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Description
Following the detection of several edge-welded bellows (EWBs) leaks in the Large Hadron Collider (LHC) beam intercepting devices, an investigation campaign was initiated to better understand the fracture behaviour of EWBs subjected to lateral stroke loading. The campaign led to dedicated experimental fatigue tests performed on multiple EWB geometries, originating from different production batches and tested at various cyclic amplitudes. The effects of bake-out and the evolution of leak-rate during cycling were also evaluated. Supported by metallographic analyses of membrane edge-weld fractures, the study revealed a wide spread in EWB fatigue life.
Experimental results, combined with real movement data from EWBs installed in the LHC, were used to estimate the remaining fatigue life of EWBs used in LHC collimators. This analysis enabled the optimisation of EWB motion profiles to extend service life, the identification of collimators at risk of developing leaks, and the development of mitigation strategies to minimise operational impact. The findings highlight the importance of high safety margins when designing critical components whose service life is governed by fatigue mechanisms.
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