Effect of graphitization on the static mechanical properties of service exposed ASTM A516 Gr. 65 steam pipe metal

The focus of this research project is to establish what effect graphitization has on the static mechanical properties of service exposed ASTM A516 Grade 65 steam pipe material, which operated for prolonged periods above 425 ̊C. The research study was conducted on three graphitized service exposed steam pipe weldment samples and on a newly welded and post weld heat treated sample with graphitized service exposed steam pipe material. Macro samples were removed from each of the samples at two positions and these were evaluated with regard to graphite nodule size, nearest neighbour spacing and % planar graphitization in the parent pipe and HAZ regions on either side of the welds. It was found on all of the service exposed samples that the graphite nodules of the HAZ regions have a smaller median nodule size, smaller median nearest neighbour spacing and increased % planar graphitization in comparison to the parent pipe material. The service expose parent pipe material on either side of the weldments of the respective samples was chemically analyzed. This was done with the focus being on the deoxidizing element content (Si and Al) of the respective parent pipe regions and to what extent these elements influenced the development of planar graphitization in these regions. No correlation could be identified between the level of deoxidizing elements and the levels of % planar graphitization in the parent pipe material. Tensile and Charpy impact samples were removed from the respective service exposed samples parent material on either side of the weld and from the HAZ regions on the side with the highest levels of planar graphitization. These samples were tested and the yield and ultimate tensile strength and Charpy impact toughness of the respective samples were then evaluated to establish how these static mechanical properties were influenced by the % planar graphitization. The yield and ultimate tensile strength of the service exposed material did not show a statistically significant correlation with the % planar graphitization. The Charpy impact toughness results did however show a statistically significant negative correlation towards the % planar graphitization. This was clearly evident from the results of the HAZ regions of the service exposed weldments (Samples A-C) which had the highest levels of % planar graphitization and the lowest impact toughness, while the newly welded and post weld heat treated Sample D had no planar graphitization outside the HAZ and the highest impact toughness. This research project not only investigated how planar graphitization affects the static mechanical properties of service exposed pipe material, it also investigated on a microstructural basis, how planar graphitization nucleates and grows. The microstructural investigation showed that the free carbon required for the development of planar graphitization originated from the regions outside the HAZ, which were formed when the pearlite bands were dissolved during the welding of the steam pipe. The heat input from the welding sensitized this region for the development of planar graphitization, probably due to the formation of a “carbon-rich” matrix due to the partial dissolution of the cementite precipitates. All the carbide precipitates in this region consisted of M3C. aluminium-rich precipitates were found inside newly nucleated graphite nodules, indicating its role as a possible heterogeneous nucleation site. Growth of newly formed graphite nodules showed a preference towards high-angle grain boundaries and regions with dislocations for the initial growth stages of the graphite nodules. The microstructure of the region outside the HAZ of the newly introduced seam weld on the service exposed steam pipe material (with graphitization), was also investigated using advanced electron microscopy methods and it yielded no evidence of the development of planar graphitization

Water and salt balances of two shallow groundwater cropping systems using subjective and objective irrigation scheduling

Evidence suggests that, in general, subjective rather than objective irrigation  scheduling decisions are adopted by farmers. Irrigators have ‘calibrated’ themselves with years of experience to irrigate subjectively according to perceived crop water requirements. This study aimed to determine the associated benefits of objective versus subjective scheduling of two shallow groundwater cropping systems. Weekly measurements included rainfall and irrigation amounts, soil water content, groundwater table depth, artificial drainage volumes, and electrical conductivity of irrigation water, groundwater and drainage water.  Simulations of evaporation and transpiration were done with the SWAMP model. Based on soil water and salinity status, matric and osmotic stress during the four cropping seasons is considered unlikely. When rainfall-plusirrigation was compared to evapotranspiration, objective scheduling resulted in an under-supply of 15%, and rainfall and shallow groundwater served as supplementary water sources. Subjective scheduling did not use rainfall efficiently as a source of water and resulted in an over-supply of 10%.  Approximately 50% less salt was leached with objective compared to subjective irrigation scheduling. Under shallow groundwater conditions, irrigating subjectively according to crop water requirement results in excessive irrigation, salt addition and leaching compared to objective scheduling. Farmers can address some of the environmental problems  associated with irrigation by adopting objective scheduling and reducing the leaching fraction (< 0.15) of shallow groundwater cropping  systems.Keywords: evapotranspiration, leaching, salinity, water conservation, water degradatio

Considerations in the practical implementation of a travelling wave cochlear implant processor

