Non-destructive Condition Monitoring Research Articles

Modelling end–OF–life of radiolytically and thermally aged cable insulations by non-destructive condition monitoring parameters

Many United States nuclear power plants (NPPs) are seeking to renew life licenses to extend the operational life of the plant to an additional 20 or 40 years. Radiation and thermal degradation of insulation and jacket of cables, which are originally designed for 40 years in the second round of operation, is a critical issue which can impair the safe and reliable function of cables and ultimately the plant. The main criterion for assessing the end of life of these insulations is defined when the elongation at break (EAB) reaches 50% of its original value.In this work, a new model to estimate the end-of-life of insulation cables aged by radiation and thermal stressors is established. The model is based on correlating the effective activation energy corresponding to EAB changes to the effective activation energy corresponding to non-destructive examination condition monitoring, NDE-CM, parameters. This includes the correlation between the effective activation energy of EAB changes and the effective activation energy corresponding to CM parameters, water-uptake, Gel%, strength at break (SAB), oxidation index (OI), indenter modulus and density. The calculated effective activation energy of radiolytically aged cables is based on Time-Temperature dose-rate superposition and that of thermally aged cables is based on Time-Temperature superposition approach.The database of this model is based on cable polymer aging database (C-PAD) along with experimental results done in the university of Maryland (UMD) laboratory.The published experimental results of cable insulations aged by radiation stressor were used to validate the model. A good fit between the experimental and modeled results confirms the validity of the model.

Mechanically induced dye-release from polyurea microcapsules in a rubbery adhesive

Especially in the building industry the demand for in situ monitoring concepts of adhesive joints persists. In a new approach, microcapsules filled with special dyes, are added into a rubbery adhesive. Certain stress levels within the adhesive lead to a breakage of the capsules, which release their liquid cores. This results in a detectable colour change and thus, enables non-destructive condition monitoring of the bond. Dye-filled polyurea microcapsules were produced by interfacial polymerization by varying synthesis parameters while their influence on capsule morphology and wall thickness was determined. The morphology and thermal properties of the microcapsules were characterized by scanning electron microscopy and dynamic differential calorimetry, respectively. Subsequently, the method of nanoindentation was used to study the deformation and fracture behaviour of the microcapsules. Finally, it was analysed to what extent the microcapsules break within a polymer matrix, e.g. by critical stress levels or deformations. This development is a new quality assurance method for glass façades.

Implementation of Non-Destructive Condition Monitoring Techniques on Low-Voltage Nuclear Cables: II. Thermal Aging of EPR/CSPE Cables

Determining the aging state of low-voltage nuclear power plant cables using a nondestructive and reliable condition monitoring technique is highly desirable as the cables experience multiple aging stresses during the service period. This paper deals with the implementation and investigation of such nondestructive techniques, which can detect the overall aging state of low-voltage instrumentation and control (I&C) cables, which are subjected to accelerated thermal aging. The dielectric spectroscopy, extended voltage response, and polarization–depolarization current as nondestructive electrical aging techniques were used for the investigation purpose, while the elongation at break was also adopted as a mechanical measurement and for comparison. Prominent variations in the electrical parameters for the insulation and jacket were observed, whereas the elongation at break for both materials also decreased under thermal aging. Based on the electrical techniques, aging markers were selected that showed a strong correlation with the aging and elongation at break, proving the ability of the adopted electrical methods as a nondestructive condition monitoring technique.

Multi scale aging assessment of low-voltage cables subjected to radio-chemical aging: Towards an electrical diagnostic technique

In this article, the aging behavior of nuclear-grade low voltage cables, characterized by different geometries and insulation compositions, is investigated. Cables were subjected to radio-chemical aging at different dose rates (7 Gy/h, 66 Gy/h and 400 Gy/h), in order to simulate typical aging environments inside nuclear plants. The changes of insulation properties due to aging are investigated at different scales, aiming at highlighting possible correlations between molecular-scale properties and global macroscopic material behavior (e.g., mechanical and electrical ones). Microscale material behavior is investigated by means of FTIR spectroscopy and oxidation induction time (OIT) measurements, in order to evaluate material composition changes and material resistance to oxidation, respectively. On the other side, mechanical and electrical macroscopical properties are examined through tensile stress and dielectric spectroscopy measurements. It is found that aging is deeply influenced by the effect of additives (e.g. antioxidants) inside the insulation. In particular, the presence of antioxidants delays oxidation process allowing material modifications during the early aging states to be evaluated. Dielectric spectroscopy is demonstrated to properly follow all the stages of the degradation process, confirming its appropriateness as a non-destructive condition monitoring technique for cables. Finally, the evolution with aging of the dielectric response is associated with the variations of the considered chemical and mechanical properties, allowing the derivation of correlation master curves.

