Investigation of delayed formation of wax deposits in polyethylene pipe using a flow-loop

Abstract

After the start of the flow in a home-built flow-loop, the thickness of a waxy layer deposited on a stainless steel (SS) test section was found to increase immediately, while deposition was delayed for around 4 h on a polyethylene (PE) test section. The radial thermal gradient, wax precipitation rate, radial diffusivity of wax, and shear stresses at the surface of the deposit layer were calculated, eliminating these factors as sources of different deposition behavior. However, the contact angles of oils containing precipitated wax crystals on PE surfaces were found to increase more with increasing wax content than those on SS surfaces. Consistent with this, while the wax contents of deposits were found to be around 18 wt % for both PE and SS pipes, the adhesion of the deposit on the PE surface was found to be much weaker than on the SS surface, as evidenced by the easier of removal of the deposit from PE than from SS pipes when heated in vertical orientation under gravity. These results point to pipe wall wettability as a significant factor in both initial growth of wax deposit, and ease of removal.