Speech processing in the human cochlea introduces travelling waves on the basilar membrane. These travelling waves have largely been ignored in most processing strategies. This study implements a hydrodynamical model in a speech processing strategy in order to investigate the neural spike train patterns for a travelling wave processing strategy. In cochlear implants a trade-off remains between the simulation rate and the number of electrode channels. This trade-off was investigated in the proposed travelling wave strategy. Taking into consideration existing current spread and electrical stimulation models, predicted neural spike train responses have shown that stimulating fewer channels (six and four) at stimulation rates of 2 400 pps and 3 600 pps gives better approximations of predicted normal hearing responses for input frequencies of 200 Hz, 600 Hz and 1 kHz, compared to stimulating more channels at lower channel stimulation rates. The predicted neural spike train patterns suggest that these resulting neural patterns might contain both spatial and temporal information that could be extracted by the auditory system. For a frequency of 4 kHz the predicted neural patterns for a channel-number stimulation-rate configuration of 2 - 7 200 pps suggested that although there is no travelling wave delay information, the predicted neural patterns still contain temporal information. The predicted ISI histograms show peaks at the input tone period and multiples thereof, with clusters of spikes evident around the tone period in the predicted spatio-temporal neural spike train patterns. Similar peaks at the tone period were observed for calculated ISI histograms for predicted normal hearing neural patterns and measured neural responses. The predicted spatio-temporal neural patterns for the input frequency of 200 Hz show the travelling wave delay with clusters of spikes at the tone period. This travelling wave delay can also be seen from predicted normal hearing neural responses. The current spread, however, shows a significant distortion effect around the characteristic frequency place where the travelling wave delay increases rapidly. Spacing electrodes more closely results in an increase in this distortion, with the nerve fibre threshold decreasing in adjacent populations of nerve fibres, increasing the probability of firing. The current spread showed a more limited distortion effect on travelling wave delays when electrodes were spaced across the cochlea, at an electrode spacing of 6.08 mm. ISI histogram results also showed increased peaks around the tone period and multiples thereof. These predicted neural spike train patterns suggest that travelling waves in processing strategies, although mostly ignored, might provide the auditory system with both the spatial and temporal information needed for better pitch perception.Dissertation (MEng)--University of Pretoria, 2012.Electrical, Electronic and Computer EngineeringMEngUnrestricte

Soil Organic Matter Storage in Irrigated Tsitsikamma Dairy Farms with Minimum Tilled Pasture Mixtures: Case Studies

In recent years, pasture production changed from conventional tilled single pastures to minimum tilled mixed pastures in the Tsitsikamma region, South Africa. However, storage of soil organic matter (SOM) under minimum tilled mixed pastures is not yet quantified. This study evaluated SOM indices in the upper 60 cm soil of six-year-old mixed pastures in the Upper (UT) and Lower (LT) Tsitsikamma regions. Soil samples were collected at 0–15, 15–30, 30–45, and 45–60 cm soil layers of five farms (F1, F2, F3, F4, and F5) treated with different rates of fertilizer (NPK) alone and in combination with dairy effluent (DE) and/or poultry manure (PM). Results of this study indicated that there were no significant differences in bulk density, total nitrogen (N), and rate of potentially mineralizable N (PMN) between farms in the UT region. In the LT region, NPK, DE, and PM combinations improved soil C accumulation relative to the soil application of NPK. Higher C/N ratios in the LT region suggested adequate C for microbial energy and maintenance. Integrating manure into minimum tilled pasture mixtures as a replacement for synthetic fertilizers seems to be a feasible option to promote SOM storage, but remains only feasible by applying site-specific management strategies

Soil Organic Matter Storage in Irrigated Tsitsikamma Dairy Farms with Minimum Tilled Pasture Mixtures: Case Studies

In recent years, pasture production changed from conventional tilled single pastures to minimum tilled mixed pastures in the Tsitsikamma region, South Africa. However, storage of soil organic matter (SOM) under minimum tilled mixed pastures is not yet quantified. This study evaluated SOM indices in the upper 60 cm soil of six-year-old mixed pastures in the Upper (UT) and Lower (LT) Tsitsikamma regions. Soil samples were collected at 0–15, 15–30, 30–45, and 45–60 cm soil layers of five farms (F1, F2, F3, F4, and F5) treated with different rates of fertilizer (NPK) alone and in combination with dairy effluent (DE) and/or poultry manure (PM). Results of this study indicated that there were no significant differences in bulk density, total nitrogen (N), and rate of potentially mineralizable N (PMN) between farms in the UT region. In the LT region, NPK, DE, and PM combinations improved soil C accumulation relative to the soil application of NPK. Higher C/N ratios in the LT region suggested adequate C for microbial energy and maintenance. Integrating manure into minimum tilled pasture mixtures as a replacement for synthetic fertilizers seems to be a feasible option to promote SOM storage, but remains only feasible by applying site-specific management strategies

Evaluation of BAYESIL for automated annotation of 1 H NMR data using limited sample volumes: application to African elephant serum

Introduction Technological advancements enabled the analyses of limited sample volumes on 1 H NMR. Manual spectral profiling of the data is, however, complex, and timely. Objective To evaluate the performance of BAYESIL for automated identification and quantification of 1 H NMR spectra of limited volume samples. Method Aliquots of a pooled African elephant serum sample were analyzed using standard and reduced volumes. Perfor mance was evaluated on confidence scores, non-detects and laboratory CV. Results Of the 47 compounds detected, 28 had favorable performances. The approach could differentiate samples based on biological variation. Conclusions BAYESIL is valuable for limited sample 1 H NMR data analyses