An elegant solution for high hold-back tension requirements.
Offshore operations are becoming increasingly demanding, with new projects being conducted in deeper waters and more diverse or exposed locations. The deepwater environment poses a special challenge for the installation of flexibles, as the hold-back tensions generated there are significantly greater than those encountered in shallower installations.
Technip Norge AS approached Aquatic in May 2011 seeking to hire a tracked tensioner spread with 85-te hold-back tension capacity to cope with calculated dynamic loads. When it received the initial request, Aquatic did not have a tensioner system with sufficient capacity to satisfy this requirement. As a catalyst to adapting systems to meet the requirements of the deepwater flexibles installation market, the company decided to develop a solution for first use on this particular Technip Norge project.
Drawing on more than 35 years’ experience of the offshore installation of flexibles, Aquatic’s specialist in-house engineering team promptly developed a solution for Technip Norge by combining two 50-te-rated tracked tensioners with a central management and control system.
The Aquatic team adapted a new-build 50-te tensioner called the AQTT-10E-50 DUAL, which can be used either individually or paired with another 50-te-rated tensioner to achieve almost double the line-pull capacity of a single tensioner.
The two tensioner systems, which are essentially identical in specification, are placed in-series and synchronised centrally via an electronic management system. Given the efficiencies of the individual tensioner system, the maximum line-pull rating for the dual system is equivalent to 96 te. A single control cabin offers central manipulation and monitoring of the system. The two in-line four-track tensioners provide a total contact length of 7 m with an applicable product, so sensitive product grip settings can be accommodated.
The central feature of the new dual-tensioner system is a specially designed hydraulic manifold that enables the two machines to work in tandem. The dual-tensioner system is designed to operate from a single electrohydraulic power pack, which provides hydraulic power to the tensioners via the manifold. The manifold regulates and diverts the hydraulic fluid into two equal streams so that both tensioners operate at exactly the same flow rate and pressure, thereby ensuring a fully balanced operation.
The key to providing effective engineering solutions is to understand exactly what customers and the market require and to work with the objective of ensuring that a system is developed to meet the conditions of a specific project. The collaboration with Technip Norge included gaining detailed understanding of its needs and cooperation in testing the new dual-tensioner system at Aquatic’s operational facility in Peterhead, UK, before its mobilisation onto the Technip vessel.
During 2012, the system was used successfully on several umbilical and riser installation jobs, including projects in the Goliat, Hyme and Vigdis developments in the Norwegian sector of the North Sea, and the Rochelle development in the UK North Sea for Technip UK. Aquatic’s second 96-te dual-tensioner spread came online in February 2013.
Craig Evans, Aquatic proposals engineer, states, “Modularity is a vital consideration for any offshore equipment spread. The modular nature of the AQTT-10E-50 DUAL system makes it simple for us to strip it down into component pieces and stow it inside a standard container for transportation by road or sea.
“The ability to transport our equipment in standard (12-m) shipping containers means that it can be installed on relatively small vessels of opportunity that operate from more economical quayside locations. This enables faster mobilisation and demobilisation, and provides an ideal solution to the logistics challenges and cost issues faced by operators.
“In part, Aquatic’s reputation has grown because it can help customers to minimise vessel downtime, which reduces project costs for them. We have received further requests for similar work, including possible floating production, storage and offloading facility mooring line work using synthetic fibre ropes.