Failure Analysis of a Gas Pipeline at the Kinked Dent Location with Crack Indications

Pipeline failure causes can be divided in two groups: corrosion damage and mechanical damage. Mechanical damage usually includes dents, wrinkles, gouges, and combinations thereof. Dents can be considered the most common mechanical damage. In our study, a dent was located at the lower pipe region (5-7o'clock) as a consequence of indentation of the rocks on which the pipe was placed. The damaged pipe section was analyzed using visual, non-destructive testing (NDT), optical microscopy, scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), hardness testing and transmission electron microscopy (TEM) analyses were performed to determine the origin, form, and mechanism of the crack indications at the dent location. Finite element method (FEM) was used for the creation and propagation cracks. The presence of micro-cracks in the dent region was confirmed, the formation of which on both pipe surfaces was related to the corrosion process. A deformation hardening was identified in the refined structure region in the kinked dent location. TEM analysis confirmed a higher concentration of dislocations in the deformed area compared to recrystallized area (undeformed area). The hardness and TEM analyses of the crack indications date them from to manufacturing process of the gas pipe. The FEM models of the pipe dent process supported this contention and confirm random presence of the crack indications in the dent location. The indications detected by NDT and the associated change in microstructure and mechanical properties occurred during the production process of the pipe. The dent, which included the mentioned indications, occurred during the operation of the pipeline.