Development of a non-destructive, quantitative residual stress assessment tool

A nondestructive tool will be developed to quatitatively assess residual stress in pipelines from the exterior and through coatings. Residual stress is a critical factor that determines the cracking susceptibility of pipeline steels, but existing methods for measuring mechanical damage in pipeline steels are incapable of quantifying the residual stress levels. A larger gouge or dent does not necessarily signify worse damage that a smaller gouge or dent; it is more important to focus on the actual residual stress levels induced by damage. Knowledge of the residual stress levels provides an accurate means to assess the severity of the damage and improve the pipeline integrity, ultimately reducing the amount of unneccessary removal and repair applications. The unique use of low frequency impendance sensors will allow for through thickness pipeline integrity assessment. Phase I will low-frequency impendance analysis to perform in-situ residual stress measurements on simulated mechanically damaged pipeline steel to compare with finite element and other stress estimation techniques. Phase II and Phase III efforts will develop a calibrated portable low frequency impedance toll for in-situ assessment of pipeline damage without removal of coatings.