Service Life Assessment Research Articles

Tracking supervision of service performance and life assessment of defective 15Cr1Mo1V steel pipeline

A large number of inclusion defects were found during the metal supervision process of the Russian-made 15Cr1Mo1V steel main steam pipeline of a thermal power unit. In this paper, the tracking supervision research of the 15Cr1Mo1V steel pipeline (three elbows with the most serious inclusions at different service time) is carried out in order to find out the variation and distribution law of the material's strength, toughness, metallographic structure and creep rupture strength. And on this basis, a creep fatigue life assessment is performed. The results show that the tensile strength, impact absorption energy and creep rupture property of the material decreased with the increase of the service time. The ductile-brittle transition temperature increased as time prolonging, all above room temperature, which means that the material is brittle. The main inclusions are MnS and SiO2 which are usually plastic, and the most serious inclusions are grade 3. Longitudinal inclusions are mostly of long-chain features, but no crack was found at the inclusion tips; the transverse inclusions are granular. The creep fatigue crack evaluation for the defects of plastic inclusions such as MnS and SiO2 shows that the crack propagation length at the inclusion tip after over 105 h of service is tiny which is consistent with the microscopic result, which means that the influence of the plastic inclusion on the structural integrity can be neglected. With the increase of the service time, the endurance strength gradually and slowly decreased. The presence of the inclusions did not accelerate the decline rate of the endurance strength, but might have an impact on the initial endurance strength of the new material. Meanwhile, brittle inclusion defects tend to generate stress concentration and induce the formation of cracks, so it is also necessary to strengthen the supervision and inspection of the inclusions and judge the inclusion category in the subsequent operation.

Numerical Study on Chloride Ingress in Cement-Based Coating Systems and Service Life Assessment

AbstractChloride-induced corrosion is a critical issue for RC structures. Cement-based coatings can be used to protect concrete structures with unsatisfactory quality against chloride ingress. To e...

Tracking Supervision of Service Performance and Life Assessment of Defective 15Cr1Mo1V Steel Pipeline

A large number of inclusion defects were found during the metal supervision process of 15Cr1Mo1V steel main steam pipeline of the Russian-made thermal power unit. In this paper, the tracking supervision research of 15Cr1Mo1V steel pipe elbow with inclusion defects is carried out. The variation law of strength, toughness, metallographic structure and creep rupture strength with inclusion defects at different operating time is studied. Type and composition of inclusions are analysed and creep fatigue crack evaluation of the most serious inclusion defects discovered is performed. The results show that with the increase of service time, the room temperature and high temperature strength of the material gradually decreased, the impact toughness deteriorated, the ductile-brittle transition temperature increased and greater than room temperature, the metallurgical organization aging grade rose from 3 to 4, creep rupture strength decreased, creep aging was increasingly serious, and creep residual life reduced. The main inclusions are plastic MnS、SiO2 and severe inclusion levels up to 3. Longitudinal inclusions are mostly long-chain features, and the ends are sharp but no sharp cracks are found at the sharp ends; the transverse inclusions are granular. Creep fatigue crack evaluation show that there was no obvious growth of material inclusion defects with the increase of service time, it is necessary to strengthen the supervision and inspection of brittle inclusions in the follow-up operation.

The Impact of Zinc Coating Specifications on Corrosion Resistance аnd Durability of Steels

The article contains the findings on impact of zinc coating specifications on corrosion resistance and service life of steels of various chemical composition used often in modern industries. Characteristics such as type, class, chemical compound and thickness of zinc-based coatings are also addressed. Experiments were performed in which corrosion rate and useful life of zinc coatings in probable operating-like conditions — i.e., in environments of varying degrees of corrosive power (humid and high-chloride environments) were determined. It has been established which one of the environments is the most corrosive for steels depending on the zinc-based coatings’ specifications. Qualitative (visual) and quantitative (gravimetric) assessment of corrosion resistance and service life of chosen steels is presented. Optimal hot dip galvanized coating specifications were determined using statistical analysis.

ASR: Practical investigative techniques and field monitoring systems used to assess ASR for service life modeling.

