Advanced dynamic positioning (DP) vessels can now meet critical safety regulations while gaining operational flexibility, efficiency and cost savings through new design and monitoring methods.
More and more operators are asking their drilling contractors to operate their DP units in closed-bus mode, in order to save on fuel and maintenance costs and to reduce the environmental footprint. It also enables a significant reduction in engine hours, with less wear and tear on the engine, and expanded windows for maintenance in a cold engine room.
Dynamic positioning operations are strictly regulated, as loss of position can have dire consequences. Loss of power is a main risk, and complete redundant design including generators and thrusters has been required. This comes at great cost during operations, and the industry has for many years worked on smarter solutions with equivalent safety.
The traditional systems are designed for open bus mode, meaning completely separated power systems and when operated in closed bus mode the closed bus-ties may create a failure propagation path, undermining fundamental design requirements defined in IMO and classification rules. A closed bus system is a much more complex and tightly integrated system, which is demanding to build, verify and operate safely.
“Despite being the subject of discussion in expert DP circles for years, the industry has never come to a clear agreement on how to safely use closed bus configurations, ” says Aleks Karlsen, DNV GL’s principal specialist in DP. The discussions have revolved around the necessity of short-circuit tests, and the potential for damaging equipment on units not designed with this in mind.
To manage these risks, DNV GL is now issuing an Offshore Technical Guide providing guidance on how systems based on closed bus-ties configuration can be designed and verified with additional protection and monitoring facilities, ensuring integrity and robustness. The guidance addresses the critical issue of testing by recommending test requirements that safeguard equipment from damage during testing, while at the same time obtaining sufficient evidence of robustness.
Approval of a closed bus DP unit requires validation of the fault tolerance of the connected system, including live short-circuit testing of worst case failure modes. Extensive experience with operations and testing proves that live earth fault and short-circuit tests are necessary. Major equipment manufacturers confirm that such testing is not only possible, but necessary. Other stakeholders, including flag state authorities, coastal state authorities, and major oil companies have also made it clear that proper testing of all failure modes is necessary.
“This is a critical safety issue. As stated in the IMO’s (International Maritime Organization) DP guidelines, a loss of position is not to occur in the event of a single failure of any active or static system or component, including failure caused by fire or flooding. The solution we provide through our Offshore Technical Guidance sets design requirements that enable live short-circuit tests to be carried out with minimum risk of damaging the equipment. Once engineering and calculation methods have matured to become more reliable and accurate compared to testing data, our requirements to testing may be adjusted accordingly. Right now, only testing provides sufficiently reliable data, ” says Aleks Karlsen.
DNV GL’s DP expertise build on its industry leading position within Classification (referencing the innovative DYNPOS Enhanced Reliability notations), and the DP knowledge and expertise of its Noble Denton consultants. (GL Noble Denton was part of the DNV and GL merger.)
DNV GL’s DP assurance and FMEA/FMECA services are used on all types of offshore support vessel, from large drill ships to smaller high-speed offshore crew boats. DNV GL’s clients include oil companies, ship owners, shipyards and specialist equipment vendors. DNV GL works to international, national, class and IMCA standards as well as equipment-specific regulations, such as those for diving or crane equipment.
About DNV GL
As of 12 September 2013, DNV and GL have merged to form DNV GL. Driven by our purpose of safeguarding life, property and the environment, DNV GL enables organizations to advance the safety and sustainability of their business. We provide classification and technical assurance along with software and independent expert advisory services to the maritime, oil & gas and energy industries. We also provide certification services to customers across a wide range of industries. With our origins stretching back to 1864, our reach today is global. Operating in more than 100 countries, our 17, 000 professionals are dedicated to helping our customers make the world safer, smarter and greener.
About DNV GL – Oil & Gas
In the oil and gas industry, GL Noble Denton and DNV’s Oil & Gas business have joined forces to enable safe, reliable and enhanced performance in projects and operations. We provide a broad range of services, such as technical assurance; marine assurance and advisory; risk management advisory and offshore classification. Our 5, 500 people combine industry expertise, multidisciplinary skills and innovation to solve complex challenges for our customers. Together with our partners, we drive the industry forward by developing best practices and standards across the asset lifecycle.