Integrity Assessment Of Components Research Articles

Material Characterization using Barkhausen Noise Analysis Technique - A Review

Background/Objective: Material characterization is an essential part during manufacturing cycle of component as it assesses the surface integrity of component. Assessment of surface integrity is important since it decides the fatigue strength and service life of manufactured component. Microhardness, microstructure and residual stress are key elements of surface integrity. Modern manufacturing industries relies on laboratory based technique such as microhardness tester, optical metallographic inspection and X-ray Diffraction (XRD) techniques for measurement of key elements of surface integrity. The laboratory based techniques are not eco-friendly and as well as time consuming. Methods/Statistical Analysis: Barkhausen Noise (BN) analysis is a preferred and advanced technique for material characterization when an external magnetic field is applied over a ferromagnetic material, it changes the global magnetization occurs by motion of magnetic domain wall as these domain wall align these stress in the direction of applied magnetic field. A voltage pulse is generated due to motion of magnetic domain, which can be detected as signal by sensor. This included voltage pulse is known as BN signal. Findings: Conventional material characterization techniques such as hardness tester, optical microscopic and XRD are extensive time consuming laboratory based technique and difficult to integrate in manufacturing environment. On the other hand, BN technique is less costly, fast, eco-friendly NDT which can be easily integrated with manufacturing cycle for component. Application: Barkhausen Noise measurement is generally associated with hysteresis loop measurement.BN signal parameters such as Root Mean Square (RMS) value, amplitude, peak position as well as hysteresis loop properties coercively, remanence are sensitive towards change in micro-hardness, microstructure In this way, BN analysis technique can assess the surface integrity of manufactured component. In the present review paper, a critical and wide literature survey is conducted to summarize and highlight the successful attempts of BN techniques for surface integrity assessment of components, by using various manufacturing process such as machining, welding, heat treatment and grinding.

Advances on creep–fatigue damage assessment in notched components

AbstractIn this paper, the extended Direct Steady Cyclic Analysis method (eDSCA) within the Linear Matching Method Framework (LMMF) is combined with the Stress Modified Ductility Exhaustion method and the modified Cavity Growth Factor (CGF) for the first time. This new procedure is used to systematically investigate the effect of several load parameters including load level, load type and creep dwell duration on the creep–fatigue crack initiation process in a notched specimen. The results obtained are verified through a direct comparison with experimental results available in the literature demonstrating great accuracy in predicting the crack initiation life and the driving mechanisms. Furthermore, this extensive numerical study highlighted the possible detrimental effect of the creep–ratchetting mechanism on the crack growth process. This work has a significant impact on structural integrity assessments of complex industrial components and for the better understanding of creep–fatigue lab scale tests.

Damage analysis and integrity assessment of a few steam-reformer components at a syn-gas plant

Study deals with damage-analysis and integrity-assessment for a few components of a steam-reformer at a syn-gas generation plant, including catalyst tubes and hot-collectors. Selected components include the ones which either suffered from a fluid-leakage in the service or noticed with a constant high-temperature exposure during normal plant operation. The field investigation activities included visual inspection, dimensional check, die-penetrant test and pressure-drop measurements. Laboratory investigation, made on selective samples, included precise and detailed dimensional-measurement, visual examination, die penetrant test, microstructural characterization, creep-rupture test, etc. As a result of diagnostic analysis, creep was identified as the principal mechanism of degradation of the studied components. Catalyst tubes were found to be in sound condition and, hence, recommended to continue in use for the remaining period of the service-life, even after high-temperature exposure in the past. Other items; however, were noticed with a limited residual creep strength, hence, rejected for future use. Further, recommendations were made for improvement in practices of process- and operation-management, to avoid pre-mature deterioration of the reformer components. In addition, suggestions were given for enhancing the versatility and reliability of plant inspection and monitoring methods, using latest tools and technology of the field. Moreover, suitability and limitation of different analytical approaches regarding interpretation of test and inspection results are highlighted.

