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压力容器开孔接管应力类别的解读及应用
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Abstract:
接管是将压力容器与管道连接的一个必不可少的构件。由于涉及介质压力、接管上的外载荷、管系热胀推力及热载荷，在容器开孔接管处的应力分析较为复杂。在补强范围内，关于弯曲应力的类别和评定限值一直以来都存在争议；在补强范围外，2023版ASME VIII-2与我国新标准GB/T 4732-2024关于由外部弯矩引起的整体弯曲应力沿接管厚度的平均值(不包括相连管系自由端位移约束引起的)是划分为一次局部薄膜应力PL还是一次总体薄膜应力Pm同样也存在差异。因此，对于补强区内的弯曲应力，本文从理论和有限元结果两方面进行论证，建议将弯曲应力归为一次应力，一次薄膜加弯曲应力的许用限值取SIII = 2.2S。对于补强区外由外部弯矩引起的整体弯曲应力沿接管厚度的平均值(不包括相连管系自由端位移约束引起的)，以压力容器中典型的带接管的筒体为例，采用弹性分析方法和极限载荷分析方法进行对比。结果表明，外部弯矩同样会引起一次总体薄膜应力Pm，若认为只引起一次局部薄膜应力PL是不安全的。
Nozzles are an essential component for connecting pressure vessels and pipelines. Stress analysis in opening nozzles of pressure vessels is complex due to the medium pressure, external loads on nozzles, thermal expansion thrusts of piping system and thermal loads. The type and assessment limits of bending stress have always been controversial within the limits of reinforcement. Outside the limits of reinforcement, there is also a difference between the 2023 edition of ASME VIII-2 and GB/T 4732-2024 regarding the holistic bending stress averaged through nozzle thickness caused by external moments (excluding those attributable to restrained free end displacements of attached piping) should be classified as primary local membrane stress PL or primary general membrane stress Pm. Therefore, the paper presents demonstrations from both theoretical and finite element analysis results for the bending stress within the limits of reinforcement. It is recommended to classify the bending stress as primary stress, and the allowable limit of primary membrane plus bending stress is taken as SIII = 2.2S. For the holistic bending stress averaged through nozzle thickness (excluding those attributable to restrained free end displacements of attached piping) caused by external moments outside the reinforcement, the typical cylinder with a nozzle in the pressure vessels is taken as an example. Then the elastic analysis and limit load analysis are carried out for comparison. The results show that external moments can also induce the primary general membrane stress Pm, it is unsafe to assume that only primary local membrane stress PL is caused.
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