DTRS56-04-T-0009 Evaluation of the Interaction of Mechanical Damage and Welds

Abstract

This project was completed to support the development of a guidance note for the disposition of welds interacting with pipe wall mechanical damage (dents, wrinkles, and ovality) and thus allow a more rational treatment of these forms of damage. The intent is not to evaluate the life of welds interacting with dents wrinkles and ovality, but rather to identify when the interaction is significant and needs to be considered explicitly. Based upon the criteria developed in this project, inspection results that indicate the presence of pipe wall deformation in the vicinity of a girth weld or long seam weld can be used to assess if the interaction is significant and must be treated as a repairable defect. This project report includes a discussion of the following work: � Development of criteria for weld interaction with restrained rock dents, pipe ovality, and wrinkles; � Development of a means of considering pressure fluctuation severity in these criteria, and � Development of guidance and recommendations on how to consider the effects of soil confinement. The criteria do not predict the actual life of a mechanical damage feature, but instead, present a means of defining the interaction distance between a damage feature and a weld. The processes have been established based on numerical modeling results with a detailed consideration of the effects of both physical and numerical variables. Due to the virtually limitless combination of weld seam geometries, weld quality, and residual stress fields, these parameters were not explicitly included in the numerical models. Instead, potential weld quality issues and residual stresses are addressed using an appropriate and conservative fatigue design curve while the weld geometry effects have been included with the selection of a stress concentration factor applied to the numerical modeling results.