Assessment of steel components and reinforced concrete structures under steam explosion conditions

Even though extensive researches have been performed for steam explosion due to their complex mechanisms and inherent uncertainties, establishment of severe accident management guidelines and strategies is one of state-of-the arts in nuclear industry. The goal of this research is primarily to examine effects of vessel failure modes and locations on nuclear facilities under typical steam explosion conditions. Both discrete and integrated models were employed from the viewpoint of structural integrity assessment of steel components and evaluation of the cracking and crushing in reinforced concrete structures. Thereafter, comparison of systematic analysis results was performed; despite the vessel failure modes were dominant, resulting maximum stresses at the all steel components were sufficiently lower than the corresponding yield strengths. Two failure criteria for the reinforced concrete structures such as the limiting failure ratio of concrete and the limiting strains for rebar and liner plate were satisfied under steam explosion conditions. Moreover, stresses of steel components and reinforced concrete structures were reduced with maximum difference of 12% when the integrated model was adopted comparing to those of discrete models.

Characterization of heat affected zones produced by thermal cutting processes by means of Small Punch tests

Thermal cutting processes introduce changes in the heat affected zone (HAZ), which can lead to a significant reduction of the service life of components. In order to assess their influence, different cutting processes have been analysed on a structural steel. The characterization of the reduced volumes of HAZ posed a major challenge, since conventional techniques require greater pieces of material. Alternative miniature techniques had to be applied, such as Small Punch tests and microhardness measurements, from which the material tensile properties and fracture toughness values have been obtained. Results show that oxyfuel HAZ exhibit minor alterations of the material, while plasma cutting seems to improve the material tensile properties and fracture toughness. Besides, the suitability and accuracy of the Small Punch technique for similar applications can be derived from this work, turning it into a promising candidate to perform integrity assessments of actual components.

Importance and Methods of Residual Stress Profile Measurement

The contribution is dedicated to surface integrity assessment of components from the point of view of residual stress profile after machining and finishing technologies. Residual stresses play the key role for dynamic life and service reliability of the part, especially rotating aircraft airfoils made of titanium and nickel base alloys. Except a brief summary of measurement methods practical experience with application of Beam deflection method combined with electrolytic etching is published. Specific measurement results for real aircraft Ti6Al4V airfoils and Ti6Al4V plates following its manufacturing technology are the subject of experimental part.

Structural integrity assessment of glass components in Concentrated Solar Power (CSP) systems

Due to the importance of glass components in Concentrated Solar Power (CSP) systems, an integrated assessment procedure conceived to facilitate the design of an intrinsically brittle component, limiting the amount of calculations, is presented. Since the fracture strength of brittle materials depends on the size and distribution of flaws as well as the duration of loading, conventional design approaches are generally very conservative and large safety factors are often used. However, these large safety factors are somewhat arbitrary and not satisfactory, because it is not very clear what the true factor of safety really is. In this paper, it is firstly reviewed and discussed the advanced methods to characterise the strength of glass. Then, based on the Weibull statistical method and the resulting probabilistic theory of the weakest link, a new modelling framework is proposed to consider different possible failure mechanisms (over-loading fracture and stress corrosion induced failure). In this way, the size effect as well as the multi-axial stress effect (including the contact stress between the glass component and the mount assembly) are considered. The integrated assessment procedure for structural glass elements is developed and implemented as a post-process of finite element analysis. The proposed procedure is demonstrated trough an application example: the design of a glass window to be used in a solar furnace reaction chamber.

Prediction of retained residual stresses in laboratory fracture mechanics specimens extracted from welded components

The measurement of weld material fracture toughness properties is important for the structural integrity assessment of engineering components. However, welds can contain high levels of residual stress and these can be retained in fracture mechanics specimens, particularly when machined from non-stress relieved welds. Retained residual stresses can make the measurement of valid fracture toughness properties difficult. This paper describes the results of analytical work undertaken to investigate factors that can influence the magnitude and distribution of residual stresses retained in fracture mechanics specimen blanks extracted from as-welded ferritic and austenitic stainless steel plates. The results indicate that significant levels of residual stress can be retained in specimen blanks prior to notching, and that the magnitude and distribution of stress is dependent upon material properties, specimen geometry and size, and extraction location through the thickness of the weld. Finite element modelling is shown to provide a useful approach for estimating the level and distributions of retained residual stresses. A new stress partitioning approach has been developed to estimate retained stress levels and results compare favourably with FE analysis and available experimental data. The approach can help guide the selection of specimen geometry and machining strategies to minimise the level of residual stresses retained in fracture mechanics specimen blanks extracted from non stress-relieved welds and thus improve the measurement of weld fracture toughness properties.

