机械性能的变化趋势是：密度增加，含油率下降，布氏硬度增加，而压溃强度先降低后增加。
Development tendency of mechanical properties is: density increase oil content ratio decreases, Brinall hardness increases, crushing strength goes down first and then goes up.
综合考虑规范对立管强度的要求，防止发生压溃和屈曲扩展的要求及限制立管发生漂浮的要求三个条件，确定了满足条件的最小壁厚。
Considering the requirements of riser strength, system collapse, propagated buckling and limitation of floating, the smallest thickness that meets the requirements is determined.
分别利用塑性铰理论和压溃理讨论了强度计算问题，提出了强度承载能力计算公式和压溃荷载计算方法。
With the help of plastic hinge theory and collapse theory, the formulas for calculating strength failure load and the method for computing collapse load were established respectively.
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