Among the two great families of external coatings of pipelines - FBE coatings and 3-LPE - each one has its advantages and disadvantages. In both cases, FBE is applied in direct contact to the freshly grit blasted pipe in order to provide good anchoring to steel. 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. Therefore, it is necessary to better investigate the adhesion strength of fusion-bonded epoxy (FBE) primer to steel taking into account the water diffusing through the topcoat within the lifetime of pipeline. A methodology was developed to examine the adhesion of sublayers to steel under wet exposure: peel tests were carried out on pipe rings industrially coated with FBE and adhesive layers only, aged, in vapour to simulate the water ingress through the topcoat. This methodology could be included in selection or pre-qualification tests. From this study, it can be clearly concluded that the bonding strength of FBE primer to steel can be sensitive to wet ageing due to water diffused from external exposition. This water diffusion through any polymeric top-coat is expected within the lifetime of pipe, according to permeability data. Thus, an additional methodology based on the ageing of bi-layer FBE/adhesive coatings is proposed to provide an accelerated evaluation of the FBE adhesion to steel during wet ageing. Indeed, the first step associated with water diffusion through the polyolefin top-coat is suppressed. This methodology will allow to discuss the influence of external damaging factors (medium, temperature) but also intrinsic material factors (epoxy chemistry, layer thickness) on the bonding strength between steel and FBE primer layer. Since a good resistance of the coating-to-steel adhesion is mandatory for the long term performance of 3-LPE, the methodology proposed could help designers and operators to select a FBE primer chemistry and thickness in complement to traditional testing protocols dedicated to 3-LPE under CP and including an artificial defect within the coating.


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    Title :

    Contribution to a better FBE selection for 3 layer polyolefin coatings


    Contributors:
    Sauvant-Moynot, V. (author) / Duval, S. (author) / Kittel, J. (author) / Lefebvre, X. (author)


    Publication date :

    2005


    Size :

    15 Seiten, 11 Bilder, 4 Tabellen, 14 Quellen



    Type of media :

    Conference paper


    Type of material :

    Print


    Language :

    English




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