Project Review
RetroBuoy installed on the Neptune SPAR structure to supplement failing cathodic protection on the hull.
Overview
In August / September 2009, Deepwater Corrosion Services retrofitted the cathodic protection system on the Neptune Spar. The original cathodic protection system on the hull was approximately 300 sacrificial aluminum anodes. Neptune required a life extension significantly in excess of the original 15 year service life, including the CP system. At the request of the operator, DCSI designed, supplied and commissioned a 15 year life extension impressed current CP system (ICCP).
The retrofit cathodic protection (CP) system consisted of:
• 2 x custom 500 Amp RetroBuoys with shear keys
• 2 x transformer rectifiers
• 6,660 plus feet of dynamic, 7-conductor 3/0 AWG subsea power cable
• 2 x Polatrak DR 3 reference electrodes (installed at Neptune's keel during the cable pull-in)
Installation
Installed in 1997, Neptune is a classic spar located in the Gulf of Mexico (Viosca Knoll block 826), in approximately 1,930 feet of seawater. Flowlines and umbilicals are pulled in through three sets of blister tubes located on the side of the spar hull.
The two RetroBuoys were manufactured in Deepwater's Houston, Texas facilities and terminated on to JDR cables, dockside, in Fourchon, Louisiana. Both assemblies were then loaded onto Oceaneering's 254-feet long multi-service vessel, Ocean Intervention II. For each system, the RetroBuoy was deployed through an A-frame to its seabed target box. The RetroBuoys were designed with a shear key mudmat to pierce the soil and withstand forces exerted by meteorological / oceanographic conditions and the Spar's lateral drilling offset.
The cathodic protection monitoring system comprises two each PolaTrak DR-3 dual reference electrodes terminated to dual armored, shielded, twisted pair 12 AWG cables. The DR-3 probes are mounted near the lower opening of the blister tube at the keel. The cables were piggy-backed up along the section of subsea power cable routed through the blister tubes and terminated into a topside junction box. Cathodic protection potential measurements are monitored and recorded by the on-board SCADA system.
The entire subsea system was installed in less than 72 hours.
Image Gallery
View from the Ocean Intervention II, looking aft, with the second of two RetroBuoys ready to be deployed. The first RetroBuoys cable can be seen on the right going over the cable lay chute. Neptune Spar in the background.
JDRs pull-in head, associated bend strain reliever and the orange jacketed power cable. The pull-in head houses the topside cable pigtails.
The RetroBuoys junction box houses the subsea cable terminations between the main power cable and the individual MMO anode cables.
With the power cable now terminated, this RetroBuoy is ready for loading onto the vessel.
View of the Ocean Intervention II from the Neptune Spar, repositioning for the installation of the second RetroBuoy. The first RetroBuoy was now successfully installed in less than 36 hours.
As with many offshore operations much of the work happens at night.
Overboarding of the first of two RetroBuoys through the stern A-frame and down the lay chute.
The Neptune Spar sits in 1,930 feet of seawater in the Gulf of Mexico.
Another view of the RetroBuoy terminated to the power cable, ready for loading onto the installation vessel.
The first RetroBuoy is installed on the seabed with the shear key embedded, MMO anodes not yet deployed.
The DR-3 CP monitoring system is positioned below the centralizer pipe, adjacent to the large bend strain reliever that will be positioned near the spar keel.
The DR-3 is now installed in the blister slot near the spar keel.
RetroBuoy set on the seabed at 1,925 water depth. All flotation modules have been deployed by the ROV. The retrofit anode system is now ready for commissioning.
© 2011 Deepwater Corrosion Services Inc. Tel: (713) 983-7117 Fax: (713) 983 8858
All specifications subject to change without notice