Project Review
RetroSled system used to replace failing cathodic protection on a pipeline in Equatorial Guinea

Overview

In 2006, Deepwater Corrosion Services, Inc. conducted a pipeline anode retrofit of an offshore process pipeline in Equatorial Guinea. The pipeline, located in water depths of 200 ft., had low cathodic protection potentials, prompting Deepwater's cathodic protection design team to select the larger, expanding version of the RetroSled system, in order to re-polarize the pipeline quickly.

The retrofit cathodic protection (CP) system consisted of:

• 4 x Expanding RetroSled (aka ExpandaSled)
• 8 x RetroClamp (2 per aluminum anode sled)

Installation

After the equipment was shipped to the shore base, it was loaded on board a dynamic positioning (DP1) vessel, equipped with an ROV.  The retrofit system included four ExpandaSleds (expanding RetroSleds), complete with two RetroClamps each, to be installed without the assistance of divers. Prior to deployment, the RetroClamps and Tie-Back Cables were secured to the ExpandaSled frames using cable ties.  Meanwhile, lifting slings and tag lines are attached to the collapsed sled. During deployment, the Sleds, in folded configuration, were lifted safely off deck and lowered to awaiting ROV for final positioning on the sea floor. Sleds were placed parallel, approximately 15 ft. off the pipeline.

The ROV then hauled the RetroClamps across the sea floor, laying them next to pipeline, breaking cable ties along the way. After, the ROV transfered the winch line from the ExpandaSled’s lifting eyes to a nylon rope on the expanding eyes.  The DP1 vessel then manuevered approximately 30 meters in expansion direction, while slowly coming up on winch until one half of the sled was extended (the operator repeated this manuever for the other side of the Sled).

After the sled was opened, the RetroClamps were secured onto desired pipeline locations by tightenting the T-handle contact bolt until secure.  In the pictures you can see the manipulator arm putting the RetroClamps in to place. A CP probe was present to verify connection.

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