The offshore pipeline standard has been updated to reflect the latest pipeline research & developments by DNV GL. The standard, previously called DNV-OS-F101 is now renamed DNVGL-ST-F101*. Around 65% of all new projects globally are designed according to the standard, first issued in 1976.
The new revision reflects the conclusions of joint industry projects (JIP’s) by DNV GL and other leading industry players such as DNV GL’s JIP providing guidance for installation of rigid and flexible pipes, umbilicals and power cables. The JIP presented the typical challenges that should be addressed in planning and design of marine operations and the common basis for installation design of pipelines, umbilicals and cables. The rigid pipeline criteria from this JIP is now captured in the new standard.
DNVGL-ST-F101 now also incorporates input from a JIP on pipe-in-pipe (PiP) systems, which explored challenges related to existing PiP systems and shortcomings of current design standards related to PiP systems. The standard now reflects findings on selection of safety classes, limit state criteria, additional guidelines specific to PiP and code breaks.
A number of requirements related to linepipe fabrication, welding and NDT have been updated to reflect state-of-the art technologies, based on hands-on experience from DNV GL’s 14 laboratories and numerous field inspectors. The laboratories support the pipeline industry with material testing, corrosion testing, full-scale testing, flow testing and failure analysis.
DNV GL’s JIP on subsea repair (DNVGL-RP-F113) which aimed to reduce the time and cost spent on the design and execution of pipeline repairs and a JIP on pre-commissioning of submarine pipelines (DNVGL-RP-F115) are also referred and partially implemented to ensure consistency.
Another modification to the standard expected to be well received by the industry is that the requirements for replacement of the system pressure test have become more flexible and do not rule out pipelines in shallower water. Removing the requirement to fill the empty pipeline with water can significantly reduce cost for pipeline operators, although some additional work will be required to prove an equivalent safety level.
“The standard illustrates what can be achieved when the industry works collaboratively. For example, the outcome of a workshop on dimensions including key industry players has now been built into the standard. The outcome was a compromise between pipe mills and installation contracts on how well pipe joints fit together to enable welding,” says Colin McKinnon, Chairman of DNV GL’s Pipeline Committee and technical director of subsea & export systems at Wood.
The revision also takes into account the findings from two JIPs run outside DNV GL: the Atteris Crossway JIP in Australia onshore crossings and the Atkins Safebuck JIP that provides a modified local buckling criterion.
“The offshore pipeline standard is a living entity and is maintained by an active committee of users. DNV GL’s standards are updated to reflect the findings of joint industry projects, often involving DNV GL’s laboratories and test sites. These are the key factors to their success, widespread global adoption, and continued progression.” says Elisabeth Tørstad, CEO DNV GL - Oil & Gas.
In addition to the changes resulting from JIPs, the section on fracture assessment has been removed from the standard to an updated revision of the recommended practice DNVGL-RP-F108. The standard now gives requirements to when an Engineering Critical Assessment should be performed but points to the RP on how this may be done. This allows the user to use alternative methods as long as these have been validated. The requirements to fracture and fatigue also introduce the concept of “sensitive welds” similar to some other standards which needs extra focus both in design and construction.
The DNV GL offshore pipeline standard has been revised approximately every fifth year and is available free of charge for the benefit of the industry.
