Failure Analysis of Fractured Connection Bolts in the High-Pressure Valve Body of 22Cr12NiWMoV Alloy in a 1000 MW Ultra-Supercritical Unit

The failure analysis was conducted on the fractured connection bolts (specifications: M36 × 250 mm double-ended bolts, material of 22Cr12NiWMoV) of the high-pressure valve body in a 1000 MW ultra-supercritical electric power unit. Experimental analyses were performed using macroscopic observation, chemical composition analysis, metallographic examination, hardness testing, and mechanical property testing to identify the causes of fracture. The results indicated that the primary cause of the fractured connection bolts was improper installation leading to the initiation of micro-cracks at stress concentration points, subsequently resulting in fatigue failure under alternating stress.