Aging Mechanisms and Non-Destructive Aging Indicators of XLPE/CSPE Unshielded LV Nuclear Power Cables Subjected to Simultaneous Radiation-Mechanical Aging.

Low-voltage cable systems in nuclear power plants are key components that have a crucial role in the safe operation of nuclear facilities. Thus, the aging management of cable systems is of utmost importance as they cannot easily or economically be replaced or upgraded. Therefore, there is a continuous need to develop reliable non-destructive condition monitoring techniques, mostly based on the measurement of the dielectric properties of cable insulation. This paper introduces the changing of dielectric and mechanical properties of XLPE insulated and CSPE jacketed unshielded low-voltage nuclear power plant power cable in case of simultaneous mechanical and radiation aging. The cable samples were bent and exposed to 400 kGy gamma irradiation with a 0.5 kGy/hr dose rate. Dielectric response (real and imaginary permittivity) in the 0.1 Hz−1 kHz frequency range, extended voltage response (EVR), and the Shore D hardness test techniques were measured to track aging. The electrical and mechanical parameters have increased monotonically with aging, except the imaginary permittivity, which increased only at frequencies higher than 10 Hz. Furthermore, different quantities were deducted based on the frequency and permittivity data. The electrical parameters and deducted quantities correlation with aging and mechanical parameters were investigated. Since the deducted quantities and the electrical parameters are strongly correlated with absorbed dose and mechanical properties, the electrical measurements can be applied as a non-destructive aging indicator for XLPE/CSPE unshielded low-voltage nuclear power cables.

Implementation of Non-Destructive Electrical Condition Monitoring Techniques on Low-Voltage Nuclear Cables: I. Irradiation Aging of EPR/CSPE Cables

In a nuclear power plant environment, low-voltage cables experience different stresses during their service life which challenge their integrity. A non-destructive and reliable condition monitoring technique is desired to determine the state of these low-voltage cables during service and for the life extension of nuclear power plants. Hence, in this research work, an EPR/CSPE-based low-voltage cable was exposed to γ-rays for five different absorbed doses. The overall behavior of the cable under stress was characterized by frequency and time domain electrical measurements (capacitance, tan δ, and Extended Voltage Response) and a mechanical measurement (elongation at break). Significant variations in the electrical parameters were observed, as was a decline in the elongation at break values. A strong correlation between the measurement methods was observed, showing the ability of the electrical methods to be adopted as a non-destructive condition monitoring technique.

Nondestructive Testing and Condition Monitoring Techniques Based on Infrared Imaging

Nondestructive Testing and Condition Monitoring Techniques Based on Infrared Imaging

Application of Non-Destructive Condition Monitoring Techniques on Irradiated Low Voltage Unshielded Nuclear Power Cables

In this paper, the effect of radiation stress on the overall degradation of jacket and insulation of low voltage unshielded power cable used in nuclear power plants is discussed. The XLPE insulated and CSPE jacketed cable samples were exposed to a total dose of 400 kGy γ-irradiation with 0.5 kGy/h dose-rate. Dielectric spectroscopy; complex permittivity, and extended voltage response; namely slopes of decay and return voltages were used to study the effect of the irradiation on the cable with an aim to establish the application of these techniques for a non-destructive condition monitoring of the unshielded cables. Shore D hardness was also used to investigate the mechanical characteristic of the cable. It was observed that the radiation stress affected the electrical and mechanical properties of the cable polymeric components i.e. insulation and jacket. The imaginary part of permittivity at low frequency; 100 Hz, the slope of return voltage, and hardness showed a significant increase with absorbed dose showing the effect of irradiation on the jacket and insulating material, as well. A strong correlation was observed between the imaginary part of permittivity at 100 Hz, slopes of return voltage, and hardness. The results show the dielectric measurement techniques are potential non-destructive condition monitoring methods for the unshielded low voltage nuclear power plant power cables for on-site diagnosis.

