An offshore pipeline had been recently laid and, as part of the commissioning process, an in-line inspection (ILI) was performed using ILI tools. The data from the high-resolution deformation tool showed numerous dent anomaly indications at various locations in the upper section of the pipe over a long distance. It was speculated that the damage had resulted from a single dragged anchor incident before the pipeline was trenched. This data set was correlated to Magnetic Flux Leakage (MFL) inspection tool data to confirm external mechanical damage.

Denting Analysis

Pipeline sections with anomalies found either close to girth welds, or with associated corrosion defects were automatically selected for repair due to the increased risk of failure at these locations.
A total of fifteen anomalies remained; Andrew Francis & Associates (AFAA) Ltd were contracted to perform analyses and assessments in order to determine if the pipeline sections were fit-for-purpose at the maximum allowable operating pressure.

Due to the sharp nature of some of the dents, elastic-plastic finite element analyses (FEA) were performed using denting profiles generated from the calliper data of the ILI run. API-579 level 3 assessments were then carried out using the FEA results.
Of the 15 dents 3 were recommended to be repaired, 12 were found to be acceptable. A high confidence was achieved in the safety of unrepaired damage, due to the close agreement between the ILI data and FE results, and the additional assessments performed.

Denting, Equivalent Stress