Remaining Life Assessment Research Articles

FAILURE MODE AND EFFECT ANALYSIS (FMEA) AS TREATMENT OF PREDICTIVE PREVENTION AND LEAKAGE OF BOILER TYPE BALANCE DRAF FAN

Risk analysis aims to prevent the incompatibility of a system used in the testing process including the Boiler system. At the Labuan 2 Steam Power Plant (PLTU) 2, the Boiler component was declared very often to have a pipe leak. Failure Mode And Effect Analysis (FMEA) is a method used to analyze the risk of failure. This method is represented by calculating the value of RPN (Risk Priority Number) obtained from the results of the multiplication of S (severty), O (occurrence), and D (detection). The highest analysis results are shown at 480 (in the steam drum component in the form of abnormal steam and water level failure). The cause is human error. Next three levels below are (1) Economizer component, which is 360 causes of combustion side ash erosion, material lifetime, and economizer tube fibration; (2) super heater tube and re-heater tube components which are 320 due to Corrosion, Overheat Flyash erosion, Sub blower erosion, Welding error; and (3) Walltube which is 320 causes of overheating and sub blower erosion. The recommendation for the analysis of FMEA testing to predict mantenance is done by applying remaining life assessment after 8,000 hours / operational.

Creep performance and damage mechanism for Allvac 718Plus superalloy

The creep behavior, creep damage and creep life of 718Plus alloy were investigated at temperatures ranging from 650 to 750 °C in air. The fracture surface, microstructure evolution and deformation mechanisms were studied by optical, scanning and transmission electron microscope (SEM and TEM). The results show that creep curves of 718Plus alloy consist of primary stage and tertiary stage without steady-state region. The Monkman-Grant relationship of 718Plus alloy can be described by tr = 9.32E-2/(ε̇min)0.75 and apparent creep activation energy of 718Plus alloy is about 572.7 kJ/mol. Further investigation shows creep damage of alloy at 650 °C can be mainly ascribed to the effect of grain boundary sliding (GBS) and microtwinning. The alloy shows transgranular fracture at high stress, while it presents ductile fracture at low stress due to the nucleation, growth and linkage of creep voids. At 750 °C, the alloy failed in the form of ductile fracture mainly due to the microstructure instability and dislocation glide. At higher stress of 700 °C, the effect of GBS is mainly responsible for the creep damage of 718Plus alloy, while GBS, dislocation glide and microstructure instability work together and lead to the creep damage of alloys at lower stress of 700 °C. The fracture mechanism map and fracture models for 718Plus alloy were constructed. Remaining life assessment of 718Plus alloys was also evaluated by Larson-Miller parameter method.

Life time extension of turbine rotating components under risk constraints: A state-of-the-art review and case study

This paper presents a methodology for life time extension of turbine rotating components under risk constraints subject to fatigue crack damage. A state-of-the-art review is given to reveal the historical perspective and the current practice of life time extension. The evaluation of the fatigue life of these components is highly important to mechanical integrity, and in many cases is centered on the ultrasonic inspection data and fracture mechanics. Due to the inherent uncertainty and stochastic nature of the fatigue crack propagation, the remaining life assessment needs to incorporate various uncertainties for risk mitigation. Among the uncertainties, the sizing uncertainty of an embedded crack is significant because the crack cannot be directly accessed and need to be assessed indirectly using ultrasonic inspection. The assessment result is uncertain owing to the unknown orientation of the crack and inspection competency. This uncertainty can be quantified by correlating the actual flaw size and the reported flaw size. This study investigates the method of extending the fatigue life by scientific quantification and minimization of this uncertainty. By analyzing the sizing performance based on the previous sizing data and the present sizing data using the method of model-assisted probability of detection, the life extension can be realized without compromising the risk requirement in a probabilistic framework. The overall method is demonstrated using a realistic steam turbine rotor with actual ultrasonic inspection data.

Remaining Life Assessment of Superheater Tube in Boiler of Coal Fired Power Plant

Risk Based Inspection (RBI) would be able to establish an effective structural integrity management program, which reduces plant downtime, industry and regulatory burdens, and continue to maintain plant safety. The object of this research is final superheater of boiler coal fired power plant. Both straight tube and elbow tube of final superheater is in a medium risk category. Elbow tube has higher risk ranking because of the higher corrosion rate due to fly ash corrosion. The remaining life of straight tube is about 26 years and elbow tube is only about 7 years using corrosion rate calculations. Base on risk ranking and remaining life assessment, inspection planning can be developed for the next 3 years and prioritize at an elbow tube of the final superheater section. It can be one of the considerations for the company to pending yearly inspection in order to improve cost efficiency and reduce downtime.

