STUDY OF A FAILURE A DECOHESION FAILURE IN A THREE LAYER COATING OF A 24” GAS PIPELINE IN VERACRUZ IN SOUTH EAST MEXICO

FBE has proved to be a reliable coating in terms of adhesion to metal substrate and there are not many reports of this type of coating failures in the literature. We report the case study of a gas pipeline generalized three layer system FBE coating failure causing severe economical and operational damages after only 5 years of service. The report was initially based on an inline inspection report of three sites of metal losses that motivated excavation and coatings inspection works. Visual and field measurements were performed to document FBE and /or polyolefin and polyethylene adhesion failures, as well as ground properties including pH and microbial content.  Further work included a full CIS DCVG study, and excavations at coating failures. Extensive work was performed to document metal surface preparation and chloride or other possible deposits. Scanning electron microscopy – energy dispersive x-ray spectroscopy (SEM-EDS), differential Scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR), were performed on coating samples of the three polymeric layers to determine the possible failure mechanism. The studies ruled out disbondment caused by excessive CP, poor surface preparation, lack of cleaning and also ruled out the presence of chloride or other pollutants deleterious to the metal/FBE adhesion. The adhesion failures were associated to poor temperature control in the plant where the FBE, the polyolefine and the polyethylene ware applied. The present study concluded that the most deleterious consequence to be anticipated is the likelihood of CP blockage in disbanded zones where electrolyte could penetrate and cause corrosion, which forces to modify the integrity management plan at least in the frequency of in line inspections.