Effects of impact loads on CRA-Lined pipelines

Abstract

Third party threats from accidentally dropped objects could cause external impact loading that may potentially affect the integrity and safety of a subsea pipeline system. These incidents may occur during installation, construction and operation phases of the project.To evaluate the structural integrity of carbon steel (CS) subsea pipelines due to dropped objects events, risk assessment is conducted following the procedure detailed in DNV-RP-F107, which gives a closed-form formula for predicting the impact-energy capacity of the CS pipeline and assumes an acceptance criterion of limiting the dent-depth ratio to 5% of pipe diameter for a no-leakage condition. In the case of CS pipelines mechanically-lined with corrosion resistant alloy (CRA), the applicability of the impact-energy formula and the acceptance criterion is, however, largely unknown considering that CRA-lined pipes involve additional modes of failure in the form of liner separation and its potential for subsequent fatigue failure during operation.This paper discusses finite element modelling undertaken to evaluate the structural response of a CRA-lined pipeline subjected to external impact loads. Results confirm that liner separation is of minor importance and the use of the established acceptance criterion derived for plain carbon steel pipes can be justified to apply to CRA-lined pipelines.