Comparison of characteristic of anti-scaling coating for subsurface safety valve for use in oil and gas industry
Authors: Baraka-Lokmane Salima , J. Charpentier Thibaut V , Neville Anne , Hurtevent Christian , Ordonez-Varela John Richard , Moeller Nielsen Frank , Eroini Violette , Olsen John Helge , Ellingsen Jon Arne , Bache Oystein 
Published: May 2016

Abstract
A subsurface safety valve is used to shut in a well automatically, if the wellhead equipment or other surface production equipment fails. It is almost always installed as a vital component on the completion. In many industrial systems, scale formation causes significant problems, not when it precipitates in bulk solution but when it deposits on the surface. Surface scaling is a complex phenomenon where several processes such as heterogeneous crystallization or particle adhesion are inextricably linked and occur simultaneously. The sub-surface safety valve can accumulate carbonate, sulphate and sulphide scale. Even a thin layer of scale can impede the smooth operation of the valve and pose serious regulatory and safety risks. In this study twenty coatings from seven different natures have been tested. These coatings are Fluoropolymers, Composite (fluotopolymer matrix), Sol-gelnano-coating, Textured hydrophobic paint, Diamond Like Carbon (DLC), Polished Inconel and Nitro carburated Inconel. Whilst the anti-scaling capability of the coating is the key functional element, it is extremely important that the coating presents other important parameters such as hydrophobicity property, surface roughness, coatingthickness and hardness, resistance to erosion, corrosion and temperature as well as coating adhesion. In this paper the controlling factors of anti-scaling coatings are discussed. Promising coatings with anti-scaling properties have been identified.

Introduction
The spring cavities and the inner wall of the sub-surface safety valve can accumulate deposits of carbonate, sulphate and sulphide scale. The precipitated scale can impede the smooth operation of the valve and pose serious regulatory and safety risks such as the malfunctioning during well blow-out. There are several techniques used to remove scale; these include the use of chemical inhibitors, chemical scale removers and mechanical methods. Scale control at surfaces may be addressed by anti-scaling coatings and surface engineering options. In the desalination units and heat exchangers, there have been a few attempts at using surface engineering to control scale deposition (Cheong et al., 2008). Surface deposition and precipitation are interlinked but it has been shown that they have very different kinetics and that controlling bulk precipitation does not by default control surface scaling. In order to fully understand a scaling system both an appreciation of the bulk precipitation and surface deposition characteristics must be obtained (Chen et al., 2003). In surface deposition the important steps are (i) nucleation of crystals, (ii) the growth of these crystals at the surface site and (iii) the adhesion of crystals to create a scale layer. Application of 'non stick' materials is considered as a promising method to alleviate scale deposition (Wang and Neville, 2005).