Modeling of cartographic parameters in the flow part of an energy machine for safe vibro-drying of grain

The present article is devoted to the modeling of a gas-air flow at the nozzle of the energy machine designed for the use in the agricultural sector. The machine has an option of secure vibro-drying of grain crops and their control, which increases the drying performance both in the steady-state and transient modes. The article also presents a mathematical model describing acoustic processes in a flow part of the energy machine and suggests the ways to improve them for their safe operation. The authors outline the principles of construction of complex drying systems of aero-acoustic cartography, which allow controlling the parameters of energy machines serving grain crops drying and the climatic parameters depending on the volume of grain dryers. This is very important for productivity increase and automated control in real time, supplemented by methods and means of measurements of gas-dynamic parameters in the flow and at the nozzle of the energy machine. These methods are aimed at increasing information capacity and the level of algorithmic non-destructive condition monitoring of rotor blades as well as providing data in terms of parametric and structural uncertainties of the gas-air flow as controlled by the internal cross-section of the flow part, and the output section of the energy machine. Statistical approaches are used to determine the coordinates of sensors and the recovery error on the example of a model problem for monitoring the radiation field created by a continuous monopole emitter. The possibility of using fiber technologies for vibro-drying of grain is a new contribution to the improvement and effective management of grain drying process.

A non-destructive fault diagnosis method for a diaphragm compressor in the hydrogen refueling station

Costly and time-consuming maintenance of the hydrogen compressors due to their frequent breakdown severely hinders the deployment and promotion of hydrogen refueling station (HRS), and effective condition monitoring and fault diagnosis is the key to reduce the unscheduled downtime of the compressor. This paper proposes a non-destructive method for fault diagnosis of diaphragm compressors for HRSs based on the acoustic emission (AE) signal. The AE signals in the time domain are segmented into angle-domain signals correspond to a working cycle. The feature events of the moving components are determined through the measured AE signal in both angle-domain and angle-frequency domain based on short-term Fourier transform (STFT). Those feature events signals are innovatively applied to identify the typical abnormal conditions of excessively high oil pressure, slightly inadequate oil pressure and seriously inadequate oil pressure, replacing the traditional and destructive pressure measuring method. The results show that this method can be used to effectively diagnose abnormal working conditions and indicate that this method can be utilized as a powerful tool in the non-destructive condition monitoring and fault diagnosis of the diaphragm compressors.

A new non-destructive method for fault diagnosis of reciprocating compressor by measuring the piston rod strain

As an established method to analyse the thermodynamic process inside the cylinder, the p-V diagram can identify typical faults such as leakages through the sealing rings and self-acting valves, loosening and fluttering of the vales, etc. However, the installation of the pressure sensor within the cylinder for recording the p-V diagram may lead to degradation of the cylinder integrity, and hereby potential leakage and lowered strength of the cylinder. This paper presents a new non-destructive method for fault diagnosis of the reciprocating compressor by measuring the piston rod strain, from which the p-V diagram was transformed. An algorithm for reconstruction of the p-V diagram was proposed based on the key feature points on the piston rod load curve that reflect the opening and closing events of the compressor valves. The reconstruction method was validated by comparing the calculated p-V diagrams with the experimental results. The reconstructed p-V diagrams were further used for fault diagnosis of the reciprocating compressors, with which the acoustic emission method was integrated. The results show that this method can easily monitor the working conditions and identify whether and where leakage, fluttering and delayed closing of the valves occur, which indicates that this method can be utilized as a powerful tool of non-destructive condition monitoring and fault diagnosis of the reciprocating compressors.

A new method for nondestructive fault diagnosis of reciprocating compressor by means of strain-based p–V diagram

Abstract As an established method to analyse the thermodynamic process inside a cylinder, the pressure–volume (p–V) diagram can identify typical faults within industrial reciprocating compressors, such as leakages through the sealing rings and self-acting valves, and loosening and fluttering of the valves. However, the installation of a pressure sensor within the cylinder for recording the p–V diagram may lead to degraded strength and potential leakage associated with the cylinder and hence, deteriorated integrity of the cylinder. This study proposes a new nondestructive method to record the p–V diagram of the reciprocating compressor by measuring the piston rod strain. An algorithm for reconstructing the p–V diagram was proposed based on the key feature points on the piston rod load curve that reflects the opening and closing events of the compressor valves. The algorithm was validated by comparing the p–V diagrams obtained from direct pressure measurement and strain-based derivation. The reconstructed p–V diagrams were further used for the fault diagnosis of the reciprocating compressors. The results indicate that this method is able to easily monitor the operating conditions and identify whether and where faults such as leakage and fluttering of the valves occur, and it can be utilized as a powerful tool in the nondestructive condition monitoring and fault diagnosis of the reciprocating compressors.

