A Brief Discussion on the Main Causes of Refractory Wear at the Converter Tapping Hole

The converter tapping port is an important passage for tapping steel from the converter. During tapping, molten steel is poured through the tapping port into the ladle, as shown in Figure 1. When the tapping port bricks are partially damaged, molten steel passes through the bricks to the shell area, causing the shell steel plate at the flange and shell connection to melt through, resulting in slag and steel leakage. After steel penetration occurs, the remaining molten steel needs to be mixed with a large amount of lime for slag adjustment, then the remaining molten steel in the furnace is poured into the ladle through the large furnace mouth to prevent extensive shell damage. Since there is no slag-blocking measure at the large furnace mouth tapping, slag and steel flow out together, causing severe phosphorus return during slag tapping, which easily leads to high phosphorus in the final product and furnace mouth burn-through.

After steel penetration occurs at the converter tapping port, inspection of the converter's tapping port passage reveals obvious melting damage to the tapping port bricks. The location of steel penetration (or leakage) is shown in Figure 2.

As seen in Figure 2, the specific location of steel penetration is about 200mm west from the inner side of the tapping port. The overall refractory bricks of the tapping port have some cracks, and molten steel leaks through these cracks. The number of steel penetrations at the tapping port occurred between 49 and 105 times.
Based on the analysis of the above steel penetration accident at the converter tapping port, the main causes of steel penetration at the converter tapping port are as follows:
1. Tapping port angle
The tapping port angle of the converter is usually designed between 0° and 15°. Most domestic steel plants use a 0° tapping port design, while the 200-ton converter in Xichang uses a 10° tapping port design. The 10° angle design helps shorten the ladle car travel during tapping and improves tapping efficiency. However, during tapping, molten steel cannot freely fall vertically; it moves inclinedly within the 10° angled channel, experiencing a force directed backward toward the furnace, significantly increasing tapping friction and causing increased stress on the tapping port. The vortex formed by the rotating steel flow during tapping accelerates refractory erosion, easily causing local pits in the tapping port channel. The angle design of the tapping port is difficult to improve and can only be compensated by other measures.

2. Seat brick damage
The seat bricks near the furnace interior of the tapping port show a thickness trend of "thinner at the bottom and thicker at the top," making the inner side of the converter a weak point. As the number of smelting heats increases, the converter's furnace refractory is gradually eroded, and the large rear surface erosion causes the seat brick thickness to gradually thin. In the mid to late furnace life, due to long-term molten steel scouring, the thinnest part of the rear large surface refractory is only 300~400mm thick. At this time, the seat brick thickness inside the tapping port is only about 100mm. When subjected to external impact during tapping port replacement, the seat bricks easily crack, reducing their erosion resistance. To achieve a long furnace life, slag splashing and slag hanging spraying repair methods are used to increase the thickness of the tapping port and rear large surface to 700~800mm. At this point, the converter tapping port seat bricks consist of bonded slag layers and repair material filling layers, whose erosion resistance is significantly lower than that of seat bricks.
Damage to the seat bricks is the fundamental cause of steel penetration at the tapping port. The damaged tapping port brick lining has an incomplete shape and a high-risk state of internal cracks. When maintenance is insufficient, high-temperature molten steel seeps out through the seat brick gaps. When this molten steel meets oxidized steel in the gaps, it reacts with magnesia-carbon bricks, accelerating erosion, causing the seat bricks to become friable, perforated, and damaged, as shown in Figure 3.

3. Void water hammer effect
During tapping, bubbles adsorbed on the rough refractory surface rise, causing molten steel to fill the opposite direction of bubble ascent, generating impact forces that scour the refractory material. This phenomenon is called the void water hammer effect. The water hammer effect of molten steel significantly impacts steel penetration at the tapping port. Once steel penetration occurs, the seat bricks are basically damaged, and the risk of further penetration increases significantly.
A schematic of the damaged tapping port brick lining is shown in Figure 4. From the post-demolition anatomy of the tapping port area, a gap channel has formed between the flange and shell connection to the tapping passage. After steel penetration, the hole was re-bored and filled with bonding material, compacted with sprayed repair material, and finally sprayed with slurry to form a dense bonding layer in the originally burned-through tapping passage. However, the bonding layer is inferior to magnesia-carbon bricks, and the seat bricks remain full of holes. When the internal seat bricks of the tapping port are poorly maintained or gaps form between the tapping port and seat bricks, the water hammer effect at the gap is significant, making steel leakage very likely to recur.

4. Spraying process and repair material quality
After the tapping port replacement, the gaps between the furnace lining bricks, the outer seat bricks of the tapping port, and the tapping port bricks need to be filled with repair material. The refractory material and water are mixed and sprayed together into the gaps using a spray gun. The spraying process parameters such as viscosity and spray angle greatly affect the density of the gap filling, thereby significantly influencing the number of tapping cycles.

The repair material used for filling joints, under the residual heat of the steelmaking converter (>1000°C), undergoes water boiling and evaporation, and after a period of sintering, forms a dense sintered layer to meet the needs of molten steel smelting and scouring. Quality indicators such as MgO content in the refractory and the erosion resistance of the sintered material also significantly affect the number of tapping cycles at the tapping port.