Structural Design of a Bow - Coupling Bend Pipe

Abstract

Despite the technological improvements in the dredging industry in the last decades, there are components that have not been investigated accordingly. One of them is the bow coupling bend pipe which can be found on trailing suction hopper dredgers. In contrast to most pipelines, the specific bend pipe is not only a means of transport for the dredged material but has a structural role, as well. Currently, it provides support to the subsequent pipes, which have no other connection to the vessel than the bow coupling bend pipe. Moreover, the abrasive nature of the slurry causes severe wear in the dredging pipes, with even more damage in bend pipes. These two factors lead to the relatively frequent replacement of a large amount of material, which also translates to an uneconomical procedure.

The objective of this thesis is to explore the potential of designing a new bow coupling bend pipe, which focuses on the reduction of the replaced material and the extension of its lifetime. This can be achieved by analysing the two aforementioned factors, in order to improve the management of the original material, resulting in an economical solution.

This study does not only analyse the design of bow coupling but also contributes to the understanding of slurry wear in bend pipes. Precisely, the report starts with a thorough explanation of slurry transport, describing also the three mechanisms of slurry wear and the parameters that influence the wear rates in a bend pipe. Furthermore, a literature review on the wear profile of bend pipes takes place in order to determine the expected wear pattern in the bow-coupling bend pipe. A total of five different wear zones are proposed to
describe the wear rates in specific areas in the bend. The lack of research on slurry wear in large-scale bend pipes necessitated the use of assumptions to adapt the literature outcome on the bow coupling bend pipe. The information obtained from that research is used for the development of various concepts, considering also other aspects that contribute to the main goal of the thesis. Several concepts are investigated and compared based on the priorities of the project. The final design is further discussed, proceeding to modifications that improve its performance. The final geometry and materials of the system are defined in the finite element analysis. To do that, company guidelines and related standards were used to define the loads on the system as well as required realistic scenarios in which the design had to prove its structural feasibility. Finally, before providing recommendations for future work, the proposed design is compared with the current one, highlighting improvements in the three aspects of the thesis objective.

In particular, using almost 60% of the material required for the current design, the new solution extends the bend pipe’s lifetime at least three times. That proves the remarkable effectiveness of the new design in the management of the pipe material, which is also directly linked with economic benefit. It is estimated that the capital expenditure of the new system will be twice as high as the current case, while the replacement cost is reduced by about half.