Global’s Cougar and Falcon ROV systems were mobilized to Hawaii to facilitate repairs on the 40” coldwater pipeline transition section in 500 feet of water off of Keahole Point on the island of Hawaii for the Natural Energy Laboratory of Hawaii Authority (NELHA).
The 40” pipeline is unique in the fact that it is installed with gravity anchors to a depth of 457 feet and from there to a depth of 2000 feet it takes the form of an inverted floating catenary. An installation error when the pipeline was originally installed in 1987 led to future failures of chain bridals and anchor chains. In addition growth on the pipeline was weighing it down.
The ROV crew, operating off of the Healy Tibbitts 544 crane barge, was tasked with restoring the pipeline to an as designed condition. The Cougar ROV cut loose and replaced two 500 foot 1-1/2” stud link restraining chain bridals. The pipe had to be cleaned and obstructions cut loose for the installation of new pipe clamps in three places. 1-1/2 tons of flotation was added at each clamp location. Two 1-1/2” stud link chain bridals were added at the bottoms of the clamps and secured to a 40 ton gravity anchor. A 1-5/8”stud link chain bridal was added to the offshore bridal. Special underwater tooling was designed and manufactured including a hydraulic chain tensioner, 3-1/2 and 10 ton winches and 40 and 48 inch hydraulic actuated pipe clamps that were tested in Seattle before being deployed to Hawaii.