Erosion-corrosion behaviour of steels used in slurry pipelines

The regular replacement and maintenance of steel pipes used to transport the slurry processed in oil sands mining and extraction represent a major expense for oil sands operations. Erosion-corrosion tests reveal that the performance of the steels is strongly influenced by the slurry velocity, which affects the severity of the erosioncorrosion synergy. In this study, the erosion-corrosion behavior of API 5L X65, X70, and X80 steels was assessed at two different slurry velocities (3.5 and 5 m/s) and two different aeration levels or dissolved oxygen (DO) levels (0.6 and 3.8 ppm). Results of the tests were compared to those of an ASTM A1053 Gr.50 dual-phase (DP) stainless steel and AR400 hard plate. The tests were performed at 60 degrees C in sand-containing slurry (20% vol. silica) with 500 ppm chloride, which replicated common field conditions. Characterization of the steels was carried out with optical and scanning electron microscopy, energy dispersive x-ray spectrometry, x-ray diffraction technique, micro-mechanical probe, and electrochemical testing. The results showed that at the DO level of 3.8 ppm, the DP stainless steel featured the highest erosion-corrosion resistance at the slurry velocity of 3.5 m/s, while its performance was inferior to that of the carbon steels as the slurry velocity was increased to 5.5 m/s. At the lower DO level, the DP stainless steel erosion resistance was relatively similar to the carbon steels but deteriorated as slurry velocity was increased. Possible mechanisms responsible for the observed variations in the erosion-corrosion resistance under the testing conditions are analyzed and discussed.