Estimating the Ultimate Energy Dissipation Capacity of Steel Pipe Dampers

Steel pipe damper specimen tests are very important but expensive and time consuming. Therefore efficient tools are needed to minimize the expense and the time by avoiding unnecessary or unneeded tests. This paper elaborates a practical component integrity assessment using finite element ductile fracture simulation based on local approach, and estimates the ultimate energy dissipation capacity of steel pipe dampers using energy based damage model. Ductile fracture in steel components that happens in fewer than twenty constant amplitude loading cycles is known as Ultra Low Cycle Fatigue (ULCF). Under ULCFs load steel pipe dampers experienced large scale cyclic yielding. Accurate preliminary prediction of ductile fracture is critical to estimate the performance of steel pipe dampers. The hysteretic behavior and ultimate energy dissipation capacity are investigated via finite element simulation after the component integrity assessment has been done. A micromechanics-based model which provide accurate criteria for predicting ductile fracture and an energy-based damage model to quantify the ultimate energy dissipation capacity of steel pipe dampers are applied. Using these approaches, ultimate energy dissipation capacity of steel pipe dampers can be estimated under various patterns of loadings. The approaches described here can also be applied to other steel dampers subjected to randomly flexural/shear stress reversals.

Creep–fatigue crack development from short crack starters

A series of isothermal strain controlled creep–fatigue tests on fully instrumented cylindrical specimens with shallow chordal crack starters has been conducted for an advanced 9%Cr turbine rotor steel at 600 and 625°C. Cyclic/hold wave shapes involving a dwell period at peak strain in tension or compression were also performed with crack development being monitored by means of electrical potential drop instrumentation. It is found that temperature, total strain range and hold period are the most influential factors on short creep–fatigue crack propagation rates and specimen life. In order to establish a reliable relationship to represent subcritical crack development for high temperature component integrity assessment, the effectiveness of candidate correlating parameters such as cyclic strain range, cyclic J integral and strain energy density factor have been evaluated. Their application to circumstances involving short crack development due to fatigue, and interacting and non-interacting creep loading are evaluated with reference to the evidence determined from post-test metallurgical examination.

Theoretical and experimental study of fatigue growth of interacting cracks

Life assessment of structures weakened by interacting cracks represents an important and very challenging problem. Subsequently, the main objective of this paper is to address this problem by developing a new computational technique. It is based on the classical strip-yield model and plasticity-induced crack closure concept. It also utilises the 3D fundamental solution for an edge dislocation. The crack advance scheme adopts the cycle-by-cycle calculations of the effective stress intensity factors and crack increments. The modelling results are validated against an experimental study focusing on fatigue behaviour of two closely spaced collinear cracks in wide plates with different thicknesses. It is confirmed that non-linear effects associated with crack interaction have a significant influence on fatigue life and cannot be disregarded in life and integrity assessments of structural components.

Fatigue Crack Growth Behavior of Ferritic and Austenitic Steels at Elevated Temperatures

Abstract For the integrity assessment and damage-tolerant design of components operating at elevated temperatures under cyclic loading conditions, evaluation of fatigue crack growth (FCG) properties in the threshold and Paris regimes is important. The FCG behaviors of a modified 9Cr-1Mo steel (P91) and SS 316L(N) for applications in the prototype fast breeder reactor to be commissioned shortly at Kalpakkam, India have been studied extensively in our laboratory over a wide range of temperatures. Some aspects of high-temperature FCG observed in these investigations will be reviewed in this paper. It has been observed that for many engineering alloys, dynamic strain aging plays an important role in the temperature-dependent variations in deformation and fracture behavior, including the FCG parameters. Another important aspect in deciding the FCG behavior is the crack closure behavior, the mechanisms of which may vary with temperature. Effect of crack closure and DSA on the FCG properties of P91 steel and SS 316L(N) welds will be discussed. The DSA mechanism has been identified from the activation energy for the process determined from the temperature dependence of the crack tip strain rates. During FCG of engineering materials, there can be stress shielding at the crack tip because of various factors, like crack bridging, branching, closure, etc. Effect of stress shielding at the crack tip at different conditions was quantified using a procedure incorporating the inter relations between compliance, crack length, and stress intensity factor. The paper will summarize the results of the above studies.

