ROVworld Subsea Information

SeaBotix LBV in demanding offshore survey
Date: Friday, October 22, 2010 @ 12:00:00 EDT

SeaBotix LBV in demanding offshore surveyMark Stepanek of Pro-ROV was contracted to conduct an offshore oil pipeline and single point mooring survey off the island of St. Eustatius located in the Caribbean. The client NuStar Energy (previously Valero Energy) had a requirement to inspect a 1.5 mile (2.6km) section of a 48 inch (1.2m) oil pipeline in a depth of 225 feet (70m). Additionally, there was a single point mooring (SPM) that required inspection of its anchor chains.

The project had a few uphill challenges in that the client's service contractor REDS Caribbean had previously attempted such work with a small MicroROV with disastrous results. Unfortunately the equipment was not up to the task. Plus the weather can be quite demanding. Utilizing the newest MiniROV LBV200-4 system from SeaBotix Inc. Pro-ROV was confident in the ability to accomplish the tasks set by NuStar Energy, even with the demanding conditions.

Once mobilized and onsite the conditions were deemed reasonable with low wind and current. However, by the time the vessel was secured to the SPM the current had picked up. With six anchor chains to inspect in depths to 225 ft (70m) there were concerns about being pushed into the anchor chains by the current during the inspection process resulting in tether entanglement.

The SeaBotix LBV200-4 is a capable offshore tool with powerful brushless DC thrusters (including lateral), small diameter low drag tether, auto functions and high quality color video. Mark is a competent pilot with experience conducting such surveys, which is equally as important as the equipment.

Deployment of the LBV was simple enough with the first anchor chain successfully inspected from top to bottom while maintaining a head on attitude with the current. For the next chain the challenge increased as the LBV now had to be at angle to the current. Utilizing the lateral thruster control on the LBV Mark was able to maintain the correct angle of view on the anchor chain as the LBV descended to the bottom. Each chain became increasingly difficult as the current continued to flow faster.

After approximately three hours all six chains were satisfactorily inspected and signed off by the two onboard ABS representatives. Good news for NuStar was that the chains were in good condition and had not moved. It was estimated that current flow had increased to around 2 knots.

Next up was the pipeline inspection. To cover a 1.5 mile (2.6km) section of pipeline the Valero survey vessel was used for live boating. Conditions varied with higher currents, wind, rain and moderate sea state. The plan was to descend to the pipeline and track along the 1.5 mile (2.6km) section with the LBV while maintaining a steady course with the vessel. Since conditions had worsened it was felt that a clump weight set back approximately 80 feet (25m) from the LBV was to be used. This method reduces drag on the LBV even though the umbilical is such a small diameter. Fortunately the pipeline was laid in a relatively straight line making the track more simple. With the LBV deployed and on the beginning section of the pipeline auto heading was used to hold a straight track as the LBV and vessel began following the pipeline.

The vessel was able to maintain a steady course and with the clump weight and powerful thruster on the LBV the progress was good. With success much like the anchor chain survey the inspection was completed in a relatively short period of time. Similar results as well in that the pipeline was in good condition and met with approval from the onboard ABS representatives. NuStar, REDS Caribbean and ABS were all happy with the survey and quality of video/data captured.

Planning, suitable equipment and competent operators all contributed to the success.

This article comes from ROVworld Subsea Information

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