根据材料的第三、第四强度理论，本文讨论了锅炉下封头的安全性。
Finally, the safety of the boiler is estimated according the 3rd and the 4th strength theory of material.
应用第四强度理论，求解杆柱在扭矩和轴向力条件下的复合应力，设计抽油杆柱。
Rod strings are designed by computing compound stress with the fourth strength energy on the condition of torque and axial force.
作为第四强度理论的近似计算，目前在套管柱强度设计中广泛应用双向应力椭圆理论。
The Bilateral Stress Elliptic(ellipse of plasticity) Theory is widely used in casing strength designing, as an approximate alternative to the four th strength theory.
文章采用第四强度理论来确定最大下泵深度，并在文留油田的应用中取得了较好的效果。
This paper adopts the fourth theory of strength to decide the maximum depth of tubing pump. A better effectiveness is attained through applying the method in Wenliu Oilfield.
并利用第四强度理论，对连续油管在轴向拉力与内外压力的作用下的综合应力进行了校核。
And use the fourth strength theory, the axial tension in the coiled tubing under the influence of internal and external pressure from a comprehensive stress of checking.
并利用第四强度理论，对连续油管在轴向拉力与内外压力的作用下的综合应力进行了校核。
And use the fourth strength theory, the axial tension in the coiled tubing under the influence of internal and external pressure from a comprehensive stress of checking.
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