Alkali Silica Reaction (ASR) is a common deterioration mechanism affecting many concrete structures of any type and age. Initially identified more than 60 years ago (Stanton, 1930), this mechanism is based on the chemical reactions between certain siliceous minerals present in the aggregate and the alkalinity of the concrete in the presence of moisture (internal RH). While certain deterioration patterns are clearly associated with ASR, such as gel exudation, aggregate expansion, and characteristic cracking, the material degradation can often be misdiagnosed to the untrained eye. In addition, certain elements of a structure can be severely affected while neighboring elements of the same batch/ mix design do not bear signs of deterioration or impact. Thus far, in situ field monitoring of ASR affected structures is related to moisture measurements, electrical resistivity, expansion, service life models are based on fracture mechanics of the aggregate. The impact to the concrete is loss of integrity, decreased compressive strength, shear and tensile strength. Some observed structures have split, with such force, that the concrete structure had cracks greater than 25mm where steel retention bands have split. The authors of this paper were engaged in two instances to provide service life assessments for ‘corrosion related degradation’ on ASR affected structures. In all instances the elements which were assessed were structural, load bearing elements, which if failed could pose a significant risk to owner, user, or end recipient. The need to develop an assessment technique for monitoring and service life assessments which are practical and efficient is being developed. The paper will discuss the development of the approach, from visual indicators identifying condition hierarchies, to long term condition monitoring for various concrete parameters combined with laboratory testing (expansion and residual alkalis) and mathematical modeling. Three case studies will be presented to illustrate conditions and process.

On the problem of quantitative service life assessment for high-strength steel welded structures under the effect of corrosion medium

Nowadays there are some standards and approved procedures for fatigue strength estimation for welded structures subjected to high cycle loading where the strength of material is not actually taken into account. However for structures made of high-strength steels a situation is more specific due to a couple of aspects. First, high-strength steels are applied when the design stress is increased, that translates the analysis from the high-cycle to the low-cycle fatigue having its own specificity. Second, the trend of low-alloy steels to develop stress corrosion cracking mechanisms with their strength increase is widely known. In view of the above, there is a necessity of more detailed determination of the limiting states of a structure taking into account the load frequency. Links of both factors with the design features of welded joints and their welding and assembling technology are observed. A procedure for fatigue durability prediction of high-strength welded joints based on numerical simulation of fatigue process is presented.

Determination of the work life of low-temperature heating surfaces

Prolongation of heat and power equipment resource, which for the time being, is the only way out of the critical situation, gives a significant economic effect. Considering the uniform nature and low rate of low-temperature corrosion when burning water-fuel emulsions with water content of 30%, method for estimating service life of metal low-temperature heating surfaces at pipe metal surfaces temperature above 60°C has been proposed, at which uniform corrosion is observed. In the published literature, there are practically no data of impact on service life of low-temperature heating surfaces simultaneous influence of corrosion rates on gas and water sides of heating surfaces. The reliability of conclusion about the reliability of pipe heating surfaces largely depends on validity of conclusions made on the basis of calculations and especially taking into account experimental data of processes affecting reliability. It is on the basis of calculation results that it is possible to identify most tense elements that need to be subjected to detailed control. Therefore, in essence, reliability of entire methodology for assessing achieved and remaining resources depends on them. The paper presents a method for conducting computational studies of simultaneous influence of corrosion processes on gas and water sides of pipes and comparative assessment of service life of low-temperature heating surfaces when the limit states of metal are reached at acceptable and limit values of tensions and minimum possible thickness of pipe wall under influence of gas-chemical and water-chemical regimes and considering the data of experimental studies of processes affecting the reliability of work. To determine the time of calculated and residual service life of metal under uniform corrosion, a method for determining minimum residual thickness of metal has been presented, which still provides predestructive maximum allowable tension for remaining pipe wall thickness

Service life and life cycle assessment of reinforced concrete systems with limestone calcined clay cement (LC3)

This paper presents data on the chloride diffusion coefficient (Dcl), ageing coefficient (m) and chloride threshold (Clth) related to seven concrete mixes (four M35 and three M50) with OPC, OPC + PFA (pulverised fuel ash) and limestone-calcined clay cement (LC3). Using these, the service lives of a typical bridge pier and girder with the PFA and LC3 concrete were found to be much higher than those with OPC concrete of similar strength. From life-cycle assessment, the CO2 footprint of PFA and LC3 concrete were found to be significantly lower than those of OPC concrete of similar strength. Further, the CO2 emissions per unit of concrete per year of estimated service life, as a combined indicator of service life and carbon footprint, are similar for concrete with PFA and LC3, which are much lower than that with OPC.

