Surface Material Effects on Wax Deposition in Noncoated Pipelines

Abstract

Nonsteel pipes are being more widely used in gathering and transporting oil and gas due to their low-cost and anticorrosion properties. Most of the existing literature studies wax deposition on pristine steel surfaces, with very limited attention to nonsteel pipes. To fill this gap, in the current work, we aim to elucidate the surface material effects on wax deposition in noncoated and nonsteel pipelines. Copper and PTFE were chosen as the surface materials for their high (1362 mN/m) and low (18 mN/m) surface free energy, respectively, so that a wide range of surface free energies was created to maximize the strength of the effect observed. For the first time, a customized cold finger apparatus with specially designed cold fingers was constructed to generate consistent surface temperatures when different surface materials were employed, so that the thermal effects and surface effects on wax deposition could be isolated. Continuous thickness data was collected via a custom computer vision software, and deposits were weighed and analyzed for composition after the tests were finished. It was found that the deposits formed on PTFE and copper have similar thickness but the deposits formed on PTFE have a higher fraction of heavy components, with a slightly larger mass. The differences in deposit mass, thickness, and composition between PTFE and copper are relatively small, contrary to the much larger effects reported in the prior literature in which no attempts were made to control the surface temperatures. These observations indicate that depositional differences between different noncoated surface materials could also be caused by alterations to the heat transfer process, rather than through the surface energy and chemistry alone, an important insight that would benefit the design of remediation practices (i.e., pigging) for wax deposition in non-steel pipelines.