本文選題：HDPE管　切入點：熱熔焊接　出處：《西南石油大學》2017年碩士論文　論文類型：學位論文

【摘要】：高密度聚乙烯管(HDPE管)具有適度的剛度、良好的柔性、可靠的連接性能和優(yōu)良的輸送性能,因此比其他塑料管材更適用于做燃氣管。隨著西氣東輸、城市管網(wǎng)建設等工程項目的進行,聚乙烯燃氣管在國內的使用呈快速增長的趨勢。燃氣輸送用高密度聚乙烯管要保證絕對的安全可靠,質量的控制必須非常嚴格,而其焊接接頭性能的可靠性對安全施工及應用有著重要的影響。因此本文開展了高密度聚乙烯管熱熔焊接數(shù)值模擬研究,這對獲得高密度聚乙烯管材焊接接頭性能、改進焊接工藝、提高管材的應用安全等均十分有益。論文的研究內容如下:(1)針對熱熔焊接工藝特點,并參考CJJ63-2008《聚乙烯燃氣管道工程技術規(guī)程》,通過ANSYS間接耦合的方法建立高密度聚乙烯管熱熔焊接三維有限元模型。模型中考慮了固液相變潛熱、管件與空氣的對流換熱以及粘彈性材料的溫度相關性等問題,并將焊接過程分為加熱階段、切換階段和冷卻階段,其中加熱階段對比解析解、冷卻階段對比試驗,驗證了有限元仿真溫度場結果的準確性,進而研究了焊接過程應力場的分布,本模型能夠較為準確地模擬出焊接過程中溫度場及應力場的分布。(2)建立了加熱階段的溫度場解析模型,其實質是對移動邊界傳熱問題(Nuemann解)的研究,求解建立的數(shù)學模型,得到液固兩相溫度的分布、沿軸向溫度關于時間和位置的分布規(guī)律、加熱時間與熔融層厚度的關系。(3)分析了焊接加熱時間、切換時間、加熱板溫度等工藝參數(shù)對溫度場分布及熔融層厚度的影響。熔融層厚度會隨著加熱板溫度和加熱時間的增加而增加。要想獲得相同的熔融層厚度,加熱板溫度越高,所需要的時間越短。切換階段,焊件失去熱源并與空氣發(fā)生對流換熱,熱量流失嚴重,因此切換時間越短越好。(4)溫度場的分析結果顯示:加熱過程中由于材料導熱性能較差,溫度由焊接端面向非焊接端面擴散較慢,熔融層厚度約為3mm-4mm。冷卻過程中熔融層厚度逐漸變薄,內外表面冷卻速度不同,易使融合面局部產(chǎn)生大量微小縮孔、粘結強度不夠,焊接接頭品質下降。建議在熱熔焊接冷卻階段采取措施使管道內外表面降溫速率一致,這對焊接接頭的品質有著重要的影響。(5)應力場的分析結果顯示:加熱過程中焊接端面受熱膨脹,其膨脹趨勢受到附近較冷區(qū)域的限制,形成熱壓縮,產(chǎn)生壓應力。瞬時應力最大值出現(xiàn)在管道內表面距離加熱端5mm-10mm處。由于材料粘彈性的特點,在冷卻過程中,管材邊冷卻邊松弛,最終內應力松弛完畢,不存在殘余應力。分析結果對實際焊接過程有著重要的指導意義,給焊接工藝人員在制定焊接工藝參數(shù)提供參考依據(jù)。
[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.
【學位授予單位】：西南石油大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TE973.3

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