连续油管在内压作用下直径增长模型的建立

Modelling the diametral growth of coiled tubing under the action of an internal pressure.

根据疲劳循环屈服强度衰减模型和弹塑性变形理论，推导了连续油管在内压作用下的直径增长（鼓胀）的理论模型。模型推导过程是：首先根据线性弹性理论和变形塑性理论推导出周向应变的数学表达式，进而导出径向应变。再通过合理的假设，建立用于计算直径增长的计算机逻辑框图。理论模型计算结果表明，当连续油管在内压下循环弯曲时，疲劳循环屈服强度衰减不可避免地导致直径增长。最后，进行了连续油管循环弯曲试验，试验数据与理论模型相当吻合，验证了理论模型的正确性。这一模型将为理解连续油管鼓胀的机理以及准确预测连续油管直径增长提供一个有效的工具。

In this article, a new theoretical model on diametral growth (or ballooning) of coiled tubing(CT) under the action of an internal pressure is derived based on fatigue cyclic softening and elasticity and deformation plasticity theories. First, mathematical expressions for hoop strain based on linear elasticity theory and deformation plasticity theory, and thus diametral strain is derived. Then, a logic computational diagram is constructed for calculating diametral growth by assuming fatigue cyclic softening, namely yield strength reduction as tubing fatigues. The model results show that when the CT is cycled under the action of an internal pressure, fatigue cyclic softening inevitably leads to the diametral growth. Finally, test results prove the theoretical model to be correct: the model result agrees quite satisfactory with test data for 175(4445mm) OD, 0175(4445mm) wall thickness CT. This new model shall provide an effective tool both in understanding the mechanism of the CT ballooning and for a