外压作用下大口径直缝焊接钢管几何缺陷和材料非均匀性影响的精确评估

在深海中,外部挤毁压力会导致受静水压力的主干线钢管发生破坏。这种失效模式是一种不稳定的现象,这是由钢管的几何形状和材料特性所决定,并通过将这些特性组合在一起而发生。这种极限破坏压力很难精确确定,对此二十年来的研究还未能搞清全部的问题。从分析和计算的角度分析受外部均匀压力的大口径直缝焊接钢管环的弹塑性破坏,且详细检验椭圆形的实际形状和材料非均匀性的重要影响。此研究受近来很多关于大口径直缝焊接钢管上所切环的实验研究的启发,且发现材料非均匀性会影响破坏模式,有时会在环的承载能力方面发生不可预料的降低,促进了潜在破坏模式的发生。重要的是,显示了这种性能很难遵循数值改变,包括例如Riks和提高弧长等鲁棒策略方法。此问题有助于对一些看上去异常的试验结果给出解释。

Towards an Accurate Assessment of UOE Pipes Under External Pressure : Effects of Geometriclm-perfection and Material Inhomogeneity

In deep and ultra-deep waters the diameter of trunk lines coupled with the hydrostatic pressure tends to lead to failure of the pipeline by external collapse.This failure mode is an instability phenomenon that is governed by the geometry of the pipeline and its material properties and takes place through a subtle combination of its properties. As such the exact limiting collapse pressure is very difficult to determine and twenty years of studies seem to have not managed to clarify entirely the matter. In the present paper the elastic-plastic collapse of test rings from UOE formed pipes under external uniform pressure is analysed both from an analytical and a computational viewpoint and the significance of the actual shape of the out of roundness and of the material inhomogeneity is examined in details.The work has been motivated by a number of accurate experimental tests recently performed on rings cut from UOE pipes and it is found that the material inhomogeneity can affect the collapse modes and produce an occasionally unforeseen reduction in the carrying capacity of the rings prompting a swing between the underlying collapsing modes.Importantly , it is shown that this behaviour can turn quite difficult to follow numerically , also by means of robust strategies such as Riks and improved arc-length.The features of the problem can help to give reason of some apparently anomalous experimental results.