LNG TANK용 9%니켈강의 레이저-아크 하이브리드 용접특성에 대한연구

Abstract

Recently, the world is suffering from the rapid change of the earth due to environmental pollution. Various policies and regulations have been made to prevent global climate change, and environmental concerns are growing ever more. In accordance with this, many organizations such as IMO are strengthening more specific regulations and policies on marine environmental pollution. In particular, IMO should tighten regulations on the emission of marine vessels. In order to meet these regulations, marine vessels should be equipped with scrubber installations, low-sulfur oil, and LNG propulsion.

There are 9% nickel, STS, AL alloys and high Mn which are the raw materials of dual LNG propulsion line tanks. 9% Nickel steel is one of the materials that exhibits unstable welding conditions such as unique magnetization phenomena and high temperature and low temperature cracks. However, it has low temperature toughness compared to other materials and has suitable physical properties for low temperature tank. In order to overcome the disadvantages of this welding, we try to compare the mechanical properties of FCAW(Flux core arc welding) welding by 9% nickel steel welding by Laser arc hybrid welding.

9% Nickel steel, 12KW CO₂ Laser Welding machine is equipped with arc, wire uses H company to apply various parameters such as arc current, voltage, I-butt gap, travel speed, etc. to find suitable conditions for Laser arc welding and found that the best welding conditions were found at the speed of 12KW 250A, 25V, and 0.625m /min by conducting and finding laser welding quality evaluate according to UN ISO13919-1 Mechanical performance evaluation of Laser-arc hybrid welds showed a tensile strength of about 719 MPa. The impact strength of the weld portion of the laser arc hybrid shows a value of about 10 J higher than that of the FCAW weld at about 116 J.

Therefore, it was possible to obtain a sounder weldability than FCAW at the time of Co2 laser-GMA hybrid welds to 9% nickel steel, and additionally apply 1 pass in comparison with the one applied for 5 pass or more at FCAW welding. It can be considered that the improvement of productivity at the time of on-site application can be obtained.