Reeling lay or R-lay is a popular technique for effectively installing ERW line pipes in deepwater. This paper explores the ovality and the collapse pressure of HF-ERW line pipes installed by reeling lay. The change of ovality is evaluated by a full-scale bending-unbending test. The combined effect of the ovality and the wall thickness to outside diameter ratio (t/D) on the collapse pressure is derived from finite element analysis and the prediction formula constructed by DNV and Tamano. This study provides a reliable and beneficial solution for line pipe design in deepwater using R-lay.
Reeling lay or R-lay is a popular technique for effectively installing HF-ERW line pipes in deepwater. The advantages of R-lay are high installation speed and onshore welding. However, R-lay line pipes are subjected to cyclic bending and unbending deformation during installation. Offshore line pipes normally require resistance under external pressure, so-called collapse resistance. The cross section of pipe deforms from the circle shape to ellipse because of the plastic deformation in R-Lay. If the cross section of pipe deforms to the ellipse shape, the collapse pressure gradually decreases. An investigation of the relation between collapse pressure and the shape of the cross section is required.
The collapse pressure of HF-ERW pipes with an outside diameter of 323.9 mm, wall thickness of 14.6 mm, and grade X65 was evaluated (Tsuru, Tomioka, Shitamono, Ozaki, Karjadi, Boyd and Demmink, 2015). However, although the ovality changed due to the outside diameter of the pipes and the spool radius of the reel barge, the relation between ovality after reeling and collapse pressure for several pipe configurations has not been investigated. This paper examines the change in the pipe ovality and the collapse pressure after such cyclic bending deformation. In addition, the applicability of a conventional formula is discussed for the collapse pressure prediction.