﻿ 球面对锥面特殊螺纹气密封性能影响因素分析
 西南石油大学学报(自然科学版)  2017, Vol. 39 Issue (6): 162-166

1. 重庆科技学院石油与天然气工程学院, 重庆 沙坪坝 401331;
2. "油气藏地质及开发工程"国家重点实验室·西南石油大学, 四川成地 质及开发工程, 四川 成都 610500

Analysis of Factors Influencing Hermetic Seal Performance with a Spherical-conical Surface and Special Screw Threads
XU Honglin1 , YANG Bin1, SHI Taihe2, ZHANG Zhi2
1. School of Petroleum and Natural Gas Engineering, Chongqing University of Science & Technology, Shapingba, Chongqing 401331, China;
2. State Key Laboratory of Oil & Gas Reservoirs Geology and Exploitation, Southwest Petroleum University, Chengdu, Sichuan 610500, China
Abstract: A theoretical model for calculating the hermetic seal pressure of special screw threads subjected to an applied torque from a spherical-conical sealing surface is established. The influence of the spherical radius, cone and taper, and applied torque of the sealing face are studied. According to the results, the hermetic seal pressure of the screw threads declines according to a power law with increasing spherical radius; the hermetic seal pressure declines gradually with an increase in the cone and taper; and the hermetic seal pressure increases parabolically with increase in the make-up torque added to the sealing surface. Generally, the spherical radius and make-up torque added to the sealing surface have a significant impact on the hermetic seal performance of the special screw threads. It is suggested to optimize the spherical radius while properly controlling the applied torque such that the stress distribution of the sealed contacts can simultaneously satisfy the hermetic seal performance and stop the yielding of the sealing surface.
Key words: oil casing     special screw threads     spherical seal     hermetic seal pressure     influence factors

1 特殊螺纹气密封压力理论模型 1.1 球面对锥面密封接触应力

 图1 特殊螺纹球面对锥面径向过盈接触密封示意图 Fig. 1 The schematic diagram of radial interference sealing contact

 ${p_{{\rm{sN}}}}\left( x \right) = \dfrac{{{E^*}}}{{4{R_{\rm{s}}}}}\sqrt {w_{\rm{s}}^2 - {x^2}} \\ {\kern 40pt}\left( { - {w_{\rm{s}}} \leqslant x \leqslant {w_{\rm{s}}}, 0 ＜ 2{w_{\rm{s}}} \ll {R_{\rm{s}}}} \right)$ (1)

$E^{*}$ —当量弹性模量，MPa；

$R_{\rm s}$ —球面半径，mm；

$w_{\rm s}$ —密封面接触半宽，mm；

$x$ —接触面横坐标，mm。

 $\dfrac{1}{{{E^*}}} = \dfrac{1}{2}\left( {\dfrac{{1 - \nu _{\rm{p}}^2}}{{{E_{\rm{p}}}}} + \dfrac{{1 - \nu _{\rm{c}}^2}}{{{E_{\rm{c}}}}}} \right)$ (2)

${E_{\rm{p}}}$ ${E_{\rm{c}}}$ —接触副中管体球面和接箍锥面弹性模量，MPa。

 ${w_{\rm{s}}} = \dfrac{{20}}{\pi }\sqrt {\dfrac{{10{R_{\rm{s}}}{T_{{\rm{se}}}}}}{{{E^*}{r_{\rm{s}}}\left\{ {\dfrac{{{t_s}}}{{\sqrt {4 + t_{\rm{s}}^2} }}\left[{\dfrac{P}{{2\pi }} + \dfrac{{{\mu _{\rm{t}}}}}{{\cos \alpha }} {\dfrac{{2{E_7} + \left( {g-{L_7}} \right){t_{\rm{t}}}}}{4}} } \right] + {\mu _{\rm s}}{r_{\rm s}}} \right\}}}}$ (3)

