Muhayat N, Matien Y A, Sukanto H, Saputro Y C N
Mechanical Engineering Department, Sebelas Maret University, Surakarta, Indonesia.
UPTB Solo Technopark, Technical Unit on Regional Development Planning Board Surakarta, Indonesia.
Heliyon. 2020 Feb 7;6(2):e03366. doi: 10.1016/j.heliyon.2020.e03366. eCollection 2020 Feb.
Underwater welding is widely used for maintenance and repairs of underwater structures such as undersea pipes, offshore structures and nuclear power plants. In practice, underwater welding has the disadvantage related to high cooling rate and unstable welding arc due to the water hydrostatic pressure. This affects the microstructure and mechanical properties of underwater welded joints. Many of previous research works on underwater welding have been carried out only on a laboratory scale in shallow water depth, whereas underwater welding was used to weld in the depth of the water with a metre scale. Undersea structures experience fatigue load due to the fluctuation force of water flow. Therefore, this study aims to determine the effect of water depth on the fatigue life of underwater welded joints. Low carbon steel SS400 specimens were welded underwater with depths of 2.5 m, 5 m and 10 m. The air welded joint was also evaluated for comparison purposes. Fatigue life was evaluated according to the ASTM E466 standard by using a rotary bending machine. Furthermore, tensile test, micro hardness measurement and microstructure evaluation were also conducted for gathering supporting data. The fatigue and tensile strength of the air welded joints were higher than those of the underwater welded joints. The porosities caused by the dissolved hydrogen gas, carbon (monoxide and dioxide) gases and water vapor in weld metal of the underwater welded joints decreased the fatigue and tensile strength. An interesting phenomenon on the underwater welded joints was that the deeper the water level, the higher became the fatigue, tensile strength as well as hardness. Based on the microstructure analysis, the number of acicular ferrite structures in weld metal increased as the water level depth increased.
水下焊接广泛应用于水下结构的维护和修理，如海底管道、海上结构和核电站。在实际操作中，由于水的静水压力，水下焊接存在冷却速度快和焊接电弧不稳定的缺点。这会影响水下焊接接头的微观结构和力学性能。以往许多关于水下焊接的研究工作仅在浅水区的实验室规模上进行，而水下焊接是用于在米级水深进行焊接的。海底结构由于水流的波动力而承受疲劳载荷。因此，本研究旨在确定水深对水下焊接接头疲劳寿命的影响。采用低碳钢SS400试样在2.5米、5米和10米的水深下进行水下焊接。还对气焊接头进行了评估以作比较。根据ASTM E466标准，使用旋转弯曲机评估疲劳寿命。此外，还进行了拉伸试验、显微硬度测量和微观结构评估以收集支持数据。气焊接头的疲劳强度和拉伸强度高于水下焊接接头。水下焊接接头焊缝金属中溶解的氢气、碳（一氧化碳和二氧化碳）气体以及水蒸气所导致的气孔降低了疲劳强度和拉伸强度。水下焊接接头上一个有趣的现象是，水位越深，疲劳强度、拉伸强度以及硬度就越高。基于微观结构分析，焊缝金属中针状铁素体结构的数量随着水位深度的增加而增加。
