Following a survey of all of the techniques capable of preventing third-party damage to its gas transmission pipelines, Gaz de France has selected two of them, “Electromagnetic Detection” and “Positioning by Satellite”.

The first technique is based on detection of the magnetic field existing around transmission pipes excited by a driving current. A receiver is mounted on the excavation equipment to detect the magnetic field, thereby preventing any risk of hitting the pipe.

The second technique consists in locating excavators by satellite. Each excavator needs to be equipped with a GPS beacon to know its position. Using the map of the transmission network stored in data-base form — i.e. digitized, the system calculates the position of the excavator relative to the pipes buried in its vicinity so as to avoid any accidental contact.

The main features, advantages and drawbacks of the two techniques are presented in this paper.

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