TABLE OF CONTENTS Collapse of as-received pipe under external pressure and the main factors that govern it have been discussed in Chapters 4 and 5. Here we consider the collapse resistance of pipes that have suffered local damage in the form of a dent. Offshore pipelines are relatively large scale structures installed in hostile environments. Damage in the form of dents is one of the most common causes of pipeline failures [6.1, 6.2]. They occur due to impact by foreign objects and other causes during transportation of the pipe, during installation and trenching, and during the operation of the line. Dents reduce the local collapse capacity of the pipe, and can be the initiators of propagating buckles [6.3, 6.4]. In addition, for gas lines under high internal pressure, dents, sometimes accompanied by gouges, are often the prelude to burst failures [6.5]. Once a dent is detected, the operator must decide on the integrity of the structure. Repairs are generally complicated and costly. Thus, the ability to assess the integrity of the dented pipe analytically is very important.
Results from experimental studies of the collapse performance of dented pipes are reviewed first. The results are used to develop a practical measure of the "magnitude" of the dent with regard to collapse resistance. The experiments are complemented by numerical results of denting followed by collapse. The chapter ends by the discussion of universal collapse resistance curves proposed by Park and Kyriakides [6.6] as a design tool for dented pipes.
Kyriakides
