The difficulty of obtaining information about the presence, route and nature of buried pipes or lines resides in the fact that, most of the time, nothing is visible from the outside and that the existing planes often prove to be imprecise, incomplete, and even sometimes erroneous or nonexistent.
To save time, reduce costs and also improve safety, it is important to be able to detect the presence of such pipes and lines, and to locate them accurately, without digging the ground, nor destroying the structures when carrying out subsequent works. In general, the processes used must be simple to implement by site personnel with modest qualifications. Furthermore, the equipment used to implement these detection processes must be robust and reliable and its cost must remain lower than the investment that would require updating by excavation of the buried structures or of their warning mesh to ensure their presence.
Several processes may be used for detecting buried pipes.
Detection in electromagnetic way is the most commonly used method. This electromagnetic detection can be performed by injecting, using a current generator, an electric signal in an electrically conductive linear element associated with a pipe to be identified and disposed following the route of the latter, and this via connection boxes installed at regular distances along the pipe to serve as access points, and by using an electromagnetic detector arranged to sense an electromagnetic field created by an alternating current flowing in the electrically conductive element.
In a manner known per se, the electrically conductive element is covered with a cylindrical sheath made from electrically insulating material and is secured on the pipe to be identified using fastening means, such as for example circlips, self-gripping tapes, or adhesive tapes.
Such fastening means allow, for the most part, to move the electrically conductive element on the outer surface of the optically invisible object to be identified, especially when the optically invisible object is of circular section. These movements of the electrically conductive element may lead to imprecise positioning of the electrically conductive element, and thus to imprecise and difficult detection of the optically invisible associated object.
Yet, taking into account the drastic changes in the accuracy standards as far as detection of optically invisible object is concerned, it is necessary to ensure optimum positioning of the electrically conductive element, including after burial of the optically invisible associated object.