Water Diffusion Tests Research Articles

Performance Evaluation of Thermally-Aged RTV Silicone Rubber/TiO2 Nanocomposites in Mineral Oil for Transformer Bushings

The room temperature vulcanized (RTV) silicone rubber is regarded as a coating material for power transformer bushings. However, the performance of silicone rubber may get severely degraded in the event of leakage of mineral oil from the transformer. Nevertheless, little attention has been paid to exploring the viability of silicone rubber nanocomposites in retarding transformer oil-induced damages. Therefore, this article investigates the effect of mineral oil on silicone rubber material doped with Titania (TiO2) nanofillers. Silicone rubber nanocomposites with 1, 3, 5, and 7 wt.% of nano-TiO2 were synthesized and thermally aged in transformer oil at 80oC for 18 hours. Performance evaluation was done based on the experimental outcomes of 3-D microscopy, fourier transform infrared spectroscopy (FTIR), contact angle, corona inception voltage (CIV), thermogravimetric analysis (TGA), infrared thermography, surface potential, and water diffusion tests. Finally, based on the experimental investigations, 5 wt.% nanocomposite was found to be superior in performance against transformer oil-induced degradation.

Research of cycloaliphatic epoxy resin and silicone rubber composite insulator interface based on four‐electrode system and temperature rise model

AbstractInterface degradation between mandrel and sheath can cause a decrease in insulation performance and mechanical strength of composite insulators. In this study, the interface ageing properties of cycloaliphatic epoxy resin and silicone rubber composite insulator were compared. A water diffusion test was adopted to simulate the composite insulator ageing in a hot and humid environment. A four‐electrode system was built to detect leakage current at different locations (mandrel, sheath and interface), which is an important basis for evaluating insulator performance. The ageing degree of insulator could be quantitatively characterised by leakage current change. It was found that the infiltrated moisture had a great effect on insulation performance. Based on the water absorption test result, the interface performance of two insulators was mainly influenced by their sheath sealing quality. As an auxiliary evaluation method, temperature rise during the test was recorded using an infrared camera. The experiment results showed that interface degradation was the main factor for the insulation performance decrease of silicone rubber composite insulators. However, insulation level reduction of the cycloaliphatic epoxy resin was caused by the wet sheath. In addition, a model for temperature rise of cycloaliphatic epoxy resin insulators was proposed based on good correspondence between sheath material and insulation. The model incorporated multiple processes such as ageing and heating of insulators, and it can predict the early temperature rise well.

Process Improvement to Restrain Emergency Heating Defect of Composite Insulator

The rod in the composite insulator is a load-bearing component, and glass-fiber-reinforced plastic (GRP) has always been regarded as the most suitable material. However, the investigation reveals that the performance shortcomings of GRP rods are the main cause of emergency heating defects of 131 new 500-kV ac composite insulators in South China. The finite-element simulation is conducted to understand the potential mechanism of heating. It is demonstrated that the holes with moisture distort the electric field, increasing heating power. A hole with moisture in the GRP rod longer than 500 mm could lead to emergency heating defects with temperature rise exceeding 5 K. For the holes in the GRP rod are formed by adjacent voids, the emergency heating defect is inevitable unless the porosity decreases. The fiber infiltration process of the GRP rods is analyzed on the basis of Darcy&#x2019;s Law, and an improved process is proposed to reduce porosity. Maintaining the mass fraction of fiber by at least 70&#x0025; and replacing the damp infiltration fluid in time in the production of GRP rods are necessary to restrain porosity. 300-h water diffusion test with a 50-<inline-formula> <tex-math notation="LaTeX">$\mu \text{A}$ </tex-math></inline-formula> threshold is an effective evaluation method of the GRP rod performance. This method should be used before putting composite insulators into operation.

