Operational Experience with the Cold Water Pipe at the Natural Energy Laboratory of Hawaii

The 2000-ft. deep, 5500-ft. long, 12-in. diameter polyethylene cold water pipe and pumping system which the State of Hawaii installed at NELH in December 1981, has operated nearly continuously since August of 1982. Following an initial review of the system design, this paper discusses some of the problems encountered in its maintenance and operation. These include 1) pump specification and performance problems, 2) electrical supply cable failures, 3) submersible pump motor corrosion and resultant failures, 4) nearshore pipeline mounting failures caused by both routine motions and by large waves, and 5) onshore pipeline protection system failures. The offshore location of the pumps exacerbates these operational problems by making maintenance and repair extremely dangerous if not impossible when the waves are large. Specific design constraints suggested for future deep water pipelines include: 1) locate the pumps as far onshore as possible; 2) consider previous manufacturer experience in sizing and selecting pumps and motors; 3) avoid submersible motors for long term operation in seawater; 4) specify stainless steel metallurgy sparingly and carefully, and ensure that the specifications are followed; 5) design electrical cables and conduits for permanence, but include provisions for cable changeouts; 6) avoid pipeline or cable runs parallel to shore; and 7) overdesign all onshore and nearshore components.