Surface Material Effects on Wax Deposition in Noncoated Pipelines

Nonsteel pipes are being more widelyused in gatheringand transportingoil and gas due to their low-cost and anticorrosion properties. Mostof the existing literature studies wax deposition on pristine steelsurfaces, with very limited attention to nonsteel pipes. To fill thisgap, in the current work, we aim to elucidate the surface materialeffects on wax deposition in noncoated and nonsteel pipelines. Copperand PTFE were chosen as the surface materials for their high (1362mN/m) and low (18 mN/m) surface free energy, respectively, so thata wide range of surface free energies was created to maximize thestrength of the effect observed. For the first time, a customizedcold finger apparatus with specially designed cold fingers was constructedto generate consistent surface temperatures when different surfacematerials were employed, so that the thermal effects and surface effectson wax deposition could be isolated. Continuous thickness data wascollected via a custom computer vision software, and deposits wereweighed and analyzed for composition after the tests were finished.It was found that the deposits formed on PTFE and copper have similarthickness but the deposits formed on PTFE have a higher fraction ofheavy components, with a slightly larger mass. The differences indeposit mass, thickness, and composition between PTFE and copper arerelatively small, contrary to the much larger effects reported inthe prior literature in which no attempts were made to control thesurface temperatures. These observations indicate that depositionaldifferences between different noncoated surface materials could alsobe caused by alterations to the heat transfer process, rather thanthrough the surface energy and chemistry alone, an important insightthat would benefit the design of remediation practices (i.e., pigging)for wax deposition in non-steel pipelines.