Study on the Corrosion Mechanism of a Gathering Pipeline in Daniudi Gas Field

Abstract

To clarify the corrosion problem of a certain gathering and transportation pipeline in the Daniudi gas field, corrosion rate tests, micro-morphology observations and corrosion product analyses were conducted on the corrosion coupons and corroded pipe sections on-site. The corrosion mechanism of the gathering pipeline in an H2S/CO2 coexistence environment was studied to provide a basis for formulating corresponding corrosion protection measures. Results showed that the average corrosion rate of the corrosion coupon was 0.092 3 mm/a, which was higher than the 0.076 0 mm/a required by the industry standard. The local corrosion rate was 0.157 0 mm/a, the pitting corrosion coefficient was 2.7, and the maximum depth of the corrosion pit on the test piece of the corroded pipe section was 88 μm. The corrosion product film had a loose structure and poor protection performance. The corrosion products mainly contained C, O and S elements, which were much higher than the chemical composition of 20 carbon steel. The corrosion products were mainly composed of FeCO3, FeS and Fe2O3, indicating that the corrosion of the gathering pipeline was mainly caused by CO2 and H2S when encountering humid environments.

Keywords

• daniudi gas field; gathering pipeline; h₂s/co₂ coexistence; corrosion mechanism