At 2.19 a.m., there was an explosion in the main chamber of the tundish and next to the chamber wall of strand 1 of the casting machine. A large amount of steel was ejected during the explosion. The ejection of steel damaged an oxygen pipe and a gas pipe in this area. The resulting fire in this area damaged a hydraulic line, which further intensified the fire. At the same time, the mould overflowed and the content of the tundish flowed onto the casting platform. This caused a second explosion, the cause of which is not known.
The hydraulic system automatically cut out because the minimum tank level had been reached. The emergency gate valves for oxygen and natural gas were closed.
The fire could then be extinguished by the plant fire service and the fire brigade. Smoke emissions from the roof of the steel works could be seen.
Liquid steel flows from a casting ladle into a tundish, which serves as a buffer vessel and to feed the steel to the individual strands of the casting machine. When the channel is sufficiently full, the stopper is opened and the steel flows into the casting mould.
The tundish must be preheated with the stopper and immersion nozzles to prevent the liquid crude steel from overcooling and solidifying when the tundish is filled for the first time. It takes between 2.0 and 3.0 hours to fully heat through the refractory lining and achieve a surface temperature of 1 100-1 300 °C.
At 2.06 a.m., the tundish had been heated and was used for casting in a continuous slab casting machine. At 02:07:41, the stopper of the tundish was opened and the casting process could be started.
The fire was extinguished by the plant fire service and the fire brigade.
Rebuilding damaged parts of the plant.
The exact cause of the damage cannot be established.
It is clear that there must have been water in the area of the splash core, which rapidly evaporated at the time of the explosion (volume increases 1 700 times when water turns into steam). It is not known for certain where this water came from. However, it is likely that it came from a wet gunning mix, possibly water vapour from the heating process that had condensed in the pores of the repair compound.
It would however appear that the water had been stored in the pores of the repair compound which was found under the splash core.
As the trailing steel referred to above came into contact with the stored water, there was suddenly enough energy available for evaporation and the explosion occurred approximately 12 minutes after casting.
- Design change to the tundish to prevent steel from trailing.
- Improvement of the tundish heating process to ensure that the refractory mass dries more evenly.
- Construction of a stair tower in the area behind the casting platform to create an additional escape route.
- Protective screen in front of the main media shut-off valves so that they can be operated from a protected area.
- Testing of additional leakage monitoring systems in the hydraulic system.
- Trials with alternative repair compounds.
