The Effect of Carbon Dioxide Pressure in Carbon Steel Corrosion in 5 Wt.% NaCl Solution Using Flow Loop

Abstract

The pipelines transport a raw, unrefined well stream, usually consisting of a multiphase flow of gas, oil and water contained carbon dioxide, hydrogen sulfide and chlorides at elevated temperatures. Internal corrosion is the important factor affecting the reliability and longevity of subsea oil and gas pipelines in the oil and gas field. In the pipeline design, the measurement of corrosion rate was evaluated under similar corrosion environments using flow loop. The flow loop installed at KITECH located in Korea was made of UNS 31603 with internal diameter 1 inch and corrosion tests can be performed up to 7 m/s liquid velocity and up to 12 m/s gas velocity under maximum pressure 10 MPa. The flow loop system was comprises of a progressive cavity pump, separator, corrosion test section and corrosion monitoring equipment such as electrical resistance probes, linear polarization resistance probes. Corrosion inhibitor performance test, gas hydrate test etc. can be conducted with the system. Material of the coupon was API 5L X52 and weight loss coupon method was adopted based on NACE Standard RP 0775-2005. Measurement of corrosion rate was conducted under test conditions, 0 and 0.5 MPa, dissolved oxygen concentration less than 10 ppb, temperature 313 K, for 24 hours in NaCl 5wt. % solution at the velocity of 3 and 4 m/s respectively. The test results showed that corrosion rate increased at higher flow rate and the predominant factor of corrosion was not chloride concentration but pH of the internal liquid of the flow loop.