Effects of chlorinated polypropylene based-adhesives on the bonding performance of an epoxy core rod and polyolefin sheath for composite insulators

One of the key technologies of composite insulators is the bonding between the core rod and sheath. This paper explores the use of chlorinated polypropylene-based adhesives to bond a polyolefin sheath material and an epoxy core rod. Dye penetration tests, bonding strength tests and water diffusion tests were carried out to evaluate the adhesiveness. The results demonstrated that the sample bonded by the chlorinated polypropylene/γ-methacryloxypropyltrimethoxysilane adhesive had the best interface tightness, and the bonding strength reached 7.34 MPa. Furthermore, the leakage current was as low as 41 μA after the sample was placed in boiling water for 100 h. This work provides a key bonding technology for polyolefin materials used as composite insulator sheaths.

Improved Current Sensor for Water Diffusion Testing of Composite Insulators.

An improved current sensor aimed at measuring currents of different parts in composite insulator samples was proposed. Conventional current sensors used in water diffusion tests aim to examine the performance of composite insulators, however, it is difficult for the conventional current sensors to locate the defects. Thus, we designed a new electrode structure to measure the currents of different components in short samples of composite insulators. Based on a finite analysis method, the influence of relative permittivity and conductivity on the current was analyzed. New samples with different interfaces and samples after operation were tested using the new and conventional current sensors. The performance of a certain part in short samples can be diagnosed by analyzing the current and phase information extracted from the test results. By comparing the test results of new and traditional current sensors, it was proved that the new electrode structure is more effective in locating the defects of insulators.

Research on aged interfaces of composite insulators after extended water diffusion tests

Over the years, several abnormal fractures of composite insulators had occurred in southern China, with the poor interface quality being regarded as the main reason of this kind of accidents. In this research, an improved water diffusion test method was proposed. We carried out 100–300 hours' water diffusion tests on the insulators which were new or had been operated for different years or abnormally heated, and the variation situation of adhesion during boiling process has also been analyzed. Besides, a microscopic analysis on superficial core material of aging insulators has been conducted to study the aging mechanism of interface. According to the analysis results, 300 hours' water diffusion test was proved to be able to screen out the samples with poor adhesive property or hydrolysis resistance. It was more effective compared with 100 hours water diffusion test which has been recommended by existing standards. According to our observation, there was a significant corresponding relationship between the results of 300 h water diffusion test and the variation of adhesion during boiling. In general, the water diffusion and microanalysis of abnormally heated insulators indicated that for insulators fail to pass the 300 h water diffusion test, hydrolysis was an important reason leading to interface quality reduction.

Diffusivity in Cement-Silica Fume Based Materials: Experimental and Computer Modeling Results on Mortars

Silica fume cement (SFC) based materials are largely used as a containment barrier for nuclear waste management. The safety of this storage mode depends on the knowledge of the effective diffusion coefficients of such materials. This work proposes a combination of computer models able to estimate the diffusion coefficients of SFC pastes and mortars, from a single investigation of the microstructure by nitrogen adsorption. The approach used consists firstly in manufacturing SFC mortars by varying sand volume fraction from 30 to 65% while silica fume replacement and water to binder ratio were respectively set at 10% and 0.4. Nitrogen adsorption tests were then performed and collected data on C-S-H nature are introduced into a SFC pastes hydration model. The latter provides the mineral composition which is an input parameter in the multilayer transport model that estimates the effective diffusion coefficient (De) of cement pastes. For mortars, a 3D biphasic model (sand and cement matrix) was used to compute the (De) of mortars at different inclusion volume fractions. The numerical results were approved by comparison to experimental data obtained from tritiated water (HTO) diffusion tests performed on manufactured mortars.

Effect of the size reduction on the bulk tensile and double cantilever beam specimens used in cohesive zone models

Cohesive zone elements used in finite element analysis are a reliable way to design and predict the behaviour of the joint. The characterisation of the traction separation law used in these models is done using tensile and fracture tests, and the parameters of such laws depend on humidity and temperature. Water diffusion tests are therefore necessary, which are dependent on specimen geometry, meaning a bigger specimen takes longer to fully saturate. To solve this problem and increase the efficiency of the ageing process, smaller tensile bulk and double cantilever beam (DCB) specimens are necessary. Another advantage of smaller DCB specimens is that they can be tested in smaller high-temperature chambers, where normal DCB specimens do not fit. Smaller geometries of the bulk tensile and DCB tests are analysed, and a proposed geometry for each test is shown to produce very satisfactory results, validating the use of these specimens.

