Condition monitoring methods applied to degradation of chlorosulfonated polyethylene cable jacketing materials

The Use of Iron(II,III) Oxide (Fe3O4) as a Cross-Linking Agent for Unfilled and Filled Chlorosulfonated Polyethylene (CSM) and Study of the Vulcanizates Properties

This paper discusses the cross-linking behaviors, mechanical and dynamical properties, and flammability of elastomeric composites containing unconventionally cured chlorosulfonated polyethylene (CSM). The purpose of this work was to verify the CSM ability to cross-link with iron(II,III) oxide (Fe₃O₄) and to produce flame retardant materials. During the first series of tests, three types of CSM were used, differing in the content of bound chlorine (29-43%). The results showed that the CSM with 43% bound chlorine (Hypalon 30, CSM43) was the most advantageous type of chlorosulfonated polyethylene in terms of its properties. It exhibited a short vulcanization time, a high degree of cross-linking, and very good mechanical properties. In the next stage, the CSM composites with various fillers (talc, arsil, kaolin, chalcedonite, or carbon black) were prepared, because filled rubber materials are of the greatest practical importance. The cross-linking kinetics, equilibrium swelling, mechanical and dynamic properties as well as flammability were studied. It was found that the addition of fillers led to a decrease in the degree of cross-linking, an increase in the vulcanization time (in the case of talc, arsil, or kaolin), an increase in the overall mechanical strength (in the case of carbon black, arsil or talc). All filled vulcanizates proved to be non-flammable, as the specific oxygen index value exceeded 37.5%.

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.

Comparison of Mechanical and Low-Frequency Dielectric Properties of Thermally and Thermo-Mechanically Aged Low Voltage CSPE/XLPE Nuclear Power Plant Cables

During the service period of low-voltage nuclear cables, multiple stresses influence the aging of polymeric materials of cables. Thermal and radiation stresses are considered service aging factors in qualification tests, while the standards usually do not prescribe mechanical stress. CSPE/XLPE insulated nuclear cable samples were exposed to thermal and combined thermo-mechanical aging for more than 1200 h at 120 °C. The real and imaginary parts of permittivity were measured in the 200 μHz to 50 mHz range as dielectric properties. The Shore D hardness of the samples was measured to analyze the mechanical characteristics of the cable. To characterize the dielectric spectrum, derived quantities, namely central real and imaginary permittivities and real and imaginary permittivities’ central frequencies were calculated. The change of dielectric spectra did not show a clear trend with aging, but the imaginary permittivity’s central frequency was higher by 0.5 mHz in the case of thermo-mechanically aged samples. The Shore D hardness was also higher on the thermo-mechanically aged samples. These findings show the combined aging has a higher impact on the insulation properties. Hence, involving the mechanical stress in the aging procedure of cable qualification enables the design of more robust cables in a harsh environment.

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.

Radio-Oxidation Ageing of XLPE Containing Different Additives and Filler: Effect on the Gases Emission and Consumption

In the lifetime extension of nuclear power plants (NPPs) context, aging of electric cables has to be very well understood in order to predict their end-of-life and thus to replace them on time. Therefore, evaluation and understanding of the ageing mechanism of the cable insulating material is mandatory under conditions as close as possible of those encountered in NPPs. In this context, different formulated crosslinked polyethylenes (XLPE)—one of the polymers used nowadays to manufacture the insulator layer—have been irradiated under oxidative conditions, at two different dose rates and at different aging doses. Gases emitted and consumed from the irradiated polymers were quantified to identify the primary processes happening in the materials and thus the interactions involved between the different molecules composing the formulated polymers.

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.

Single-sided Nuclear Magnetic Resonance for condition monitoring of cross-linked polyethylene exposed to aggressive media

The potential of single-sided Nuclear Magnetic Resonance (NMR) to monitor truly non-invasive changes in polymer materials during aging under aggressive media is for the first time evaluated. For this, the NMR method is used in combination with other condition monitoring methods including mechanical measurements, mass uptake, and differential scanning calorimetry. It is validated by studying for the first time the aging kinetics of silane cross-linked polyethylene (PEX) exposed to media used in oil and gas production and transportation, including aliphatic and aromatic hydrocarbons, sulphur solvents, and corrosion inhibitors in combination with CO2 and H2S. All investigated parameters changed, with the strongest effects detected for the NMR chain mobility and in the presence of hydrocarbons. Furthermore, a universal linear correlation curve could be established between the depression of the tensile strength and the chain mobility. This result represents a fundamental step towards establishing single-sided NMR as a new analytical tool for in situ condition monitoring of polyethylene working under sour conditions. The proposed approach can be easily extended to other polymer materials.