Abstract: One year after the commissioning of a cracking furnace in an enterprise, cracks and leakage were detected in the welded joints of the mixer during operation. After shutting down the furnace for inspection, five cracks were identified in the mixer. To accurately determine the causes of the cracks, comprehensive analyses including macroscopic morphology, metallographic examination, hardness testing, and chemical composition evaluation were conducted on the welds, integrating factors such as construction practices and operational parameters. The investigation concluded that thermal fatigue cracking in the dissimilar steel welded joints was the cause of the leakage. This paper proposed targeted solutions to address the root causes discussed above.

Key words: cracking furnace, weld crack, dissimilar steel, thermal fatigue