Experimental Study on Bead on Plate (BOP) Welding of 6 mm Thick 9% Nickel Steel by Fiber Laser Welding

Nine percent nickel steel has excellent properties in a cryogenic environment, so it has recently been used as a tank material for most LNG fuel-powered ships. However, 9% nickel steel causes arc deflection due to its tendency of magnetization during manual FCAW welding and the currently used filler metal is 10–25 times more expensive as a base metal compared to other materials, depending on manufacturers. Furthermore, the properties of its filler metal cause limitation in the welding position. To overcome these disadvantages, in this study, the tendency of penetration shape was analyzed through a fiber laser Bead on Plate (BOP) welding for 9% nickel steel with a thickness of 6 mm and a range of welding conditions for 1-pass laser butt welding of 6 mm thick 9% nickel steel with I-Groove were derived. Through this study, basic data capable of deriving optimal conditions for laser butt welding of 9% nickel steel with a thickness of 6 mm were obtained.

Fatigue and Fracture Behavior of Cryogenic Materials Applied to LNG Fuel Storage Tanks for Coastal Ships

The aim of this study is to investigate the applicability of automatic plasma arc welding (PAW) to cryogenic materials used in liquefied natural gas (LNG) fuel storage tanks based on experimental data. The mechanical properties of the materials were tested at room and cryogenic temperatures to investigate the fatigue and fracture performances of weld joints made by PAW. In addition, the influence of welding parameters on the welded joints such as material types and temperature were considered in this experimental study. Based on the results obtained by this experimental study, it was observed that the experimental results of all materials at room and cryogenic temperatures satisfied all the requirements of each mechanical test. Finally, we propose the experimental results of PAW that can be used in the structural design of LNG fuel storage tank applications.

Structural Integrity Assessment of Independent Type-C Cylindrical Tanks Using Finite Element Analysis: Comparative Study Using Stainless Steel and Aluminum Alloy

The International Maritime Organization stipulates that greenhouse gas emissions from ships should be reduced by at least 50% relative to the amount observed in 2008. Consequently, the demand for liquefied natural gas (LNG)-fueled ships has increased significantly. Therefore, an independent type-C cylindrical tank, which is typically applied as an LNG fuel tank, should be investigated. In this study, structural integrity assessments using finite element analysis are performed on C-type LNG fuel tanks for a sea-cleaning vessel. In addition, the applicability of stainless steel and aluminum alloys is evaluated for LNG tank construction. Structural analyses and fatigue limit evaluations, including heat transfer analyses for the tank based on IGC code requirements, are performed, and the results are compared. The results of this study are expected to facilitate the selection of materials used for independent type-C tanks.

Numerical Study on the Tank Heel Determination Using Smoothed Particle Hydrodynamics

Tank heel minimization is a significant issue in the design of LNG fuel tanks because it is associated with stable suction pump operation and thermal shock requirements during LNG bunkering. This study examined how the LNG tank heel is minimized, maintaining a suction pump fully submerged in LNG during dynamic vessel motion. The study assumed two LNG fuel tanks mounted on the forward deck of a 50,000 deadweight class oil product carrier. Information on the dimensions and shape of the LNG fuel tank was determined from Wartsila’s brochure, and the specifications of Vanzetti’s suction pump were referred to. The LNG fuel tank and LNG heel were modeled as rigid elements and hydrodynamically smoothed-particles, respectively. The number of particles could be determined by performing even keel analyzes by adding or subtracting particles until the target head was satisfied under the gravity load. To simulate the motion of the LNG fuel tank, the pitch and roll periods and amplitudes of the ship were calculated using the DNV classification rules. Visual observations of the dynamic flow during the pitch and roll motions with respect to the ship’s center of mass showed that the roll motion was more critical from the viewpoint of the LNG heel than the pitch motion. After performing the simulations for three cycles of roll and pitch motions, the suction pump submergence was reviewed in the last cycle. Under the conditions assumed in this study, a filling ratio of 15% was determined as the minimum LNG tank heel. Although the LNG heel has customarily been determined, the LNG heel needs to be determined through hydrodynamic analyses of each vessel because it depends on the shape of the fuel tank and the vessel motion characteristics.