A fatigue crack growth model for interacting cracks in a plate of arbitrary thickness

ABSTRACTFatigue and fracture assessment of structures weakened by multiple site damage, such as two or more interacting cracks, represents a very challenging problem. A proper analysis of this problem often requires advanced modelling approaches. The objective of this paper is to develop a general theoretical approach and investigate the fatigue behaviour of two interacting cracks. The developed approach is based on the classical strip yield model and plasticity induced crack closure concept. It also utilises the 3D fundamental solution for an edge dislocation. The crack advance scheme adopts the cycle‐by‐cycle calculations of the effective stress intensity factors and crack increments. The modelling results were validated against experimental data available in the literature. Further, the nonlinear effects of the crack interaction and plate thickness on the crack opening stresses and crack growth rates were studied with the new approach for the problem geometry. It was demonstrated that the both effects could have a significant influence on fatigue life and cannot be disregarded in life and integrity assessments of structural components with multiple site damage.

Guidelines for Integrity and Lifetime Assessment of Components and Piping in WWER NPPs during Operation (VERLIFE)

VERLIFE – “Unified Procedure for Lifetime Assessment of Components and Piping in WWER NPPs during Operation “was developed within the 5th Framework Programme of the European Union in 2003 and later upgraded within the 6th Framework Programme “COVERS – Safety of WWER NPPs” of the European Union in 2008.This Procedure has to fill the gap in original Soviet/Russian Codes and Rules for WWER type NPPs, as these codes were developed only for design and manufacture and were not changed since their second edition in 1989.VERLIFE Procedure is based on these Russian codes but incorporates also new developments in research, mainly in fracture mechanics, and also some principal approaches used in PWR codes.To assure that VERLIFE Procedure will remain a living document, new 3-years IAEA project (in close co-operation with another project 6th Framework Programme of the European Union “NULIFE – Plant Life Management of NPPs”) started in 2009.Within this project, upgrading/updating of the VERLIFE procedure is prepared together with the extension by (at least) following procedures:-Lifetime of reactor pressure vessel internals-Leak-before-break concept for WWER NPPs-No-break-zone for WWER NPPs-Probabilistic approach for failure and lifetime assessment of WWER reactor pressure vessels and primary piping (including Risk-informed ISI)-Qualification of NDT procedures-Thermal fatigue evaluation-Supports of components and pipingFinal document, after its approval by expert groups of the IAEA and NULIFE, will be issued in 2014 as “IAEA VERLIFE Guidelines for Integrity and Lifetime Assessment of Components and Piping in WWER NPPs”.

Evaluation of Fatigue Crack Growth Behaviour of SS 316 LN Steel under Mixed Mode Loading (Mode I & II)

Abstract Integrity assessment and life prediction of components under cyclic loading make use of crack growth data determined under opening mode (mode I). However, many service failures occur from growth of cracks subjected to mixed mode loadings, combinations of modes I, II and III. Many efforts to determine crack growth behavior under mixed mode loading have been reported. Many different specimen geometries have been used to produce different combinations of mixed mode loadings under different test conditions. A set of loading grips were designed and fabricated to carry out fracture and fatigue crack growth (FCG) tests using standard compact tension (CT) specimens under mode I+II loading with different levels of mode mixity. Mixed mode FCG experiments were carried out at room temperature on SS 316 LN with a load ratio 0.1, and cyclic loading frequency 15 Hz. Crack growth was monitored using DCPD technique. The FCG results are discussed in terms of KI (Mode-I) and KII (Mode-II) components and combined stress intensity factor KV at different loading angles. The results are compared with those under pure mode I loading.

