If a pipeline buckles in the presence of sufficiently large external pressure, a propagating buckle is initiated. The buckle propagates along the pipeline until it encounters a region of adverse conditions--low pressure or an arresting device. This paper suggests a new buckle arrestor design. It is comprised of a rod tightly wound around the pipe to form a number of turns. The ends of the rod are welded in order to secure it in place. Its main characteristic is that it can be used in continuous pipelaying methods (e.g., reel pipelaying). It can also be used in the case of pipes coated with concrete where it can be inserted into the concrete. This arrestor has the unique quality of restricting the stress concentration at the discontinuity in the case where bending moment is applied to the pipe and does not affect the bending rigidity of the pipe. Experiments have shown that its efficiency is comparable to other arrestors. An empirical expression for the arrestor efficiency is presented.
During offshore pipelaying operations, a continuous length of pipe is payed out from a vessel into the water (fig. 1). The pipeline is under the combined effect of bending, tension and pressure. Circumstances exist under which the buckling limit of the pipe can be exceeded, causing local buckling. Local buckling or large local plastic deformation (dents) can also occur after the laying operation is completed due to falling objects (anchors or other heavy equipment) or due to natural causes such as earthquakes, sea bottom instabilities or undersea currents.
When any type of large dent occurs at any point in the pipeline, the collapse at that point may propagate along the pipeline for great distances in both directions due to the hydrostatic pressure. In such an event it is desirable to restrict the length of pipe destroyed, to as small a length of pipe as possible, which is subsequently replaced. This is achieved by the proper use of a buckle arresting device.
Buckle arrestor is the name given to any device which locally reinforces the pipe and prevents the buckle from propagating any further. These are installed at regular intervals along the pipeline and if properly designed restrict the damage to the pipe to the section?, between two arrestors (fig. 1). A designer then has to choose a balance between a more economical pipeline and the possibility of damage occurring to a length? of the pipe. Some of the factors one should consider in deciding the value of ? are the total length of the pipe, the diameter, thickness and unit length cost of the pipe, the water depth at which it is laid and the cost of retraction and replacement of a unit length of damaged pipeline.
A number of arresting devices have been suggested to date. They vary in shape, cost, ease of application, etc.
