where subsequent inspections have shown through-wall internal oxidation, mostly at butt welds of 16Mo3 boiler tubes. In several cases the oxide had retained a thick pit plug even after local penetration of the tube wall. The original initiation site is no longer visible as it was removed by oxidation, but away from the most severe damage the internal oxidation appears to have initiated immediately downstream after a protruding weld root. This location, estimated oxidation rate and oxide appearance suggest that the mechanism is related to locally intensive heating in addition to flow turbulence. In the damage history of the same boiler wall, the first comparable leaks were recorded at shop welds with strongly protruding root shape, presumably inducing particularly strongly turbulent flow, and even then only after long term service. The most recent failures, however, occurred at normal repair welds or even within parent material, and after much shorter time in service. The characteristic features and causative factors of the tube failures are discussed in the paper, based on the available evidence and experience from operation and maintenance.

Steam driven turbogenerator units with size up to nearly 2 GW provide large fraction of the electric power in the world. Steam turbines may show good reliability, but their disturbances tend to be associated with significant cost so that preventive and corrective maintenance is generally easily justified. However, it is often not simple or convenient to implement repairs or replacements when unexpected damage is found at the time of opening the casing. This is because many turbine components are large in size or unique by design, and possibly only available from a limited number of suppliers and even then with a long lead time. Fortunately alternative measures can be often taken, and two types of steam turbine damage are considered here: steam erosion of inner casings and other stationary components subjected to flowing wet steam, and steam leaks of the main flange surfaces. From the user point of view, it may matter that much of the manufacturers' knowledge on turbines resides far away, partly because unlike some decades ago, the number of manufacturers in the world is now small. Together with low number of comparable machines, this may to some extent limit the local availability of expertise and experience for successful maintenance. It helps however that many features such as materials and operating conditions in steam turbines are not particularly daunting in the required knowledge accumulation, and that today the manufacturers may agree to offer help in the turbine maintenance regardless of the original manufacturer. Challenges may appear when outsourced turnkey maintenance implies shipping of major turbine sections or components to factory, to correspondingly extend the shutdown period because of the geographic distance involved, even if the maintenance project were to stay within schedule. It is demonstrated in the paper that successful on-site repair is often a viable and attractive alternative to conventional full repairs or replacements.

Risk-based inspection (RBI) has become common approach to support asset management in e.g. refineries, chemical industry in general and a few other industrial sectors. Although there are regionally established traditions to use RBI also in power plants, recently the interest has been spreading to include a widening base of common power plants. This is partly due to increasingly established standard practices, tools and availability of the techniques also for smaller scale users, and partly due to the generally established benefits and needs for safety and optimization of resources. In this paper we show how RBI was applied in a small scale for the main steam line of a CHP (combined heat and power) plant in Finland. The experience showed some typical features of initiating RBI, for example how important and beneficial (although at first somewhat tedious) it is to systematically gather and handle the required background information of design, fabrication, inspections, maintenance and operational history for RBI of an ageing plant. In the case of the example plant, the steam system had been significantly modified because of process changes, and the level of documentation was not equally thorough everywhere. Existing conventional guidelines and experience were found to be useful to support relatively lean RBI by suggesting typical areas of elevated probability of failure and therefore recommended areas to be inspected, for example at welds of large branches, locations of high strains in thermal system displacement or deviations in the function of the piping supports. Observed indications in the inspections were largely consistent with expectations and only resulted in repairs within the planned outage period. The resulting risk-based (or -informed) inspection and action plans are the main outcomes of the RBI exercise, aiming to produce the best justification and return on the maintenance investment, and to support safe operation and long-term lifecycle performance of the plant.

