On the arresting efficiency of slip-on buckle arrestors for offshore pipelines

Slip-on buckle arrestors are tight-fitting rings placed over the pipe at intervals of several hundred meters. They locally increase the pipe resistance to collapse by providing additional circumferential rigidity, and thus impede downstream propagation of collapse. This type of arrestor offers important advantages over other designs as it does not require welding. Alternatively, when split in two and by the addition of flanges, it can be clamped onto a continuous pipe. This is an essential characteristic for lines installed by the reeling method. It has long been known that such devices often cannot reach higher levels of arresting efficiency. 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. Previous work on the subject from the 1970s dealt with relatively thin-walled pipes used in shallow waters. The subject has recently been revisited and bounds for this deficiency in performance have been established. The deficiency depends on the pipe D/t and on the steel grade. This paper presents the results of a more detailed study of such arrestors for pipes with lower D/t values (18-35) suitable for moderately deep and deep waters. The arresting efficiency has been studied parametrically through experiments and full scale numerical simulations. The results have also shown the previously developed efficiency bounds to be viable. A new empirical design formula has been developed. Used in conjunction with the efficiency bounds, it provides a reliable method for an expanded use of slip-on type buckle arrestors in many deepwater applications. (C) 2004 Elsevier Ltd. All rights reserved.