Technologies applicable to in-line evaluation of pipe wall stress

This paper describes nondestructive technologies for measurement of bulk stress in the wall of a transmission pipeline. It is particularly concerned with those technologies which can be applied in-line in an operating pipeline (i.e., in an instrumented pig). The qualities required of an in-line technology include ruggedness, reasonable low power consumption, operator independence, and the ability to make measurements while moving through the pipe. Several of the most sensitive and accurate stress-measuring techniques do not meet these in-line requirements. Both ultrasonic and electromagnetic methods can be applied, and the presentation will contrast the characteristics of the most promising versions of each. Finally, a report will be given of test results from the ongoing evaluation of a new, patented stress sensor.