A new buckle arrestor for pipe-in-pipe (PIP) was developed and tested by the Coflexip Stena Offshore Group, one of the most experienced in rigid reeled and deepwater technologies. It allows reeled installation, giving a time advantage over other installation methods, and allows design against propagation buckling. It consists of a local injection of a material in the PIP annulus. Material injection on the vessel ramp during laying is base case. Experiments on epoxy and full scale injections were performed to optimize the cure time, a critical parameter. Buckle tests were performed and proved the high performance of the arrestor. Comparison with Finite Element analysis is made. The effect of the arrestor on the PIP thermal performance is detailed. Extensive developments such as waterstop and bulkhead functions as well as pre-reeling installation are discussed.
Pipelines used in deepwater are usually coated with insulation layers in order to reduce the formation of wax due to heat loss. In some cases, conventional coatings are replaced with PIP systems, which provide higher insulation. The PIP is composed of a carrier pipe (the external pipe) and a fiowline (the inner pipe). The carrier provides a mechanical protection. The gap between the two pipes provides the insulation of the flowline and is filled with insulation material. Centralisers fixed on the flowline at regular intervals are often used to maintain the flowline centrally. Excessive loads, dents induced during laying of a pipeline or impact of an object will reduce the collapse pressure of the pipe and can lead to its collapse (Park and Kyriakides, 1996; Yeh and Kyriakides, 1986; Corona and Kyriakides, 1988).