Insulation condition assessment of high‐voltage rotating machines using hybrid techniques

The enduring life span of the machine insulation will be decided based on degradation level in motor and generator stator windings. The non-destructive diagnostic tools like dielectric loss and capacitance test and partial discharge (PD) analysis, recognized to access the deterioration in the insulation system of rotating machines. The experiments reveal various characteristic parameters such as leakage current, dielectric dissipation factor, the capacitance value, and PD magnitude. The integrity of the rotating machine can be find out by analyzing these parameters. This research study shows the hybrid method for prediction of insulation condition in the stator winding by utilizing the artificial neural network (ANN) with gravitational search algorithm in comparison with ANN and ANN–genetic algorithm. The advent of expert systems ensures the quality assurance and service life assessment of the high-voltage assets. It offers a predictive maintenance solution to personnel dealt with power utilities thereby increasing the uptime, reliability, and productivity, which in turn reducing the operating costs, downtime and unplanned outages. For testing and predicting the insulation status, several 11 kV machines are considered. The predicted results using hybrid techniques extend a close agreement with reference to the data obtained from the experiments performed. The proposed method indicate the competent and trustworthy, by the presented test results.

Study of the impact of NPP rated thermal power uprate on process behavior at different transient conditions

Today, objective preconditions have been formed to find the ways on how to increase cost-effectiveness of NPPs operation, while providing the required safety level. One of such ways to increase thermal nominal power of power unit. The paper provides for the results of reactor behavior analysis at increased thermal power above nominal received using a one-dimensional system computer code RELAP5/MOD3.2 and relevant model of VVER-1000 (V-320) power unit. Calculation analyses are performed for quasi-static reactor operating conditions and transients using realistic approach in terms of initial performance parameters of reactor installation. In researches, representative initial events for transients have been selected according to the principle described further. For an abnormal operation, an event has been selected based on its high frequency and consequences, which require decreasing reactor power down to 50 % of nominal thermal power. For emergency conditions an event has been selected which is caused by external extreme impacts typical for Ukrainian NPP sites resulting in the worst consequences. Thus, the transients are represented by events associated with failure of a single turbine-driven feed water pump and total station blackout unit. To analyze emergency conditions caused by long-term blackout, they were additionally accompanied by a leakage through reactor coolant pump seals. Given that increase of steam flow in a turbine at increased thermal power above nominal requires additional studies on residual service life assessment of its critical components, a 3-D model of high-pressure rotor of a full speed turbine is proposed for further studies. Based on the calculations a comparative analysis of major parameters of the reactor at rated and increased thermal power is performed with assessment of significant factors to be considered in further studies on increase of installed thermal output of NPP unit.

경과년수에 따른 도장재 물리적 상태와 수명평가

경과년수에 따른 도장재 물리적 상태와 수명평가

Acoustic Emission Method for Locating and Identifying Active Destructive Processes in Operating Facilities

Durability, safety, and usability are the three foundations of structural reliability, vital in the economic and social context. As the locating and tracking of potential damage and evaluating its impact on the condition of the structure are part of service life assessment, relevant methods should be developed that would detect the onset of the deterioration process and enable the monitoring of its progress within the entire volume of the structure, not only in the areas selected in a subjective way. The acoustic emission (AE) method relying on the analysis of active destructive processes can be the best choice. This article reports the results of the application of the AE method for identifying active destructive processes and tracking their development during the routine operation of various types of structures.

