Corrosion Assessments of P91 Under Partial Upgrading of Bitumen

Despite of the fast development of clean energy technologies, petroleum is still considered as the largest source for daily energy consumption.1 As the world’s 4th largest crude oil producer and 3rd exporter, Canada produces 4.97 MMb/d of crude oil as of 2020.2 As the depletion of conventional crude oil reserve, more efforts have been taken to economically exploit the unconventional resources including oilsands bitumen. Canada has vast reserves of crude oil, i.e., 171 billion barrels, 166.3 billion barrels of which are oil sands reserves.3 The heavy oil in oil sands (called bitumen), is too viscus to be directly transported through pipelines to the market. Currently, the oilsands bitumen is blended with diluent so it can be transported or sold to petroleum refineries for further upgrading to the marketable synthetic crude oil (SCO). The disadvantages of using diluent for bitumen transportation, particularly the occupancy of pipeline capacity, have inspired the “partial upgrading” techniques.4 Unlike complete upgrading bitumen to produce SCO, partial upgrading is developed to improve the properties of bitumen so it can freely flow in pipeline. In other words, the partially upgraded bitumen must meet the pipeline transportation specifications, i.e., density of 940 kg/m3 or lower at 15.0 °C, kinematic viscosity of 350 cSt or lower at pipeline temperature, with total olefin content no higher than 1.0 wt% 1-decene equivalent. Mild thermal cracking, or visbreaking, is an important process to realize viscosity reduction. In thermal cracking, the breakage of large molecules in bitumen is regulated to a moderate degree to prevent excessive formation of gaseous products and coke.5 The conditions for the visbreaker to partically upgrade the oilsands bitumen could be milder (400 °C or lower) than those typically operated in petroleum refining.6 However, in this process, reactive molecules/radicals are likely produced which could be more corrosive than their parent compounds, causing the integrity degradation of reactor constructional alloys.