Electrochemical Evaluation of Pipelines Materials of the Miravalles Geothermal Field in Costa Rica

G. Tres,^a* E. Saborío,^a J. Urruchurtu,^b J. Malo^b

^aInstituto Costarricense de Electricidad, Costa Rica

^bInstituto de Investigaciones Electricas, Mexico

 

Received 22 March 2007; accepted 27 July 2007

 

Abstract

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.

Keywords: linear polarization, electrochemical noise, geothermal brine, steel carbon.

 

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* Corresponding author. E-mail address: Gtres@ice.go.cr