Evaluation Of Residual Life Research Articles

Advancing the Reliability of Residual Life Assessment for Turbines through Strain Gauge Measurements: Key Aspects and Latest Developments

Abstract With the need for flexible operation and an aging hydropower fleet, the importance of residual life assessment for turbines has been on the rise. While prediction methods are continuously improving, the most reliable data about the health status of a machine is obtained through measurement campaigns. Unlike fatigue evaluations during the design stage that include safety factors, residual life assessments require higher precision to enable owners to evaluate their assets and investments. The increased precision of a measurement campaign justifies the additional costs incurred. This article emphasizes the significance of a careful review of all aspects, including load history, measurement data, transposition method, and material data. It also presents the latest developments in accordance with IEC 63230 and provides an example prototype measurement to underscore the importance of each aspect. Special attention is given to the transposition of strain data from the measurement location to the hot spot position and its impact on load sequences and stochastic loads. Through a sensitivity study, the article aims to provide a better understanding of the importance of each aspect in the residual life evaluation process.

Study on Mechanical and Microstructural Evolution of P92 Pipes During Long-Time Operation

To investigate the mechanical properties and microstructure evolution of P92 steel during long-term service, the operated P92 main steam pipes from the first ultra-supercritical units in China were sectioned into samples representing various service durations and stresses (0# (as-received state, 1# (82,000 h, 67.3 MPa), 2# (85,000 h, 78.0 MPa), and 3# (100,000 h, 80.3 MPa)). Thereafter, a comprehensive assessment of their mechanical properties, including tensile strength, impact, hardness, and creep resistance, as well as a detailed microstructure analysis, was carried out. The effect of stress on the aging of material properties during operation is discussed. The results show that the circumferential stress caused by the increase in the internal steam pressure can significantly promote the creep life consumption of P92 steel, resulting in the degradation of mechanical properties and the expedited aging of the microstructure. The Rp0.2 and Rm of the P92 main steam pipe at room temperature and 605 °C decreased with the service time increase, reflecting the influence of stress in operation, which is expected to be used for the residual life evaluation of P92 steel. The relationship between the impact absorption energy (FATT50), Brinell hardness, and the operating time of P92 operating pipes is non-monotonic, indicating that these parameters are not sensitive indicators of material aging due to stress. The evaluation of performance degradation in P92 operating pipes due to stress-induced aging is not reliably discernible through optical metallography alone. To achieve a thorough assessment, the use of transmission electron microscopy (TEM) is essential.

Additional study of failure behavior for ship propeller: The comparative analysis of life evaluation approaches between BP neural network, LSTM and TV-HSMM

The study focuses on investigating the appropriate method for evaluating the residual life of a propeller and analyzing its fracture characteristics. A fluid-structure interaction simulation is conducted to qualitatively analyze the stress distribution of the propeller during operation, identifying regions prone to stress concentration. Subsequently, fracture surface characteristics are examined, revealing quasi-cleavage fracture features such as tongue striations, dimples, and tearing ridges in the initiation and propagation regions. Additionally, composite fracture characteristics and geometric mutations are observed on the edge of the fracture surface. Three residual life evaluation methods are then proposed, utilizing BP neural network, LSTM, and TV-HSMM. Comparative analysis suggests that the TV-HSMM method offers the advantage of minimal error in residual life evaluation. However, the models based on BP neural network and LSTM are preferred for their lower average error and distribution trends that closely resemble actual life data.

Hot spot stress distribution and fatigue life evaluation of steel-UHPC deck in a long-span cable-stayed bridge

The steel-UHPC composite deck is an effective solution to fatigue cracks of orthotropic steel decks (OSD) in steel bridges. However, limited research has been reported on the hot spot stress distribution of the steel-UHPC composite deck. This study investigates the hot spot stress distribution and residual fatigue life evaluation of the steel-UHPC deck in a long-span cable-stayed bridge. The two extrapolation points' strain at fatigue-prone details were continuously measured under in-service traffic flow. The hot spot stress time history at each detail of the conventional OSD deck and steel-UHPC deck were analyzed and compared. The residual fatigue life of each detail was calculated. A three-dimensional finite element (FE) model was established and validated through experimental results. The bridge deck's deflection, the asphalt pavement's tensile stress, and the stress distribution at the floor beam cutout were numerically studied using the validated FE model. The results showed that the UHPC layer significantly reduced the hot spot stress and extended the fatigue life at each fatigue detail. The UHPC layer reduced the bridge deck's deflection and the asphalt pavement's tensile stress. Compared with nominal stress method, the hot spot stress method can better describe the large stress gradient distribution induced by the stress concentration at fatigue detail.

