THERMAL BUCKLING AND PROGRESSIVE OVALIZATION OF PIPES - EXPERIENCES AT THE TTS SODIUM TEST FACILITY AND THEIR ANALYSIS

Two remarkable thermally induced deformation mechanisms of pipes which may have serious effects on structural integrity, thermal buckling an d progressive ovalization, were observed on the horizontal piping of t he sodium test facility, called TTS, with which cyclic thermal transie nt tests of structures had been conducted. The thermal buckling, which was caused by thermal stratification, occurred at a circumferentially welded region of the pipe where a noticeable geometrical imperfection existed. The buckling was analyzed comprehensively for this pipe, usi ng both the finite element method and a simplified method based on Gel lin's analysis results. The predictions were reasonable and gave confi dence in accounting for the sodium leakage encountered at the TTS. It was also demonstrated by the finite element analyses that the progress ive ovalization of the pipe cross-section from a circular to a downwar d triangular shape can be caused by cyclic thermal stratification unde r the existence of cover gas in the pipe.