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代码代表了管道自由跨度评估的设计建议中的最新词汇。在重要代码（例如API RP 1111）仅参考DnV以获得进一步指导的情况下，这是正确的。在这20年的大部分时间里，大多数关于涡旋脱落引起的振动的设计规范，包括DnV，都已经说过，而且总体上仍然使轴向管道力与涡旋脱落问题无关。然而，众所周知，压缩元件的自然周期以及轴向压缩力也增加。三月。 2002 DnV发布了一种新的自由跨度推荐实践，其中尝试将整体自由跨度屈曲问题与涡流引起的振动耦合起来。所有尝试使用它的管道工程市场的人都一定会同意，该代码通过引入与更复杂的数值技术相关的更通用的程序，极大地改善了管道的自由跨度极限极限状态和疲劳设计。同年晚些时候，作者进行了一个大型项目，在该项目中，使用上述代码是一项合同要求。但是，如果所有者一方面坚持使用新的DnV代码，另一方面他不愿意接受由计算得出的非常短的自由跨度限制。这不一定意味着新代码是错误的，因为可能是以前的代码高估了允许的跨度，但是，除了短跨度之外，还发现新代码具有一定的适用性限制，这，基本上排除了大范围的常见管道尺寸。因此，作者被迫更深入地研究该问题，从而得出有趣的结论，这些结论将在本文中进行介绍。这些指出了代码的一些保守方面，并提出了一些建议，以解决这些问题，以便通过适当地关注自由泛曲屈曲问题来使用DnV安全方法并仍然产生更大的跨度。
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