The Hardening Process and Morphology of a Wax Deposit in a Pipe Flow

Paraffins crystallize out from waxy oil solution as temperature is lowered and form a deposit on transportation pipelines. The deposit becomes hard with an increase in its solid content, making cleaning difficult. A good knowledge of the crystal morphology is essential to understand the hardness of the deposit. The morphology of the deposit on a cold pipe was studied with scanning electron microscopy. The crystal morphology changed gradually from a round, plate-like crystal to mal-crystals and spherulites as the deposit grew. The deposit became harder with a decrease in its oil cavities created by lateral growing of macroplate crystals and formation of mal-crystals. The morphology change gradually occurs at temperatures between the cloud point and wax dissolution temperature depends on cooling rates. The results revealed another aging mechanism is the change in crystals morphology.