热力管道锻制三通最小允许壁厚有限元分析

Finite Element Analysis of Minimum Allowable Wall Thickness of Forged Tee for Heating Pipeline

介绍三通补强设计方法。结合算例,采用有限元分析法对不同荷载条件下热力管道锻制三通最小允许壁厚进行模拟计算。在三通补强设计方法中,等面积法、压力面积法仅考虑了薄膜应力,未考虑弯曲应力、峰值应力的影响,有限元分析法考虑全面、精度高。算例中的锻制三通为分流三通,长度为2400 mm,总管、直支管外直径均为1420 mm,侧支管外直径为1220 mm。分别在仅考虑内压、全部荷载条件(内压、温度、土压荷载以及土壤约束等)下,对三通最小允许壁厚进行有限元模拟计算。全部荷载条件下的三通最小允许壁厚大于仅考虑内压条件下的壁厚。预热安装可使三通最小允许壁厚减小,但减小幅度有限。采用较高强度钢材可减小三通最小允许壁厚。三通位于锚固段内将承受较大的轴向力。当三通位于过渡段时,总管、直支管热膨胀方向与Z型管段长臂热膨胀方向应保持一致,且Z型管段长臂长度应小于2倍的变形段长度。承受高弯矩时三通最小允许壁厚要比承受高轴向力时大,这是由于三通失效的主要原因是疲劳破坏,而弯矩是产生疲劳的主要原因。

The design methods of tee reinforcement are introduced.Combined with the calculation example,the finite element analysis method is used to simulate the minimum allowable wall thickness of the heating pipeline forged tee under different load conditions.Among the three reinforcement design methods,the equal area method and the pressure area method only consider the film stress,not consider the effects of bending stress and peak stress.The finite element analysis method considers comprehensive and high accuracy.The forged tee in the calculation example is a split tee with a length of 2400 mm.The outer diameter of the main pipe and the straight branch pipe are 1420 mm,and the outer diameter of the side branch pipe is 1220 mm.Under the consideration of internal pressure and all load conditions(internal pressure,temperature,earth pressure load and soil constraints,etc.),the minimum allowable wall thickness of the tee is calculated by finite element simulation.The minimum allowable wall thickness of the tee under all load conditions is greater than that under only internal pressure.The preheating installation can reduce the minimum allowable wall thickness of the tee,but the reduction is limited.The use of higher strength steel can reduce the minimum allowable wall thickness of the tee.The tee located in the anchoring section will withstand greater axial force.When the tee is located in the transition section,the thermal expansion direction of the main pipe and straight branch pipe should be consistent with the thermal expansion direction of the long arm of the Z-shaped pipe section,and the length of the long arm of the Z-shaped pipe section should be less than 2 times the length of the deformed section.The minimum allowable wall thickness of the tee when subjected to high bending moments is greater than that when subjected to high axial forces.This is because the main reason for the failure of the tee is fatigue failure,and the bending moment is the main cause of fatigue.