In many production fluids encountered in the oil and gasindustry, the formation of mineral scales such as BaSO4 andCaCO3 causes major problems with respect to flow assurance.It has recently become apparent that in order to fullyunderstand a scaling system both an appreciation of the bulkprecipitation and surface deposition characteristics must beobtained [1]. In surface deposition the important steps are (I).Nucleation of crystals, (ii) the growth of these crystals at thesurface site and (iii) finally the adhesion of crystals to create ascale layer. In some instances where scaling causesoperational problems (e.g in heat exchangers in desalinationunits) application of ‘non-stick' materials are considered as apromising method to alleviate scale deposition. To date, therehave been few instances where surface modification or surfacecoatings have been considered seriously for scale control inthe oil and gas industry.In this paper results are reported from experiments toinvestigate calcium carbonate scale formation and adhesion atsolid surfaces. Two aspects relevant to adhesion areconsidered: 1. The influence of the substrate on the extent ofsurface scale formation; 2. The critical shear stress required forremoval of scale. Four substrates were investigated in thestudy, UNS S31603 (stainless steel), electrochemicallypretreated UNS S31603 and two coatings: DLC (diamond likecarbon) and PTFE (polytetrafluoroethylene). Depositionexperiments were conducted from supersaturated solutions ofcalcium carbonate at 50°C. In order to investigate the criticalshear stress for removing scale on different substrates, asubmerged impinging jet (SIJ). It has been shown that theamount of scale formed at the surface is dependent on surfaceenergy and on physical surface roughness. The surfaceenergy, and in particular the polar component, is an importantfactor in adhesion – as are the morphology and crystalarrangement in the surface scale deposit.
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