Risk-based approaches can help in selecting and prioritizing future choices and schedules so that decisions are justified by the associated risk. The paper will give examples of applications from conventional power plants, where degrading physical condition can increase the risk of failure and decrease asset value: a single detailed example illustrated the approach, which is also anchored in the new European standard EN 16991 (prEN 16991:2016) and applied in large-scale industrial projects world-wide. To manage the risk, implemented inspections and maintenance can help to limit the probability of failure (PoF) and its uncertainty. Failure statistics of similar components operating in similar environments may provide fair estimates of PoF, but biased or lacking comparable statistics may require adjustment through e.g. additional measurements or expert information for the application. In parallel, inspection and monitoring data can more directly help in assessing the evolution of PoF. An example of the latter is a power plant heat exchanger, with inspection and failure criteria considered for a full life cycle that included multiple inspections by the same inspecting party and equipment. Uneven spatial distribution of in-service wall loss without changes in mechanisms or loss rates at a given location nevertheless required a change of inspection strategy during the life cycle.

This report describes candidate resilience issues and indicators to be used when assessing, predicting and monitoring resilience of Smart Critical Infrastructures (SCIs). A total of 233 candidate issues and 1264 indicators are provided for various threats, SCIs and the five phases of the resilience cycle used in the SmartResilience project. Structured candidate issues and indicators are mainly provided by collecting existing issues/indicators from the risk, safety, security, crisis management, business continuity and similar domains, considering resilience as an "umbrella". The main intended reader is the person (user) - within a city or area, or a specific SCI - who is responsible for performing the resilience assessment, prediction or monitoring, including carrying out necessary calculations. This can be an in-house person performing e.g. selfassessment, or it may be an external assessor. The issues and indicators presented in this report and stored in the SmartResilience database are candidate issues and indicators. Each user is responsible for finding a relevant and complete set of issues and indicators for his/her own case study. The report may be used together with the SmartResilience methodology and the Guideline for assessing, predicting and monitoring resilience of SCIs developed in the SmartResilience project.

The report discusses the challenges posed by four types of threats -terrorist attacks, cyber attacks, extreme weather and social unrest- on the SmartResilience case studies. The way this analysis was conducted was by assessing these threats using a 5x5 framework matrix. The two axes of the matrix were phases (understand risks, anticipate/prepare, absorb/withstand, respond/recover, adapt/learn) and dimensions (system/physical, information/data, organizational/business, societal/political, cognitive/decision-making). Each individual matrix block was discussed by subject experts who identified specific challenges and implications for each matrix element and rated its relevance (high, medium, low). In terms of the results, the system/physical dimension received the highest number of important challenges. Overall, the most important singular element was to understand risks in the organizational/business dimension. The least importance was attributed to the adapt/learn phase.

Tubular heat exchangers (HE) are common and often physically large in power and process industries, e.g. in steam generators, boilers, preheaters, furnaces and many other essential applications to transfer heat of process fluids. HE performance is important for managing the overall efficiency, economy, life and predictable maintainability of the process & plant: typical investment cycle ~ 20-60 years, opportunity for planned inspections and maintenance once every ~ 1-6 years. Intervening damage or failures will reduce equipment life and increase the risk of unplanned shutdown/maintenance, business interruptions and high cost recovery. Systematic countermeasures include risk-based methods, such as risk-based inspections (RBI).

