Pipes are under actions of internal and external pressure of fluid in oil well drilling and production, so the stability of the pipes is affected by the pressures. The traditional mechanical model and fictitious force were discussed. A mechanical model representing true tubular conditions was established. Equations of calculating equivalent axis force used for stability analysis of pipes were established based on constant axis strain. The results show that the internal and external pressure of fluid and their change have no effect on stability of hanging pipes, and have effect on equivalent axis force and stability of pipes fixed at two ends. For pipes fixed at two ends, equivalent axis force decreases with internal pressure increasing and increases with external pressure increasing. The increase of internal pressure or decrease of external pressure may make equivalent axis force negative, even less than critical buckling force.%油井生产过程中,油井管柱因一直受到内外流体的压力而其稳定性有可能受到影响.对传统理论的力学模型及虚构拉力进行讨论,建立真实反映油井管柱状态的力学模型,并根据轴向应变为常数建立管柱稳定性分析等效轴向力计算公式.研究表明:内外流体压力及其变化对悬挂的管柱稳定性没有影响,对两端受约束的管柱的等效轴向力和稳定性有影响;管内流体压力增加,轴向拉力降低;管外流体压力增加,轴向拉力增加;管内压力增加或管外压力降低,可能使管柱的等效轴向力变为负值,甚至小于管柱的临界失稳载荷.
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