Corrosion Testing of Casing Steels in Acidic Two Phase Production Fluid and the Field Testing at Yanaizu-Nishiyama Geothermal Field, Japan

Abstract

The material corrosion test in acidic fluid and two-phase condition was carried out at Yanaizu-Nishiyama geothermal field. The test was carried out using 30 mm size test piece of carbon steel, low metal alloy and stainless steel settled in the small loop flow system. The test condition was pH 3.8,165 degreeC and 4.5L/min flow rate condition. And to estimate the corrosion rate in two-phase line, we used the estimation formula including Cr equivalent of material (Kurata et al., 1992) as follows; Log (C.R) = 6.696 -1930 (1/T) - 0.622 (pH) - 0.085 (Creq). The estimated corrosion rate of carbon steel at pH 3.8 and 165 degreeC was calculated about 1.6 mm/year. On the other hand, the field experimental data was from 0.1 to 0.3 mm/year and lower than estimated rate. The corrosion rate of other steels had the similar trend as carbon steel. And at autoclave test using hot water single phase on the same pH and temperature, the corrosion rate was the similar value as estimated rate. Then, the reason of smaller corrosion rate at field test was considered as the lower water/vapor ratio in two-phase line and the precipitation of As and Sb metal especially on carbon steel in lower pH condition.