This invention relates to a monitoring system for monitoring a degree of corrosion of a metal pipe, such as a gas pipe, or the like.
A metal pipe of the type described is more or less subjected to corrosion, such as electrolytic corrosion, when surrounded by a mass. For example, when it is buried in soil or immersed in water the soil and water form the mass. The cathodic protection is usually used in the art to protect the pipe from being corroded, as by an electrolyte which may be in the mass, as will later be described with reference to a few figures of the accompanying drawing. At any rate, a degree of corrosion of the pipe should be periodically monitored in some way or other to carry out maintenance of the pipe. Otherwise, unexpected breaks often take place somewhere on the pipe. In order to save time and labor, it is preferable for the degree of corrosion be automatically monitored at a remote station.
A monitoring system disclosed in Japanese Patent Publication No. Syo 53-6552, namely, 6552/78, comprises a pipe surrounded by a mass, a pair of cables along the pipe, a plurality of relays connected across the cable pair and spaced from one another, an indicator, and a plurality of measuring electrodes connected to the indicator through the contacts of the respective relays. When one of the relays is selectively put into operation through the cable pair, the corresponding measuring electrode is electrically connected to the indicator through the contact of the operated relay. As a result, the indicator is supplied with an electric potential between the pipe and the measuring electrode. A degree of corrosion is detected from the electric potential given to the indicator. Thus, it is possible to remotely monitor the degree of corrosion of the pipe.
With this system, the cables should be extended along the pipe in the air or soil. Therefore, extra spaces have to be prepared to lay the cables along the pipe. In addition, the cables may be broken, as during road repairing when they are buried in soil along a street. Restoration of the cable is very difficult once they are broken.