The latest American Petroleum Institute Recommended Practice API RP1111, 2015 recommends repair capability for subsea flowlines and strength assessment for damaged flowlines before and during repair. In this paper, ultimate strength assessment for corroded pipe is carried out for two limit states. One is the collapse limit state resulting from external overpressure. Another is the buckling/collapsed limit state resulting from combined bending and external overpressure. A large range of corroded conditions as well as D/t (diameter to thickness) ratios are selected for the assessment including lower D/t ratios. The assessment was carried out using Finite Element Analysis (FEA). In the FEA, ultimate capacities of both intact and corroded pipes subject to bending and/or external pressure are captured. In the Finite Element Modeling (FEM), a perfect elastic-plastic stress-strain relationship is selected to simulate the pipe's nonlinear material properties. An initial pipe ovality imperfection is also included in the FEM. The captured ultimate capacity from the FEA is compared with ultimate strength results calculated from equations of the two limit states given in API RP 1111, 2015, API STD 2RD, 2013 and ABS Subsea Pipeline Guide, 2014. The purpose of comparison is to examine the applicability of these equations to lower D/t ratio in both intact and corroded conditions. For cases that the limit state equations are not applicable, the FEA method introduced in this paper can be applied as an alternative approach for the ultimate strength assessment of subsea flowline.

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