Time-dependent creep analysis and life assessment of 304 L austenitic stainless steel thick pressurized truncated conical shells

This paper presents a semi-analytical solution for the creep analysis and life assessment of 304L austenitic stainless steel thick truncated conical shells using multilayered method based on the first order shear deformation theory (FSDT). The cone is subjected to the non-uniform internal pressure and temperature gradient. Damages are obtained in thick truncated conical shell using Robinson's linear life fraction damage rule, and time to rupture and remaining life assessment is determined by Larson-Miller Parameter (LMP). The creep response of the material is described by Norton's law. In the multilayer method, the truncated cone is divided into n homogeneous disks, and n sets of differential equations with constant coefficients. This set of equations is solved analytically by applying boundary and continuity conditions between the layers. The results obtained analytically have been compared with the numerical results of the finite element method. The results show that the multilayered method based on FSDT has an acceptable amount of accuracy when one wants to obtain radial displacement, radial, circumferential and shear stresses. It is shown that non-uniform pressure has significant influences on the creep damages and remaining life of the truncated cone.

Review of Remaining Life Assessment of External Pressure Vessel in Creep Range

Review of Remaining Life Assessment of External Pressure Vessel in Creep Range

Remaining life assessment for boiler tubes affected by combined effect of wall thinning and overheating

Boilers, the most troublesome components of electric power, chemical and processing plants generate high costs in unscheduled shutdowns, repairs and power replacement. Every occurrence of ruptured tubes leads to emergency shutdown of the entire plant. This paper describes the joint international effort to develop faster and more efficient methods for condition assessment and remaining life prediction for boiler tubes made of low-carbon steel. Authors have undertaken a systematic research with the major objective to correlate the results of combined nondestructive testing (NDT) with condition assessment of boiler tubes. The evaluation included non-contact wall thickness measurement with EMAT technology plus internal oxide layer measurement with specialized ultrasonics. While the first method shows the remaining tube wall thickness, thus allowing calculating total stress, the latter one has the potential to characterize microstructure degradation, which up to now could only be determined by destructive analysis. The special attention was directed towards identification and analysis of creep damage due to overheating. In recent years, techniques were developed to identify heat damage by measuring the thickness of internal oxide scale because even a thin scale can seriously impede heat transfer causing elevation of temperature in tube wall. A combined effect of wall thinning and the “degree of overheating” on tube remaining life was investigated. The uniqueness of this work lies in one of the first attempts to develop and validate a tool for methodology for condition assessment and remaining life prediction, for Steel20 tube material, while most of previous authors had concentrated on Cr-Mo steels. Another contribution is the combined treatment of two different damage mechanisms and practical utilization of two various NDT techniques. To-date, both results are treated separately, and consequently separate reject criteria exist for overheating and separate for wall thinning. As a result of work presented in this paper, a procedure was recommended to calculate the tube remaining life based on the results of two ultrasonic tests.

Power Plant Remaining Life Assessment Case Study

Research & Development in Material Science Power Plant Remaining Life Assessment Case Study Nirmalendu Bandyopadhyay* Department of Industrial Engineering, Sarsuna Satellite Township, India *Corresponding author: Nirmalendu Bandyopadhyay, Department of Industrial Engineering, Independent Consulting Engineer, H2/100 Sarsuna Satellite Township, Kolkata-700061, India Submission: September 21, 2017; Published: November 03, 2017 DOI: 10.31031/RDMS.2017.01.000523 ISSN : 2576-8840Volume1 Issue5

Towards optimised and reconstructable sampling inspection of pipe integrity for improved efficiency of non-destructive testing

Abstract This work proposes a sampling inspection framework for point measurement non-destructive testing of pipelines to improve its time and cost efficiencies. Remaining pipe wall thickness data from limited dense inspection are modelled with spatial statistics approaches. The spatial dependence in the available data and some subjective requirements provide a reference for selecting a most efficient sampling inspection scheme. With the learned model and the selected sampling scheme, the effort of inspecting the residual part of the same pipeline or cohort will be significantly reduced from dense inspection to sampling inspection, and the full information can be reconstructed from samples while maintaining a reasonable accuracy. The recovered thickness map can be used as an equivalent measure to the dense inspection for subsequent structural analysis for failure risk estimation or remaining life assessment.

Study of Fatigue Properties of Materials through Cyclic Automated Ball Indentation and Cyclic Small Punch Test Methods

One of the important inputs while estimating the remaining life of critical components is the fatigue property of materials. Fatigue data, in the form of stress vs. cycles to failure (or) strain vs. cycles to failure (or) fatigue crack growth rate data is used to predict the residual life. Material’s fatigue property degrades with time and usage; hence, it is appropriate to use the current properties for remaining life assessment. Often the quantity of material available for generating fatigue data is limited, especially, if the material is scooped out of existing component of a power plant. Further, fatigue response being probabilistic in nature, requires multiple specimens to be tested at any given stress/strain levels. This has prompted us to develop test procedures to determine the fatigue data of materials from a limited volume of material. This paper presents the results of cyclic ball indentation test method as well as cyclic small punch test method that is used to generate the fatigue data at different stress levels. There are several fine details relating to these test techniques – viz., establishing a equivalent damage criteria for failure life with standard LCF/HCF test specimens. The influence of one of the variables, viz., friction at the specimen-tool interface of a small punch test is investigated through numerical simulation and the results are presented here.

