Abstract

Pipeline transportation systems are the most cost-effective method to transport liquid or supercritical CO2 from points of capture to sites where it will be permanently stored or used for industrial purposes. Many factors complicate designing an efficient CO2 transmission pipeline and selecting materials. These factors include gas chemistry and impurities (O2, H2O, H2S), pressure, and velocity. The presence of impurities in supercritical CO2 can promote steel corrosion. The objective of this study was to investigate the corrosion behavior of three pipeline steels (X56, X65, and X100) exposed to dense-phase CO2 at 100 bar CO2 partial pressure and 30 °C. The corrosion performance of each steel was evaluated in a CO2 saturated water phase and dense-phase CO2 utilizing an immersion autoclave. The weight loss method was used to investigate the corrosion performance of the pipeline steels in dense-phase CO2. Post-corrosion surface characterization was performed by scanning electron microscopy equipped with energy dispersive X-ray spectroscopy. The data obtained show that each steel's corrosion degradation is more dominant in the CO2 saturated water phase compared to dense-phase CO2.

Introduction

High-pressure steel pipeline is a common, cost-effective method for transporting CO2 from its point of capture to storage sites1. In pipeline transport systems, CO2 is mostly transported in its liquid or supercritical phase, depending on the operating pressure2,3, which requires compression of CO2 gas to a pressure above 80 bar (Figure 1) and avoid a two-phase flow regime in the steel pipelines. In the USA, the longest CO2 pipelines, which transport more than 40 MtCO2 per year from production point to sites in Texas, where the CO2 is used for enhanced oil recovery (EOR), operate in the "dense phase" mode and at ambient temperature and high pressure 1. However, steel pipelines are susceptible to corrosion during the transportation of CO2, due to the presence of moisture and corrosive impurities such as H2S and O2. The type and content of these impurities depends on the CO2 point source and capture technology4.

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