During the last 20 years the DnV code has represented the latest word in design recommendations for pipeline free span evaluations. This is true to the extent that important codes, such as API RP 1111, simply refer to DnV for further guidelines. During most of these 20 years the majority of the design codes which did have anything to say about vibrations due to vortex shedding, including DnV, had and in general still have, dissociated axial pipeline forces from the vortex shedding problem. It is well known, however, that the natural period of a compressed element increases as does also the axial compressive force. In March. 2002 DnV released a new free span recommended practice, in which an attempt was made to couple the global free span buckling problem and that of vortex induced vibrations. All those of the pipeline engineering market, who have attempted to use it, will certainly agree that this code has greatly improved the pipeline free span Ultimate limit state and fatigue design by introducing more general procedures associated to more sophisticated numerical techniques. Later that same year the authors undertook a large project, in which the use of the aforementioned code was a contractual requirement. If on one hand, however, the owner insisted upon the use of the new DnV code, on the other he was not willing to accept the very short free span limits, which were resulting from the calculations. This does not necessarily imply that the new code was wrong, because it could be, that previous codes had overestimated the allowable spans, but, in addition to the short spans, it was also found that the new code has some limits of applicability, which, basically, exclude a large range of common pipeline sizes. Because of this the authors were forced to look at the problem in further depth, thus resulting interesting conclusions, which will be presented in this paper. These point out some conservative aspects of the code, and make suggestions as to how these can be overcome in order to use the DnV safety approach and still produce larger spans, by properly focusing on the frees pan buckling problem.
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机译：在过去的20年中，DNV码代表了流水线自由跨度评估的设计建议中的最新词。这是符合重要代码，例如API RP 1111的程度，简单地指的是进一步的指导。在这20年中的大部分时间里，大多数设计代码都有任何关于由于涡旋脱落而导致的振动，包括DNV，并且总的来说，从涡旋脱落问题中解开了轴向管道力。然而，众所周知，压缩元件的自然周期也随着轴向压缩力而增加。三月。 2002年DNV发布了一个新的自由跨度推荐的实践，其中尝试将全球自由跨度屈曲问题耦合，以及涡旋引起的振动。所有试图使用它的管道工程市场肯定会同意，通过引入与更复杂的数值技术相关的更多一般程序，这段代码极大地改善了流水线自由跨度极限状态和疲劳设计。同年，作者承诺了一个大型项目，其中使用上述守则是合同要求。但是，如果一方面，所有者坚持使用新的DNV码，另一方面，他不愿意接受那些由计算产生的非常短的自由跨度限制。这并不一定意味着新代码错误，因为它可能是，以前的代码高估了允许的跨度，但是，除了短暂的跨度之外，还发现新代码有一些适用性的限制，这基本上，排除了大量的常见管道尺寸。因此，这位作者被迫在进一步深入看待问题，从而产生了有趣的结论，这将在本文中提出。这些指出了代码的一些保守方面，并提出了如何通过DNV安全方法来克服这些方面的建议，并通过正确关注释放潘屈曲问题，仍然产生更大的跨度。
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