We conclude on the governing mechanism of burn-through and identify the area of highest risk for burn-through occurrence due to a specific combination of loading in this area. In order to investigate the mechanism of burn-through during in-service welding, an exploratory study combining both experiments and finite element simulations was presented. Combined with the theory of high-temperature failure, the initial position of burn-through and its mechanism were discussed. The results showed that burn-through was a kind of intergranular brittle rupture happened at the cooling stage of in-service welding. It started from the partially melted zone, and the cracks expanded along the weakened grain boundaries. When the cracks eventually penetrated to the inner wall, burn-through happened.

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