The complexity of computer control systems on board rigs is a cause of major commissioning bottlenecks. The DNV GL class notation ISDS provides a structured approach to system integration, accelerating the process, improving reliability and enabling substantial savings.
When a new offshore rig has been installed above the wellhead, it is by no means ready to go into operation. It can take months until all on-board systems – and in particular, the numerous industrial control systems (ICS) operating the drilling and support equipment – have been installed and tested successfully and are ready to go. “Many things can go wrong, and having a stable software environment in place plays a key role,” says Mark Bessell, COO of the drilling contractor Songa Offshore, which operates a number of rigs in the North Atlantic and North Sea.
But in the case of Songa Offshore’s four new CAT-D semisubmersible rigs built at the Korean shipyard DSME for drilling projects in the North Sea, things took a much more favourable course: “The acceptance phase of the first unit was completed within four weeks, which is a notable achievement for such a sophisticated rig.” Even at the current low crude oil prices, being able to start operations three months earlier than expected is a huge benefit for the operator. What enabled this accomplishment, which saved Songa millions of euros, is the DNV GL standard and class notation ISDS.
Managing integrated software
IT complexity on board offshore rigs and other vessels has been a key concern at DNV GL for years, and in 2008 legacy DNV introduced its recommended practice “Integrated Software Dependent Systems” (ISDS) (DNV-RP-D201), followed in 2010 by the ISDS offshore standard (DNV-OS-D203) for the ISDS standard and class notation, to help builders and operators better coordinate the specification, development, implementation and maintenance of software systems and related quality assurance processes throughout the lifetime of a vessel. The ISDS standard establishes a systematic approach to ensuring the reliability, availability, maintainability and safety of integrated, software-dependent systems.
The list of integrated software systems on board a CAT-D rig is long (refer to box). Software is not always properly addressed during design and reliability analyses, and is often unfinished when systems are delivered to the yard. Interfaces may not be fully engineered or tested and typically need to be coordinated at the vessel level. Software updates are implemented on the fly: tuning, bug fixes, thousands of changes to software on hundreds of different programmable logic controllers (PLCs) and computers. Tracking and timely testing all this is a real challenge.
Contrary to other class notations, ISDS addresses the development process rather than only focusing on the finished product, and the reliability, availability, maintainability and safety (RAMS) stipulations ensure proper tracking of failure mode assessments throughout the project. This is in line with the approach taken by other industries to ensure system and software integrity.
Tracking and standardization
The four new units of Songa Offshore, one of the early adopters of the ISDS approach, are ISDS-compliant. The ISDS implementation process standardizes all software modifications across the four rigs, transferring learning from one rig to the remaining ones. All software systems are tracked from the yard after factory acceptance through to commissioning and operation. Since all software versions used at various stages are documented, the last functional version can be easily identified if an interface isn’t working. The result is an identical software environment across the entire fleet. Songa’s fleet operations management confirms that the software quality focus on the CAT-D project has made a noticeable difference in improving reliability, accelerating commissioning and reducing downtime. “Before, a new rig would be delivered without any software control,” says Martin Coward, Engineering Manager for the project. “We never knew whether and how a specific software version had been tested. Changes made during commissioning might have unexpected consequences for other systems without being traceable.” Now for the first time an ISDScompliant drill rig has stood the test of time after drilling for months through extreme weather, delivering tangible benefits to its operators. Patrick Rossi, DNV GL ISDS Project Manager for CAT-D, confirms: “We had very few software integration issues within the ISDS scope.” At DSME yard the benefits of ISDS are being felt, as well: “Having software tracking information gave us a clear picture of the situation throughout the project up to delivery,” says Myeong-Ki Han, Head of Systems Integration R&D at DSME. But it is during operations that the added value truly shows. “Overall we have had good performance on the rigs and the focus on software handling is continuing into operation. Some of the issues we have seen in operation were related to the initial exclusion of the switchboards from the scope of ISDS. Such system interfacing with the power management systems needs to be included and properly addressed for example during FMEA testing of future HIL/ISDS process,” says Trond Jan Øglend, E&I Engineer for Songa CAT-D OPS Prep. Martin Coward of Songa adds: “The control we were able to get over the supplied software has made the whole ISDS project worthwhile.”