高密度聚乙烯管热熔焊接数值模拟研究

发布时间：2018-03-05 14:16

本文选题：HDPE管　切入点：热熔焊接　出处：《西南石油大学》2017年硕士论文　论文类型：学位论文

【摘要】：高密度聚乙烯管(HDPE管)具有适度的刚度、良好的柔性、可靠的连接性能和优良的输送性能,因此比其他塑料管材更适用于做燃气管。随着西气东输、城市管网建设等工程项目的进行,聚乙烯燃气管在国内的使用呈快速增长的趋势。燃气输送用高密度聚乙烯管要保证绝对的安全可靠,质量的控制必须非常严格,而其焊接接头性能的可靠性对安全施工及应用有着重要的影响。因此本文开展了高密度聚乙烯管热熔焊接数值模拟研究,这对获得高密度聚乙烯管材焊接接头性能、改进焊接工艺、提高管材的应用安全等均十分有益。论文的研究内容如下:(1)针对热熔焊接工艺特点,并参考CJJ63-2008《聚乙烯燃气管道工程技术规程》,通过ANSYS间接耦合的方法建立高密度聚乙烯管热熔焊接三维有限元模型。模型中考虑了固液相变潜热、管件与空气的对流换热以及粘弹性材料的温度相关性等问题,并将焊接过程分为加热阶段、切换阶段和冷却阶段,其中加热阶段对比解析解、冷却阶段对比试验,验证了有限元仿真温度场结果的准确性,进而研究了焊接过程应力场的分布,本模型能够较为准确地模拟出焊接过程中温度场及应力场的分布。(2)建立了加热阶段的温度场解析模型,其实质是对移动边界传热问题(Nuemann解)的研究,求解建立的数学模型,得到液固两相温度的分布、沿轴向温度关于时间和位置的分布规律、加热时间与熔融层厚度的关系。(3)分析了焊接加热时间、切换时间、加热板温度等工艺参数对温度场分布及熔融层厚度的影响。熔融层厚度会随着加热板温度和加热时间的增加而增加。要想获得相同的熔融层厚度,加热板温度越高,所需要的时间越短。切换阶段,焊件失去热源并与空气发生对流换热,热量流失严重,因此切换时间越短越好。(4)温度场的分析结果显示:加热过程中由于材料导热性能较差,温度由焊接端面向非焊接端面扩散较慢,熔融层厚度约为3mm-4mm。冷却过程中熔融层厚度逐渐变薄,内外表面冷却速度不同,易使融合面局部产生大量微小缩孔、粘结强度不够,焊接接头品质下降。建议在热熔焊接冷却阶段采取措施使管道内外表面降温速率一致,这对焊接接头的品质有着重要的影响。(5)应力场的分析结果显示:加热过程中焊接端面受热膨胀,其膨胀趋势受到附近较冷区域的限制,形成热压缩,产生压应力。瞬时应力最大值出现在管道内表面距离加热端5mm-10mm处。由于材料粘弹性的特点,在冷却过程中,管材边冷却边松弛,最终内应力松弛完毕,不存在残余应力。分析结果对实际焊接过程有着重要的指导意义,给焊接工艺人员在制定焊接工艺参数提供参考依据。
[Abstract]:HDPE pipe with moderate stiffness, good flexibility, reliable connection performance and excellent transportation performance, so it is more suitable than other plastic pipe to make gas pipe. With the development of urban pipe network construction and other engineering projects, the use of polyethylene gas pipe in China is increasing rapidly. In order to ensure absolute safety and reliability, the quality control of high density polyethylene pipe for gas transmission must be very strict. The reliability of the welded joints has an important effect on the safety construction and application. Therefore, the numerical simulation of the hot melt welding of HDPE pipes is carried out in this paper, which can be used to obtain the welding properties of HDPE pipes. It is very beneficial to improve the welding process and improve the safety of pipe application. The research contents of this paper are as follows: (1) aiming at the characteristics of the hot melt welding process, With reference to CJJ63-2008, the three-dimensional finite element model of heat fusion welding of high density polyethylene pipe is established by ANSYS indirect coupling method. The latent heat of solid-liquid phase transition is considered in the model. The convection heat transfer between pipe fittings and air and the temperature dependence of viscoelastic materials are discussed. The welding process is divided into three stages: heating phase, switching stage and cooling stage, in which the analytical solution is compared in the heating stage and the contrast test is made in the cooling stage. The accuracy of temperature field simulation by finite element method is verified, and the distribution of stress field in welding process is studied. This model can accurately simulate the distribution of temperature field and stress field in welding process. The analytical model of temperature field in heating stage is established. The essence of this model is to study the heat transfer problem of moving boundary and to solve the mathematical model. The distribution of liquid-solid two-phase temperature, the distribution of temperature along axial direction about time and position, and the relationship between heating time and melting layer thickness are obtained. The welding heating time and switching time are analyzed. The influence of process parameters such as heating plate temperature on temperature field distribution and melting layer thickness. The thickness of melting layer increases with the increase of heating plate temperature and heating time. The shorter the time is, the shorter the time is. In the switching stage, the welding piece loses heat source and convection heat transfer with air, so the shorter the switching time is, the better the temperature field is. The results show that the thermal conductivity of the material is poor during the heating process. The temperature diffuses slowly from the welding end face to the non-welded end face, and the thickness of the melt layer is about 3mm-4mm. during the cooling process, the thickness of the melt layer gradually becomes thinner, and the cooling rate of the inner and outer surfaces is different, so it is easy to produce a large number of tiny shrinkage holes in the fusion surface, and the bond strength is not enough. The quality of welded joint is decreased. It is suggested that measures should be taken during the cooling stage of hot melt welding to keep the cooling rate of the inner and outer surfaces of the pipeline consistent. This has an important effect on the quality of welded joints. The results of stress field analysis show that the welding end face is heated to expand during heating, and its expansion trend is limited by the colder region nearby, resulting in thermal compression. The maximum instantaneous stress occurs between 5 mm and 10 mm from the inner surface of the pipe to the heating end. Due to the viscoelastic characteristics of the material, during the cooling process, the cooling edge of the pipe is relaxed and the internal stress is relaxed. There is no residual stress. The analysis results have important guiding significance for the actual welding process, and provide reference for welding technologists in the formulation of welding process parameters.
【学位授予单位】：西南石油大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TE973.3

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