Service Life Assessment Research Articles

Input Value Correlation in Chloride Ion Ingress Modelling and Concrete Structures Reliability

The assessment of service life of a structure can be performed via mathematical modelling – either analytical or numerical and it can be viewed as a necessary pre-requisite for life-cycle engineering decisions. Many works concerning the modelling and testing of degradation effects for engineering systems are reported in the literature. The present paper discusses the degradation modelling of reinforced concrete structures and concentrates on the damage they sustain due to chloride ingress, namely a special aspect: the influence of statistical correlation among input variables on the reliability.

A Probabilistic Study on Hydraulic Conductivity of Concrete at Mesoscale

Hydraulic conductivity of concrete can be used as a key indicator in assessment of service life of concrete structures. In this paper, a probabilistic investigation on hydraulic conductivity of concrete is conducted, allowing for variation in hydraulic properties of concrete constituents. Concrete is modeled as a three-phase composite at mesoscale, consisting of mortar, aggregates, and the interfacial transition zone (ITZ). A finite element (FE) method is developed to calculate the hydraulic conductivity of concrete, which is then verified using available experimental results. Based on a large pool of samples generated from Monte Carlo simulation, a conceptual model relating hydraulic conductivity of concrete to aggregate volume fraction ratio and hydraulic conductivity of mortar and the ITZ is proposed. It is shown from the probabilistic-based sensitivity analysis that hydraulic conductivity and thickness of the ITZ are among the most influential factors affecting the bulk hydraulic conductivity of concrete. It is also shown that for high aggregate volume fraction ratios, due to increasing volume of the ITZ, the coefficient of variation of hydraulic conductivity can be as high as 0.36.

Fatigue lifetime modeling of oxide/oxide composites

The assessment of service life of composite thermo-structural parts is a primary issue for the aeronautic industry. To this end, a unified damage model for woven composites undergoing both static and fatigue loadings is presented here. Its specificity resides in its rate damage evolution law, which enables to predict the behaviour of the material under cyclic or random fatigue loadings.

Elastic, plastic, fracture analysis of masonry arches: A multi-span bridge case study

Abstract In this work a comparison is presented between elastic, plastic, and fracture analysis of the monumental arch bridge of Porta Napoli, Taranto (Italy). By means of a FEM model and applying the Mery’s Method, the behavior of the curved structure under service loads is verified, while considering the Safe Theorem approach byHeyman, the ultimate carrying capacity of the structure is investigated. Moreover, by using Fracture Mechanics concepts, the damage process which takes place when the conditions assessed through linear elastic analysis are no longer valid, and before the set-in of the conditions established by means of the plastic limit analysis, is numerically analyzed. The study of these transitions returns an accurate and effective whole service life assessment of the Porta Napoli masonry arch bridge.

Remaining Service Life Assessment of the Effect of Existing Defects on Turbine Rotors

Present-day approaches to problems of substantiating the possibility of further operation of power equipment after long accumulated operating time in the presence of defects and deviations from the requirements of the standards are presented for the example of rotors of powerful turbine generator sets. The serviceability of the structure for an extended period is confirmed on the basis of works based on a calculated assessment of safety factors according to various limit states criteria.

Calculation of low-cycle fatigue in accordance with the national standard and strength codes

Over the most recent 15 years, the Russian power industry has largely relied on imported equipment manufactured in compliance with foreign standards and procedures. This inevitably necessitates their harmonization with the regulatory documents of the Russian Federation, which include calculations of strength, low cycle fatigue, and assessment of the equipment service life. An important regulatory document providing the engineering foundation for cyclic strength and life assessment for high-load components of the boiler and steamline of a water/steam circuit is RD 10-249-98:2000: Standard Method of Strength Estimation in Stationary Boilers and Steam and Water Piping. In January 2015, the National Standard of the Russian Federation 12952-3:2001 was introduced regulating the issues of design and calculation of the pressure parts of water-tube boilers and auxiliary installations. Thus, there appeared to be two documents simultaneously valid in the same energy field and using different methods for calculating the low-cycle fatigue strength, which leads to different results. In this connection, the current situation can lead to incorrect ideas about the cyclic strength and the service life of high-temperature boiler parts. The article shows that the results of calculations performed in accordance with GOST R 55682.3-2013/EN 12952-3: 2001 are less conservative than the results of the standard RD 10-249-98. Since the calculation of the expected service life of boiler parts should use GOST R 55682.3-2013/EN 12952-3: 2001, it becomes necessary to establish the applicability scope of each of the above documents.

