With a purpose of identifying the failure mode and associating the ultimate strength of piping components against seismic integrity, many kinds of failure tests have been conducted for thick wall piping for light water reactors (LWRs). However, there are little failure test data on thin wall piping for sodium cooled fast reactors (SFRs). In this paper, a series of failure tests on thin wall elbows for SFRs is presented. Based on the tests, the failure mode of a thin wall piping component under seismic loads was identified to be fatigue. The safety margin included in the current design methodology was clarified quantitatively.