As a critical component of the internal blowout prevention system in ultra-deep drilling, the reliability of the torsion spring within flapper float valves is pivotal to well control safety and drilling efficiency. The failure mechanism of fractured torsion springs retrieved from field operations was elucidated, a theoretical dynamic response model accounting was established for fluid vortex-induced vibration effects, and finite element simulation to predict fatigue life was employed. Results indicate that fatigue fracture constitutes the primary failure mode, driven by high-frequency vibrations induced by drilling fluid impact. Crucially, wear defects on the wire’s inner surface alter the stress distribution topology, causing the maximum stress concentration zone to migrate from the fixed end to the worn region on the valve plate side, thereby acting as the critical initiation site for fatigue cracks. Quantitative analysis reveals that under varying pumping parameters, the continuous fatigue life of an intact spring ranges from 55 to 420 hours. Conversely, surface wear defects precipitate a catastrophic reduction in service life by orders of magnitude, with a minimum survival time of merely 1 hour. These findings provide a theoretical basis for the design optimization of float valves and the dynamic adjustment of drilling strategies, holding significant engineering value for ensuring safe and efficient ultra-deep well operations.
ZHANG Zheng, CHEN Xiu-an, SHI Chao, GUO Yan-bao.
Failure Mechanism and Reliability of Torsion Spring for Flapper Float Valve in Ultra-deep Wells[J].
Science Technology and Engineering, 2026, 26(23): 9936-9944 DOI:10.12404/j.issn.1671-1815.2506982
进一步使用扫描电子显微镜(scanning electron microscope,SEM)(Quanta 200F,FEI)对扭簧断口微观形貌进行表征分析。典型疲劳断口可分为三个区域:疲劳源区、疲劳扩展区和瞬时断裂区[17]。然而,现场失效扭簧断口形貌仅呈现两个明显的疲劳扩展区(B1、B2)和两个瞬时断裂区(C1、C2),如图3(a)所示。
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