Fatigue limit state design of fast boats

Typically, the dominant load for the structural design of a planing hull is slamming, while sailing fast at head seas. The slamming is a violent fluid structure interaction, where dynamics, hydro-elasticity, and nonlinear structural effects may be important. Considering these effects in a rational design may reduce the scantlings as compare to design by rules, which assess the scantlings by applying a quasi-static design pressure and linear beam theory. More substantial reduction of the scantlings is expected in a limit state design, where extreme loading conditions and flexible structure increase the importance of hydro-elasticity and non-linearity. While applied rules specify allowable stresses that typically provide a service life of 20 years, without the need to check for fatigue; rational limit state design must incorporate the Fatigue Limit State (FLS). This paper presents a rational limit state design method for planing hulls, which apply hydro-elastic nonlinear dynamic structural analysis, to assess the fatigue service life, based on an operation plan specified by the client. The method integrates design rules with direct analysis of fluid-structure interaction and principles of representation of random sea, to a practical design procedure. Furthermore, a parametric analysis is applied to provide a database of 450 cases that may be used by designers for the assessment of fatigue service life in a practical range of geometrical parameters and service conditions. A design example demonstrates the potential of the method to reduce the scantlings.

Multiple linear regression and fuzzy logic models applied to the functional service life prediction of cultural heritage

Abstract In this research, a proposal for the assessment of the functional service life of built heritage applying statistical tools is described. A fuzzy inference system is applied in order to establish a ranking in terms of functional service life for the built heritage, thus allowing prioritizing the maintenance and preventive conservation actions in homogeneous groups of buildings, and optimizing the costs involved in maintenance operations. The functionality of a sample of 100 parish churches was evaluated. However, the selection of maintenance strategies for buildings is usually a multiple criteria decision-making problem, encompassing various variables and constraints. Therefore, a multiple linear regression analysis is applied in order to rank the variables in terms of influence in the serviceability estimation of heritage buildings. Currently, social, environmental and economic reasons are raising concern about the durability and functional service life of heritage sites. The results obtained in this study are useful to researchers and stakeholders responsible for the maintenance of historical buildings, since they allow reducing their probability of failure. The preventive maintenance programs can be considered as a cost-effective and environmentally sustainable option to extend the serviceability of heritage buildings.

An end of service life assessment of PMMA lenses from veteran concentrator photovoltaic systems

The optical performance of poly(methyl methacrylate) lenses from veteran concentrator photovoltaic modules was examined after the end of their service life. Lenses from the Martin-Marietta and Intersol module designs were examined from the “Solar Village” site near Riyadh, Saudi Arabia, as well as the Phoenix Sky Harbor airport, followed by the Arizona Public Service Solar Test and Research (APS-STaR) center in Tempe, Arizona. The various lens specimens were deployed for 20, 27, and 22 years, respectively. Optical characterizations included lens efficiency (Solar Simulator instrument), material transmittance and haze (of coupons cut from veteran lenses, then measured again after their faceted back surface was polished, and then measured again after the incident front surface was polished), and direct transmittance (as a function of detector's acceptance angle, using the Very Low Angular Beam Spread (“VLABS”) instrument). Lens efficiency measurements compared the central region to the entire lens, also using hot and cold mirror measurements to diagnose differences in performance. A series of subsequent characterizations was performed because a decrease in performance of greater than 10% was observed for some of the veteran lenses. The optimal focal distance of the lenses was quantified using the Solar Simulator, and then correlated to lens curvature using a recently developed measurement technique. Surface roughness was examined using atomic force microscopy and scanning electron microscopy. Facet geometry (tip and valley radius) was quantified on cross-sectioned specimens. Molecular weight was compared between the incident and faceted surfaces of the lenses.

Creep test with use of miniaturized specimens

Application of the mini samples methods is very common especially for residual service life assessment of the components operating in the energy sector. Residual lifetime of operating device can be evaluated using standard tests, but these usually cannot be performed due to limited material amount that can be extracted from the components. It is possible to use in these cases a semi destructive sampling of materials and testing methods employing miniature specimens. This article deals with comparison of the creep results obtained with the use of on standard test bars and sub sized samples such as Small Punch Test and newly proposed miniature samples that are axially loaded. The experiment was performed on steam line steel CSN 15 128 after operation. Emphasis was put to practical use of the test results and therefore residual life was assessed with the use of standard and new mini specimens. The results obtained for standard and mini samples exhibit very good agreement without necessity of any correlation as in the case of SPT and thus much more straight forward approach can be applied even for “unknown materials”.