Comments on “Modeling of Nuclear Species Diffusion Through Cement-Based Materials” by Wattez et al. (2013)

We propose a simpler alternative to Wattez et al.’s method for the exploitation of tritiated water diffusion tests in cement-based materials.

Link between microstructure and tritiated water diffusivity in mortars

Ions and radionuclide diffusivity in concrete is one of the most important factors that determine service life and safety assessment of cement based structures in nuclear power plants and radioactive-waste repositories. Apart from the influence of cement paste microstructure, the presence of aggregates may have an impact on transport properties of the material. The well-known interfacial transition zone, denoted by ITZ, is created near the aggregates and characterized by a greater porosity. The goal of this study is to investigate the competition between the more diffusing ITZ zone and the less diffusing aggregates. To this end, several series of tritiated water diffusion tests are conducted on mortars characterized by different water-to-cement ratios and sand volume fractions. In parallel, microstructure of these materials is explored by mercury and water porosimetry. It was observed that at low sand content (0% - 50%), diffusion properties of mortars are dominated by aggregates dilution effect. At 60% sand, diffusion increases significantly suggesting that percolation's pores threshold has been reached. Results indicate also that sand particle size distribution has a great impact on the diffusivity of mortars.

Analysis of a fractured 500 kV composite insulator - identification of aging mechanisms and their causes

In this paper, a fractured 500 kV ac composite insulator, whose fracture characteristics differ significantly from those of brittle fracture, is analyzed in order to identify the aging mechanisms involved and their causes. Several sheath punctures occurred along the insulator which apparently originated from inside the insulator. Removal of the sheath revealed weak adhesion as well as tracking along the sheath-core interface. Weak microscopic as well as macroscopic interfaces were indicated by the insulator's weak performance in the water diffusion and dye penetration test according to IEC 62217. The core material was analyzed by means of FTIR identifying glass corrosion, ion exchange and hydrolysis as major degradation mechanisms. Based on the results of analysis, a water induced aging process is proposed and recommendations for online monitoring of composite insulators with respect to interfacial aging are given.

Computer modelling of tritiated water diffusion test for cement based materials

In durability-based design, diffusivity of ions through cement based materials is one of the most important factors that determine the service life of concrete structures. This paper gives a method and numerical tool to estimate and predict in a short time the effective diffusion coefficient of cement paste, mortar or concrete starting from the microstructure scale and taking into account important factors like calcium silicate hydrate (C–S–H) and interfacial transition zone (ITZ) phases. The numerical model works in two main steps. First, the CEMHYD3D model is used to generate a realistic 3D Representative Volume Element of the cement based material at different scales. Second, the finite element method is used to simulate diffusion of tritiated water (HTO) through a saturated material. The method is then applied to simulate the well-known HTO diffusion test and to derive the effective diffusion coefficient of the heterogeneous material based on Fick’s law. In order to validate the proposed tool, the effective diffusion coefficient of two cement pastes and two mortars with water-to-cement ratio (w/c) of 0.25 and 0.45 are computed and successfully compared to experimental data. The model results provide an approximation for diffusivity through the C–S–H and ITZ phases. Finally, the model is applied to investigate the effect of changes in the microstructure due to the leaching of portlandite, hydrated aluminates and sulfoaluminate phases on the increase of the effective diffusion coefficient.

