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<p>The actuators of main steam and main feedwater isolation valves contain over twenty types of EPDM O-rings operating under sustained compression at approximately 50&#xa0;°C. Compression stress relaxation (CSR) gradually degrades sealing contact stress, jeopardizing reliable valve actuation. The current 3-year replacement interval is overly conservative, and testing all specifications individually is costly. An evaluation method based on representative cross-sectional diameters is proposed. Six specifications covering four diameters (1.78, 2.62, 3.53, and 5.33&#xa0;mm) underwent accelerated CSR aging at 60<b>-</b>90&#xa0;°C. A stretched exponential model combined with the Arrhenius equation was used for life prediction, while finite element analysis and SEM revealed the size-effect mechanism. The results show a nonlinear decay in stress retention. Smaller cross-sectional diameters and their higher compression ratios result in higher von Mises stress, faster aging, and more severe surface damage, indicating a size effect driven by the coupled influence of cross-sectional diameter and compression ratio, with relatively weak inner diameter influence. Using 50% stress retention as the failure criterion, the predicted service life at 50&#xa0;°C ranges from 7 to 13&#xa0;years, significantly exceeding the current interval. This method enables efficient multi-size O-ring aging characterization and supports replacement interval optimization.</p>

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Aging Life Prediction of Multi-Size Rubber O-Rings Based on Compression Stress Relaxation

  • 期刊论文

  • 发表日期：

    2026年8月4日

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  • Ziming Wang,
  • Zhenggang Li,
  • Jiale Gao,
  • Zhi Zhang,
  • Yong Sang

摘要

The actuators of main steam and main feedwater isolation valves contain over twenty types of EPDM O-rings operating under sustained compression at approximately 50 °C. Compression stress relaxation (CSR) gradually degrades sealing contact stress, jeopardizing reliable valve actuation. The current 3-year replacement interval is overly conservative, and testing all specifications individually is costly. An evaluation method based on representative cross-sectional diameters is proposed. Six specifications covering four diameters (1.78, 2.62, 3.53, and 5.33 mm) underwent accelerated CSR aging at 60-90 °C. A stretched exponential model combined with the Arrhenius equation was used for life prediction, while finite element analysis and SEM revealed the size-effect mechanism. The results show a nonlinear decay in stress retention. Smaller cross-sectional diameters and their higher compression ratios result in higher von Mises stress, faster aging, and more severe surface damage, indicating a size effect driven by the coupled influence of cross-sectional diameter and compression ratio, with relatively weak inner diameter influence. Using 50% stress retention as the failure criterion, the predicted service life at 50 °C ranges from 7 to 13 years, significantly exceeding the current interval. This method enables efficient multi-size O-ring aging characterization and supports replacement interval optimization.