Effects of soil resistivity on currents induced on pipelines

The goal of cathodic protection is to prevent corrosion by maintaining buried pipelines at a constant potential with respect to the surrounding soil. In practice, however, the implementation is very complicated since many factors can contribute to the current flowing off the pipe. Design requires characterization of the parameters impacting the corrosion process, such as soil resistivity, size of the pipe and quality of the coating.In the present paper, we have studied the effect of geomagnetic fields on the pipe-induced currents considering it as an additional cause of corrosion. A theoretical method implemented to model the induced currents was tested in a previous work and the effect during disturbed days was quantified. This theoretical model indicated that the intensity of the current induced in a pipeline by the varying geomagnetic field depends on the intensity and rate of change of the field and the electrical resistivity of the soil. This induced current is in equilibrium with the host current and there is no current drainage between the pipeline and the host until, along the length of the pipeline, the host resistivity becomes different. At that point, current must flow between the pipe and host in order to establish a new equilibrium. It is this drainage current, flowing between the pipeline and the host, which causes corrosion problems.Following these results, experimental tests were performed in Tierra del Fuego. In this zone, a geophysical study was made to determine the discontinuities in soil resistivities and simultaneous measurements of the geomagnetic field and the drainage of current were recorded at different sites. The results obtained from the correlation of the data are consistent with the theoretical predictions.     

Technical Evaluation of Glauconies as Alternative Potassium Fertilizer from the Salamanca Formation,Patagonia, Southwest Argentina

The aim of this work was to evaluate the Salamanca Formation greensands as an alternative potassium fertilizer to KCl. Glauconitic pellets from this formation tend to naturally concentrate in 600–250 μm (BS 250) and 250–125 μm (BS 125) fractions. After dry sieving and magnetic separation, these fractions were used for chemical, lixiviation, and specific surface analyses and agronomic evaluations. Two concentrated products were obtained: GL250c (600–250 μm) and GL125c (250–125 μm) representing 40.9 % of total sample. GL250c contains 2.97 % K₂O, and GL125c contains 4.05 % K₂O, representing 27 and 60 % increase in K-content compared to the bulk sample. Grain size of both concentrates decreased significantly through lixiviation tests. Potassium release curves from lixiviation waters show that K-liberation from GL250c was more effective in the first 15 days but decreased after that whereas liberation from GL125c continued to increase after 15 days probably due to higher K-content (36 % higher than GL250c). Specific area could have influenced liberation rates because after leaching it increased 27 % for the finer fraction and by only 16 % for the coarser one. From agronomic assays, measured over 75 days with five harvests, the first four harvests yield best results from KCl probably due to fast K-liberation rates from the salt. However, after overall harvests, fertilization efficiency using either GL250c or GL125c was very similar to and slightly higher than KCl fertilization. As equivalent results were found using either GL250c or GL125c, sieving to obtain these fractions seems not necessary. The results indicate that greensands from the Salamanca Formation are effective slow release alternative K source for fertilizers with low cost of production and treatment compared to operation costs required for mining K soluble salts at depth.     

Climate controls on rainfall isotopes and their effects on cave drip water and speleothem growth: the case of Molinos cave (Teruel,NE Spain)

The interpretation of stable isotopes in speleothems in terms of past temperature variability or precipitation rates requires a comprehensive understanding of the climatic factors and processes that influence the δ¹⁸O signal in the way through the atmosphere to the cave, where carbonate precipitates acquiring its final isotopic composition. This study presents for the first time in the Iberia Peninsula an integrated analysis of the isotopic composition of rainfall (δ¹⁸O_p) during 2010–2012 years and, through a detailed monitoring survey, the transference of the primary isotopic signal throughout the soil and epikarst into the Molinos cave (Teruel, NE Spain). Both air temperature and amount of precipitation have an important effect on δ¹⁸O_p values, clearly imprinting a seasonal variability modulated by an amount effect when rainfall events are more frequent or intense. Air mass history and atmospheric circulation influences are considered through the study of weather types, synoptic-scale climate patterns and large-scale atmospheric circulation indexes (North Atlantic Oscillation and Western Mediterranean Oscillation) revealing a dominant source effect on δ¹⁸O_p values in this region where tropical North Atlantic and Western Mediterranean are the two moisture source regions. A delay of 2–3 months occurs between the dripwater oxygen isotopic composition (δ¹⁸O_d) respect to δ¹⁸O_p values as a consequence of large residence time in the epikarst. Limited calcite precipitates are found from winter to spring when δ¹⁸O_d values are less negative and dripwater rates are constant. This study suggests that NE Iberian δ¹⁸O_calcite proxy records are best interpreted as reflecting a combination of parameters, not just paleotemperature or paleorainfall and, if extending present-day situation towards the recent past, a biased signal towards winter values should be expected in Molinos speleothem records.