程方杰,孔康骞 ,武少杰,李为卫

AuthorsHTML:程方杰 ^{1, 2}，孔康骞 ¹ ，武少杰 ^{1, 2}，李为卫 ³

AuthorsListE:Cheng Fangjie,Kong Kangqian,Wu Shaojie,,Li Weiwei
AuthorsHTMLE:Cheng Fangjie^{1, 2}，Kong Kangqian¹，Wu Shaojie¹, ²，Li Weiwei³
Unit:1. 天津大学材料科学与工程学院，天津 300350；
2. 天津市现代连接技术重点实验室，天津 300350；
3. 中国石油管材研究所，西安 710077

Unit_EngLish:1. School of Materials Science and Engineering，Tianjin University，Tianjin 300350，China；
2. Tianjin Key Laboratory of Advanced Joining Technology，Tianjin 300350，China；
3. Tubular Goods Research Center，CNPC，Xi’an 710077，China

Abstract_Chinese:在海底管线铺设时的环焊缝全自动焊过程中，一般采用带铜衬垫的内对口器配合大热输入焊接参数进行强 制成形．由于高温熔池直接和刚性铜衬垫接触，焊根背面不能形成圆滑过渡的焊趾，应力集中较为严重；同时铜衬 垫也烧损严重，存在焊缝渗铜和夹铜的风险，需要不定期进行更换．针对铜衬垫所存在的上述问题，本研究提出在 铜衬垫表面再放置一层很薄的耐高温柔性衬垫材料，以避免铜衬垫与高温熔池的直接接触．基于有限元方法 (FEM)，使用有限元软件 ABAQUS 系统研究了柔性衬垫的厚度及材料的热导率、比热容等关键热物性参数对焊接 温度场的影响规律以及衬垫对焊道背面成形的特殊作用．模拟结果表明，柔性衬垫的存在使得铜衬垫表面的峰值温 度从 700 ℃大幅下降至 90 ℃以下，但其厚度对焊接温度场的影响很小；柔性衬垫的密度和比热容对焊接温度场的 影响也很小；但柔性衬垫的热导率会明显影响熔池的大小、冷却速度及温度梯度的分布，进而对焊道的成形以及接 头的组织和性能造成影响．模拟和试验结果都表明，合适的柔性衬垫材料可以大大降低铜衬垫表面的峰值温度，避 免其烧损，同时还可以有效改善根部焊道的背面成形，使得铜衬垫作用下形成的周期性宽窄不均的背面熔宽变得均 匀，且焊趾过渡也变得圆滑．
Abstract_English:When laying submarine pipelines，during the automatic welding process of a circumferential weld，an internal clamp with a copper pad is generally utilized，so that a large heat input can be applied to force a root pass as a gap appears in the pad. However，the high-temperature molten pool is in direct contact with the copper pad，which means that a rough transitional weld toe will form that can cause a serious stress concentration. The copper pad can also be seriously burned，which means there is a risk of copper infiltration and slag inclusion in the weld，so the pad must be replaced frequently. Considering the above problems with the cooper pad，in this study，we placed a thin flexible pad with high-temperature resistance on the surface of the copper pad to prevent its direct contact with the high-temperature molten pool. Using simulation technology for the finite element method(FEM)，we studied the influence of pad thickness and its thermal properties，such as the thermal conductivity and specific heat capacity，on the welding temperature field. We also used the software ABAQUS to study the effect of the pad on the appearance of the back of the root pass. The simulation results show that the presence of a flexible pad significantly reduces the peaktemperature on the top surface of the copper pad from 700 ℃ to below 90 ℃，but its thickness had little effect on the welding temperature field，along with its density and specific heat capacity. However，the thermal conductivity of the pad obviously influenced the size of the molten pool，the cooling rate，and the distribution of temperature gradi\u0002ents，which affect the formation of the weld bead，microstructure，and performance of the joint. Both the simulated and experimental results show that the use of a suitable flexible pad material can significantly reduce the peak tem\u0002perature of the top surface of the copper pad to prevent burning of the pad and improve the back appearance of the root pass. When a flexible pad is used，the otherwise irregular back on the root pass becomes regular and the weld toe becomes smooth.
Keyword_Chinese:全自动焊；管道打底焊；根部成形；铜衬垫；有限元方法
Keywords_English:automatic welding；pipeline root weld；root-pass appearance；copper pad；finite element method

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