{"id":406,"date":"2020-02-03T10:40:49","date_gmt":"2020-02-03T09:40:49","guid":{"rendered":"http:\/\/yvcharron.com\/?page_id=406"},"modified":"2020-12-16T12:28:40","modified_gmt":"2020-12-16T11:28:40","slug":"coating-characteristics-testing","status":"publish","type":"page","link":"https:\/\/yvcharron.com\/index.php\/coating-characteristics-testing\/","title":{"rendered":"Coating characteristics and aerodynamic testing"},"content":{"rendered":"\n
Keywords: Coating properties surface characteristics aerodynamic testing high pressure high velocity<\/p>\n\n\n\n
Coating surface characteristics<\/h2>\n\n\n\n
The internal coatings<\/strong> for pipelines exhibit complex fluid friction<\/strong>. Firstly, the surface condition analyzed locally in terms of roughness parameters<\/strong>, Ra or Rz is different from that of shot blasted steel often taken as a reference. Secondly, although sometimes smooth locally, the surface of a coating may have long wavelength corrugations<\/strong> contributing to greater friction than that predicted from a measurement of local roughness. Finally a third parameter can intervene with certain types of coating which is the parietal (or wall) sliding<\/strong>. This phenomenon could be explained by a slight distancing on the molecular scale of the fluid from the wall promoting the flow of the gas (an acceleration). This phenomenon is particularly important when the boundary layer (viscous) presents a small thickness.<\/p>\n\n\n\n <\/figcaption><\/figure>\n\n\n\n
This last phenomenon is the opposite of that is sometimes observed with chemically modified coatings<\/strong> after contact with certain chemical agents leading to an attraction of molecules towards the wall, consequently, to a braking of the flow (a deceleration).<\/p>\n\n\n\n
It is therefore important to know the aerodynamic performance of a pipeline internal coating, for new as well as for aged coatings.<\/strong><\/p>\n\n\n\n
Coating aerodynamic testing<\/h2>\n\n\n\n
An aerodynamic testing device has been designed for this purpose<\/strong>. The operating principle is based on the rotation of a gas, in a closed enclosure under pressure, using a rotating cylinder. The braking of the gas by the fixed external wall makes it possible to deduce the friction factor of that wall at the origin of this braking. The device allows measurement of gas friction under conditions of high pressure (up to 100 bar) and very high velocity (up to 40 m\/s), i.e. with a very thin layer thickness (less than one micrometer). Transcribed in terms of Reynolds number, this gaseous friction can be translated in a condition of similitude based on a constant product of the density and the velocity of the flow.<\/p>\n\n\n\n
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