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Feature Article

VENUS Subsea Cabled Observatory Infrastructure Repaired
Bringing the System Back Into Operation in the Strait of Georgia

AUTHORS:


Matthew Stewart

Adrian Round



The new cable termination and node junction can are inspected prior to final assembly and installation.
A failure occurred in a key component of the Victoria Experimental Network Under the Sea (VENUS) portion of the Ocean Networks Canada (ONC, based in Victoria, Canada) subsea cabled observatory in August 2012. The Strait of Georgia array of the observatory, located near Vancouver, Canada, was brought down by the failure of a critical subsea connector. In February 2013, aboard the cable ship (CS) Wave Venture, a joint team from OceanWorks International Corp. (Burnaby, Canada), the University of Victoria and Global Marine Systems Ltd. (Chelmsford, England) successfully repaired this segment of the network by recovering major components, replacing damaged parts and redeploying the system.

The VENUS Observatory is operated by ONC, an initiative of the University of Victoria, and its first node was deployed in the Saanich Inlet in early 2006. The observatory has been collecting data continuously for more than seven years and is helping to push the boundaries of ocean science. Many disciplines have benefited from scientific experiments conducted on VENUS, which have covered diverse areas such as forensics, sediment dynamics, physical and chemical oceanography, and benthic ecology. The flexibility of high-bandwidth, high-power cabled observatories is proving to be a powerful research tool.

The Strait of Georgia array of the cabled observatory, deployed between May 2007 and February 2008, consists of a shore cable landing station and two nodes: the Central Node (300-meter depth) and the East Node (170-meter depth). All power and communications are provided from the shore station. A 30-kilometer cable connects the shore station to the Central Node. From the Central Node, an additional 9 kilometers of cable connects the power and communications with the East Node.


Removable Pod Concept
Each VENUS node houses electronics for high-power distribution and high-bandwidth data communication. To facilitate maintenance, OceanWorks designed the nodes to be divided into two major physical components: the node base and the node pod. The node base is a heavy steel structure that acts as a termination for the subsea fiber-optic cable. It is intended to be a permanent installation not normally recovered during the life of the observatory. Due to the permanent nature of the installation, the complexity of the node base has been minimized. It contains only small pressure vessels interconnecting the subsea fiber-optic cable and the ROV mateable optical fiber and electrical connectors. The node pod contains all the components that might need maintenance or upgrades over the 20-year life of the observatory. Larger pressure vessels house all of the node power and communication electronics and provide eight ROV mateable interfaces to science instruments. The node pod is designed to be removed from the node base by ROV for upgrade or maintenance. It is mechanically connected to the node base by a series of ROV operable latches and electro-optically connected by a pair of ROV mateable connectors. The utility of this design has already been proven when each VENUS node pod was recently recovered for an engineering upgrade to improve electronics and increase the number of science ports.


Continual Learning And Risk Mitigation
As with most leading-edge ocean engineering projects, both the initial budget and project time lines were tight. The design team expended considerable effort to minimize the overall engineering risk and improve the probability of success of the observatory within the budget available. One such design decision was the material selection for the pressure vessels.

All pressure vessels in the original VENUS deployment were built from 2205 duplex stainless steel. The use of titanium was considered but was not supportable with the available budget. Over the past seven years of operations, crevice corrosion was found on some duplex-to-duplex contact points during planned maintenance. This corrosion varied greatly from component to component depending on the local conditions.

The biggest risk with the corrosion surrounded the node base pressure vessels (node junction cans). The junction cans are sealed by two O-rings, which are captured in a steel-steel interface. A corrosion failure in the junction cans could create a leak and result in an electrical fault. A failure of this nature would render an entire network array inoperable. The inability to inspect the node junction cans for corrosion increased the risk even further. To continue this article please click here.



Matthew Stewart, professional engineer, has been an electrical engineer with Oceanworks International Corp. for 11 years, specializing in system integration and design of subsea electrical and electronic systems. He was the lead project engineer and project manager for the first VENUS array in Saanich Inlet.


Adrian Round is the director, Observatory Operations for Ocean Networks Canada. He served in the Royal Canadian Navy for 26 years before joining the VENUS Project. For nine years he led the design, construction and operation of the VENUS observatory. In January 2013, he assumed his current role.







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