Over the last 16 months, Sonardyne International Ltd’s acoustic positioning technology has been used by Subsea 7 during the tow-out and installation of over 40km of pipeline bundle for multiple contracts.
Subsea 7 was awarded multiple EPIC (Engineering, Procurement, Installation and Commissioning) contracts resulting in the fabrication and installation of eight bundles including the longest bundle to date – a 28km pipeline, delivered as four 7km bundles. Each pipeline bundle was assembled at Subsea 7’s onshore facility at Wick in Scotland then transported to site using the company’s pioneering method of Controlled Depth Tow Method (CDTM). Here bundle configurations are suspended between two tow vessels at a controlled depth below the surface, a technique that requires real-time acoustic positioning and data telemetry monitoring of the pipeline down its entire length.
To achieve this, Sonardyne Compatt 6 transponders were installed along each bundle at intervals of 700-900 metres whilst the company’s Lodestar Attitude Heading and Reference Systems (AHRS) were used to monitor the bundle tails. This suite of sensors was used to wirelessly transmit data relating to depth, heading, internal carrier pressure and tow wire angles to the escort ROV Support Vessel (RSV). A full set of sensor reading updates were sent every 20-40 seconds. Custom designed software allowed the survey teams onboard to analyse the data throughout each tow to ensure that each pipeline did not sag or snake excessively due to the effects of tow speed, tide and sea state, and that it was ‘flying’ at the required depth to avoid submerged objects. During a tow-out, the towmaster is able to alter the depth profile of a pipeline bundle by various methods including varying the tow speed.
Nick Street, Project Manager at Sonardyne said, “We’re delighted that the ongoing reliability and accuracy of our equipment has resulted in the successful delivery of Subsea 7’s pipeline bundle contracts. Our latest Wideband 2 signal architecture, present in all our 6G products, was designed specifically for use in the most challenging acoustic environments such as this case, and it has performed remarkably well.”
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Press Release, September 04, 2012