Canadian Athabasca oilsand bitumen crudes, characterized as corrosive by the classical naphthenic model, are producing negligible naphthenic acid corrosion in crude and vacuum units after more than 50 years of cumulative operation. A new theory proposes that the corrosivity of naphthenic acids in Athabasca oilsand bitumen crudes is a function of its molecular weight, molecular structure, true boiling point, reactive sulfidic species, and local environment. The concept of Alpha (bad type) and Beta (good type) naphthenic acids is introduced. The Alpha naphthenic acids are characterized as corrosive, with low molecular weights, and Beta as non-corrosive and inhibitive, with high molecular weights. Hot extraction wash of the raw oil sand mixture appears to preferentially remove the higher water-soluble Alpha fraction leaving the less corrosive, less water-soluble, Beta fraction. Naphthenic acid surviving after thermal hydroprocessing tends to be of the inhibitive Beta type. Case histories, material selection, and corrosion reduction possibilities with opportunity crudes are discussed.
Keywords: Naphthenic acid, TAN, naphthenic acid corrosion (NAC), oilsand bitumen crude, opportunity crude, alpha, beta, reactive sulfur