In the past, mechanical properties have been the main criteria for selecting materials at the Miravalles Geothermal Field. Consideration of the corrosion resistance has been a secondary concern. The goal of this study was to determine the uniform corrosion rate of carbon steels currently used on pipelines (ASTM A 53, ASTM A515, ASTM A234 and API-5L) and compare this rate with the ASTM A-36 standard. The first step was the development of laboratory electrochemical and weight loss experiments. Ultrasonic thickness measurements of pipes for brine, steam and liquid-steam lines, in both straight and curve sections, showed negligible lost in material over the seven year period they have been on operation. The electrochemical study involved polarization curve analysis and corrosion rate measurements by Linear Polarization Resistance (LPR) and Electrochemical Noise Measurements (ENM). Electrochemical cells include triple and conventional testers (SCE as reference and platinum electrode as auxiliary) using brine degassed with nitrogen at 93 ± 2 ºC. According to the results, the ASTM-A36 has a similar general corrosion rate to those currently used on pipelines.
This research was made to determine the corrosion rate of the copper cable used in grounding and lightning systems, at the electrical generation plants from the Costarrican Electrical Institute. The methods used were linear polarization resistance (LPR), and the weight loss one. This report includes both, laboratory and field tests of corrosion rates, using as electrolytes two products commercially available. Moreover, some electrochemical experiments were developed at the laboratory, in order to know the reaction mechanisms. The goal of this study was to generate criteria for the maintenance and/or the substitution of copper cables according to their deterioration. The results showed that the corrosion rate in "A" is at least ten times higher than in "B". In addition, several samples in the "A" electrolyte had pitting corrosion. The study indicates that from the point of view of the corrosion it is preferable to use product "B" like filling, since the generalized corrosion of copper is lower and in addition localized damage does not appear.
The goal of this study was to evaluate the internal corrosion in a liquid-steam pipeline (type A515 low carbon steel) of the Geothermal Field of Miravalles (CGM) in Costa Rica, and to determine the corrosion thickness for future geothermal fields. The monitoring was carried out using the following techniques: linear polarization resistance (LPR), electrical resistance (ER), and weight loss. The results show for neutral or alkaline pH conditions and slightly free of oxygen, that the corrosion thickness should be 1.8 mm, in order to guarantee the integrity of the pipe over the field lifetime.
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