High sensitivity binary gas integrity test for membrane filters

A novel non-destructive integrity test for microporous and ultraporous membranes has been developed that is far more sensitive to detecting defects than a conventional gas–liquid diffusion test. The test developed here uses a binary gas mixture and is based on the principle of differing gas permeabilities through the liquid layer of a wetted membrane that results in a concentration enhancement of the faster permeating gas. In an integral membrane, the permeate composition can be predicted based on the transport properties of the gases permeating through the liquid layer and the known operating conditions. A deviation from the expected concentration is an indication of the presence of a defect or open pores. Unlike the gas–liquid diffusion test, the binary gas test has low sensitivity to membrane porosity, liquid layer thickness, and membrane area. Consequently, integral devices will exhibit a relatively narrow range of test values, resulting in a superior defect signal-to-noise ratio. In this study, a binary gas integrity test method was developed and applied to a newly developed virus clearance filter. The binary gas test was demonstrated to provide a significantly higher level of virus retention assurance compared to the air–water diffusion test, and can be implemented by the filter manufacturer as an additional quality assurance test prior to shipping the product to users.

Innovative study of non-steady-state tritiated water diffusion test

The objective of this paper is to propose a new method for testing molecular diffusion in saturated cement materials. A saturated specimen of porous materials was placed between two compartments; the upstream compartment contained tritiated water (HTO) and the downstream compartment a solution without HTO. The activity gradient between the compartments induced a flux of tritiated water through the sample. Usually, the flux of HTO is repeatedly measured by analysing the content of the downstream cell in the steady state. In this work, a theoretical study based on Fick's laws is used to show that it is possible to determine the diffusion coefficient D Fick1 by considering only two measurements obtained in the non-steady state, in the downstream compartment of a diffusion cell. A significant saving of time (approximately half) can be obtained. An experimental study of this innovative method is presented.

Study of water movement in concrete

An investigation on the movement of water in 100% Portland cement concretes is presented. The water diffusion and sorptivity tests, together with the accelerated water permeability test, are performed to determine the transport parameters that characterise the mechanisms of water diffusion, sorptivity and permeability in concrete respectively. The effects of pore humidity, ambient temperature, environmental relative humidity, applied hydrostatic pressure gradient and water-cement ratio are also explored. The results obtained from the tests on water diffusion, sorptivity and permeability show good agreement with those reported in the literature. The study of water movement has practical implications on the prediction of transport and distribution of aggressive chemical agents in concrete, as well as on the development of rational and quantitative durability assessment for concrete structures exposed to different climatic and environmental conditions.

Study of water movement in concrete

An investigation on the movement of water in 100% Portland cement concretes is presented. The water diffusion and sorptivity tests, together with the accelerated water permeability test, are performed to determine the transport parameters that characterise the mechanisms of water diffusion, sorptivity and permeability in concrete respectively. The effects of pore humidity, ambient temperature, environmental relative humidity, applied hydrostatic pressure gradient and water-cement ratio are also explored. The results obtained from the tests on water diffusion, sorptivity and permeability show good agreement with those reported in the literature. The study of water movement has practical implications on the prediction of transport and distribution of aggressive chemical agents in concrete, as well as on the development of rational and quantitative durability assessment for concrete structures exposed to different climatic and environmental conditions.

Factors Affecting Expansion of Corn Meals with Poor and Good Expansion Properties

ABSTRACTTwo corn meals, one with good and one with poor expansion properties, were used to study the critical factors responsible for poor expansion during corn curl extrusion. Screening tests revealed that the corn meal with poor expansion had a slightly larger particle size. This sample also had a larger proportion of opaque particles compared to the corn meal with good expansion. Extrusion of coarse corn grits showed that larger particle size alone could cause poor expansion. Water diffusion tests showed that the sample containing more opaque particles was more competitive for water. As a result, in corn that contained both opaque and vitreous particles less water was available to the vitreous particles. The underplastisized (dry) vitreous particles remained glassy (unmelted) during extrusion, resulting in reduced expansion of the extrudates. The results suggest that addition of water to the conditioning cylinder of the extruder would overcome poor expansion.

