TABLE OF CONTENTS The interaction between fishing gear and a pipeline is one of the most severe design cases for an offshore pipeline system. The reason for the severity of the impact, pullover and hooking is not well described by the industry today. The damage to the pipeline (and to the fishing gear & ship) is very dependent on the type of fishing gear and the pipeline conditions, e.g. the weight and velocity of the fishing gear and the wall thickness, coating and flexibility of the pipeline. The most important issue with respect to design of fishing gear resistant pipelines is the ability to make a realistic description of the applied loads and their time history, and pipeline resistance, i.e. the pipeline configuration on the seabed including freespan and the pipe stiffness. The summary of loads, response analysis and acceptance criteria are listed in Table 12.1.
| Time | Load | Solution | Design acceptance criteria | Design parameters | |
|---|---|---|---|---|---|
| Impact | mseconds | mass velocity | mass-spring system dynamics | dent damage in pipe <0.035D | energy absorption capacity of pipe coating |
| Pullover | seconds | time history of horizontal & vertical loads | time domain dynamics | allowable moment, allowable stress/strain | Heights & length of free spans |
| Hooking | minutes | vertical displacement | static solution | allowable moment. allowable stress/strain | fishing gear frequency free spans |
Bottom trawling is typically conducted with two types of trawl gear in North Sea: Otter and Beam. Otter trawling occurs down to depths of...