Riskipohjainen tarkastus (RBI) tahtaa riskien mukaan priorisoituun tarkastusten kohdentamiseen ja ajoitukseen rakenteissa etenevan tai epaillyn vaurion (ikaantymisen) varalta. Asianmukainen tarkastus vahentaa arvioitua riskia pienentamalla vauriotodennakoisyytta tai ainakin sen epavarmuutta. Tassa tyossa on kasitelty esimerkkina kaytetynkaukolammonvaihtimen tarkastustietojen hyodyntamista RBl-nakokulmasta. Lammonvaihdinputkien tarkastus- ja vauriokriteereja on tata varten tarkasteltu yhden elinikasyklin eli uudelleenputkitusten valiselta ajalta, johon on sisaltynyt kuusi saman ta.rkastustoimittajan ultraaanitarkastusta. Lammonvaihtimen putket ohentuivat kaytossa epatasaisesti, mutta eivat hallitsemattomasti putkien ulkopinnan pisaraeroosion vaikutuksesta. Tarkastukset keskittyivat lyhimman elinian kokeviin alle tuhanteen putkeen, joista kasvava osa tulpattiin elinikasyklin kuluessa vuotojen ja alasajojen valttamiseksi. Putki- ja aluekohtaisesta ohenemisnopeudesta huolimatta maksimiohenemien jakaumat olivat yhdenmukaisia ja oheneminen eteni ennustettavasti samalla mekanismilla ja odotetuissa mittausvirherajoissa. Arvion mukaan kaytetyt tarkastus- ja toimenpidekriteerit ovat olleet asianmukaisia seka ennakoivan kunnossapidon eli oheneman ja tulppausten kannalta etta vaurioriskin eli kayttokeskeytysten(vuotojen) nakokulmasta. Onnistumisia kuvaa se, etta ensimmaista vuotoa seuranneella toimenpideohjelmalla uusia vuotoja ei esiintynyt seitsemaan vuoteen.

The ferritic-martensitic steel P91 (X10CrMoVNb9-1) is widely used in high temperature steam systems of power plants, and it is a candidate material for Gen-IV reactors. In comparison to austenitic steels, thick-wall P91 has relatively attractive mechanical and physical properties combined with resistance to stress corrosion cracking in water-steam environments. This study aimed to explore the combined cyclic, creep and relaxation behaviour of P91 material up to a component wall thickness of 60 mm. Uniaxial specimens were subjected to cyclic loadings with periodic forward creep or relaxation at peak stress. The results indicate that prior creep or intermediate relaxation periods up to 72 h will influence the subsequent cyclic softening of P91, but do not significantly reduce the cyclic life. In contrast, prior cycling has a detrimental effect on the subsequent creep life. A simplified creep-fatigue model is shown to predict life better than usual code-based approaches for cyclic service of P91 steel. Improved verification of all models would benefit from the availability of more extensive long-term data on P91 steel.

For higher efficiency and competitive overall performance, it would be an advantage to be able to safely exceed the highest operational values, currently up to about 600-620°C/25-30 MPa in supercritical (SC) boiler plants. Under such operating conditions the oxidation resistance in SC water tends to limit the potential for further improvement of efficiency. The way to increase the oxidation resistance of traditional austenitic boiler tubes e.g. TP 347H is to do additional cold work on the boiler tube inner surface. In the current paper the effect of cold work on the oxidation resistance of TP347H and TP347HFG has been evaluated by shot peened samples with different parameters and subjecting those samples to supercritical oxidation exposure. The results show an improvement in the oxidation resistance of the alloys, especially in the large grained alloy TP347H. Also the uniformity of the deformation layer was seen to have an influence on the oxidation resistance, since the oxide nodules start to grow at locations with the thinnest or no deformation layer.

Steam turbine is a rotating machine and therefore fatigue is an important damage mechanism to consider already in turbine design, and it is remains necessary to consider the risk of initiation and growth of fatigue cracks in the later in-service inspection and maintenance activities. With successful design and fabrication, and operation within the intended limits, the expected fatigue life is relatively long but nevertheless finite and variable. The design features and materials of steam turbine blades are generally well established, and conventional methods of inspection and maintenance are widely applied to monitor and limit the evolution of in-service damage. As the fatigue performance of a blade is simultaneously sensitive to material characteristics, structural/loading geometry and surface condition, the combined potential range of these factors explains in principle the observed wide scatter in turbine blade life. In this paper, examples on reduced blade life are discussed based on recent experience with a case example.