Microencapsulated markers for damage detection in adhesive joints

ABSTRACTThe durability of adhesive bonds is not only affected by the quality of the bonding procedure but also by aging processes which influence the bond performance negatively on a long time scale. Especially the building industry, where safety related joints are increasingly boned with adhesives, demands new quality assurance methods. Therefore, appropriate monitoring techniques for developing cracks or critical stresses are essential.A new approach for in situ monitoring of transparent/opaque adhesives will be presented in this paper. Microcapsules, filled with special dyes, are embedded into adhesive systems. Upon breakage through cracks or exceedance of certain stress levels within the adhesive seam, the capsules release their liquid cores which leads to a detectable color change and, thus, enables non-destructive condition monitoring of the bond. In order to examine the feasibility of the approach, microcapsules are formed via interfacial polymerization. Microscopy techniques such as optical or scanning electron microscopy allow to study the capsule morphology, shape and dimensions (size and wall thickness) in dependence to the preparation procedure. Thereupon, the durability and release behavior are investigated with thermal analyses (differential scanning calorimetry and thermogravimetric analyses). Atomic force-based nanoindentation measurements give an insight into the size-dependency of mechanical properties like stiffness and burst forces.Finally, the principle of health monitoring is evaluated by dispersing the prepared capsules in the adhesive systems.Apart from the experimental examinations, numerical simulations of the crack propagation within the adhesive matrix are performed to demonstrate the effect of different microcapsule sizes and capsule walls on the fracture behavior.This preliminary study demonstrates the basic feasibility of the approach, but there is still a great need for investigations in order to employ the concept for industrial purposes.

Non-destructive online condition monitoring and trend prediction of lubricating oil in a steam turbine

Non-destructive online condition monitoring and trend prediction of lubricating oil in a steam turbine

Non-destructive condition monitoring of aged ethylene-propylene copolymer cable insulation samples using dielectric spectroscopy and NMR spectroscopy

The causes of changes in dielectric response as a result of thermal and irradiative ageing of cable insulation of ethylene propylene copolymer rubber containing 38 wt.% filler were investigated. Samples were aged in three different combinations of irradiation dose rate and temperature, 0.42 kGy h−1 at 85 °C, and 1.58 kGy h−1 at 55 and 85 °C, and subsequently studied by dielectric spectroscopy, NMR spectroscopy using a portable spectrometer, and tensile testing. The extractable mass fraction and density were determined and related to the imaginary part of the dielectric permittivity at 100 kHz. The ageing led to an increase in the dielectric permittivity, stiffness, density and degree of oxidation, together with a decrease in both strain-at-break and relaxation time, as revealed by NMR spectroscopy. Except for the strain-at-break, the properties changed in a linear fashion with increasing imaginary part of the dielectric permittivity at 100 kHz, with particularly good agreement with respect to the density. As these properties are affected by the degree of oxidation, the results show that both NMR using a portable spectrometer and dielectric spectroscopy can be used as condition monitoring techniques to detect the degree of oxidation in complex systems such as filled copolymers.

Prevention of In-Service Failure of Seal Valve Axles of Blast Furnace Through Non-destructive Condition Monitoring

The upper and lower seal valves together form a key part in the top charging system of blast furnaces. The valves serve to create a gas-tight chamber during the charging of furnaces preventing the escape of blast furnace gas into the atmosphere during the operation. The axles in these valves are an integral part in the sealing mechanism of the valve flaps. Several accounts of failure of these axles in service at a Blast Furnace prompted the need for a predictive maintenance practice. This paper accounts for the failure analysis done on these axles to arrive at the root cause of failure and further the implementation of suitable NDT techniques for condition monitoring of the axles. This ultimately led to prevention of further in-service failures.

