Experimental and analytical study of creep cracks damage in high temperature sodium plant branch connections

Abstract The paper describes the experimental investigation of the structural integrity of branch connections operating in high temperature environments and both the relevant technological tests and the structural analysis design verification of the most critical zones. The paper begins with a brief description of the operating conditions of the ESPRESSO sodium plant. The structural integrity problems of some ‘T” branch connections in the sodium plant are then presented. During a thermal cycling test a hydraulic packing loss is pointed out by a small amount of sodium leakage. Radiographic examinations revealed both a crack in the entire thickness and second partial crack in another branch connection. A series of technological tests was executed in which the presence of the cracks clearly indicated creep damage. To clarify the structural reliability of the most critical components a theoretical analysis of creep damage for the two branch connections was performed in detail. For this aim both elastic and inelastic analyses were carried out, with the general purpose CASTEM system developed at CEA Saclay, to determine the stress fields of the two components. The study tried to take into account the effects of the residual welding stresses in the creep regime. The main conclusions concerning the applications of the different existing rules are presented and compared.