The Japanese government accepted utilizing seismic isolation technology for nuclear power plants with the 2006 revision to the Nuclear Power Plant Seismic Design Review Guidance. The public-private sectors formed a team in 2010 to begin development of a seismically isolated nuclear power plant using the existing lead rubber bearing. This paper focuses on the main steam crossover piping. A low cycle ratcheting fatigue test based on the relative displacement and inertia load by earthquake between the buildings was performed to confirm the failure modes and ultimate strength (i.e. fatigue life) of pipe elbow. As a result, the ultimate strength under combined loads was sufficiently higher than the design criteria and it was confirmed the structural integrity of the main steam crossover piping.