Characterization of the aging state of modified HP steels by ultrasonic signal processing and the effect of creep voids in the interdendritic region

HP austenitic stainless steels are extensively used in the oil and gas industry as radiant tubes in reformer and pyrolysis furnaces. These steels exhibit high resistance to oxidation, thermal stability, and creep resistance at elevated temperatures.Their microstructure changes as a function of temperature, leading to different aging states. In addition, creep voids can be formed due to furnace operating conditions such as time and stress. Therefore, the characterization of the microstructural conditions is necessary for service life assessment. This study aims at characterizing two modified HP steel samples with different aging states and volumetric fraction of creep voids via scanning electron microscopy and ultrasonic testing. Fast Fourier transforms were applied to the second backwall echo of the acquired ultrasonic signal. Spectral analysis established a correlation between the microstructural conditions and the signal response. According to the methodology developed, the ultrasonic parameters and spectral analysis results were sensitive to microstructural changes caused by aging and the presence of creep voids.

Optimization of Design and Life-Cycle Management for Steel–Concrete Composite Bridges

Sustainable structural design considers all actions and decisions pertaining to the economic, social and environmental impacts throughout the service life of a structure. For bridges, life-cycle analysis (LCA) includes an inspection and maintenance scenario for bridge components. The assessment of the average service life for each component is generally based on the experience of experts so that the applied measures and actions maintain the whole bridge in a good condition. However, this approach is limited. Firstly, defining a standard framework for maintenance does not take all uncertainties (epistemic and random) into account in terms of the degradation of different bridge components in varying types of environment. Secondly, some degradation processes accelerate or decelerate over time, so kinetic modelling is needed. Thirdly, it is not flexible enough to be included in an optimization process where different maintenance actions and intervals are sought (e.g. minimizing economic, environmental and societal impacts, maximizing accessibility and service level of a structure, etc.) while satisfying quality constraints. The approach proposed in this paper intends to resolve these three issues and is illustrated through the design of steel–concrete composite bridges.

Use of Non-Destructive Tests for the Assessment of Integrity and Service Life of Hydro-Mechanical Equipment

Technical diagnostics of hydromechanical equipment, is based on testing procedures including the history of the exploitation with expert knowledge of structures and operating conditions, as well as, on the analysis of results performed by experts with appropriate experience and knowledge in design, exploitation, maintenance, reliability, fracture mechanics etc. Degradation of properties of the material and/or welded joints of hydro-mechanical equipment is being caused by the simultaneous influence of a large number of factors. First of all, it is thought of technological, metallurgical, structural and conditions of exploitation. In this paper, the selection of methodology for the rehabilitation of hydro-mechanical equipment is presented based on the previously conducted assessment of state of equipment using the nondestructive testing methods. Repair welding, repair of damaged surfaces by cold metallization, corrections of existing structural solutions of metallic components in order to improve their technical characteristics and extend the service life are presented.

ИНЖЕНЕРНЫЕ МЕТОДЫ ПРОГНОЗИРОВАНИЯ ОСТАТОЧНОГО РЕСУРСА ОБОРУДОВАНИЯ

One of the most important indicators of reliability of technical objects is their durability. Probabilistic and statistical methods used for group assessment of service life of marine equipment at the stage of its design are unsuitable for individual assessment of a residual resource during operation due to the great values of coefficients of the resource variation and significant discrepancies between the proposed and actual operation models. Improving the reliability of estimates can be achieved by controlling the actual operation and monitoring of diagnostic parameters which characterize degradation of the actual technical state of equipment. The article considers on specific examples the features of predictive extrapolation of time-series observations over diagnostic parameter and application of forecasting method based on the actual history of operational loadings. It is stated that the extrapolation method, in spite of such advantages as using a minimum number of controlled parameters and versatility, has a number of shortcomings that reduce its effectiveness in the evaluation of residual resource of multi-mode objects. To extend the use of extrapolative forecasting there have been proposed special methods of adjusting time series using the Euler method, linear and nonlinear regression models and the estimation approach of residual resource, which provides a preliminary study of physico-chemical deterioration of technical condition of equipment and subsequent measurement of the equivalent hours of the resource using results of the check operation and the hypotheses of linear summation of damage.

