Abstract

Erosion-corrosion is a complex mechanism of material degradation resulting from interactions between electrochemical and mechanical processes. The consequences of erosion-corrosion are severe with economic penalties resulting from premature failure of components, increased downtime and increased maintenance costs.

The use of carbon steel in conjunction with corrosion inhibitors in preventing erosion-corrosion has been observed as an economically viable solution for oil and gas piping systems. In order to produce highly effective corrosion inhibitors for erosion-corrosion environment, it is important to understand how inhibitors act on each of the material loss components in erosion-corrosion. Although research into corrosion inhibition has been extensively conducted, there is less published work dealing with inhibitors retarding erosion-corrosion.

This paper is to evaluate the efficiency of a corrosion inhibitor under severe liquid-solid impingement. It investigates the adsorption properties of films in addition to the inhibitor action on the components of erosion-corrosion using surface analysis techniques. The experiments have been conducted using a jet impingement rig capable of producing a jet with velocity of 20m/s in a CO2-saturated environment. An assessment of the total damage is made using gravimetric techniques and visual observation. The performance of the inhibitor in this extremely aggressive erosion-corrosion condition is discussed. This paper will identify the role that inhibitors can play in reducing damage in addition to that caused by corrosion and improving erosion-corrosion performance.

Introduction

Erosion-corrosion of carbon steel in CO2 saturated brine has practical importance in oil and gas production lines, especially for oil production and gas condensate systems. In recent years, CO2-saturated water is pumped into wells to facilitate oil recovery, and active exploitation of deep natural gas reservoirs, the entire sweet gas pipeline can be exposed to severe CO2 corrosion conditions1,2. When sand is present in the production line, severe erosion-corrosion damage can occur. Even very small amounts of entrained sand can lead to substantial damage.

Erosion-corrosion is a tribo-corrosion material loss mechanism involving mechanical, electrochemical and interactive processes. Therefore, the material loss includes chemical dissolution (which can be increased by mass transfer increases at the surface), mechanical erosion caused by fluid flow and /or impingement of particles on the pipe wall and electrochemical corrosion enhanced erosion and vice versa3–5.

In the literature, there are considerable studies about CO2 corrosion6–15. A great effort has been expended on multiphase and single-phase flow studies. Nesic et al. have developed models based on two-phase flow erosion-corrosion16. As corrosion product scale is often formed during the corrosion of carbon steel in carbon dioxide saturated brine solutions, there is the potential for pitting and mesa-type corrosion. Depending on the flow conditions, Shadley et al.17 determined the corrosion regimes to be 1) FeCO3 scale formation and low metal loss rates at low velocity 2) sand abrasion and removal of the scale and high metal loss rates at high velocities and 3) partial removal of scale and localized pitting at intermediate velocities. Of course the regimes and the transition velocities will be dependent on the environment as well as the material.

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