Liquefied natural gas (LNG) transport carriers are exposed to a risk by the repeated bump in the LNG container during
the vessel traveling over the wave in ocean. The liquid inside the container, especially when it was not fully contained,
make a strong bump onto the insulation panel of the tank wall. The insulation panel consists of several layers of thick
polyurethane foam (PUF) to maintain the LNG below the cryogenic temperature, -162°C. Due to the repeated shock on
the PUF, a crack could be developed on the tank wall causing a tremendous disaster for LNG carriers. To prevent the
accidental crack on the tank, a continuous monitoring of the strain imposed on the PUF is recommended. In this work, a
fiber-optic Bragg grating was imbedded inside the PUF for monitoring the strain parallel to the impact direction. The
optical fiber sensor with a small diameter of 125 μm was suitable to be inserted in the PUF through a small hole drilled
after the PUF was cured. In-situ monitoring of the strain producing the change of Bragg reflection wavelength, a high
speed wavelength interrogation method was employed by using an arrayed waveguide grating. By dropping a heavy
mass on the PUF, we measured the strain imposed on the insulation panel.
The aim of this study is to investigate dynamic failure initiation and failure modes of insulation panels of LNG carriers. Insulation panels of LNG cargo tanks may include mechanical failures such as cracks as well as delaminations within the layers due to impact sloshing loads and fatigue loadings, and these failures cause a significant decrease of structural integrity. In this study, a structural health monitoring system, employing fiber optic sensors is developed for monitoring various failures that can occur in LNG insulation panels. Fiber optic sensors have the advantage of being embedded inside of insulation panels. The signal of embedded fiber optic sensors is used to calculate the strain of insulation panels and is processed by digital filtering to identify damage initiations. It has been observed that the presence of defects and delaminations produce noticeable changes in the strain measurement in a predictable manner. In addition, fiber optic sensors are used to measure static and dynamic strain variations of insulation panels with and without damage. It is expected that this study will be used as a fundamental study for the safety assessment of the LNG insulation panels.