Residual design life-based evaluation of structural retrofitting on high-rise reinforced concrete buildings

The deteriorating structural performance of aging high-rise reinforced concrete (RC) buildings has brought increasing attention to the necessity of retrofitting in developed regions. In this context, the present paper introduces a novel approach by reversing the conventional service life-based structural design procedure. The proposed approach establishes a residual design life evaluation framework, enabling a comprehensive assessment of the performances of existing RC buildings both before and after retrofitting. This assessment framework takes into account various load scenarios, including wind and earthquake forces, etc., and yields an intuitive index based on design codes, termed "residual design life", which serves as valuable information for decision-makers. To exemplify the framework's application, a case study involving a high-rise RC building is presented. Initially, the influence of the adopted design codes on the residual life of the aging building is investigated. Subsequently, three commonly employed structural-level retrofit methods, namely steel bracing, RC wall addition, and exoskeleton, are examined. The findings reveal that the residual design life of the existing building decreases as the adopted design code transitions from an outdated version to the current one. However, the implementation of structural-level retrofit interventions proves highly effective in enhancing the building's residual life, particularly when failure is primarily governed by column capacities and storey drift. Nonetheless, it should be noted that certain structural-level interventions may increase the load on adjacent beams, potentially leading to a negative impact on the building's residual life when the condition of the beams becomes the predominant factor. Furthermore, the obtained residual life of the retrofitted building could be used to assist in conducting life-cycle analysis and further investigations and contribute to the understanding regarding structural performance and safety in the built environment.

Response of Reinforced Concrete Beams under the Combined Effect of Cyclic Loading and Carbonation

To compare the deterioration mechanism of reinforced concrete beams between the combined effect of cyclic loading and carbonation and the sum of both individual factors, an optimized test procedure was introduced in this study. The macroscopic and microscopic results showed that the decrease in carbonation resistance of concrete could be attributed to the changes in pore structures and crack patterns introduced by cyclic loading. However, the carbonation process of flexural tensile concrete corresponding to different test procedures presented different trends. It indicated that the combined action of carbonation and fatigue damage was more serious than the damage caused by the effect of superposition. Finally, a theoretical carbonation model of concrete subjected to the combined damage was proposed and validated by comparing it with previous experimental results. The research findings are significant for improving the accuracy of evaluation of residual service life of reinforced concrete bridges and early warning of durability protection.

Activities to Advance Residual Life Evaluation Techniques for Highly Aged Power Boiler Materials

Activities to Advance Residual Life Evaluation Techniques for Highly Aged Power Boiler Materials

Activities to advance residual life evaluation techniques for highly aged power boiler materials

ABSTRACT In Japan, national guidelines of residual life evaluation for aged thermal power equipment were formulated in 1999. Several issues had recently come to light with the increase in ageing systems, including the emergence of unexpected mode of creep damage, the verification of practical applicability of the damage calibration curve generated in the laboratory, how to deal with creep-fatigue damage due to increased numbers of plant starts and stops, occurrence of plastic deformation in the accelerated creep test and the need for the creep damage monitoring method during plant operation. The Working Group to Advance Residual Life Evaluation Techniques was established in 2011 within the Society of Materials Science, Japan, to identify issues and discuss improvement measures. This paper provides an overview of the results of the working group activities.

Life evaluation of rolling element bearings using stochastic neighbor embedding deep regression

Accurate residual service life (RSL) evaluation of rolling element bearings is significant for prognostics and health management to guarantee rotating machinery safety, availability, and efficiency. This work develops a method called stochastic neighbor embedding deep regression (SNEDR) to enhance the estimation performance of the RSL. First, the appropriate features originating from the vibration data of the tested REB are extracted. The state indicators are subsequently established with the extracted features by introducing the stochastic neighbor embedding. By doing that, the random errors and noises generated from the vibration signals can be minimized, and the evaluation performance may be improved. Finally, the regression model based on the state indicators and the long short-term memory network with time information representation capacity is generated for the RSL evaluation. The availability of the SNEDR is validated by the real data derived from a bear failure experiment. Furthermore, a peer method is introduced for a comparative study. Experimental results show that the SNEDR outperforms the competing method and can yield more reasonable and accurate evaluation results.

