The influence of flame spraying parameters on coating microstructure and electrical conductivity of aluminum- 12silicon coatings deposited on polyurethane substrates was studied. In order to evaluate the effect of the spray parameters on temperature distribution and its corresponding effect on coating characteristics, an analytical model based on a Green’s function approach was employed. It was found that the addition of air to the flame decreased the temperature within the substrate. Dynamic mechanical analysis (DMA) of the PU substrate revealed that the PU softened as the temperature increased. Therefore, by increasing the pressure of the air injected into the flame spray torch from 35 kPa to 69 kPa, the particles impacted a stiffer substrate. This led to increased deformation of the particles into splats upon impact, improved interlocking, and the overall coating had lower porosity and lower electrical resistance. The results obtained indicated that coating properties are sensitive to both thermal spraying parameters and temperature distribution within the substrate when depositing on elastomeric materials. The effect of torch stand-off distance on coating properties was also evaluated. It was found that higher air pressure can cool the substrate and, therefore, allow for a decrease of the stand-off distance. As a result of shorter stand-off distances, a coating with lower porosity and electrical resistance was deposited.

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.