Continuous Monitoring of Pipe Coating During Pulling Operation in a Horizontal Directional Drilling (HDD)
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When pipeline routes have to cross traffic infrastructure, rivers, biotopes such as mountains and so on, the choice nowadays is almost exclusively trenchless pipe laying, and for trenchless pipe laying over longer distances it has been horizontal directional drilling that has become the proven method. As stated, for example, in the federal government’s pipeline provision, cathodic protection in line with the German Industrial Standard EN 12954 is normally required for the metal pipeline that is then pulled into place.Despite the precaution of additional coating, the mechanical stress involved, such the destroying effect of sharp-edged stones, as the pipeline is pulled into the borehole often leads to coating damage. Depending on the size of the resulting coating defects and the electrolyte’s electrical conductivity in the bedding zone, it may no longer be possible to achieve the cathodic polarization required for cathodic corrosion protection.The Pull & Check test procedure involves continuously testing the pipe coating while the pipe is being pulled into the horizontally drilled bore hole. From a procedural point of view, this method of testing is tied to the overall time taken to pull the pipe into position. The main advantage of this method is that any coating defect occurring during pipe pullback shows up straight away. This allows immediate measures to be taken to pull the pipe back, repair the coating damage and continue the operation, thus achieving the desired – undamaged or technically acceptable – coating quality and also avoids the situation in which a pipe run that is already damaged is pulled all the way into position before those responsible can be informed that the coating requires patching
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