Materials Performance

MAY 2015

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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58 MAY 2015 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 54, NO. 5 MATERIALS SELECTION & DESIGN I The corrosion behavior of 3Cr alloy steel and L245 carbon steel in oil/ water mixture emulsions with 10, 30, and 80% water cut at 60 °C were in- vestigated. At 10 and 30% water cut, the corrosion product scales of the two steels were thin, compact, and dominated by iron carbonate (FeCO 3 ). At 80% water cut, a Cr-rich layer formed on the 3Cr steel surface, while the scale of L245 steel was compact internally but porous externally. In oil and gas production, many factors influence the corrosion behavior of pipelines in crude oil/water-mixed environments, including water cut, flow patterns and veloc- ity of oil and water, pressure, temperature, and the compositions and microstructure of pipeline steels. Among these factors, the water cut, as well as the flow patterns and velocity that influence surface wettability, have been widely investigated. 1-2 The solubil- ity of water in crude oil is low ; however, water can be entrained in oil as droplets, forming a water-in-oil emulsion. The corro- sion rate of pipelines in this environment is generally low. At low water cut and higher velocity, corrosion is not an issue due to water entrained in the oil. With the increase of water cut, water can be separated from the emulsion and exists as a free water phase, which is often present in the bottom of horizontal pipelines and wets the pipeline walls, increasing the corrosion rate. In the last four decades, many corro- sion prediction models in mixed environ- ments of crude oil and water have been proposed by researchers. 3-7 However, these data are insufficient for accurately assess- ing the corrosion risk of pipelines in crude oil-and-water mixed emulsions, especially for Cr-containing alloy steels. This study investigated the corrosion of Cr-alloy steel and carbon steel with different water cut percentages under high-temperature and high-pressure conditions. Experimental Procedures The 3Cr and L245 steels were used in this series of experiments, and their chemi- cal compositions are presented in Table 1. The test samples were machined with a dimension of 10 by 10 by 2 mm. Before the experiments, the samples were successively ground with 150, 400, and 800 grit silicon carbide papers, then rinsed with acetone and blown dry. The test solution was a mixture of water and crude oil. The crude oil was extracted from an oil and gas field in China, and the water solution was simulated from deion- ized water and analytical grade reagents (Table 2). All the experiments were con- ducted in a 3-L high-temperature and high- pressure autoclave under the test condi- tions listed in Table 3. Th e morphologies of th e corrosion product scales formed on sample surfaces w e re o b s e r v e d b y s c a n n i n g e l e c t r o n micros copy (SEM), the chemical composi- tions were analyzed by energy dispersive Effects of Crude Oil on the Corrosion Behavior of Pipeline Steel Under Wet CO 2 Conditions liang Wei, Xiaolu Pang, and keWei gao, University of Science and Technology Beijing, Beijing, China

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