Safety factors in structural integrity assessment of components with defects

Purpose– The purpose of this paper is to develop basic principles of deterministic structural integrity assessment of a component with a crack- or notch-like defect by including safety factors against fracture and plastic collapse in criteria equations of linear and nonlinear fracture mechanics.Design/methodology/approach– The safety factors against fracture are calculated by demanding that the applied critical stress should not be less than the yield stress of the material for a component with a crack or a notch of the acceptable size. Structural integrity assessment of the engineering components damaged by crack- or notch-like defects is discussed from view point of the failure assessment diagram (FAD). The methodology of the FAD has been employed for the structural integrity analysis and assessment of acceptable sizes of throw-thickness notch in a plate under tension and surface longitudinal notch-like defects in a pressure vessel.Findings– Basic equations have been presented to calculate the safety factor against fracture for critical values of the stress intensity factor, crack tip opening displacement (CTOD), the J-integral and the FAD as well as to estimate an acceptable (safe) region for an engineering component with a crack- or notch-like defect of the acceptable size. It was shown that safety factors against fracture depend on both the safety factor against plastic collapse and employed fracture mechanics criterion. The effect of crack/notch tip constraint is incorporated into criteria equations for the calculation of safety factors against fracture.Originality/value– The deterministic method of fracture mechanics is recommended for structural integrity assessment of a component with a crack- or notch-like defect by including safety factors against fracture and plastic collapse in criteria equations of linear and nonlinear fracture mechanics.

Development of new correlations for improved integrity assessment of pipes and pipe bends

To investigate several unresolved issues and to improve upon the existing equations for integrity assessment of pipes and pipe bends used in nuclear reactors, a comprehensive Component Integrity Test Program (CITP) was initiated at Bhabha Atomic Research Centre (BARC), India. As a part of this program, several fracture tests have been conducted on straight pipes and pipe bends, which forms a valuable data base. Simultaneously, analytical work has been undertaken to propose the improvements in the existing equations for optimized and more accurate integrity assessment of piping components. As an outcome of this analytical investigations, generalized equation of ηpl and γ have been proposed to evaluate J–R curve, study of transferability of fracture properties from specimen to component has been done to highlight the role of constraint parameter, new limit moment equations of elbows have been proposed and new J and COD estimation schemes of throughwall cracked elbows have been proposed. All these newly proposed equations have been experimentally validated with the test data generated under CITP.

On the application of the theory of critical distances to the structural integrity assessment of stress risers

Purpose – The purpose of this paper is to present and validate a methodology for the structural integrity assessment of components containing a variety of stress risers and subjected to static conditions.Design/methodology/approach – The methodology is based on the use of the apparent fracture toughness prediction provided by the theory of critical distances (in this case, the line method), together with a well‐known, widely‐used engineering tool in structural integrity assessments: failure assessment diagrams. In order to validate the proposed methodology, an experimental programme has been conducted, testing 38 specimens made of aluminium alloy Al7075‐T651, each of them containing a certain stress riser. The comparison between the experimental results and the corresponding predictions provided by the proposed assessment methodology has also allowed the situations for which the theory of critical distances provides accurate predictions to be defined.Findings – The results show that the methodology provid...

Structural integrity assessment of metallic components under multiaxial fatigue: the C–S criterion and its evolution

ABSTRACTThe present paper discusses the evolution of a critical plane‐based multiaxial high‐cycle fatigue criterion, known as Carpinteri–Spagnoli criterion. By proposing appropriate changes to the original formulation, the extended versions of the aforementioned criterion are able to assess smooth and notched metallic structural components subjected to different fatigue loading conditions, such as multiaxial in‐phase and out‐of‐phase synchronous cyclic loading, asynchronous cyclic loading and random loading. The results obtained through this criterion are compared with some experimental results related to relevant data reported in the literature.

On a coupled mode at sharp notches subjected to anti-plane loading

Abstract When a crack or sharp notch is subjected to anti-plane shear loading the boundary conditions negate the transverse shear stress components at the free surfaces and generate a coupled in-plane shear stress field, which can be singular. For sharp V-notches with zero notch opening angle (or cracks) this 3D phenomenon was known for a long period of time. However this mode was largely ignored in stress analysis of notched components. Till now it is still unclear how significant this mode is and whether it has to be taken into consideration in integrity and failure analysis of engineering structures. The present paper is aimed to investigate this singular mode by means of the 3D Finite Element method, which is applied to notched plates with different notch opening angles and plate thicknesses. The stress state associated with the coupled mode is localised and quickly decays with the distance from the notch tip. Therefore, the obtained theoretical results can be applied to a wide range of notched components provided that the boundaries are sufficiently far from the notch tip. Among these results is the effect of the plate thickness on the intensity of the coupled mode; the latter increases with the decrease of the plate thickness. Significance of these new results to failure and integrity assessments of plate and shell components with sharp notches, including through-the-thickness cracks, is discussed in the final section of the paper.