Metallographic Investigation of Premature Failure of a Blast Furnace Copper Tuyere

The present work is a result of the detailed metallographic investigation carried out to ascertain the cause and mechanism of premature failure observed in a particular batch of water-cooled copper tuyeres of a recently commissioned blast furnace (BF) at JSW Steel Ltd., Dolvi Works. In the present case, the tuyere failures were observed to occur in the form of cracks selectively at specific location-the inner circumferential weld joining the inner wall to the tuyere nose. Improper welding/lack of fusion was identified as the underlying cause of this failure with a minor design flaw acting as the point of initiation of the same. Based on the observations, the following mechanism of failure was proposed: the design flaw (i.e., the notch between inner wall and tuyere nose) and the narrow clearance in between the base metals in the no fusion zone provides a pathway for ingress of cooling water into the weld joint. Sustained high pressure exerted by the water in a localized region leads to initiation of cracking which gets accentuated by the presence of welding defects such as a voids. The propagation of the crack then takes place along the weaker weld bead/base metal interface, eventually leading to crack opening on the surface. Thus, this work highlighted that in the absence of any identifiable correlations between the tuyere failures and abnormalities in BF operating conditions, the most critical factor affecting tuyere performance and service life is its design and quality of its weld joints.