Evaluation and Remaining Life Assessment of Separator and Demister in a Geothermal Power Generation Plant

Evaluation and remaining life assessment of separator and demister for 55 MW geothermal power generation plant have been conducted. The equipment has been used for 27 years and has stopped operating due to the failure of steam turbine. Before it is operated back, the condition of separator and demister needs to be evaluated and their remaining life assessment has to be calculated to anticipate the future repair. The methods used for evaluation were UT phased array, thickness measurement, chemical composition, hardness test and deposit composition analysis. The remaining life assessment was calculated in correlation with thickness reduction. The results showed that the chemical composition and hardness of materials met the standard of SA 516 Gr 70. No evidence of internal defect was found in both equipment. The demister in all part is still in good condition and its remaining life was beyond 20 years. In separator, the reduction in thickness extremely occurred on top head and cone. The remaining life of top head separator was below 1.2 years and cone separator was not more than 4.7 years. Deposit analysis taken from demister gave evidence the presence of sulfur, silica, iron oxide, and sulfide iron.

Microstructure Evolution and Creep Properties of 2.25Cr-1Mo Ferrite-Pearlite and Ferrite-bainite Steels After Exposure to Elevated Temperatures

2.25Cr-1Mo steels are widely used in thermoelectric power plants. Under operational temperatures, their properties degrade due to microstructural changes related to carbide coalescence and stoichiometric transformations. The extent of such microstructural changes is controlled by stress, temperature and time. Therefore, these factors can be used to evaluate damage and as life assessment tools for the individual component. In the past, ferrite-pearlite was the predominate microstructure in commercial Cr-Mo steel products, owing to the well-known methodologies for remaining life assessment based degradation. Currently, the ferrite-bainite microstructure obtained through a more economical route is most commonly used for this steel grade. However, there is no consensus in the literature about microstructural changes that can be used as a degradation pattern for ferrite-bainite steels. This paper compares the aged microstructures and creep properties of ferrite-pearlite and ferrite-bainite 2.25Cr-1Mo steels. Aging was conducted at 500, 575 and 600oC until 2,000 h, and creep tests were performed at 575oC under a stress of 100 MPa. Microstructural changes were characterized by optical microscopy scanning electron microscopy. Metallographic observations of the ferrite-bainite steel show a more stable behavior at the ageing temperatures and time considered. However, creep tests revealed that the ferrite-pearlite microstructure possesses a better rupture time performance. Carbide size distribution and stoichiometric evolution of the carbides provided by transmission electron microscopy support the creep behavior. These results show that the current techniques for evaluating microstructural degradation of 2.25Cr-1Mo steels must be reconsidered.

Proposal of Creep Remaining Life Assessment Method by using High-Temperature Indentation Creep Test

Proposal of Creep Remaining Life Assessment Method by using High-Temperature Indentation Creep Test

Intrinsic ductility for structural materials as a function of stress and temperature

In recent years, a method has been developed to measure current creep strength at nearly constant structure in a high precision stress relaxation test (SRT), covering at least five decades in creep rate in a one day test. Results have been reported on a wide range of metallic alloys, polymers, composites and ceramics. In the present paper it is shown that these same data can be used to determine a measure of intrinsic ductility over the same range of stress, using results on a low alloy Cr–Mo–V steel. This is based on an experimental and theoretical correlation between elongation at failure and strain rate sensitivity, m. This refined SRT test can now be used to evaluate both the intrinsic creep strength and the intrinsic ductility as a function of stress in a single short-time test. The test can detect embrittling phenomena at very low creep rates as a function of temperature. This measure of ductility may be used directly in engineering design and remaining life assessment.

Performance-based remaining life assessment of reinforced concrete bridge girders

Performance-based remaining life assessment of reinforced concrete bridge girders, subject to chloride-induced corrosion of reinforcement, is addressed in this paper. Towards this, a methodology that takes into consideration the human judgmental aspects in expert decision making regarding condition state assessment is proposed. The condition of the bridge girder is specified by the assignment of a condition state from a set of predefined condition states, considering both serviceability-and ultimate-limit states, and, the performance of the bridge girder is described using performability measure. A non-homogeneous Markov chain is used for modelling the stochastic evolution of condition state of the bridge girder with time. The thinking process of the expert in condition state assessment is modelled within a probabilistic framework using Brunswikian theory and probabilistic mental models. The remaining life is determined as the time over which the performance of the girder is above the required performance level. The usefulness of the methodology is illustrated through the remaining life assessment of a reinforced concrete T-beam bridge girder.

