Pipelines Can Be Designed to Resist Impact From Dragging Anchors and Fishing Boards

Abstract Marine pipelines are being laid in more adverse areas of the world. There have been locations in which protection by burial has not been possible. Also, in these same areas, there have been problems from dragging anchors and fishing boards hitting the pipelines. An engineering approach has been developed to determine:Whether there is a problem concerning burial for protection and,If there is a problem, how to solve the pipe protection aspect from the technical standpoint without excessive cost. This paper describes some of the anchors and fishing boards in common use to day and how an engineer can assess the risk of damage from these items. Further, a discussion has been prepared defining the various modes of protection that can be used to reduce the risk of damage to an acceptable level. One of the important points in the decision making aspect is the determination of extent of possible damage in terms of number of occurrences. Once this is established, the most economical protection system can be chosen within an acceptable risk level. A typical case has been selected for illustrating the design considerations and the types of protection that can be employed. Introduction In some areas of the world, because of either adverse marine environment or soils conditions, pipelines cannot be buried. Because of this non-burial these pipelines are exposed to damage from such items as dragging anchors and fishing boards (see Drawing 104). The engineer now has to address himself to the problem of providing a suitable protection system for the pipeline structure to prevent damage by-these items. A technically acceptable method is to permit anchors to "walk" over the pipeline and to provide a sufficient armored coating on the pipeline to resist impact from dragging fishing boards. This paper discusses the technical and cost aspects of armored concrete coatings on pipelines, and engineered backfill for providing the necessary protection. Also discussed is a rational approach to provide engineering for determining the soils conditions and the marine environment such that a decision can be made to spend the money on burial or on the armored pipe system. Considerations There are several considerations which govern the selection of a particular type of protection. These include:Consideration of damage to non-buried pipelines by anchors and fishing boards (Drawing 101).Consideration of risk of damage and cost of repair to a buried pipeline by dragging anchors (Reference 1).Depth of instability of the soils (soils liquefaction) during storm conditions (References 2 and 3).General bottom soils erosion caused by currents (References 2 and 3).Localized erosion caused by pipe interference with currents (References 2 and 3).Stability of pipelines resting on the bottom in the marine environment (References 2 and 3).Governmental regulations.Plans for deepening an existing water way. This paper considers Item 1 from the standpoint of protecting a pipeline which cannot be buried. For pipelines that can be buried (Item 2), see Reference 1. For Items 2 through 5, see References 2 and 3.