Risk-based inspection (RBI) can offer justified priorities in timing and targeting of in-service inspections and maintenance action for power and process plants. For this purpose, recommended procedures and tools are increasingly supported by the evolving standardization on risk based assessments and RBI. Successful RBI generally requires availability of background data on design, fabrication, operation and maintenance history, evaluation of the current condition and its expected deterioration in systems and components of interest, and expertise of the RBI team to conduct the assessments. This paper aims to show some RBI related observations, modelling and experiences when considering the accumulating damage, life-limiting mechanisms and failures in high temperature components of thermal power plants. An example is shown from a pilot scale application of RBI on a steam system of a combined heat and power (CHP) plant after more than 200 000 h of service. The implications and experiences are discussed in terms of the implemented inspection and maintenance actions, and perceived benefits of RBI.

Ultrasonic testing is the main tool to inspect the structural integrity of primary circuit components in nuclear power plants (NPPs) during in-service inspection (ISI). In order to validate an inspection method and to train inspectors, reference flaws are needed. However, there are not enough real flaws available to be used for these purposes so artificial flaws must be used. Ultrasonic response from an artificial flaw must be representative enough so that it can be used as a reference flaw. Otherwise this could lead to a false result during an ISI. Unfortunately ultrasonic testing is highly dependent on the geometry of the component, the flaw type and the material in which ultrasound propagates. Therefore numerous flaws are needed to cover the probable flaw types, sizes and locations. The aim is to study artificial flaws and acquire wider knowledge on ultrasonic indications from artificial flaws in austenitic stainless steel weld and to compare them to the results from CIVA simulation. The study focuses on notches made by electrical discharge machining (EDM). EDM notches were chosen, since they represent a rough estimate of a crack type flaw and they are fairly quick and easy to manufacture.

Elastic pipe stress analyses are frequently performed to check that the stresses in pipe systems are allowed. For operation in the creep range such analyses may describe the stress distribution in the beginning but not after creep relaxation starts to take place. In the present work effects of creep are considered. A pipe system of P22 material that had been analysed by software for elastic analysis was also modelled for creep. By use of tabled creep data the following was studied: - Creep stress relaxation in the pipe system, - The effects of starts and stops on stress and strain distributions, - Creep in T-pieces with super imposed system stresses from the pipe system creep analysis. The creep properties of a virgin weld and a service exposed weld were determined by impression creep testing. The tests were performed in the parent metal, different parts of the HAZ and the weld metal. A weld was included in the model and analysed with these data. Resulting creep strain distributions from analyses with tabled and present creep test data were compared to each other and also to actual creep damage that was observed in components from the system.

The understanding of the creep behavior of nuclear fuel claddings is essential to predict safely and reliably the thermal performance and mechanical integrity of fuel rods. Fuel cladding tubes experience a range of changing conditions during their reactor life, further complicating the analysis. Today's nuclear reactors widely use zirconium alloys as fuel cladding material. Zirconium alloys exhibit anisotropic creep properties and their creep behavior depends significantly on the material condition. As for envisaged Gen-IV reactors, modified austenitic stainless steels and ODS alloys are candidate materials for claddings because of higher temperatures expected in operating conditions. This paper describes the research activities related to the creep behavior of cladding materials carried out at VTT. These activities include experimental research using the newly developed Pneumatic Loading Apparatus (PLA), which is capable of testing the steady state and transient creep properties of fuel cladding specimens with internal pressure of up to 700 bar and an additional axial force of up to 4 kN in tensile or compressive direction. Furthermore, creep models for cladding materials are being developed using viscoelastic modelling approach and Logistic Creep Strain Prediction (LCSP) method.