Machine learning for durability and service-life assessment of reinforced concrete structures: Recent advances and future directions

Abstract Accurate service-life prediction of structures is vital for taking appropriate measures in a time- and cost-effective manner. However, the conventional prediction models rely on simplified assumptions, leading to inaccurate estimations. The paper reviews the capability of machine learning in addressing the limitations of classical prediction models. This is due to its ability to capture the complex physical and chemical process of the deterioration mechanism. The paper also presents previous researches that proposed the applicability of machine learning in assisting durability assessment of reinforced concrete structures. The advantages of employing machine learning for durability and service-life assessment of reinforced concrete structures are also discussed in detail. The growing trend of collecting more and more in-service data using wireless sensors facilitates the use of machine learning for durability and service-life assessment. The paper concludes by recommending the future directions based on examination of recent advances and current practices in this specific area.

Wedge Gate Valves Selected during Technological Pipeline Systems Designing Service Life Assessment

Wedge gate valves are widespread in petroleum refining industry. Manufacturers assign resources based on the valve body calculation results under the current regulatory and technical documentation. Previous studies have determined that the wedge gate valves fail before the appointed time. In some cases wedge gate valves cease to provide the locking tightness. In this regard, there was a need to adjust he wedge gate valves technical resource with account for the wedge resources, changing under the operating parameters influence.Hydrodynamic calculations were performed taking into account technological parameters using FLOWVISION. Based on these results, wedge stress-strain state (SSS) calculations were performed using FSI (fluid-structure interaction) technology. On the basis of SSS assessment the wedge number of cycles to failure was determined using a FE-SAFE module.The wedge SSS calculations ODB-file were imported to FE-SAFE module. The set calculation parameters: the dimension of physical quantities, the wedge metal physical and chemical properties, loading cycle. After calculating the wedge hooks number of cycles to failure were obtained.The calculation results showed that the wedge gate valves technical resource is primarily affected by the operating parameters such as the flow rate and pipeline system pressure. The tested valves resource values are less than those indicated by the manufacturer. The results show the need to adjust the valves assigned resource taking into account the operating parameters influence on the wedge.

Comprehensive rotor service life study for high & intermediate pressure cylinders of high power steam turbines

The paper provides a comprehensive scheme for assessment of the residual service life and extension of operating life of steam turbine rotors with expired fleet service life. The residual service life of high temperature rotors for high & intermediate pressure cylinders of К-200-130-3 steam turbine without heat grooves calculated and it was showed that the residual service life of high & intermediate pressure rotors without grooves has been extended as compared to the К-200-130-1 turbine rotors with grooves. Also residual life management by supplying hot steam to the HPC and IPC seals was investigated and it was noted their significant impact on the residual service life.

Structure service life assessment under combined loading using probability approach

This article presents a basic research approach for probabilistic assessment of vehicle structure fatigue endurance under multiaxial loading. One representative welded structural detail of the bottom joint plate of an articulated bus was selected for the case study. The character of the loading on the joint during a service test is analyzed and discussed. The methodology for estimation of the damage level in the joint builds on deterministic procedures for railway vehicle assessment based on shear, longitudinal and transverse stress components. This approach based on the equivalent stress and particular load capacity factors was expanded to include the probabilistic perspective. KEYWORDS. Service life; Combined loading; Damage; Vehicle; Probabilistic approach.

Assessment of Service Life of HCM12 Steel After 100 000 Hrs of Service

AbstractThe subject of the research was a material in the form of a ϕ38×4 pipe from HCM12 steel used for steam superheater coils in power boilers with supercritical and ultra-supercritical steam parameters. This article presents results of investigations of mechanical properties and microstructure of material of the examined tube in the as-received condition and after 100,000 h service at 585°C under creep conditions. Creep tests were carried out for the material after 100,000 h service to determine the disposable residual life. The impact of changes in mechanical properties and degradation of the microstructure on the loss of creep resistance compared to the as-received condition was assessed. The investigations have revealed that the examined steel after 100,000 h service meets the requirements for this steel in the as-received condition with regard to strength properties at room and elevated temperature. The creep tests have revealed a significant loss of creep resistance, which was estimated at around 60-70% compared to the as-received condition.

Reliability-based durability design and service life assessment of reinforced concrete deck slab of jetty structures

Reinforced concrete (RC) structures in a marine environment deteriorate with time due to chloride-induced corrosion of reinforcing bars. Since the RC deck slabs of jetty structures are exposed to a very aggressive environment, higher deterioration rates can develop. In this paper, a reliability-based durability design and service life assessment of RC jetty structures are presented. For new RC jetty structures, the concrete quality and concrete cover necessary to prevent the chloride-induced reinforcement corrosion causing the deterioration of structural performance during the whole lifetime could be determined. Based on the airborne chloride hazard depending on the vertical distance from the sea level surface to the RC deck slab, the probability associated with the steel corrosion initiation is estimated. The water to cement ratio and concrete cover to satisfy the target reliability level are provided. For evaluating the service life of existing structures, the condition state based on the visual inspection of RC structure can be provided. The deterioration process of the RC jetty structure can be modelled as a Markov process. Therefore, the transition probability matrix at time t after construction can be updated by visual inspection results. A procedure to update the transition probability matrix by the Sequential Monte Carlo Simulation method is indicated. In an illustrative example, the effect of the updating on the life-cycle reliability estimate of existing RC deck slab in a jetty structure subjected to the chloride attack is presented.