Redundancy-based service life assessment of corroded reinforced concrete elements considering parameter uncertainties

In order to assess the structural reliability and redundancy with respect to deterioration, appropriate models have to be selected which adequately describe the deterioration process. The parameters associated with these models have to be estimated based on statistical inference. In general, the uncertainties that arise from the estimation of parameters are not accounted for in reliability assessment and the obtained structural reliability indices are assumed to be constant values. When parameter uncertainties are considered, the structural reliability index can, however, be considered as a random variable which inevitably influences the full-probabilistic decision-making process. Furthermore, the structural reliability indices which are used in a reliability-based redundancy factor can be considered as random variables. Hence, this redundancy factor itself is a random variable as well. In this paper, a full-probabilistic framework is developed which allows for the service life assessment of reinforced concrete elements subjected to corrosion based on a probability-based redundancy factor and taking into account parameter uncertainties. It is proven that these parameter uncertainties have a significant influence on the lifetime estimates of concrete elements subjected to corrosion. Finally, a simplified method is proposed which allows to incorporate parameter uncertainties in the redundancy assessment.

Time Factor in the Theory of Anthropogenic Risk Prediction in Complex Dynamic Systems

The article overviews the anthropogenic risk models that take into consideration the development of different factors in time that influence the complex system. Three classes of mathematical models have been analyzed for the use in assessing the anthropogenic risk of complex dynamic systems. These models take into consideration time factor in determining the prospect of safety change of critical systems. The originality of the study is in the analysis of five time postulates in the theory of anthropogenic risk and the safety of highly important objects. It has to be stressed that the given postulates are still rarely used in practical assessment of equipment service life of critically important systems. That is why, the results of study presented in the article can be used in safety engineering and analysis of critically important complex technical systems.

New Ashton Arch – functional assessment of direct and indirect construction costs and evaluation of service life with respect to flooding risk.

The bridge crossing the Cogmanskloof River in the town of Ashton, South Africa, had a history of over-topping due to severe flood events. The poor flood resilience of the bridge was aggravated by the generally hydraulically inefficient openings, the number of substructure supports in the river course, and a high debris load during flooding. The strategically important tourist route had to be closed, while localized flood damage repairs were undertaken, with resultant adverse effects on the local economy. As part of a road safety improvement project between the towns of Ashton and Montagu, improvement of the flooding resistance at the Ashton river bridge was required. This paper documents the functional evaluation of economicand technical-assessments of the flooding risks for the existing retro-fitted bridge. A new tied-arch bridge was the selected structural form of the replacement structure – based on the assessment of the key service life and constructability criteria. The structural form of the Ashton Arch paid careful regard to the scenic location and historic character of the previous multiple arch bridge form.

Determination of Residual Fatigue Life of Welded Structures at Bucket-Wheel Excavators through the Use of Fracture Mechanics

This paper presents a methodological approach for the assessment of service life of vital welded structures of a bucket-wheel excavator Sch Rs 650/5x24 (’Thyssen Krupp’, Germany) boom, subjected to cyclic loading with a variable amplitude through the use of experimental tests carried out in order to determine operational strength and growth of a fatigue crack. Realized researches and results presented in this paper offer great possibilities for the analyses of behaviour of vital welded structures of the bucket-wheel boom. By the application of the measurement device with 8 channels for registration and processing of electric signals HBM Spider 8 and measurement tapes HBM 6/350xXY31 deformations were measured at vital welded structures of the boom in the area of the bucket-wheel, made of steels St 37.2 and St 52.3 in accordance with standard DIN 17100, or steels S235J2G3 and S355J2G3 in accordance with standard EN 10025-2. The objective of the test is to determine if there is a possibility of occurrence of plastic deformations or initial cracks due to fatigue at vital welded structures. Tests that refer to the growth of the fatigue crack located at the welded joint have been carried out by bending at three points with asymmetric load R = 0.5 (R = σmin / σmax) at the specimen with a single edge notch. Tests were performed through the use of controlled force, ranging between Fmax and Fmin at the high-frequency pulsator ‘Cracktronic’, while obtainment of data regarding the crack growth was carried out through the use of measurement gauge ARM A-10.