Field Testing of pH Modification Silica Inhibition with Chemical Corrosion Inhibition

Abstract

A field experiment was conducted at Nasuji Sector, Southern Negros Geothermal Production Field, Philippines to evaluate the use of high temperature corrosion inhibitor in brine treated with sulfuric acid. The brine with approximately 400 ppm excess silica (SiO2) was acid treated to inhibit silica polymerization.

The brine from the first separator vessel was acid treated to reduced the pH to about 4 - 4.5 and was conductively cooled from ~160 to ~120oC to simulate the temperature drop after a second flash system. The chemical corrosion inhibitor was introduced right after cooling and the corrosion rates were monitored using corrosion probes and metal coupons inserted at different sections along the pipe.

The experiment showed that the chemical corrosion inhibitor, at 10 ppm concentration, could inhibit corrosion of carbon steel pipes and lower the corrosion rate by as much as 70%, at a temperature of ~120°C and at a pH range of~ 4.0 to 4.5.