W&W Marine Completes Offshore Pipeline Inspection

In July of 2006, W&W Marine completed a contract from Gulfstream Gas & Oil to conduct a video and sonar survey of a 74 mile stretch of pipeline in the Gulf of Mexico. The natural gas line which runs from Coden, Alabama to Florida’s, Port Manatee in Tampa Bay, went on line in 2001, supplying the Pinellas county power plant.

The survey began in 48’ of water and worked Westward out to the 200’ mark. “There were a number of tasks accomplished” said Ed Watkins of W&W Marine. “From the free flight video footage of subsea tie-ins and hold down straps, to the towed flight footage of the entire 92 mile stretch, having the use of a Nova Ray® ROV, really made this job a lot easier."

“The use of high tech sonar equipment such as BlueView’s Proviewer 450E High definition imaging sonar and Imagenex’ 881SS Side Scan Sonar helped to document the pipelines location when the ocean’s visibility dropped to zero”, said William Wimpy of W&W Marine. “This sonar equipment, coupled with Hypak survey software and Easy Trak’s tracking equipment, has helped to gather a very accurate survey of this pipeline.”

W&W Marine had three main objectives to meet during the survey. The first was to obtain video footage of both the near shore and far shore subsea tie-ins. The water depth ranges from 65’ to a little over 200’ running from the near shore subsea tie in to the far shore tie in, with three valves at each tie-in requiring yearly inspection. During hurricane activity, the oceans currents can cause the valves’ cage covers to come loose, leaving the valves vulnerable to anchor dragging and debris build up. In addition, the valves were closely inspected to detect possible natural gas leaks as a result of the last hurricane.

The second objective was to inspect 32 straps located in water depths of 135’ to 158’ used to anchor the natural gas line down to the ocean floor. Each year the straps need to be visually inspected for corrosion and to monitor their zinc anodes. “With the Nova Ray® conducting it’s free flight video inspection of each strap, we could just leave it in the water and tow it down the line to its next objective” said Capt. William Wimpy. “We’d just stop and film the next strap for a few minutes and continue on all day like that."

The final objective was to obtain video footage of the entire 92 mile length of pipeline. “Starting in 48’ of water and pointing the research vessel Westward, we motored along between 1 and 3 knots gathering as much video footage as possible and when the visibility became to poor to make out the ocean floor, we turned on our sonar equipment to record what our cameras couldn’t see” said William. “It was great not having to stop just because of a thermo cline in the lower water column. This “loss of visibility” in the water occurs naturally each year when the ocean gets stirred up and can stretch from a few hundred yards to a number of miles wide.”

“Now that we have a very thorough and complete survey of this offshore pipeline, we’ll have a historical reference of the line for years to come; this survey will help with the monitoring of the line following any major ocean changes or hurricane storm surges. Marine Biologists could even use it to reference the abundant marine life, both mammalian and non-mammalian.”

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