Partial upgrading of oilsands bitumen has been considered as an effective approach to reducing the usage of diluent during the pipeline transportation of raw bitumen to its market with less economic pressure and greenhouse gases emission. Thermal cracking is a mature technology in oil and gas industry to break large molecules to smaller ones, which can be easily adopted in partial upgrading to produce a less viscous bitumen. Previous studies indicated that the temperature for thermal cracking of bitumen should be limited to 400 °C to maintain a satisfactory liquid yield. However, the corrosion of partial upgrader constructional materials under thermal cracking conditions remains a safety concern for long-term operations. In this work, a low-alloyed steel, UNS K91560, was exposed to thermal cracking of a Canadian oilsands bitumen in the temperature range of 360 – 400 °C. The samples exposed to the liquid phase experienced more severe corrosion than those exposed to the gas phase. Much higher corrosion rates were observed at enhanced upgrading temperatures. Characterization techniques such as XRD, SEM/EDS were employed to examine the formed corrosion products. The corrosion mechanisms were explored based on the characterization results.
In spite of the current focus on promoting renewable energy, oil and gas will still remain the largest energy source to support energy demand by 2050.1 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 Oilsands contains approximately 10-12% bitumen.4 This type of heavy oil is reported to have an average viscosity of as high as 106 mPa·s,5 and 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. Unlike complete upgrading bitumen to produce SCO, partial upgrading is developed to improve the properties of bitumen with the sole objective of achieving pumpable oil for being transported by transmission pipelines. 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.6