$r_{\rm s}$ —密封面平均半径，mm；

$t_{\rm s}$ —密封锥面直径上锥度，mm/mm；

$t_{\rm t}$ —螺纹直径上锥度，mm/mm；

$P$ —螺距，mm；

$\mu_{\rm t}$ —螺纹面摩擦系数，无因次；

$\mu_{\rm s}$ —密封面摩擦系数，无因次；

$\alpha$ —螺纹牙承载侧面角，(°)；

$E_7$ —螺纹中径，mm；

$g$ —非完整螺纹长度，mm；

$L_7$ —完整螺纹长度，mm。

 $\dfrac{{{E^*}{w_{\rm{s}}}}}{{4{R_{\rm{s}}}}} \leqslant {\sigma _{\rm{s}}}$ (4)

 ${T_{{\rm{sem}}}} \!=\! \dfrac{{{R_{\rm{s}}}{r_{\rm{s}}}\sigma _{\rm{s}}^2{\pi ^2}}}{{250{E^*}}}\left[{\dfrac{{{t_{\rm{s}}}}}{{\sqrt {4 \!+\! t_{\mathop{\rm s}\nolimits} ^2} }}\left( {\dfrac{P}{{2\pi }} \!+\! \dfrac{{{\mu _{\rm{t}}}}}{{\cos \alpha }}\cdot{\dfrac{{2{E_7} + g{t_{\rm t}}-{L_7} {t_{\rm t}}}}{4}}} \right) \!+\! {\mu _{\rm{s}}}{r_{\rm{s}}}} \right]$ (5)

1.2 基于密封接触能理论的气密封压力

 ${W_{\rm{a}}} = \int_{ - {w_{\rm{s}}}}^{{w_{\rm{s}}}} {p_{_{{\rm{sN}}}}^{1.4}} \left( x \right){\rm{d}}x$ (6)

 ${W_{{\rm{ac}}}} = 10 \times {\left( {\dfrac{{{p_{\rm{g}}}}}{{{p_{\rm{a}}}}}} \right)^{0.838}}$ (7)

${p_{{\rm{a}}}}$ —大气压力，MPa；

${p_{{\rm{g}}}}$ —拟密封的管内气体压力，MPa。

 ${p_{{\rm{gm}}}} = {p_{\rm a}}{\left[{\dfrac{{\int_{-{w_{\rm{s}}}}^{{w_{\rm{s}}}} {p_{_{{\rm{sN}}}}^{1.4}\left( x \right){\rm{d}}x} }}{{10}}} \right]^{\frac{1}{{0.838}}}}$ (8)

2 特殊螺纹气密封性能影响因素分析

2.1 球面半径的影响

 图2 球面半径对螺纹最大气密封压力的影响 Fig. 2 The effect of spherical radius on the maximum gas sealing pressure

2.2 锥面锥度的影响

 图3 锥面锥度对螺纹最大气密封压力的影响 Fig. 3 The effect of cone taper on the maximum gas sealing pressure

2.3 密封面附加上扣扭矩的影响

 图4 密封面附加上扣扭矩对螺纹最大气密封压力的影响 Fig. 4 The effect of additional sealing torque on the maximum gas sealing pressure

3 结论

(1) 针对球面对锥面密封结构，基于密封接触能机理建立了特殊螺纹气密封压力理论模型，为定量评价特殊螺纹气密封性能提供了一种较可靠的方法。

(2) 随球面半径增大，螺纹气密封压力呈幂指数规律降低，且降低的速度越来越小；随锥面锥度增大，螺纹气密封压力逐渐降低，但降幅较小；随密封面附加上扣扭矩增加，螺纹气密封压力呈抛物线型增大。

(3) 为提高特殊螺纹气密封性能，一方面应优化球面半径，另一方面应控制密封面作用扭矩在合理范围，既根据拟密封的气体压力确定密封面最小附加上扣扭矩，同时根据密封面极限屈服条件确定密封面最大附加上扣扭矩。