A probabilistic assessment of the influence of age factor on the service life of concretes with limestone cement/GGBS binders

The use of Supplementary Cementitious Materials (SCMs) in concrete manufacture has increased significantly in recent years. Utilising SCMs in the concrete mix reduces CO2 footprint while also generally enhancing durability. Time-dependent characteristics of concrete become more significant as SCM replacement levels increase. Service life modelling requires incorporation of accurate age factors; however limited research has been published on the influence of time-dependent characteristics of SCM concretes when manufactured with limestone cement (CEM II/A-LL). In this study, mix-specific age factors were determined based on the chloride diffusivity of concretes produced using a limestone cement binder with varying replacement levels of ground granulated blast-furnace slag (GGBS). The experimentally-determined age factors were validated against field data. Application of the validated factors in service life assessment models indicated increased sensitivity of the models to increased GGBS replacement level while affirming the enhanced durability effect of GGBS when used in combination with limestone cement.

확률론적 구조물 수명관리의 유지보수 상관관계 영향 평가

The assessment and prediction of service life of a structure are usually under uncertainty so that rational probabilistic concepts and methods have to be applied. Based on these rational assessment and prediction, optimum maintenance strategies to minimize the life-cycle cost and/or maximize the structural safety can be established. The service life assessment and prediction considering maintenance actions generally includes effects of maintenance types and times of the structural components on the service life extensions of structural system. Existing researches on the service life management have revealed the appropriate system modeling considering the correlation among the components is required for system reliability analysis and probabilistic service life estimation. However, the study on correlation among the maintenance actions is still required. This paper deals with such a study for more effective and efficient service life management. In this paper, both the preventive and essential maintenances are considered for the extended service life estimation and management.

Small Size Specimens Methods for Evaluation of Mechanical Properties

The evaluation of actual mechanical properties of the in-service structures after some time of operation or determination of local properties for detailed FEM simulation yields the necessity to obtain relevant material data with high accuracy from small volume of the experimental material. Therefore, non-destructive or semi-destructive techniques using small size samples are being developed. The use of small-scale samples also enables the evaluation of material properties in various locations of tested component; for example, the mechanical properties of the individual regions of welds, local properties determination for properties anisotropy assessment and properties determination in cases when small volume of the experimental material is available e.g. residual service life assessment of in service components, bulk nanostructured materials… There are shown results of small size tensile tests (M-TT) and small sized fatigue tests (SFT). In the case of small size specimens testing a machining becomes more pronounced that in the case of standard sized specimens. The current study brings information on the machining influence on the expected results obtained by small size specimens in the case of quasi-static tensile tests and fatigue test.

ACCUMULATED DEFORMATION MODELING OF PERMANENT WAY BASED ON ENTROPY SYSTEM

Purpose. The work provides a theoretical research about the possibility of using methods that determine the lifetime of a railway track not only in terms of total stresses, and accounting its structure and dynamic characteristics. The aim of these studies is creation the model of deformations accumulation for assessment of service life of a railway track taking into account these features. Methodology. To simulate a gradual change state during the operation (accumulation of deformations) the railway track is presented as a system that consists of many particles of different materials collected in a coherent design. It is appropriate to speak not about the appearance of deformations of a certain size in a certain section of the track, and the probability of such event on the site. If to operate the probability of occurrence of deviations, comfortable state of the system is characterized by the number of breaks of the conditional internal connections. The same state of the system may correspond to different combinations of breaks. The more breaks, the more the number of options changes in the structure of the system appropriate to its current state. Such a process can be represented as a gradual transition from an ordered state to a chaotic one. To describe the characteristics of the system used the numerical value of the entropy. Findings. Its entropy is constantly increasing at system aging. The growth of entropy is expressed by changes in the internal energy of the system, which can be determined using mechanical work forces, which leads to deformation. This gives the opportunity to show quantitative indication of breaking the bonds in the system as a consequence of performing mechanical work. According to the results of theoretical research methods for estimation of the timing of life cycles of railway operation considering such factors as the structure of the flow of trains, construction of the permanent way, the movement of trains at high speeds was developed. Originality. For the first time to simulate the accumulation of deformations of railway tracks this figure as the entropy of the system was used. Practical value. Analytic dependences have been brought to practical techniques that make it possible to analyze the track sections with different designs or with different operating conditions in terms of deformation accumulation.