High Temperature and High Pressure CO2 Corrosion

The application of corrosion inhibitors is a widely used technique to mitigate internal corrosion of carbon steel pipelines in the presence of CO2 and H2S. Such chemicals can be administered through continuous injection, batch treatment, or squeeze treatment. Traditional inhibitors tend to consist predominantly of nitrogen-containing compounds which function by establishing a protective metal film on the metal surface. However, one limitation of such chemicals is that they do not have a particularly favourable environmental profile and can bioaccumulate, thus imposing restrictions on their use. Some molecules lack the required level of biodegradability imposed by legislation.

Within the last decade, changes in regulations relating to how the bioaccumulation of surfactants must be characterised has resulted in many previously 'environmentally-friendly' chemicals receiving substitution warnings, meaning they could no longer be classified as 'green inhibitors'. This has resulted in a requirement for the development of new corrosion inhibitors that conform to European regulations. Furthermore, it also casts doubt over the suitability of any environmentally friendly inhibitors considered in publications prior to 2007, as they may no longer conform to UK regulations.

It is clear in the literature that a number of publications consider the development of environmentally acceptable corrosion inhibitors. However, in terms of the evaluation of such corrosion inhibitors, much fewer studies are provided to indicate that these chemicals are capable of adequately protecting a carbon steel surface at temperatures in excess of 90oC. With a greater number of oil and gas fields operating under higher temperatures, there is a requirement to develop inhibitors which are proven to function reliably at elevated temperatures.
Aims and Objectives
The accurate evaluation of inhibitors at high temperature is challenging in closed systems. It is essential to develop an appropriate test methodology to ensure that findings from experiments performed in a laboratory can be translated to the field with confidence, particularly in non-scaling conditions. The performance of corrosion inhibitors is also not only influenced by temperature, but by the brine chemistry and fluid hydrodynamics. Consequently, the principle aim of this study are:

1. To develop a robust methodology/experimental apparatus for evaluating inhibitor performance at elevated temperatures under well controlled/understood non-scaling and scaling conditions
2. To determine the link between surface scales characteristics and corrosion inhibitor performance by analysing the general and localised corrosion of carbon steel.

The objectives of the study are:

To achieve a better understanding of the kinetics of corrosion product formation at high temperature in autoclave tests to determine the changes in the steel surface during exposure to an uninhibited solution.
Understand the link between the characteristics of the films formed and the general/localised corrosion of carbon steel in un-inhibited environments.
Develop a robust methodology/setup for evaluating inhibitors at high temperature that can be translated to or compared with the field.
Evaluate the ability of inhibitors to penetrate through corrosion films to provide adequate protection, as well as determining the ability of inhibitors to control localised corrosion/pitting once it has initiated on a steel surface.
Consider the relationship between general and pitting corrosion across all environments to establish whether there are any trends/correlations in the data collected.