ABSTRACT

Erosion-Corrosion behavior of carbon steel material was investigated under iron carbonate scale forming conditions in a CO2 saturated environment as it was impinged by CaCO3 and sand particles. Experimental data were collected with the objective of studying the effect of an imidazoline based inhibitor on reducing CO2 corrosion of low carbon steel material in erosive environments. The erosivites of sand and CaCO3 particles were characterized for iron carbonate scale covered steel surfaces and for bare metal steel surfaces. Comparing CaCO3 and sand erosion data under dry and wet conditions, sand was found to be more erosive than CaCO3 particles. For the experimental conditions considered, the imidazoline based inhibitor provided greater corrosion protection to the bare metal carbon steel surface than the iron carbonate scale did. Consequently, lower erosion-corrosion material loss was measured with inhibitor than with the protective iron carbonate scale.

INTRODUCTION

Erosion-corrosion deterioration of carbon steel in the presence of solid particulates is a major issue in oil and gas production. Erosion can significantly influence corrosion by negatively interfering with corrosion mitigation systems, such as when a protective corrosion scale or an inhibitor film is stripped away through solid particle erosion. The combined effect of erosion and corrosion can lead to high corrosion rates, surface pitting, and, ultimately, material failure. Under certain environmental conditions in CO2 corrosion, which are typically high pH, temperature above 180 to 200°F (82 to 93°C) and low flow velocity, a protective layer of iron carbonate forms on the steel surface. This corrosion product can reduce corrosion rates when the scale completely covers the steel surface. The presence of solid particles, such as sand or calcium carbonate, can strip away this iron carbonate layer, leading to an increase in corrosion rates. In many cases, operators do not rely on scale formation to protect materials, but use chemical corrosion inhibitors to minimize material loss. Corrosion inhibitors, however, are also influenced by flows containing particulates.1-4 Solid particles such as sand and calcium carbonate can reduce inhibitor efficiency through adsorption of inhibitor to the particle surface and by stripping inhibitor from the steel surface.

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