水下立管局部干法横向焊接旋转电弧传感与熔池控制的基础研究

The underwater riser pipe system is very important due to it connects the water surface devices and seabed equipments in the construction of offshore oil-gas field. However, when adopting underwater welding method to connect the underwater riser pipes, the welding process not only affected by water, but also in the effection of gravity the molten pool often flows down，and welding bead is difficult to formation. These factors significantly hinder the application of underwater riser pipe welding. To solve these problems, a local dry welding method is adopted in this project to eliminate the ill effects of water, then the structure and pneumatic system of the chamber is optimized to form a flowing up wind field, thereby to restrain the molten pool flowing down by the blow force and cooling effect of the high pressure gas. A rotating arc welding gun is also placed inside of the micro chamber. Its cycle heating effect can reduce the heat input of welding, which lead to further decreasing the molten pool flowing. Meanwhile, the rotating arc is used as a senser to detect the position of the welded seam, which is benificial to welding seam tracking. A coupling model of flow field, force field and temperature field is built,then based on it a numerical simulation method and the experimental results are adopted to study the arc stability in the effection of environmental pressure and wind field structure. This project also study the characteristic of rotional arc, the mechanism of droplet transfer, and the law of molten pool dynamic behavior and cooling and solidification in the high pressure gas and rotating arc condition, and based on it the method to control welding bead formation also studied. To realize the automation of underwater riser pipe welding, the rotating arc sensing characteristics in the micro chamber environment is investigated, and a plural characteristic harmonic algorithm is developed for detecting the position of welding seam.

在海上油气田建设中，立管系统作为连接水面浮式装置与海底设备的导管，作用非常关键。然而，采用水下焊接方法对立管系统进行连接时，焊接过程不仅受到水的影响，而且在重力的作用下，熔融金属向下流动，使焊道难以成形，成为制约其应用的主要瓶颈。本项目拟采用局部干法焊接消除水的影响，并对排水罩结构进行优化，使其内部形成向上流动的风场，利用气流对熔池的吹袭和冷却作用，以及旋转电弧对熔池热输入的降低作用，从力和热两方面抑制熔池下淌，改善焊缝成形。同时利用旋转电弧的传感功能检测焊缝偏差。建立流场、力场和温度场耦合模型，采用数值模拟方法并结合实验手段分析排水罩内的风场结构对焊接过程稳定性的影响。研究高压气流和旋转电弧同时作用下的焊接电弧特性、熔滴过渡机理、熔池动态行为和凝固规律，制定焊缝成形控制策略。研究局部干法焊接环境下旋转电弧的传感特性，开发复函数特征谐波焊枪偏差检测算法，为实现水下立管自动化焊接提供支持。

为提高局部干法环境下横向焊接的焊缝成形质量，本项目从局部排水罩内的风场结构、电弧形态、熔滴过渡特性、熔池行为、电弧传感特性等方面开展了一系列的基础研究，试图揭示局部干法焊接条件下的焊缝成形机理，为水下焊接质量控制提供技术支持。. 本项目在对排水罩内的风场进行数值模拟的基础上，通过优化排水罩结构，实现了排水罩内气体的平稳流动，并在电弧下方形成向上流动的气流，抑制熔池下淌。研究了排水罩内侧向风场对电弧等离子体的温度场、速度场、压力场的影响规律。发现电弧弧柱的吹偏角度与侧向风速基本上呈线性关系。利用高速摄像技术对局部干法横焊电弧形态进行观察，发现排水罩内向上流动的风场促使电弧等离子体向上偏转，且电弧亮度梯度变大。. 分析了局部干法横焊的熔滴过渡特性，发现在短路过渡状态下，由于受到侧向风场的影响，更容易发生B型短路过渡。在滴状过渡时，由于熔滴体积较大，侧向风场的支托作用不明显，熔滴沿焊丝倾斜向下过渡到熔池中。在射流过渡时，侧向风场对电弧的影响较小，并使熔滴略微向上偏斜，有助于减小熔池下淌程度，获得较好的焊缝成形质量。. 对局部干法横焊的熔池行为进行了数值模拟。结果表明：局部干法条件下随着压力的增加，电弧收缩，电弧的能量密度增加，熔池的冷却速度变快；在冷却速度变快和能量密度增加的双重作用下，熔池下淌程度随压力增加呈现先减小后增大的特征。. 研究了侧向风场作用下焊缝成形质量和旋转电弧的传感特性。试验结果发现，适当控制侧风流量有助于抑制熔池下淌、改善焊缝成形。但是随着风速的增加，焊接电弧的熄弧率升高、焊接过程的稳定性变差。采用多元回归方法获得了不同侧向风速下的电弧传感模型。提出了一种基于平面拟合的焊枪偏差和电极高度检测算法，设计了软阈值小波滤波算法，并开发了相应的模糊控制算法对焊枪偏差和电极高度进行调节，初步实现了横焊焊缝的成形控制和跟踪。项目的研究结果可为实现局部干法水下自动化焊接提供技术支持。