According to the Office of Pipeline Safety incident database, mechanical damage is responsible for the largest number of reportable incidents in onshore and offshore transmission pipelines. For this reason, work to experimentally characterize the effects of dents and gouges on pipeline integrity has been undertaken for many years. The consequences of a leak or a rupture due to mechanical damage in an offshore products pipeline can have a significant environmental impact and related cost penalties. As with gas pipelines, the repair of damage offshore, along with the lost product and through-put, imposes a significant cost burden. For this reason, much work has been carried out to quantify the effects of third-party damage on the serviceability of a pipeline. This paper presents results quantifying the effects of mechanical damage in thin-walled high pressure pipelines that will assist in developing a serviceability criterion for such pipelines. The approach used in this work was to extend a model for ductile flaw growth to deal with dents and gouges by accounting for their effects on both the crack-tip stress field and the pipe steel's resistance to flaw initiation and/or growth. This paper discusses the effects of the dent/gouge as it is manifest in the pipeline's deformation behavior and the near-crack stresses and strains. The dependence of the extent of damage is presented in terms of parameters that include the nature of the contact, the internal pressure, pipeline support conditions, shape of damage tool, internal pressure, and pipe size.
The dominant incident category for onshore and offshore gas-transmission piping systems in the U. S. and elsewhere in the world is associated with outside forces. This has been the situation since formal record keeping and trend analysis of incidents began in the 1970's-and this situation is not expected to improve (e.g., see Anon, 1988).
