Corrosion degradation of pipeline carbon steels subjected to geothermal plant conditions

Purpose – The purpose of this paper is to evaluate the electrochemical behaviour of two carbon steels exposed to acidic geothermal solutions and their resistance to hydrogen induced cracking (HIC), in order to determine the effect of hydrogen damage on the failure process of the steels used for line pipe and casings at a geothermal plant. Design/methodology/approach – Samples of two different steels: ASTM A53 Grade B (line pipe) and API L80 (casing) were immersed for a duration of 96 h in the electrolyte proposed by NACE to evaluate susceptibility to HIC. Samples of the two steels embedded in nonconducting Bakelite were subjected to potentiodynamic polarisation scans at room temperature using as the electrolyte brines obtained from different wells at the Cerro Prieto geothermal plant. Hardness tests were performed on the samples before and after the HIC tests in order to determine hardness changes induced by hydrogen penetration as field results indicated embrittlement of the steels after four months of service. Findings – The steels, ASTM A53 Grade B and API L80 did not exhibit crack sensitivity as no cracks are observed in the tests specimens, though they showed an increase in hardness. The steels exhibited highcorrosion rates in the brine media at room temperature (3.3 mm/yr), which is expected to increase at higher temperatures. Originality/value – The work revealed that carbon steels used for line pipes and casings at geothermal plants can exhibit high resistance to HIC, however they corrode at high rates and may show embrittlement. It is suggested that due to the highoperation temperature, the damage induced by hydrogen resulted in hardness increase but was not sufficient to develop cracks.