Residual life evaluation of remanufacturing blanks considering the crack closure

The nonlinear continuous fatigue cumulative damage model proposed by Chaboche was modified considering the effect of crack closure on fatigue damage, and the fatigue cumulative damage and residual life evaluation model of remanufactured blanks was obtained. The related parameters of the modified model were obtained from the data of symmetric cyclic tensile and compression fatigue tests. The residual life evaluation model of remanufactured blanks was verified by the two-stage loading (high and low loading and low and high loading) tensile and compressive fatigue test. The results show that the calculated values of the model are in good agreement with the test values, which proves that the modified model can accurately predict the residual life of remanufactured blanks.

Fatigue limit and residual life evaluation of railway EA4T axles with artificial surface impacts

Fatigue limit and residual life evaluation of railway EA4T axles with artificial surface impacts

A hybrid method for determination of fatigue limit and non-destructive evaluation of composite structures after low-velocity impact loading

One of the most challenging and still unsolved problems within the design and operation of composite structures is the prediction of its behavior under fatigue loading. This problem is even more complex when a composite structure contains damage, especially low-velocity impact damage considered as one of the most dangerous types of damage in composite structures. In this paper, the authors presented the hybrid method, which combines the evaluation of a fatigue limit of structures with low-velocity impact damage (LVID) with a non-destructive evaluation of this damage using thermocouples and thermography in a single test. The tests were performed on carbon and glass fiber-reinforced composite structures with LVID of various energies. The relation between fatigue limit and impact energy was demonstrated, and the observed damage mechanisms analysis was performed. Moreover, the performance of LVID detectability is analyzed, defining minimal self-heating temperature increase necessary for detection of LVID. The proposed method demonstrated high sensitivity to impact damage and simultaneously an ability of evaluation of fatigue life of a tested structure. Finally, the recommendations on measurement setup and parameters of testing are provided. It was demonstrated that the proposed hybrid method could be successfully used for rapid, precise and non-destructive evaluation of residual life of composite structures after impact loading.

Dynamic Strain Reconstruction of Rotating Blades Based on Tip Timing and Response Transmissibility

Abstract Dynamic strain of rotating blades is critical in turbomachinery health monitoring and residual life evaluation. Though the blade tip timing (BTT) technique is promising to replace traditional strain gages, the lack of effective strain transformation through BTT hinders the implementation. In this paper, a noncontact dynamic strain reconstruction method of rotating blades is proposed based on the BTT technique and response transmissibility. First, the displacement-to-strain transmissibility (DST) considering rotational speed is derived from the frequency response functions based on blade mode shapes. A quadratic polynomial function of DST with respect to the rotational speed is provided to calibrate DST in blade rotational state. Second, the blade-tip displacement in resonance is obtained by BTT measurement and the Circumferential Fourier Fit processing method. Third, the dynamic strains of critical points on blades are calculated using the DST in conjunction with the tip displacement amplitude. In this paper, to validate the proposed method, acceleration and deceleration experiments, including both BTT and strain gages, are conducted on a spinning rotor rig. Experimental results demonstrate that the reconstructed dynamic strains of different positions on the rotating blades correspond well to the results measured by strain gages. The mean relative error between the reconstructed and measured results is generally within 8%.

Ultrasonic detection of white etching defect based on convolution neural network

<sec>Unlike classical defects formed by rolling contact fatigue, white etching defect (WED) including white etching area and white etching crack will cause surface to spall in the early stage and the service life to shorten seriously. Located in the subsurface of bearings, the tiny size WED is difficult to detect by conventional ultrasonic methods. The root cause of WED generation remains unclear. It is time consuming and expensive to prepare samples during the evolution of such defects. For characterizing the WED at early stage, five evolving states concerning the existing microscopic information are established in this paper. The immersion ultrasonic inspection process is simulated based on <i>k</i>-space pseudo spectrum method.</sec><sec>For the later evolutionary stage with crack, the bearing can be simplified into a homogeneous three-layer model by ignoring the internal grain structure. The crack depth is obtained by using the ultrasonic reflection coefficient amplitude spectrum (URCAS), with an error of 1.5%. For other states without crack, the spectrum characteristic is no longer evident with slight acoustic impedance difference between layers. The polycrystalline structure on a microscale is thus realized based on Voronoi diagram, from which the grain induced backscattering can be used to amplify the microstructure variations at different stages. The backscattering signal is influenced by the grain size and detection frequency from the simulation. Since a direct comparison of backscattering information among evolutionary stages is difficult, the five different evolutionary stages of WED are recognized with the help of deep learning. The received waveform is transformed into a time-frequency map by short-time Fourier transform. Based on RESNET network structure, the results show that the train accuracy and validation accuracy reach 92% and 97% respectively. This study provides a sound way to characterize WED, which is conducive to early failure prediction and residual life evaluation.</sec>

