Efficiency Limits for Slip-on Type Buckle Arrestors for Offshore Pipelines

Abstract

Slip-on buckle arrestors for offshore pipelines offer important advantages over other arrestor designs as they do not require welding. An additional advantage offered by the related concept of the two-part clamp-on arrestor is that it can be installed onto a continuous pipe. It has long been known that such devices often cannot reach higher arresting efficiencies. As a result, the use of slip-on arrestors in deepwater applications has been limited. The somewhat deficient performance is due to the fact that a propagating buckle can penetrate such devices via a folded-up U mode at pressures that are lower than the collapse pressure of the pipe. This can take place even for very rigid rings. A methodology for generating bounds on the maximum arresting efficiency that can be expected from slip-on arrestors is developed. An upper bound of their efficiency is related to the pressure at which a propagating buckle starts to penetrate a long and stiff circumferential confinement. A lower bound is established by relating the crossover pressure to the lowest pressure at which the buckle will propagate through the confinement. The parametric dependence of both of these pressures was established experimentally. The method developed yields the range of pipe D/t's where degradation in arresting efficiency can be expected and predicts its extent. The arresting efficiency degradation was shown to depend on the yield stress of the pipe. Pipe of higher yield stress exhibits smaller degradation in arresting efficiency.