Abstract
Multiphase flow seen in oil and gas lines can be very turbulent and its effect on corrosion has been debated for decades. However, the effect of turbulence and mechanical forces produced by flow on protective corrosion product layers and inhibitor films is not fully understood. Wall shear stress (WSS) is one of the most important parameters used to characterize flow conditions and to assess the influence of flow on corrosion. In the present study, conducted under controlled laboratory conditions, single-phase water flow and a wide range of gas-liquid flow regimes (stratified flow, slug flow and annular mist flow) have been studied in order to accurately measure WSS using a direct floating element WSS measurement probe. These measurements were complemented by visual recordings using a high speed video camera. In addition, atomic force microscopy (AFM) has been used to quantitatively study the force required to remove FeCO3 crystals from a mild steel specimen surface.
The highest WSS measured was of the order of 102 Pa in an atmospheric pressure flow systems. AFM measurements indicated that forces of the order of 107 Pa would be required to remove an iron carbonate precipitate from a mild steel surface. This is an important finding which indicates that the WSS typically seen in multiphase flow lines is not sufficient to damage FeCO3 layers which could lead to accelerated and localized corrosion.
