20 Years of life integrity of a high pressure natural gas pipe-line using strain-gages

A high-pressure natural gas-pipe-line runs underground a valley of a river in a geological unstable area on the northern outskirts of the Alps. To get the permission to establish and to operate the pipe-line, the local authorities demanded for an information system which makes it possible to detect additional mechanical stresses in the pipe-line due to unspecified bending moments caused by the sudden gliding of the soil stratum. It was decided to use strain-gages as stress-transducers. They were bonded 20 years ago to the surface of the pipe at 8 important areas, protected against humidity and damage, wired to a measuring station on an island in the river and connected with a telephone modem to the control station of the gas company. The strains were monitored continuously, recorded and so available for assuring structural integrity of the pipeline. When maximum allowable strains (stresses) would be exceeded there was a chance to close two pipe-line valves at both sides of the river. The experiences showed, that long-time monitoring of strain-gage-signals can be used as cost-effective inspection tool for older equipment to detect possible environmentally induced damage, to assess the life integrity of the pipe-line.