ABSTRACT

Pitting corrosion is an ubiquitous phenomenon in the oil and gas industry and is the leading cause of internal failures in hydrocarbon production and processing equipment. While significant effort has been made to test the effectiveness of corrosion inhibitors, these tests are best at differentiating reductions in general corrosion rates - not pitting rates. In this paper, laser surface profilometry is presented as a robust, quantitative and systematic method to assess the efficacy of chemical treatments to prevent both general and localized pitting corrosion. The results using these methods are presented using various corrosion inhibitors in both sour and sweet hydrocarbon environments.

INTRODUCTION

Direct costs of corrosion to industry in the US total $276 billion annually, which accounts for 3% of the US Gross Domestic Product.1 As a point of reference, the 2005 Atlantic hurricane season was the most costly hurricane season on record. In this season alone, damage from the three major hurricanes that made landfall in the Gulf of Mexico region totaled nearly $170 billion.2 Corrosion affects many different sectors of the U.S. economy and one of the most heavily affected is the oil and gas industry.1 In addition to other assets, the oil and gas industry utilizes nearly 500,000 miles of pipeline in the U.S. alone, which costs nearly $7 billion annually to monitor, maintain and replace. As can be seen, corrosion, while being a natural phenomenon, is a very costly one as well. Despite its prevalence, it can be minimized by the use of an effective corrosion management program. The use of an optimal corrosion management program can save nearly 30% of annual corrosion costs in the U.S. while ensuring safety to the public as well as the environment.1 The most cost-effective way to minimize the effect of internal localized corrosion is through the use of corrosion inhibitors, which specifically prevent pitting. In order to assess this, it is necessary to determine how well a given product can effectively prevent pitting.3 Several examples of pitting corrosion can be seen in Figure 1.

Figure 1: Field Examples of Pitting Corrosion(available in full paper)

An important facet of having an effective corrosion management program is to have a comprehensive understanding of the mechanism by which the corrosion occurs.4 Most often, pitting plays the primary role in corrosion in the oilfield, but corrosion inhibitors are typically chosen based on their ability to mitigate general corrosion. Often there are significant differences between general corrosion rates and pitting corrosion rates in a given system,5 and a fundamental understanding of these differences is required in order to have an optimal corrosion program. In order to assess these differences, it is crucial to produce and mitigate these pits in laboratory tests.

The development of methods for generating localized corrosion under sweet and sour conditions is discussed here, but the primary focus is the development of methods, which are being used to quantify the degree of localized corrosion. Additionally, the use of these methods to compare various corrosion inhibitors' ability to mitigate localized corrosion is made.

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