# Experimental and Numerical Predictions of Cryogenic Leakages in Welded Steel Plates
## 1 Introduction  
The accelerated development of the world's economy and the growing concern regarding environmental pollution has led to a considerable increase in demand for liquefied natural gas (LNG) [1, 2, 3, 4]. To meet this demand, several types of LNG offshore plants and carriers have been developed that are now operating over the world [5, 6]. The primary part of ships and offshore structures are weld joints [7] due to their ease of use and dependability [8]. Additionally, they are also cost-effective. However, during the welding process, the considerable local heat input and subsequent rapid cooling result in residual stress formation and dimensional distortions [9, 10, 11, 12, 13]. Owing to the compression of the fusion zone in the cooling period, the residual stresses appear in the neighborhood of the weld region in the form of normally tensile stresses [14]. As a result, these post-weld tensile residual stresses frequently contribute to the brittle fracture [15] and premature failure of the zone near the weld region [16]. In addition, in ships and offshore structures carrying LNG, some regions endure cryogenic temperature due to the leakage of LNG from pipework connections like flanges and valves during loading or unloading activities [17]. Cryogenic thermal shock occurs when a sudden thermal load acts on a plate structure around a liquefied gas storage tank or a pipeline when leakage occurs. Due to cryogenic thermal shock, deformation can occur, and crack propagation can also occur in severe cases. Recently, due to the use of eco-friendly liquefied gas fuel in ships, the importanceof the effect of cryogenic thermal shock on the mechanical performance of ship structures has been increasing. Although the use of liquefied gas is becoming more common, there needs to be a greater understanding of the problems that may occur because of cryogenic thermal shock in plate structures that contain residual stress from the welding process. Of course, sudden deformation may not occur directly due to the leakage of cryogenic liquefied gas. After cryogenic liquefied gas leaks from the storage tank and pipeline, the surrounding plate does not experience abrupt deformation immediately. However, if the ambient temperature is reduced by continuous leakage, the cryogenic liquefied gas may be directly deposited on the plate, which leads to plate deformation and crack propagation. The welded structure subjected to cryogenic temperature is considerably sensitive to crack propagation. This is because the residual stresses created during the original manufacture welding with thermal stress may remain in the structure. They could result from the weld zone suffering cryogenic temperature [18]. Crack propagation phenomena of offshore structures that contain welded joints under a cryogenic temperature are complex and difficult to predict. To prevent the catastrophic disasters derived from these phenomena, it is vital that the crack growth is studied using cryogenic temperature assessment and fatigue analysis. Several studies have investigated the crack propagation phenomena of welding structures under a cryogenic environment. [PERSON] et al. [19] focused on the tensile properties and fracture behavior of the friction-stir-welded joints of nitrogen-strengthened high manganese steel at ultralow temperatures. They showed that to obtain a desirable cryogenic tensile temperature, the effects of post-weld heat treatment on the microstructures of the friction stir welding joints should also be examined in detail. [PERSON] and [PERSON] et al. [20] conducted a series of tensile tests and Charpy impact tests at eight distinct temperatures of 20, 0, \(-\)20, \(-\)40, \(-\)80, \(-\)120, \(-\)160, and \(-\)196 \({}^{\circ}\)C, to investigate the mechanical properties of S30408 base metal and welded joints at cryogenic temperatures. Their study showed that the welded joints have a higher yield stress than the base metal. By contrast, the base metal has the maximum ultimate tensile stress and Charpy absorbed energy.