For the entirely movement of the pre-insulated packet pipes as a system the correlation between the layers must be achieved. The adherence between the service steel pipe and the polyurethane pipe will be achieved with sanding. The treatment to achieve the correlation between the polyurethane and the secure overcoat HDPE is called "Corona Treatment". During this treatment a high voltage electron bombardment is applied to the inner surface of the HDPE to separate the last C (carbon) of the chain for an unsmooth surface to achieve a better correlation between this surface and the polyurethane.