Line pipes installed via reel laying (R-lay) must exhibit collapse resistance to external pressure in addition to deformability during reeling and unreeling processes. In this study, we analyze the collapse resistance, collapse pressure, and collapse mechanism of line pipes, and examine the applicability of conventional collapse formulas for pipes after reeling.
HF-ERW pipes are used in R-lay simulation. The former has aradius of 8 m, which is equivalent to the spool radius of the deepwater construction vessel. In this study, the dominant factors affecting collapse resistance, including ovality, eccentricity, compressive stress-strain (SS) curve in the circumferential (C)direction, and residual stress of the test pipes were measured. The collapse pressures were obtained from full-scale collapse tests, finite element analysis (FEA) models with measured profile, and conventional collapse formulas.
For the pipe dimensions considered in the test program, the test results show that ovality is degraded to 4% owing to repeated bending up to 5 cycles, and the collapse pressure of the pipes is 30% lower after the bending test. Tamano's and DNV collapse formulas, which are commonly used for OCTG and line pipes, are applicable for predicting collapse pressure even after the bending test. By using DNV formula, this paper presents the guidelines for collapse design for line pipes laid via R-lay.