Fatigue performance test of metal bellows expansion joint for high-temperature helium pipeline in gas-cooled micro-reactor

The main loop of the gas-cooled micro-reactor adopts helium as the working medium. Considering the compact structure and safety, the main pipeline uses a double-layer pipeline design, and the main pipeline thermal displacement compensation is achieved through series-connected Inconel625Gr alloy bellows. Based on the design parameters (axial displacement of 40 mm, design temperature of 550℃, fatigue life of >1000 cycles), this paper establishes a fatigue testing system under high-temperature helium 550℃ environment, simulating actual operating conditions (0.1 MPa pressure, 550℃ temperature), and conducts fatigue cycle testing under axial displacement conditions of ±20 mm. The test results show that both specimens completed 2050 cycles without leakage, cracks, or failure phenomena, and both visual inspection and airtightness tests after the test were qualified. The study verified the reliability of the bellows design and provided data support for the engineering application of high-temperature helium pipelines.