In the field of industrial metallurgy, the Basic Oxygen Furnace (BOF) plays a crucial role in steelmaking. Its safe and stable operation is vital for both production efficiency and worker safety. However, BOF collapse accidents still occur from time to time, posing serious risks to plant operations and personnel.
This comprehensive article explores the types, causes, early warning signs, handling methods, and prevention strategies of BOF collapses — offering valuable guidance for steel industry professionals.
BOF collapse can be categorized into two main types:
Collapse of a newly lined BOF
Collapse due to patch repairs (gunning material failure)
For each campaign (furnace lifespan), the risk of collapse in a newly lined BOF is relatively low — typically only occurring once at most. This is because the lining materials and structural integrity are at their peak during initial use.
In contrast, the risk of collapse due to patching operations increases significantly over time. As the BOF endures high temperatures, chemical erosion, and mechanical stress, the refractory lining gradually wears down, requiring periodic repair using gunning materials.
The quality of the gunning mix, the skill level of the operators, and the post-repair drying and sintering processes all have a direct impact on the stability and lifespan of the patched lining.
That’s why patching operations are critical in BOF steelmaking. They go beyond mere surface repair — requiring expert knowledge and precise execution. The quality of these repairs determines the safety of BOF operations and steel production efficiency. Furnace operators must follow strict protocols to reduce the risk of collapse.
One of the most common causes of BOF collapse is failure to completely clean the residual slag inside the furnace before patching. If leftover molten slag remains, it can form a barrier layer between the old lining and the new gunning material.
This hinders bonding and dramatically weakens the structural integrity of the repair.
When the gunning material does not adhere properly to the old lining, it can easily detach during the next steelmaking cycle, increasing the risk of a collapse.
Strict cleaning procedures must be followed to ensure a strong bond and safe operation.
Another critical factor is the overuse of gunning material or insufficient sintering time. Both issues prevent the formation of a strong carbon-based skeleton in the repair zone.
If the gunning material is too thick, or the BOF surface is too smooth, the bonding will be weak, making the patch prone to thermal and mechanical damage during operation.
To avoid this, operators must:
Control the amount of patching material
Allow for adequate curing and sintering
Roughen the lining surface for better adhesion
The quality of magnesia-carbon bricks used in the BOF lining has a direct impact on furnace longevity. While mag-carbon bricks help reduce the chance of collapse during initial use, low-grade bricks are prone to spalling under high temperatures.
Severe spalling leads to structural weakness and eventual collapse.
To ensure long-term safety, it’s essential to:
Use high-quality refractory bricks
Ensure the materials have strong thermal shock resistance and anti-spalling properties
Timely detection of potential BOF collapse is crucial to prevent accidents and maintain furnace safety. Below are the common early warning signs operators should never ignore:
If black smoke is observed escaping from areas that were recently patched or bricked during the tilting process, it often signals an underlying stability issue. This could result from gas generation due to high-temperature reactions in the gunning material or lining bricks, indicating possible delamination or weakness in the furnace lining.
During furnace tilting, if the molten steel surface appears unusually agitated, this is a red flag. It may point to uneven temperature distribution, internal gas turbulence, or poor lining condition. These signs suggest that the furnace is not in a stable operational state and could be approaching failure.
After patching is completed, if dense black smoke gushes out from the furnace mouth during the first hot metal pour, it often indicates that a collapse has already occurred or is imminent. This is usually due to poor sintering or incomplete bonding of the gunning material. Even if a full collapse hasn’t occurred yet, the structural integrity is likely compromised and the risk remains high.
If, during the first few heats after relining, furnace gas pressure spikes accompanied by heavy smoke emissions, this is a serious warning sign. It strongly indicates lining instability or failure, posing immediate risks to safe steelmaking operations.
When a BOF collapse occurs, immediate response and strict safety measures are essential to protect personnel and minimize equipment loss.