In-Situ Hydraulic Parameters for the Canirnenellis Granite Hot Dry Rock Geothermal Energy Research Reservoir

Summary A research hot dry rock (HDR) geothermal energy reservoir is currently under development in the Carnmenellis granite in Cornwall, U.K., at a depth of about 6,600 ft [2000 m]. This paper details the performance, analysis, and interpretation of hydraulic tests using low to medium pressures and flow rates. These tests allowed an evaluation pressures and flow rates. These tests allowed an evaluation of the in-situ hydraulic parameters relevant to initial water storage and long-term leakage. Tests were analyzed using both diffusion theory and an explicit, Coupled hydraulic/mechanical computer code. At low fluid overpressures, the permeabilities, in terms of uniform diffusion, were in the range of 1 to 10d, rising to about 60 d at overpressures of about 725 psi (5 MPa). These figures imply that long-term leakage psi (5 MPa). These figures imply that long-term leakage from an HDR reservoir is minor. The computer model was able to simulate several cycles of injections and shut-ins at progressively higher pressures and flow rates with a single set of variables. Introduction An HDR geothermal energy research project is being conducted by the Camborne School of Mines (CSM) at their test facility at Rosemanowes quarry in Cornwall (Fig. 1). The facility includes two deviated wells, RH11 and RH12, each drilled to a vertical depth of about 6,600 ft [2000 m] (Fig. 2). The holes are located within the Carnmenellis granite throughout their lengths, and are inclined at 30 from vertical in their lower sections to intersect the predominantly vertical natural jointing. The primary objective of the project is to link the two wells through the natural jointing by using a combination of explosive pretreatment and hydraulic stimulation to create a heat transfer zone (or reservoir) for the circulating water. However, it was first necessary to characterize the hydraulic behavior of the rock mass with modest flow rates and fluid overpressures before the natural joint structure was modified by major hydraulic injections. The resulting information then could give reference conditions for comparing the results of the high energy tests. The information is relevant for determining the leakage losses at the limits of the stimulated reservoir. It is also of interest to compare the results with those obtained at depths of 1,000 ft [300 m] in previous experiments at the same site to obtain a depth perspective for the hydraulic behavior. Since the test depth is unique for crystalline rocks in the U.K. and is unusual elsewhere, the results are of interest for other projects involving facilities at comparable depths (e.g., liquid waste disposal and deep-mined hydroelectric pumped storage). Geological Conditions The Carnmenellis granite pluton was emplaced about 285 million years ago, and subsequently has undergone a complex tectonic history. The pluton is exposed at the ground surface over an approximately circular area of about 50 sq miles [130 km]. The Rosemanowes quarry test site is near the center of the exposure (Fig. 1). Topography is gently undulating with a maximum relief of about 330 ft [100 m]. There is a network of dominant, near orthogonal, vertical joints throughout the granite, with typical spacings of 3 to 10 ft [1 to 3 m] near the ground surface, 10 to 30 ft [3 to 10 m] at 2,500-ft [750-m] depth, and similar to wider spacing at 6,600 ft [2000 m]. Nearly horizontal joints also occur but less frequently. All joints are typically tight, away from zones of stress relief. In-situ stresses have been measured in some detail. At a depth of 6,600 ft [2000 m], the vertical, maximum, and minimum horizontal stresses are approximately 7,500 psi [52 MPa], 8,700 to 10,200 psi (60 to 70 MPa) and 4,400 psi [30 MPa], respectively. The horizontal stress directions and major near-vertical joint set strike orientations are shown in Fig. 3. The fabric of the Carnmenellis granite consists of megacrysts of alkali feldspar set in a coarse ground mass of plagioclase, alkali feldspar, micas, and trace minerals. Grain size is variable, with megacrysts up to 0.75 in. [20 mm] long and crystals in the ground mass typically 0.08 to 0.2 in. [2 to 5 mm] in diameter. The permeability of the fabric is extremely low, with values permeability of the fabric is extremely low, with values of 10(-3) d obtained by laboratory water diffusion tests. The mechanical properties may be characterized by a uniaxial compressive strength of about 19,600 psi [135 MPa], with dimensionless triaxial strength parameters m and s of 21 and 1.0 per Hoek and Brown, parameters m and s of 21 and 1.0 per Hoek and Brown, Young's modulus of 9.43 × 10(6) psi [65 GPa], and Poisson's ratio of 0.2. Poisson's ratio of 0.2. JPT P. 1982