A reverse engineering approach for modeling of barely visible impact damage by combining results of non-destructive testing and numerical simulations

An evaluation of the structural residual life for composite elements affected by low-velocity impact loading is a challenging task due to the uncertainty of an influence of the resulting damage on the mechanical properties of a structure, which cannot be truly assessed without destructive testing. To overcome this deficiency, an approach based on reverse engineering was developed. Within this approach the results of non-destructive testing (NDT) are considered, namely the results of X-ray computed tomography as well as ultrasonic testing in B- and C-scan modes, for an evaluation of the geometrical properties of damage as well as the results of numerical simulations of impact testing of the composite were used to support the experimental results. Based on the obtained results, the generic shapes of barely visible impact damage (BVID) in composite structures were determined, and based on the generic shapes and the obtained relations between the damage extent and the impact energy, a parametric computer-aided design models were developed. The obtained models allow predicting the structural response, including the estimation of the residual life of composite structures in finite element simulation environments.

Quantitative thermography for fatigue damage assessment and life prediction of welded components

The objective of this paper is to use quantitative thermography for fatigue damage assessment and life prediction of welded components. The energy dissipation during fatigue process is taken as an effective index of fatigue damage to develop a nonlinear damage accumulation model, and the model is extended to evaluate the fatigue damage and residual life of the specimen subjected to variable loading. Experiments are performed to validate its applicability, and the relationships between the fatigue damage variable to the cycle number and the accumulated energy dissipation are presented and discussed. The results show that the energy dissipation has the same trend as the temperature increment evolution, and a power law relationship between the stress range and the energy dissipation is experimentally determined. The linear relationship between the accumulated energy dissipation and the cycle number is confirmed at different constant stress levels, and the total energy dissipation to failure is shown to be a constant value. The developed nonlinear damage accumulation model is used to predict the residual fatigue life, and a good agreement is achieved. It is concluded that the developed approach is applicable for fatigue damage accumulation and residual life evaluation of materials.

S-N Fatigue Curve Determination for Corroded High-Strength Bridge Wires

AbstractAccurate residual life evaluation is crucial for maintenance of corroded bridge wires, and a stress-life (S-N) curve is determined for the fatigue strength of steel wires after corrosion. T...

Residual life evaluation of 12Cr1MoVG steel for main steam pipeline

12Cr1MoVG steel is a commonly used steel for boiler main steam pipes. With the increase of service time, the material’s endurance performance is deteriorating. In this paper, the performance analysis of the 12Cr1MoVG steel main steam pipe which has spheroidized and deteriorated after 70,000 hours of service in a power plant was carried out, and the residual life of this pipeline was evaluated. According to the evaluation, the residual life of the pipeline is more than 100000 hours.

Evaluation of residual creep life of steels using macro-pillar creep testing and Omega method

Residual creep life evaluation is an essential part of Fitness-For-Service (FFS) assessment for engineering components operating at elevated temperatures. This paper elaborates a new evaluation approach based on macro-pillar compression testing (MPCT) and Omega method. The MPCT creep test was performed at the same stress level as the tensile creep test by adjusting the testing load using an algorithm, which is also provided in this paper. The barreling effect of MPCT creep test was corrected by two proposed parameters, which were calibrated using finite element method with 6 types of Cr-Mo alloys from API 579. Finally, a 1.25Cr-0.5Mo-Si steel was prepared for both MPCT and round bar tensile creep tests at 550 ℃ and different initial stress levels. The predicted residual creep life by MPCT has an error of 2.2% at 140 MPa, 6.4% at 160 MPa and 13.5% at 180 MPa.

Influence of steam heat transfer tube damage characteristics on burst pressure

The corrosion damage and leakage of heat transfer tube of steam generator were important factors of nuclear power accident, which is closely related to the national nuclear power production safety and people's life and property. The influence of the size change of cylindrical defect on burst pressure of inconel690 alloy heat transfer tube was studied by finite element simulation and experimental measurement. According to the simulation and test data, the relationship between burst pressure and damage parameter is established. The results show that for cylindrical defects with small depth, there is an extreme point of cylinder damage diameter b which makes the damage maximum, which makes the burst pressure at a minimum. The research results can provide reference for accurate evaluation of residual life of heat transfer tubes.