Detection of Bending Stresses in Buried Pipelines

When gas or oil pipelines must be laid through sand or permafrost or other unstable soils, the pipe walls can he subjected to large bending loads if the soil shifts. In order to detect this condition and correct it, it would be useful to monitor the state of stress along the pipeline'at regular time intervals using a vehicle that is moved through the line by the fluid or gas in it. The experiments described here demonstrate that such a vehicle, using EMATs to excite and detect ultrasonic waves in the pipe wall, would be feasible because the transduction efficiency of the EMATs and thus the insertion loss of such a system can be related quantitatively to the stress level in the pipe wall.