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Plasma-sprayed aluminum oxide (A1203) and chromium oxide (Cr203) coatings were sealed by aluminum phosphates. Phosphates were formed throughout the coating, down to the substrate, and were verified by scanning electron microscopy and hardness measurements. The sealing increased the hardness of the coatings by 200 to 300 Vickers hardness (HV) units. Abrasion and erosion wear resistances were increased by the sealing treatment. Sealing also substantially closed the open porosity, as shown in electrochemical corrosion tests. The sealed structures had good resistance against corrosion during 30 days of immersion in both acidic and alkaline solutions with pH values from 0 to 10. No decrease in abrasion wear resistance was observed after immersion.

Polymer ceramic composite coatings were applied by flame spraying on preheated steel substrates. Polyamide (PA 11, nylon) powder was blended with alumina (Al2O3), aluminium nitride (AIN) or boron nitride (BN) powder with two different filler content to increase thermal conductivities of polymer coatings. Morphologies and particle sizes of polyamide and filler powders were examined by scanning electron microscope and laser scattering methods. Coating structures and thicknesses of composite coatings were studied by the polished cross sections. Thermal conductivities were measured by hot disc method. Thermal conductivities of polyamide coatings increased from 30 % up to few times by blending ceramic filler material on PA 11 powder. Structures of composite coatings were dense and filler materials were clearly observed in polyamide matrix.

Several polymeric coatings, including flame sprayed polyethylene (PE), were evaluated for use in parts of natural gas pipelines. The components of interest were for instance large valves, T-joints, weld joints of pipes and pipe bends. More than 30 different coatings were selected to laboratory scale testing and evaluation. After first preliminary tests, the most potential coatings were selected further for more detailed and long term laboratory scale studies. After these tests were finished, one coating concept, i.e. fusion bonded epoxy (FBE) + flame sprayed PE, was prepared on a small natural gas valve body for demonstration purposes. Besides this coating concept, also some other coatings, e.g. liquid epoxy + flame sprayed PE and some polyurethane coatings were found to be potential coatings for the application. The test methods and results are presented in this paper.

Several recently published studies have shown remarkable improvements in dry abrasion resistance and corrosion resistance of aluminum phosphate sealed oxide coatings when compared to unsealed ones. There are numerous applications in chemical industry where a corrosive environment is accompanied with abrasive or erosive particles. In this study the wet abrasion resistance and slurry erosion resistance of aluminum phosphate sealed and oxide coatings were studied and compared to their dry abrasion resistance. In wet abrasion tests kaolin and water mixture was used as the abrasive. In slurry erosion tests several abrasives in water with various pH values was used as the erosive medium. The coatings were characterized for microstructure and their wear mechanisms were analyzed using SEM. The results from wear tests are reported and correlated with coating properties. The influence of coating quality to the relative improvement achieved by sealing is presented and discussed.