Experimental and numerical analysis of failure in flexible pipe by a mechanism of intentional damage

The use of flexible pipe in onshore applications is now commonplace; however, there is scarce information on the modes of failure that affect its mechanical integrity, so its application in a transmission systems is risky and should require further analysis. An experimental- numerical study was performed to observe changes in the mechanical response and failure modes in this type of pipes. Pipe was perforated at a working pressure of 30 kg/cm2 (426.7 psi) to simulate experimentally the conditions generated when a hot tapping hole is illegally made to plunder petroleum products. It was found that the different pipe sections have a relatively low mechanical strength, especially the layer made of high density polyethylene. Tension and compression tests were carried out to obtain the appropriate technical data to perform static simulations, considering an external hole as the failure mechanism. After finite element modeling, it was found that flexible pipe presented an initial collapse in the HDPE inner layer at a pressure of 21.09 kg/cm2 (300 psi), which coincided with the experimental collapse induced by hot tapping drilling. This type of damage had not been studied in flexible pipelines for onshore applications. The information provided is useful in making decisions for the proper materials selection involved in the transport of hydrocarbons onshore.