An assessment of adhesion of scale and electrochemical pre-treatment for the prevention of scale deposition on metal surfaces

From an oilfield scale prevention perspective, interest recently has focused on understanding the relationship between heterogeneous nucleation and growth on pipeline surfaces (adhesion) rather than homogeneous nucleation and growth from bulk solution. Furthermore, it is recognised that homogeneous nucleation, and not adhesion, is conventionally examined in industry standard bulk “jar” type tests for the assessment of scale inhibitor performance. The trend towards understanding heterogeneous nucleation and growth has gained interest because scale adhesion is recognised as a much more serious issue than homogeneous “bulk” precipitation.

In a recent paper by Neville et al.1 a novel electrochemical approach, has been described which enabled the extent and also the rate (kinetics) of CaCO3 and BaSO4 scale formation on a solid surface to be determined. During this study it was clearly shown that the formation of an inhibitor film at a metal surface can occur and the extent of this is affected by the presence of certain cations, the inhibitor concentration and the hydrodynamic and electrode potential regimes. In laboratory studies on rotating disk electrode (RDE) coupons it has been clearly demonstrated that this film has a beneficial effect in preventing scale formation from a supersaturated solution onto a metal surface.2,3 As such there is potential to enhance scale inhibition by carrying out an electrochemical pre-treatment.

In this paper the research has been extended to include pretreatment of surfaces in a dynamic tube-blocking rig. The effect of various pre-treatment parameters on carbonate scale have been assessed and it has been shown that even in the higher temperature and pressure environment there is a benefit of using electrochemical pre-treatment.

In addition, the paper summarises other work conducted by the authors which examines the relationship between heterogeneous nucleation and growth on pipeline surfaces (adhesion) rather than homogeneous nucleation and growth from bulk solution which includes the impact of conventional scale inhibitors and film forming corrosion inhibitors.