Preload Assurance in Bolted Flanges With a Model and Test Based Optimized Assembly Procedure

M. Du, F. Song, Haoming Li, Ke Li
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Abstract

Bolted flanges are widely used to connect pipelines in many industries. To assure sealability of a flange, generation of proper preloads in the bolts during the assembly process is critical. However, in the existing standard practice, identical torques are typically applied to all bolts to assemble the flange. Due to elastic interactions between the bolts, tightening one bolt can alter the tensile loads in the other bolts. Hence, the resultant preloads can vary significantly. Even with an improved makeup sequence, the variation in the bolt preloads can be still substantial, as high as 60%. This could pose a risk of leakage. When the bolted flange works under non-benign conditions, such as vibration, pressure and temperature variation, the risk could become even higher. This paper introduces a new methodology to greatly enhance the preload assurance in bolted flanges with an optimized assembly procedure, which is enabled with advanced numerical modeling. A significantly improved uniform distribution of bolt preloads is achieved by optimizing the makeup torques, which is implemented by using physical test data as input and uniformly distributed preloads as the target function. The complexity of the elastic interactions between the flange, the sealing gasket, and the bolts presents uncertainties for the numerical model for quantitative prediction of the torque distribution that is required to yield uniform resultant bolt preloads. This paper resolves this modeling limitation through iterations between modeling and testing. These iterations calibrate and finally validate the model to generate the optimized makeup torque distribution which then leads to improved bolt preload uniformity. Based on the tests conducted on two different sizes of API flanges, 3-API-15K and 5-API-10K, the final preload distribution variation has been reduced to around 30% by utilizing the optimized makeup torque distributions.
基于模型和试验的螺栓法兰预紧保证优化装配工艺
在许多行业中,螺栓法兰被广泛用于连接管道。为了确保法兰的密封性,在装配过程中螺栓产生适当的预紧力是至关重要的。然而,在现有的标准实践中,通常对所有螺栓施加相同的扭矩来组装法兰。由于螺栓之间的弹性相互作用,拧紧一个螺栓可以改变其他螺栓的拉伸载荷。因此,产生的预载荷可能会有很大的变化。即使改进了组装顺序,螺栓预紧力的变化仍然很大,高达60%。这可能会造成泄漏的风险。当螺栓法兰在振动、压力和温度变化等非良性条件下工作时,其风险可能会更高。本文介绍了一种新的方法,通过优化装配工艺,大大提高螺栓连接法兰预紧力的保证,并采用先进的数值模拟方法。以物理试验数据为输入,以均匀预紧力为目标函数,对补紧力矩进行优化,显著改善了锚杆预紧力的均匀分布。法兰、密封垫片和螺栓之间弹性相互作用的复杂性为定量预测扭矩分布的数值模型带来了不确定性,而扭矩分布是产生均匀螺栓预紧力所必需的。本文通过建模和测试之间的迭代解决了这一建模限制。这些迭代校准并最终验证了模型,以生成优化的补扭矩分布,从而改善了螺栓预紧均匀性。通过对3-API-15K和5-API-10K两种不同尺寸API法兰的试验,优化后的补紧扭矩分布将最终预紧载荷分布变化减小到30%左右。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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