ABSTRACT

Green corrosion inhibitors have been developed to minimize environmental impacts. The first requirement of green chemicals is to pass pre-screening based on the criteria of Harmonised Mandatory Control Scheme. In addition, a green chemical should have a Hazard Quotient value of less than 1 for the UK sector; whereas in Norway, a low or reduction in the contribution to an operator's platform Environmental Impact Factor is required. Localized corrosion test protocols were adopted as part of an assessment of the effectiveness of corrosion inhibitor in laboratory tests. This paper discusses some aspects of the evaluations of corrosion inhibitors using recessed micro-electrodes and segmented weld electrode assemblies in simulated oil and gas production environment. Some examples of the applications of corrosion inhibitors to protect against under-deposit pitting and preferential weld corrosion are presented. The merits of different test methodologies are discussed.

INTRODUCTION

In oil and gas production systems, internal localized corrosion is a major cause of failure with carbon steel produced fluid handling facilities. Localized corrosion may arise as a result of damage of the surface protective film, the presence of scale deposits, the build-up of corrosion products, and variation in metallurgical composition and microstructure in a weld joint, etc. Such conditions can lead to the formation of local corrosion cells, and/or local turbulence; resulting in pitting, erosion corrosion, or preferential weld corrosion damage~-3.

As the exploration and the production of oil and gas is likely to take place in more remote regions and harsher environment, e.g. deeper formations, higher reservoir temperature and pressure, such environment is a major challenge to the engineers. This is because of the increasing likelihood of scaling problems due to the higher content of scale forming ions as well as more aggressive corrosion conditions due to the high concentration of carbon dioxide and hydrogen sulfide in the gas phase. These operating conditions can significantly enhance the risk of corrosion damage of the materials. Corrosion control options available are typically carbon steel with corrosion inhibitor and the uses of corrosion resistant alloys. The selection of either option or a combination of these options will depend upon the effectiveness as well as the economics of the corrosion control measure.

In systems where corrosion inhibitors are injected, the effectiveness of corrosion inhibitors in controlling not just general corrosion, but also the ability to minimize the risk of localized corrosion, is an important and essential requirement. Typically, the selection of corrosion inhibitor is via a series of laboratory tests, followed by field evaluations. It is therefore important that the appropriate tests are carried out to evaluate the capability of the chemicals. A number of methodologies were developed to evaluate the performance of corrosion inhibitors for protection against localized corrosion. In sweet carbon dioxide (CO2) environment, micro-recessed electrodes were employed to study the corrosion behavior of pits 4-6. For sour systems, i.e. systems containing appreciable amount of hydrogen sulfide (H2S), tests using micro-recessed electrodes 4, coupon exposures and electrochemical measurements z' 8 were used in the evaluations.

In addition to corrosion inhibition, an important aspect to be considered in the selection process is the effects on the use and discharge of chemicals to health, safety and the environment. As a consequence of wider recognition of the impact of production chemicals to the environment, more stringent environmental regulations have been in

This content is only available via PDF.
You can access this article if you purchase or spend a download.