Hydrogenation reactor is the core equipment of various hydrogenation units or hydrogenation processes. Because of the harsh service environment, the difficult manufacturing technology, the high requirements and the expensive cost, the safety of hydrogenation reactor is a very important problem. The outlet flange of hydrogenation reactor in a petrochemical company suddenly cracked after several years of use. The maximum depth of the crack from the sealing surface to the depth of the flange is 165 mm, the circumferential cracking range is about 130 degrees. The crack is in a circumferential and curved line along the sealing groove, and has small bifurcations at the tip. In order to ensure the safety of equipment operation and prevent the recurrence of this kind of accident, the causes of flange failure were systematically analyzed and the preventive measures are formulated. This paper reviewed the manufacturing quality data of the failed flange, and carried out a series of tests and analyses, such as macroscopic inspection, penetration testing, ultrasonic testing, mechanical properties test, chemical composition analysis, metallographic structure analysis, finite element stress check and so on. Combined with the use environment and the operation parameters of the flange, we preliminarily analyze that the cause of flange cracking may be manufacturing defects. In order to avoid the failure of flanges again, it is recommended that the flanges of the same batch should be tested one by one to ensure the safe and stable operation of the device.

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