Ten years of our research and several experiences in fabricating IHI layered vessels led to the development of using high-strength low-alloy steel in the 80 kg/mm**2 class and putting layered vessels made of it into practical use. Especially, as part of research and development we studied a low-cycle fatigue test using a model vessel. As a result we confirmed the safety of IHI layered vesselsmade of high-strength low-alloy steel in the 80 kg/mm**2 class.