In this paper

three liquids flowing in five pipes with the same inner diameter of 14 mm were studied to determine the relationship between the surface wettability and flow properties in laminar flow (Re 2000). This was motivated by oilfield observations of increased pressure drops in non-metallic pipes compared to those in metal pipes

which was contrary to expectations. A new expression for the frictional coefficient that considers the Reynolds number and contact angle

θ

in laminar flow for non-metallic pipes was proposed based on the experimental results of single-phase flow using dimension and regression analyses. The solutions of the anomalous phenomenon were proposed from the perspectives of the pipe diameter

contact-angle difference

and the compatibility between flexible composite pipe and JLHW105 oil according to the new formula. The surprising finding was that the surface wettability could control the frictional resistance by the critical contact angle (39.9°) obtained at the same Reynolds number. If 0°

θ

≤ 39.9°

the frictional coefficient increased as the contact angle increased. In contrast

if 39.9°

θ

180°

the frictional coefficient decreased with increasing contact

angle. The influences of the pipe diameter and contactangle difference on the pressure drop difference of JLHW105 oil showed an inversely proportional relation. A series of materials and liquids were tested. The selection of pipe material for transporting a given fluid can be based on the contact angle

surface tension

and critical limit of the contact angle obtained. The research results are expected to provide some guidelines for the selection of the appropriate pipe material for a given set of fluids.