State Assessment of Ukrainian and Other Countries Power Equipments

The power capacity growth to meet increasing electricity demand is complicated by a significant number of power units having operating lifetime expired. However, the domestic and foreign practice shows that the actual operating life of power units is often substantially longer than it is claimed by manufacturers. Lifetime extension of existing power units is a common international practice ensuring power generation at the achieved level until new power generating capacity is put into operation. The article provides analysis of the current state of power equipment of Ukrainian thermal and nuclear power plants. The main differences and problems in assessment of remaining service life of critical components of TPP and NPP units are comprehensively considered. A comparative analysis of domestic and foreign methods for equipment remaining life assessment is provided. The main problem of ensuring sustainable unit performance is raised within the article.

Advanced Methodologies for Fracture Analysis and Damage Tolerant Evaluation

The objective of the paper is to present the advanced methodologies for fracture analysis and damage tolerant evaluation of metallic structural components for efficient and safe design of structural systems meeting the functional criteria. An efficient and novel Numerically Integrated-Modified Virtual Crack Closure Integral (NI-MVCCI) technique has been demonstrated for 4-noded bilinear, 8-noded (regular & quarter-point), 9-noded Lagrangian and 12-noded cubic isoparametric family of finite elements. Another advanced numerical method, Extended Finite Element Method (XFEM) for fracture analysis of cracked stiffened panels has been discussed. Methodologies for crack growth and remaining life assessment of structural components under constant and variable amplitude loading have been presented. Brief description on residual strength evaluation has been provided. Numerical studies on fracture analysis to compute Strain Energy Release Rate (SERR), G and stress intensity factor (SIF) and remaining life assessment and residual strength evaluation have been conducted and the results are compared with the respective analytical/experimental results.

設備の余寿命診断技術

Crack occurs on machine equipment by the unexpected load, finally machine is damaged. In order to prevent machine damage, there is an effective means to assume remaining life assessment by using the crack information that contains the load history information. In this paper, we propose for the remaining life assessment methods by the crack length information, to report a case study to the spindle of the rolling mill.

Low cycle thermomechanical fatigue of VVER-440 reactor pressure vessel steels: Investigation the fatigue kinetics and development of a life assessment model

The fatigue life of the structural materials 15Ch2MFA (CrMoV-alloyed ferritic steel) and 08Ch18N10T (CrNi-alloyed, Ti-stabilized austenitic steel) of the VVER-440 reactor pressure vessels was investigated under fully reversed total strain controlled low cycle fatigue tests. The measurements were carried out in isothermal conditions at 260 °C and with thermal-mechanical conditions in temperature range of 150 to 270 °C using the GLEEBLE 3800 servo-hydraulic thermal-mechanical simulator.Owing the nominal fatigue lifetime for different testing conditions interrupted fatigue tests were carried out to investigate the kinetics of the fatigue evolution. Microstructural evaluation of the samples was performed using transmission electron microscopy as well as X-ray diffraction, and measurement of the dislocations was completed. The course of dislocation density in relation to cumulative usage factor was similar for both materials. However, the nature and distribution of dislocations were different in the individual steels and this resulted in different mechanical behaviours.Using scanning electron microscopy the crack shapes and fracture surfaces were observed and analysed. Crack propagation was assessed in relation to the actual crack size and the loading level.A new low cycle fatigue criterion is presented based on the stored energy, which accumulates in the material during fatigue loading. The new damage parameters are based on the assumption that only the stored part of the introduced energy causes the changes in the microstructure. The proposed model is physically consistent and its prediction accuracy is higher than by the classical strain amplitude and strain energy based approaches.The low cycle fatigue behaviour investigated with the developed engineering model can provide a reference for the remaining life assessment and possible operation life extension of nuclear power plant components.

Remaining life assessment methodology for aged aircraft fleet

World experience in last few decades has shown that aircraft usage varies from aircraft to aircraft, mission to mission and user to user. This paper describes the procedure to predict the remaining life of an in service aircraft based on the data from onboard flight data recorders. The proposed method uses 'rain flow cycle counting' and 'Palmgren-Miners' techniques to correlate flight parameters with usage frequency for structural life prediction and computes the impact of the actual loads resulting in 'strength degradation' and 'expected remaining life'. It identifies the most stressed areas along with fatigue life cycles thus estimating the remaining life cycles. The data acquired through the successful application of proposed methodology is also assistive in determining the maintenance cycle and its revision, which is a major cost driver during operations. The results attained through computations directly correspond to the severity of usage.