Geometric Dent Characterization

The Canadian pipeline design standard (CSA Z662) requires the repair of smooth dents with depths exceeding 6% of the pipeline’s outside diameter. This limit on dent depth is reduced in the presence of additional localized effects such as pipe wall gouges, corrosion, planar flaws or weld seams. It has been noted, however, that pipelines have operated satisfactorily with dents in excess of 10% while others with 3% dents have failed. Based upon observation of this type the question arises, “Is there more to characterizing a dent than its depth?” An ongoing group sponsored project at BMT Fleet Technology Limited (FTL) is exploring the issue of dent characterization using a dent assessment model developed at FTL. The objective of this project is to develop a rapid dent life expectancy characterization technique based upon dent geometry, line pressure history and line pipe material properties. This paper will outline the general characterization approach being considered and demonstrate some of the observed and expected relationships between service life and dent geometry. The relative importance of each dent characteristic (geometric measures, line pipe material and line pressure history) will be discussed to demonstrate the potential of the rapid characterization approach being developed.