Abstract
The International Maritime Organization (IMO) is tightening regulations to reduce greenhouse gas emissions from ship operations. As a result, the number of vessels using liquefied natural gas (LNG) as fuel has increased rapidly. At this time, ASTM A553-1 (9% nickel steel) is being used as a tank material for storing LNG as fuel because of its higher strength than other cryogenic materials. Currently, shipyards are manufacturing LNG fuel tanks using the flux cored arc welding (FCAW) method using 9% nickel steel material. However, fabrication through FCAW has two drawbacks. The first is that the welding filler is 20 times higher cost than the base metal, and the second is that the total production cost increases because the thickness of the tank increases due to the strength drop near the heat affected zone (HAZ) after welding. The laser welding of A553-1, which does not require additional welding fillers and has no yield and tensile strength reduction in the HAZ, can overcome the drawbacks of FCAW and ensure price competitiveness. Through the study of Part I (penetration shape by bead on plate), the penetration characteristics of laser welding were studied and the optimized welding conditions of 15 mm thickness of A553-1 were obtained. With optimized conditions, butt laser welding tests of A553-1 material were conducted in this study, and mechanical properties, which are tensile/yield strength, hardness, bending strength, and impact property on the cryogenic temperature of the weld zone after laser beam welding, are confirmed by comparing those after FCAW. In the case of tensile/yield strength, hardness, and bending strength at weldment, the values of laser beam welding (LBW) are higher than those of FCAW, and the value of the impact test after FCAW is higher than that of LBW, but both values are satisfied in ASTM. Through these conclusions, it is confirmed that there are no mechanical property problems in replacing the existing FCAW with LBW.
Highlights
The shipbuilding industry has been moving rapidly in response to environmental issues
By using liquefied natural gas (LNG) as fuel, CO2 emission is reduced by about 20%, nitrogen oxides (NOx) by 80%, sulfur oxides (SOx) by 90%, and particulate matter (PM) by 99% compared to when using heavy fuel oil (HFO), which is the existing marine fuel, and it is possible to satisfy the standards of Tier III [1,2,3,4]
(1) Yield strength and tensile strength: Both values of yield strength and tensile strength from performed with no filler material, which has the effect of reducing the microstructure during welding
Summary
The shipbuilding industry has been moving rapidly in response to environmental issues. (2) Inpenetration the case of depth the laser welding of A553-1, as theweld welding speed increased, the bead height, be width, and were reduced. Based on the results of the Part I study, an optimized 2-pass laser butt welding condition of 15 mm. Based on the results of the Part I study, an optimized 2-pass laser butt welding condition of 15 thickness of A553-1, predicted to be most used in LNG fuel propulsion tanks, was obtained. This is the mm thickness of A553-1, predicted to be most used in LNG fuel propulsion tanks, was obtained.
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