ABSTRACT

Mitigation of corrosion of pipelines in a crude oil reserve storage facility in Central Europe is described. This top-down study covers a number of factors affecting corrosion in crude oil such as water content, aggressivity of the water phase, kinetics of water-oil separation, effect of dissolved oxygen, effect of stored crudes quality, frequency of oil movement inside the pipes, steel grade, possible contribution of MIC, presence of deposits, and many others. One of the key roots of corrosion acceleration is the water phase separation. Several approaches were suggested to limit corrosion, considering both difficulties of design changes and economic costs.

INTRODUCTION

In the literature, corrosion problems associated with crude oil are often categorized into several classes, based on the type of equipment and "distance" from a well. The upstream operations (drilling, pumping) transport crude oil mixed with significant amounts of water and gasses, midstream operations (transport and storage before refining) deals with much drier crude with most of the water and gasses removed and upstream corrosion problems are mostly caused by chemical composition of given specific fraction and high temperature. Corrosion problems in midstream operations are usually not as severe as during drilling and initial transport, however, this step is significantly longer. Crude oil can be stored up to several years in case of e.g. strategic national crude reserves. In midstream storage tanks, corrosion related issues are usually solved by strong lining at the bottom of the tank. Organic coatings with good resistance and thicknesses up to 1 mm are used. For piping, however, uncoated steel is usually used due to difficulties associated with coating application in small inner-diameter pipes.

For a better perspective, Table 1 shows an overview of corrosion rates recorded for different parts of equipment in 6 facilities. The data show a large range of corrosion rates from 0.1 to 1.5 mm·a−1.

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