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Nouvelle stratégie de sélection des primaires d'adhésion pour revêtements tricouches

Abstract : Three layer organic coatings are being widely used to protect steel pipelines from external corrosion, in addition to cathodic protection. They consist of an epoxy primer layer (FBE) providing adhesion to steel, overlaid by an intermediate modified polyolefin layer ensuring the proper anchoring of the topcoat to the epoxy primer, and a thick polyolefin external topcoat -polyethylen or polypropylen. Since the permeability of polyolefin materials to water is not negligible, polyolefins do not prevent water ingress into sub-layers after a few months service. Then soaked water in the epoxy primer layer directly affects its adhesive properties to the steel pipe. Recent case studies reported large scale disbondments of three-layer polyolefin (3-LPE) coatings, which could favour corrosion beneath the coating and lead to possible major damage if cathodic protection is shielded. Therefore, it is necessary to better investigate the adhesion strength of fusion-bonded epoxy primer to steel taking into account the water diffusing through the topcoat within the lifetime of pipeline. A methodology was developed at IFP to examine the adhesion of FBE primer to steel under wet exposure: peel tests were carried out on pipe rings industrially coated with FBE & intermediate polyolefin layers only, aged in water to simulate the water ingress through the topcoat. This new method is proposed to contribute to the selection of FBE for anticorrosion purpose or could be further developed as accelerated method in pre-qualification tests. This paper examined the adhesive behaviour of sub-layers (FBE+intermediate polyolefin on the one hand, FBE on the other hand) aged in liquid water at 60°C. Results are compared to those obtained in vapor at the same temperature and discussed. In addition, long term ageing of complete and undamaged 3-LPE coatings were performed in liquid water at 20°C and 60°C to illustrate the effective loss of adhesion of the coating due to the water permeation and to highlight the benefits of an accelerated methodology.
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Valérie Sauvant-Moynot, Jacky Grenier, Jean Kittel. Nouvelle stratégie de sélection des primaires d'adhésion pour revêtements tricouches. 4ème Journées d'Aix sur la protection cathodique et revêtements associés, Jun 2006, Aix-en-Provence, France. ⟨hal-02475646⟩

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