MARINE LITTER
Technical flaws in HDPE pipe connection a factor in Ocean Cleanup breakdown in the Pacific / Restart is months away / Plastics pollution “gets worse by the day”
In the latest update on plans to recommence trials with clearing plastics waste from the “Pacific Gyre”, the organisers of Ocean Cleanup (Delft / The Netherlands; www.theoceancleanup.com) said they will need more time to fix the problems that led deployment of their first ocean-going vessel, “System 001”, to be interrupted in December 2018 – see Plasteurope.com of 08.01.2019. After nearly three months of studying what went wrong, the team “demobilised” the vessel in Hilo Bay, Hawaii / USA in late March 2019, as it was deemed more cost effective to prepare for relaunch from the mainland. A fresh start is “a matter of months,” the update suggested. “The problem of ocean plastic is getting worse by the day, so it is crucial that we get System 001 operational as soon as possible, after which we can start the scale-up.”

In a detailed review of the reasons for the breakdown of System 001, project engineers said that, for one thing, the dynamics of the interaction between ocean currents and the 600 m floating array had not been properly considered. The surface transport, for example, was higher, and the plastics moved faster in the direction of the wind than initially projected. Not only was the system moving too slow, but the relative speed differential between the plastics and the system occasionally shifted from positive to negative. The conclusion that the system must consistently travel faster than the plastics will form the basis used for future modifications.

A structural analysis of flaws in the was vessel conducted by the Ocean Cleanup crew in cooperation with a team of external experts that included HDPE pipe and component suppliers, university professors, research institutes and other consultants. This analysis apparently confirmed an original hypothesis that the system’s stabilisers were not to blame for the 18 m end section becoming detached but rather problems with the construction of the dovetails (the connector between the HDPE pipe and the screen).

Reflecting the production set-up at the system’s manufacturer, the dovetails were produced in one-metre segments, which evidently led to stress concentration in the floater wall, thus seriously reducing its fatigue life. Additionally, because of the increased motion on the end sections, the cracks in the HDPE pipe gradually increased and eventually caused the section to “suddenly and rapidly” detach. Work in the weeks ahead of the relaunch will focus on eliminating the causes of the stress on the floater.
12.04.2019 Plasteurope.com [242202-0]
Published on 12.04.2019

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