现有标准在进行Ω环焊接密封结构设计时，仅依据介质内压来计算螺栓预紧力，未考虑高低温下密封结构热膨胀差对螺栓载荷的影响，而这种影响在低压高温工况下尤其明显。本文针对低压高温工况下Ω环焊接密封结构，选取316L、SA336、16Mn 3种法兰及Ω环常用材料，采用数值模拟方法，研究了在现有标准计算得到的低压高温工况螺栓预紧力下，温差载荷对Ω环焊接密封结构应力分布的影响。研究结果表明，低压高温工况下结构热膨胀差导致的螺栓载荷变化量相较于螺栓预紧力的占比较大，不能忽略；由于材料性能差异，当螺栓热膨胀量大于法兰、Ω环而产生负膨胀现象时，需对螺栓载荷进行补偿，或对螺栓预紧力进行修正。

Current standards for designing Ω-ring welded sealing structures calculate bolt preload solely based on internal pressure, neglecting the influence of differential thermal expansion under temperature variations, which is particularly significant under low-pressure and high-temperature conditions. In this study, three materials commonly used for flanges and Ω-rings, such as 316L, SA336, and 16Mn, were selected for the Ω-ring welded sealing structure under low-pressure and high-temperature conditions. By employing numerical simulation methods, the influence of differential thermal expansion on the stress distribution within Ω-ring under low-pressure and high-temperature conditions was investigated. The results reveal that under low-pressure and high-temperature conditions, the variation of bolt load induced by differential thermal expansion constitutes a significant and non-negligible proportion of the initial preload. Furthermore, due to differences in material properties, when the thermal expansion of bolts exceeds that of flanges and Ω-ring, resulting in a negative expansion, compensation for the bolt load or correction of the initial preload is required.