Experimental study on coupled erosion and CO2 corrosion of steel materials for downhole casing and tubing

Key words:  CO₂ corrosion  erosion testing  coupled erosion and corrosion experiment  N80 steel  13Cr steel

Abstract:

A novel high temperature and high pressure experimental set-up for coupled erosion-corrosion testing was used to conduct coupled erosion and CO₂ corrosion experiments at simulated downhole conditions for oil and gas production. N80 and 13Cr steels were tested under different operating conditions, and the effects of CO₂ partial pressure, sand content, sand particle size, and fluid velocity on erosion-corrosion rates were investigated. The experimental results show that steels with higher resistance to CO₂ corrosion have better resistance to erosion-corrosion coupling effect. Under CO₂ partial pressure of 0-5 MPa, the erosion and corrosion coupling rate of 13Cr steel increased from 0.014 mm/a to 0.062 mm/a, while it was increased from 0.197 mm/a to 24.19 mm/a for N80 steel. Corrosion can deform and damage the surface structure of the material, and the greater the corrosion rate, the lower the erosion resistance of the material surface, and the greater of the erosion-corrosion coupling effect. The experimental results have revealed the interactions between erosion and corrosion, and also verified the effectiveness of the self-designed and constructed erosion-corrosion coupling experimental device via high-speed stirring of sandy fluid, which can be used for coupled erosion and corrosion testing of steel materials under downhole conditions.