Monitoring of the physical aging of radiation cross-linked conductive rubber blends containing clay nanofiller

Polymeric materials are widely used as insulation and jacketing materials in wire and cable. When such materials are used for long-term applications, they undergo thermal oxidation aging in the environment. It is necessary to develop an in situ and non-destructive condition monitoring (CM) method to follow the aging of cable materials. The main objective of this work was to investigate polymer composites as potential sensor materials for this purpose. Rubber/carbon black composites with a carbon black loading below the percolation threshold underwent accelerated thermal oxidation aging experiments. The results indicated that the substantial resistivity decreases of the composites could be directly related to the increases in volume fraction of the conductive carbon black, which was mainly caused by the mass loss of polymer matrix and sample shrinkage during the thermal oxidation aging process. Compared to existing CM method based on density change, the electrical resistivity is more explicit regarding its absolute changes throughout the thermal oxidation aging. The change in resistivity spanned over two orders of magnitude, whereas the composite density only increased 5%. The results offer strong evidence that resistivity measurements, which reflect property changes under thermal aging conditions, could represent a very useful and non-destructive CM approach as well as a more sensitive method than density CM approach.

Optical Nondestructive Condition Monitoring of Thermal Barrier Coatings

This paper describes recent developments of the thermal barrier sensor concept for nondestructive evaluation (NDE) of thermal barrier coatings (TBCs) and online condition monitoring in gas turbines. Increases in turbine inlet temperature in the pursuit of higher efficiency will make it necessary to improve or upgrade current thermal protection systems in gas turbines. As these become critical to safe operation, it will also be necessary to devise techniques for online condition monitoring and NDE. The authors have proposed thermal barrier sensor coatings (TBSCs) as a possible means of achieving NDE for TBCs. TBSCs are made by doping the ceramic material (currently yttria-stabilized zirconia (YSZ)) with a rare-earth activator to provide the coating with luminescence when excited with UV light. This paper describes the physics of the thermoluminescent response of such coatings and shows how this can be used to measure temperature. Calibration data are presented along with the results of comparative thermal cycle testing of TBSCs, produced using a production standard air plasma spray system. The latter show the durability of TBSCs to be similar to that of standard YSZ TBCs and indicate that the addition of the rare-earth dopant is not detrimental to the coating. Also discussed is the manufacture of functionally structured coatings with discreet doped layers. The temperature at the bond coat interface is important with respect to the life of the coating since it influences the growth rate of the thermally grown oxide layer, which in turn destabilizes the coating system as it becomes thicker. Experimental data are presented, indicating that dual-layered TBSCs can be used to detect luminescence from, and thereby the temperature within, subsurface layers covered by as much as 500 μm of standard TBC material. A theoretical analysis of the data has allowed some preliminary calculations of the transmission properties of the overcoat to be made, and these suggest that it might be possible to observe phosphorescence and measure temperature through an overcoat layer of up to approximately 1.56 mm thickness.

Dedicated On-Site Condition Monitoring of High Voltage Power Cables up to 150kV

For advanced, non-destructive on-site condition monitoring of HV power cables up to 150kV by partial discharge detection and dielectric losses measurement it is necessary to energize the disconnected cable system. One of the methods available for this purpose is based on applying damped AC voltages up to 150kV. In this paper, the use of modern technological solutions in power electronics and signal processing as well as in technical design and production methods will be discussed on the basis of the ultra light system (300kg) which is able to test cables up to 20km lengths.

An electrical approach to monitor wire and cable thermal oxidation aging condition based on carbon black filled conductive polymer composite

Polymeric materials are widely used as insulation and jacketing materials in wire and cable. When such materials are used for long-term applications, they undergo thermal oxidation aging in the environment. It is necessary to develop an in situ and nondestructive condition monitoring (CM) method to follow the aging of cable materials. The main objective of this work was to investigate low-density polyethylene/carbon black (LDPE/CB) conductive polymer composites as potential sensor materials for this purpose. LDPE/CB composites with a carbon black loading below the percolation threshold underwent accelerated thermal oxidation aging experiments. The results indicated that the substantial resistivity decreases of the LDPE/CB composites could be directly related to the increases in volume fraction of the conductive carbon black, which was mainly caused by the mass loss of polymer matrix and sample shrinkage during the thermal oxidation aging process. Compared to existing CM method based on density change, the electrical resistivity is more explicit regarding its absolute changes throughout the thermal oxidation aging. The change in resistivity spanned over four orders of magnitude, whereas the composite density only increased 10%. The results offer strong evidence that resistivity measurements, which reflect property changes under thermal aging conditions, could represent a very useful and nondestructive CM approach as well as a more sensitive method than density CM approach. Crystallinity changes in materials investigated by modulated DSC and TGA measurements indicated deterioration of crystalline regions in polymer during the thermal oxidation aging. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 513–520, 2004