采用CMT焊接方法, 在模拟水下高压环境的实验系统中分别进行了常压环境下(0.1 MPa)和环境压力为0.5 MPa下的焊接实验, 实验中采用API X65管线钢接头为研究对象. 焊接过程中采用高速摄像观察焊接电弧行为, 2种环境压力下焊接过程均稳定, 但与常压环境相比较, 0.5 MPa环境压力下的CMT焊接电弧产生收缩, 熔滴过渡频次降低. 焊后对焊缝分别取样进行力学性能检测和金相组织观察, 高压环境下焊缝及热影响区的金相组织因为环境冷却作用增强而出现上贝氏体组织, 拉伸性能没有明显变化, 低温冲击韧性下降, 但测试数据也远高于相关标准要求. 结果表明, CMT焊接方法改善了高压焊接过程的稳定性, 满足水下高压干式焊接作业要求.

Underwater hyperbaric dry welding method is one of the key technology for emergency repair of underwater pipeline leakage. Since the ambient pressure grows with water depth for application of the underwater dry hyperbaric welding method, the normal GMAW welding process tends to be unstable with the increase of the ambient pressure, which leads to the decline in the quality of welding. The cold metal transfer (CMT) welding method adopts a push-pull wire feeding mode and it has adaptive ability to control droplet transfer. In order to improve the welding quality under the hyperbaric environment, the experiments using the CMT welding method were conducted in atmospheric pressure (0.1 MPa) and 0.5 MPa environmental pressures respectively with a test system simulating the underwater hyperbaric environment. API X65 pipes were used as the base metal for welding experiments. A high-speed video camera was used to monitor the behavior of the welding arc. The welding processes at both ambient pressures were found to be stable. However, compared with the atmospheric environment, the CMT welding arc contracted at the ambient pressure of 0.5 MPa, and the droplet transfer frequency was reduced a little. Mechanical performance tests and microstructure analysis of the welds were carried out after welding. While welding in the hyperbaric environment, the upper bainite structure emerged in the microstructure of the seam and the heat-affected zone (HAZ) because of the enhanced environmental cooling effect. The tensile properties of the welds were not changed significantly. Although the low temperature impact toughness decreased, the test data were higher than the relevant limitations of standard. The experimental results show that the stability of the welding process is improved by applying the CMT welding method in the hyperbaric environment. It was verified that the CMT welding method can meet the requirements of underwater hyperbaric welding.