Different types of corrosion phenomena present a threat for economical, uninterrupted and safe operation of both conventional and nuclear power plants. Many types of corrosion damage are induced by impurities that tend to accumulate in crevices or beneath corrosion product deposits. Especially important phase for corrosion protection is during different transitions, shut-downs and at two-phase regions. Several efforts for decreasing general corrosion rate and thereby also corrosion product accumulation on power plant surfaces have been done by changing the plant water chemistry. One very promising protecting method is treating systems with film-forming amines (FFA), such as octadecylamine (ODA). FFAs form a thin, some nanometers in thickness, film on metallic surfaces. Application of ODA decreases the rate of flow assisted corrosion (FAC) in the feed water line and thus reduces the amount of iron oxide that is available for deposition. ODA has also been observed to decrease the amount of crevice corrosion and stress corrosion cracking by hindering the enrichment of chloride ions and changing electrochemical properties of the surface. Recent studies at VTT show that at high temperatures (T=228-300°C) under ammonia water chemistry, ODA reduces carbon steel corrosion rate by a factor of three and that the once-formed film also remains stable at surfaces at high temperatures.

Nuclear power plant piping systems exhibit dynamic behaviour, and piping supports keep the displacements of the pipes within acceptable limits. The aim of the research is the development of a simplified way to take into account the nonlinear displacement behaviour of the supports in linear dynamic piping analyses. The research was started as a Master's thesis with focus on supports with gaps and friction and was further continued regarding supports with gaps. The linearization procedure and methods are found in literature and they were further developed in this study. The goal is to represent the nonlinear system as accurately as possible by an equivalent linear system. The linearization procedure was investigated in time-domain and frequency-domain analyses using simplified piping systems. Frequency-domain is of particular interest as nonlinearities cannot be incorporated into classical mode-based methods. Equivalent linear systems were determined for the selected load cases and comparison was made between the equivalent linear and original nonlinear systems, time-domain and frequency-domain linearization results and three different linearization methods. Correspondence between equivalent linear and original nonlinear systems was not found accurate, time- and frequency-domain linearization gave similar results and different linearization methods resulted in equivalent linear systems very close to each other.

Slow strain rate tests on several SCWR candidate materials were done over the last 10 years at VTT. The test materials were austenitic stainless steels with 15-23% Cr and 10-15% Ni and oxide dispersion strengthened ferritic/martensitic steels with 12-20% Cr. The tests were performed in supercritical water at 250 bar in the temperature range of 500-650oC with 100-150 ppb dissolved oxygen. With regards to the stress corrosion susceptibility and ductility, the best performer in the tests was AISI 316L steel. On the other hand, large heat to heat variation can be expected: another heat of 316L was very susceptible to intergranular stress corrosion cracking. DL-EPR test revealed that at least some heats of low carbon 316 are subject to fast thermal sensitisation at 550oC in supercritical water.

The Finnish concept of high activity nuclear waste disposal is based on deep geological storage in copper canisters with cast iron inserts. The development of disposal concept and final disposal in Finland is managed and organised by Posiva Oy. Disposal canisters will be embedded in Olkiluoto bedrock at a depth of approximately 400 metres. Therefore it is essential to inspect the canisters with non-destructive testing (NDT) methods as well as possible before the final disposal. The lid of the copper disposal canister for high activity nuclear waste is sealed with a weld. Before accepting the canister to the final disposal the weld is planned to be inspected by four non-destructive testing methods. These methods are ultrasonic testing (UT), radiographic testing (RT), eddy current testing (ET) and remote visual testing (VT) using cameras. The copper overpack and the lid are also inspected with multiple NDT methods; UT, ET and VT. The nodular cast iron insert is inspected with UT and VT. In this paper the four NDT inspection methods (UT, RT, ET, VT) for inspection of different parts of the disposal canister are presented in brief. All information in this paper is collected and summarised from public reports and from the procedures of each method and inspection records. All of the four NDT methods detect defects in slightly different directions and based on different physical principles. The four methods are therefore supplements to each other in inspection of different parts of the disposal canister.

