Effect of Moisture Content on the Structural Integrity of the Bottom Plywood in the LNG Cargo Containment System

Plywood is an orthotropic material made from wood. Due to its high strength and durability, it is used in the insulation systems of LNG cargo containment system, both at the top and bottom. In the actual operational environment of LNG cargo containment system, dry nitrogen with a dew point below –45 ℃ is purged at atmospheric pressure to inert the insulation system and remove moisture. During this process, the moisture content of plywood continually decreases. Wood materials, such as plywood, exhibit varying mechanical properties depending on moisture content, with reduced elongation and bending strength at lower moisture levels. In particular, the bottom plywood for insulation panel is vulnerable to shear failure due to sloshing impact loads at the mastic bonding area; thus, sufficient structural strength must be ensured. Therefore, evaluating mechanical performance and failure behavior at low moisture content levels is essential. This study proposed a panel testing method for evaluating the deformation and failure behavior of bottom plywood. Based on experimental results considering actual operational environments, it was observed that dried plywood exhibits increased susceptibility to failure. In particular, plywood placed parallel to the mastic bonding direction presents a significantly higher risk of structural failure.