A study on the adhesive joints for the secondary barrier of LNG cargo containment system

Abstract

The secondary barrier of CCS (Cryogenic Containment System) for LNG (Liquefied Natural Gas) carrier ships has two construction methods. One is the welding method and the other is adhesively joining method. The market and ship building companies prefer the latter to the former due to the short construction time and low cost. During the curing process of adhesive joints, a uniformly distributed pressure with precisely controlled temperature should be applied to the adhesive on insulation panels generally with some level difference between insulation panels for the reliable adhesive joint with nearly constant adhesive thickness and uniform degree of cure. In order to fulfill the required functions of a large heating pad, a flexible stainless steel foil heater supported by butyl rubber air pressure bag has been employed for the lower part of the hot pad system. The film type epoxy adhesive requires usually high curing temperature and long curing time, consequently the hot pad system should have a low thermal conductivity to reduce the heat dissipation through the heating pad. Also, high specific stiffness materials should be employed for the hot pad system because the area of the heating pad should be increased to reduce the number of heating pads required because the bonding area of secondary barrier of one CCS is about 10,000 m2. In order to decrease the weight of hot pad system and heat loss through the hot pad, the upper part of the hot pad system has been built with the composite sandwich panel composed of glass fiber epoxy composite face, polystyrene (PS) and polyvinyl chloride (PVC) foam core with low thermal conductivity. Therefore, the new light weight hot pad system was composed of the composite sandwich panel, butyl rubber air bag and stainless steel foil heater for light weight, uniform pressure and high thermal insulation efficiency. The size and configuration of the composite sandwich panel was designed with FE analysis and experimentally verifie...