Dents created by third party mechanical damage are a severe integrity threat to onshore and offshore transmission pipelines. This type of damage is often associated with metal loss, which can be introduced during the initiation of a dent or develop as a result of the presence of a dent and associated coating damage. Once a dent has been found to be associated with metal loss through excavation, there is little guidance to determine the serviceability of the anomaly.
In this study, dents with associated metal loss due to corrosion examined in the field are evaluated to determine the contribution of the interacting dent and metal loss features to the associated burst pressure of the feature. Twenty dents with metal loss flaws were identified through an ILI survey while in service to capture dimensions of the dent and metal loss features. Each site was excavated and measured using a laser scanner. The laser scanner produced 3D imaging with sufficient resolution of both the dent and metal loss areas as a 3D surface mesh. The 3D surface mesh was transformed into a 3D solid mesh and analyzed using a finite element analysis software package in order to determine a predicted internal pressure that would cause failure. A subsequent statistical assessment was performed to analyze the relationship between the ILI measurements and the predicted burst pressure resulting from finite element analysis of each dent with metal loss feature. Statistical analyses were used to evaluate the prediction capabilities of burst pressures of dent with metal loss features identified through ILI, prior to excavation and direct examination.