In case a newly lined BOF collapses, take the following steps:
Quickly discharge molten steel into a prepared ladle to prevent overflow and secondary hazards.
Inspect the collapse site in detail to assess the extent of damage.
If the damage is extensive and lining integrity is compromised, the entire lining must be scrapped and rebuilt.
During this process, prioritize worker safety and loss minimization by adhering strictly to operational protocols.
Slag Removal:
Collapsed material often mixes with slag. After tapping, thoroughly clean the slag to prevent contamination of the next heat and to maintain furnace reliability and steel quality.
Adjust Metallurgical Process:
Since collapsed materials may increase non-metallic inclusions, adjust process parameters such as temperature, time, and charge ratio to ensure high steel purity and performance.
Re-patching the Lining:
The damaged areas must be repaired with high-performance gunning materials and precision workmanship. The goal is to restore structural integrity, extend the furnace’s service life, and ensure safe operation moving forward.
Always stand in safe zones with a clear escape route.
No one should be present in front of the furnace during slag tapping or steel pouring.
Conduct sampling and temperature measurement only when the BOF is tilted horizontally.
Stay alert to any abnormalities, and immediately retreat to the sides if danger is detected.
Strict adherence to these practices can greatly reduce personal risk and ensure smooth furnace operation.
For the first heat after a patching operation, safety must be prioritized:
Place visible warning signs around the furnace area.
All personnel must avoid danger zones and use alternative paths.
These precautions are essential not only for personal safety, but also for maintaining furnace integrity and process stability.
Proper furnace cleaning after each heat is essential. After tapping, all residual slag must be completely discharged. This often involves a 360-degree tilting operation to ensure that no debris remains.
A clean furnace surface improves patching performance, extends service life, and ensures a stable foundation for the next campaign. Precision cleaning is the first line of defense against collapse.
Always apply gunning material in a controlled and measured manner. During the initial patching stages (first and second applications), it’s crucial to follow the principle of “thin and even layering.”
Apply small amounts in multiple passes to ensure:
Better sintering quality
Stronger adhesion to the original lining
Lower risk of collapse due to detachment
This meticulous approach significantly enhances safety and operational efficiency.
Sintering time after patching is critical for lining stability. Adequate sintering allows the gunning material to bond firmly with the existing refractory surface.
This reduces the likelihood of spalling and collapse. Therefore, always allocate enough time for proper sintering before resuming steelmaking operations.
The first heat after patching requires special attention:
Use 100% hot metal, avoiding cold charge additions to prevent thermal shock
Control oxygen pressure and flow rate to avoid damaging the lining
Maintain a higher-than-normal refining temperature to enhance sintering
If possible, increase MgO content in the slag to improve bonding strength
These parameters help ensure a successful transition from repair to production.
Preventing collapse in a newly lined BOF starts with high-quality magnesia-carbon bricks and precise masonry:
Use bricks with superior thermal shock resistance
Ensure tight brick joints and strong interlocking
Monitor closely during early operations for any signs of spalling
Proper construction and quality materials create a solid foundation for safe steelmaking.
Before the first heat, a controlled preheating process using coke is essential to remove residual moisture and bring the lining to optimal temperature.
For the first three heats, use pure hot metal to ensure high internal temperature.
For the first 10 heats, implement continuous blowing to maintain thermal consistency, aiding the sintering of the new lining and enhancing longevity.
While BOF collapse accidents can be catastrophic, they are largely preventable with the right knowledge and practices.
By understanding the causes, warning signs, emergency response procedures, and preventive strategies, steelmaking professionals can significantly reduce the likelihood of such incidents.
In today’s evolving industrial landscape, we must also:
Explore new refractory materials and protection technologies
Improve the service life and reliability of BOF linings
Promote industry-wide knowledge sharing and collaboration
Safety is — and always will be — the top priority in metallurgical operations.
Ensuring the safe and efficient performance of core equipment like the BOF not only enhances productivity but also creates long-term value for the enterprise.