Improved endurance in fatigue tests with intermediate holds and annealing to roughly simulate steady state normal operation between fatigue transients in nuclear power plant (NPP) components has been reported [1]. Similar effect is expected in plant components - e.g. in a pressurized water reactor (PWR) surge line or in pressurizer spray lines. Quantification of this effect is a topic of continued research on fatigue performance of niobium stabilized austenitic stainless steel. Holds affect cyclic stress strain response. Stress amplitude, tensile mean stress and apparent elastic modulus are increased immediately after a hold, while decreased by cycles in between. A decrease of volume is measured during hot holds at zero external stress and a stress is generated, when applying a constant temperature hold in strain control. This all suggest cyclic accumulation of lattice defects and recovery during holds. Recovery may occur through thermally activated dislocation migration together with diffusion, grouping and annihilation of lattice defects. A mechanism informed explanation and thermodynamic model is sought for to improve transferability of laboratory data to real plant components and accuracy of fatigue usage assessment. Anticipated mechanisms behind gradual changes in material responses are discussed in relation to quantitative effects of holds.

When aiming to decrease of greenhouse gas emissions and higher cost-efficiency, power plants would benefit from increased efficiency. Advanced power plants are aiming for up to 750°C steam temperatures. Higher steam temperatures will set higher requirements to tube materials, as especially difficult fuels can cause severe corrosion conditions. Biomass and waste include chlorides, sulfates and heavy metals, such as NaCl, KCl, K2SO4, Pb and Zn, that can substantially accelerate the corrosion even at lower temperatures. Corrosion protection properties of thermal spray coatings were validated in a co-fired boiler using biomass, coal and solid recovered fuel. Material testing was performed with a temperature controlled probe at 550 and 750°C for 3000 hours. Corrosion performance of six high velocity oxy-fuel (HVOF) coatings, FeCr, Ni46Cr, Ni26Cr, NiCrAlY and Al2O3, were evaluated, and a ferritic steel T92 and a nickel based alloy 740H were applied as reference materials. Maximum corrosion rates varied from 0.01 mm/y of Ni-based coatings to 0.4 mm/y of T92 at 550°C and from 0.1 mm/y of A740H to 0.5 mm/y of Fe-based coating at 750°C. The nickel-based coatings and the ceramic Al2O3 coating gave excellent protection to the ferritic steel at 550°C and sufficient protection at 750°C.

Presently most structural integrity assessment procedures still allow the use of Charpy-V notch impact tests as a measure of fracture toughness. The use is generally made through some more or less reliable correlations between standard Charpy-V notch energy and fracture toughness or tearing resistance. Common for the present correlations is that very few studies have been made with respect to their usability to Ultra High Strength Steels (UHSS) with yield strengths in the excess of 900 MPa. This is the topic of this work. Focussing on novel directly quenched high performance steels, the applicability of the Master Curve methodology with special emphasis on the temperature dependence is examined and the validity of the standard T0-TCV28J transition temperature correlation is checked. Improvements to the criteria are proposed for further considerations. Additionally, a new simple procedure for converting sub-sized Charpy V data to full size specimens, that is in line with BS 7910, is presented. The new interpretations of the Charpy V test presented here enable an extension of present design rules like the ones in EN 1993-1-12 (2007) to steel strengths well beyond 1000 MPa. Providing a sufficient toughness for the steel is up to the steel manufacturer, but there is no basic reason why UHSS cannot be used based on an identical assessment procedure as for presently accepted steel strengths. Only 2 equations in EN 1993-1-12 (2007) needs to be changed, and the sub-size specimen conversion procedure needs to be adopted.

Alloy 690 is used in critical components of nuclear power systems. It has a high intergranular stress corrosion cracking (IGSCC) resistance, but questions remain concerning its long-term primary water stress corrosion cracking (PWSCC) resistance during the service life of pressurized water reactor (PWR) components. To study the effect of thermal ageing, four conditions of Alloy 690 (solution annealed, coldrolled and/or heat-treated) were aged at 420, 475 and 550 °C for 10 000 h and characterized by SEM, EBSD and nanoindentation. Thermal ageing of Alloy 690 triggered intergranular (IG) carbide precipitation and all conditions showed evidence of short-range ordering (SRO), with the start of a disordering reaction at 475 °C. Prior heat treatment induced ordering prior to thermal ageing, as compared to water-quenched specimens. IG carbide precipitation increased with increasing ageing temperature, as well as diffusioninduced grain boundary migration (DIGM).

