An Assessment on the Overtrawlability of Small Pipe Sizes Using a Hybrid Shell-Beam Model: an Alternative to the DNV-RP-F111 Model

Abstract

Fishing activity in offshore areas associated with oil and gas development presents a risk to the structural integrity of subsea pipelines from trawl gear interactions. In this regard, DNV-RP-F111 is the industry recommended practice and proposes a beam and spring-mass (BSM) model as well as an analytical method to assess the overtrawlability of pipelines. However, the recommended practice is only applicable for pipelines with an outer diameter of more than 10-inch. Accordingly, the present paper proposes an alternative model (the hybrid shell-beam model) to extend the applicability of the BSM model for small pipe sizes. Furthermore, the BSM, analytical, and hybrid models are examined and compared for a case of 5-inch pipe diameter. Accordingly, for the 5-inch pipe, the resulting dent depth predicted by both the BSM and the hybrid model is very close; however, the BSM model is relatively non-conservative and slightly underestimates the resulting dent depth on the pipe by 6.5%, compared to the hybrid model. Furthermore, using the analytical model leads to a very conservative dent depth on the pipe. In conclusion, the hybrid model is a suitable alternative to the BSM model for small pipe sizes.