Groundwater in Jeju Island is extensively utilized for living, agriculture, and industry, with over 20 million tons consumed monthly. This heavy usage raises concerns about groundwater pollution due to aging and corrosion of pipes, with over 90% being outdated. Effective management and corrosion prevention measures are essential to address these issues. This study aims to compare the corrosion characteristics of Shielded Metal Arc Welding (SMAW) and Gas Tungsten Arc Welding (GTAW) to analyze weld joint corrosion in the groundwater environment of Jeju Island and under ordinary temperatures. The corrosion behaviors of mild steel and stainless steel were examined by measuring weight changes over time in both conditions. Results indicate that, with the SMAW process, corrosion progressed slowly at the start and end of the weld under ordinary temperatures, while in the groundwater environment, it occurred gradually across the entire weld area. In contrast, GTAW exhibited corrosion at the weld start, end, and heat-affected zone in ordinary conditions, with gradual corrosion also observed under ground.

A heat exchanger refers to a pressure vessel that indirectly exchanges heat between low-temperature/ high-temperature fluids with a solid wall interposed therebetween, and a shell-and-tube cylindrical heat exchanger is generally applied. The shell-and-tube cylindrical heat exchanger is widely used in ships and there is a problem in that the welding area is narrow and welding defects occur a lot due to high-level welding. In particular, in the case of a ship heat exchanger, if a problem occurs in the welding part during operation, the possibility of a safety accident is high, and repair is not easy. In this study, to solve this problem, the GTAW(Gas Tungsten Arc Welding) method was applied to secure the optimum conditions for pipe welding of STS304 material with a thickness of 5.5mm and to conduct a test. Afterwards, in accordance with the ASME rules, welding performance was verified through cross-sectional observation of welds, mechanical property tests, (tensile strength, bending strength, cryogenic impact strength) and non-destructive testing(PT, RT).

This study evaluated the mechanical joining characteristics of substrate Al7075 using the filler metals of ER5356 and Al7075 to secure the joining integrity of the specimens by GTAW. The results of radiographic test show that the welded specimens meet the first level standard of KS D 2042. Besides, welding defects were not occurred. The tensile strengths of the specimens using the filler metals of Al7075 and ER5356 had 240MPa and 252MPa, respectively. The yield strengths were 132MPa and 120MPa, respectively. In case of using the filler metal of Al7075, However, in case of using the filler metal of ER5356, Two filler metals of Al7075 and ER5356 were similar to each other in tensile and yield strength.