Crack-like defects were found in a low-alloy 2.25Cr-1Mo-0.25V steel multipass welded heavy wallthickness component prior to its usage. After welding, the component had been subjected to local Intermediate Stress Relief (ISR) heat treatment at 600-650°C, with the aim at removing diffusible hydrogen and enhancing partial tempering of the weldment microstructure before the final PWHT. The objective of the present paper was to investigate the actual fracture micromechanism of the discovered damage associated with the manufacturing stage of the component, in order to explain the inherent causes of failure. The metallographic and fractographic studies demonstrated (i) cracks propagating through the weld solidification structure as quasi-cleavage fractures, (ii) the presence of micro-cracks at thereby 'opened' solidification boundaries, as well as (iii) occasional appearance of ductile 'ridges' at the fracture surface; all that were characteristic of hydrogen-induced cold cracking. In line with this, Vickers hardness measurements revealed maximum hardness as great as 381-382 HV and 371-378 HV in cases of the CGHAZ and weld metal microstructures, respectively. Furthermore, hardness traverses in the weld thickness direction revealed higher hardness values in the weld intermediate thickness than closer to the surface or the root, which was ascribed to inadequacy of the thermal effects of the ISR heat treatment. The occurrence of hydrogen cracking was attributed to simultaneous co-existence of several adverse factors: (i) excessively high weldment hardness, (ii) accidentally high initial hydrogen content of the applied SMAW electrode and (iii) inherently high structural rigidity and restraint of the component.

The probability of detection (POD) curves are often used to estimate the capability of a non-destructive testing (NDT) method to find flaws. However, the POD information typically requires very many expensive measurements, so much effort can be spared by obtaining comparable data from computer simulations. In this study CIVA ultrasound simulation software was used to generate 150 simulations from ultrasonic inspection of a nozzle. The results were used for training of neural networks that were then used to generate POD-curves. The results of POD-calculation where presented as a function of flaw characteristics and location in the component. The results show that the smallest detectable flaw size can be very different in different parts of the component. The smallest and largest detectable flaws differ by more than an order of magnitude depending of the flaw location. The benefits and limitations are discussed with respect to the used methodology that combines ultrasound simulations with metamodeling and POD-calculations.

The Conference aims to provide an updated review on current experience and emerging technology, tools and solutions for managing the condition and life of materials, components and facilities in power and process plants, including the nuclear side. At a time of a clear impact from public energy policies, turbulent fuel market, and disruptive technology, Baltica X is addressing the technical options to support the operational economy of both new and ageing plants. Venues: 7.-8.6.16 M/S Silja Symphony, 9.6.16 Radisson Blu Royal Hotel, Helsinki

In power plants, a reliable operation of the cooling water circuit is of primary importance. Where natural water is used for cooling, corrosion and biofouling may pose challenges to materials integrity. The brackish water in Baltic sea is characterized by a relatively low salt content and unique microbial communities, thus the material challenges may be different from those occurring in sea water. In this study, biofouling on and corrosion behaviour of stainless steels AISI 304L (EN 1.4307), AISI 316L (EN 1.4404) and 254 SMO (EN 1.4547) were investigated in a pilot scale cooling water circuit using brackish water of Baltic sea, obtained from Tvärminne zoological station. The pilot was in operation for 8 weeks, during which open circuit potential recording (OCP) was performed. Other electrochemical methods, cyclic anodic and cathodic polarization measurements and electrochemical impedance spectroscopy (EIS) were applied before and at the end of the pilot experiment. The biofilm coverage was calculated on surfaces. In this paper the obtained results are presented and discussed.