Introduction — Understanding BOF Converter Splashing
Major splashing incidents in Basic Oxygen Furnace (BOF/LD) converter steel manufacturing represent one of the most serious safety hazards and production disruption risks in modern steel plants. A single large splashing event can cause severe equipment damage, personnel injury, and significant production losses. Understanding the root causes, recognizing early warning signs, and applying proper corrective and preventive measures are essential competencies for every converter operator and process engineer.
This guide covers the complete technical framework for managing converter splashing based on published slag splashing research and industry equipment case studies: root cause analysis across the BOF equipment technology, immediate response procedures, operational premonition recognition, and long-term prevention strategies.
Root Cause 1 — Hot Metal Charging Splashing
Mechanism
Splashing during hot metal charging in the Basic Oxygen Furnace process occurs exclusively when the previous heat’s slag has not been fully emptied from the converter. At the end of a blow, the steel carbon content is very low, while dissolved oxygen and slag oxidizability are both high. When fresh hot metal is charged, the large carbon content of the iron reacts violently with the high-oxygen slag, triggering an explosive carbon-oxygen reaction that ejects molten iron and slag from the converter mouth.
Consequences
Hot metal charging splashing can cause severe equipment damage to the converter mouth, hood, and surrounding infrastructure. More critically, it poses a direct threat to personnel safety. This type of incident requires immediate preventive measures before any charging operation.
Corrective Measures
Before charging hot metal, the converter must be thoroughly emptied of all residual slag. For plants using slag-retaining operations, strict pre-charging procedures must be followed: reduce slag temperature (add lime), reduce slag oxidizability (add reducing agents), and verify all parameters are within specification before charging. Related equipment: proper rolling mill rolls and graphite electrodes are critical consumables in supporting stable steelmaking operations downstream.
Root Cause 2 — Blowing Process Splashing from FeO Accumulation
Mechanism
The primary cause of splashing during the BOF steelmaking blowing process is the sudden participation of accumulated iron oxide (FeO) in the decarburization reaction. During normal operation, FeO gradually accumulates in the slag but does not immediately participate in the reaction. When FeO concentration reaches a critical threshold, it suddenly accelerates the decarburization rate, causing a rapid surge in CO gas generation that ejects slag and steel from the converter.
Triggering Conditions
Two main operating conditions trigger this mechanism: (1) prolonged extended low-intensity blowing (often due to oxygen lance ignition failure), and (2) oxygen lance failure to ignite properly. Both conditions allow FeO to accumulate without active decarburization, setting up the conditions for a sudden reactive surge.
Corrective measures: Monitor oxygen lance function continuously. If the lance fails to ignite, immediately investigate and restore proper ignition. Avoid prolonged low-intensity blowing periods. Numerical modeling studies on slag splashing in BOF show that FeO accumulation patterns can be predicted with proper monitoring.
Process Parameters That Influence Splashing Behavior
Oxygen Pressure & Lance Height
Insufficient oxygen pressure is effectively equivalent to excessive lance height — the oxidation reaction becomes less intense, FeO content rises in the slag, and once it exceeds a threshold, splashing occurs. Proper oxygen pressure ensures consistent decarburization rate and prevents FeO accumulation. According to BOF equipment technology, lance height optimization is one of the most cost-effective splashing prevention measures.
Bath Temperature
A sudden short-term drop in bath temperature slows the carbon-oxygen reaction rate, causing excessive FeO accumulation. When temperature rebounds above 1470°C, the stored FeO suddenly participates in an extremely intense carbon-oxygen reaction, generating large volumes of CO gas with enormous energy in an instant, triggering splashing.
Slag-Forming Material Addition Timing
If slag-forming materials (lime, dolomite, etc.) are added too late, the sudden temperature drop suppresses the carbon-oxygen reaction. When temperature recovers, the carbon-oxygen reaction erupts violently, generating a large CO gas surge and causing splashing. Slag materials should be added in small, multiple batches to avoid sudden temperature disturbances.
Converter Volume Ratio (Furnace Volume Ratio)
Converters with a large furnace volume ratio allow the CO gas from the carbon-oxygen reaction to dissipate more easily, reducing splashing tendency. Converters with a smaller volume ratio are more prone to splashing. The Basic Oxygen Furnace process at modern steel plants typically accounts for these differences in vessel design.
On-Site Treatment Methods for Active Splashing Incidents
Foam Slag Splashing — Early Stage
Low-temperature foam slag splashing typically occurs in the early blowing stage. At this point, temperatures are relatively low and the bath reaction is not yet intense. The operator can promptly lower the lance height to intensify the carbon-oxygen reaction, reduce FeO accumulation in the slag, and rapidly raise temperature to eliminate the splashing condition.
Foam Slag Splashing — Mid-Blow Stage
For foam slag splashing during mid-blow, raising the lance appropriately on one hand reduces the carbon oxidation reaction rate and bath temperature rise rate, and on the other hand the oxygen jet impact helps disperse the foam slag and facilitates CO gas escape. When bath temperature is very high, simultaneously raise the lance and add appropriate amounts of dolomite or lime to cool the bath and thicken the slag, which also helps suppress splashing.
Metal Splashing
Metal splashing (where molten steel rather than slag is ejected) can be addressed by raising the lance to increase FeO content in the slag, and adding appropriate slag conditioners. If the splashing cause is unclear, blind treatment must be avoided. In severe cases, stop the blow and dump the slag to reduce splashing-related losses.
Operating Precautions During Splashing Events
(1) Before hot metal charging, ensure the converter is completely emptied of residual slag. (2) Control bath temperature — do not allow early-stage temperature to be too low, or mid-stage temperature to be too high. (3) Control slag FeO content through lance height and oxygen flow rate adjustment. (4) Add the second batch of slag material at appropriate timing and in small, multiple additions. When major splashing events occur, downstream continuous casting operations — which rely on properly maintained copper mould tubes, are particularly vulnerable to slag carryover and quality disruption.
Premonition Recognition — Warning Signs Before Splashing
Flame Characteristics as Warning Indicators
Skilled converter operators can identify impending splashing by observing flame characteristics in real time:
Low-intensity premonition: When the flame appears dim and temperature fails to rise over an extended period, with small amounts of slag carried out with the flame, splashing is likely imminent. The operator should promptly lower the lance to accelerate heating and reduce FeO content. According to slag splashing research, early-stage FeO monitoring is critical for low-temperature premonition detection.
High-temperature premonition: When the flame appears bright and hard, projecting straight upward with slag carried out and an irritating sound, and the slag is not melting well, high-temperature splashing is likely. Per BOF equipment technology, the combination of elevated bath temperature and insufficient deslagging is the most common high-temperature splashing trigger.
Audio-Based Slag Monitoring System
Modern BOF converters equipped with audio-based slag monitoring can detect in-furnace slag conditions by analyzing acoustic emissions during the blow. When the monitored audio curve crosses the predefined warning threshold, operators receive an advance alert. Published slag splashing research confirms that audio-based prediction systems significantly reduce splashing incident rates when properly calibrated.
FAQ — Frequently Asked Questions
Q: What is the most dangerous type of converter splashing?
A: Hot metal charging splashing is the most dangerous type. The explosive carbon-oxygen reaction can eject large quantities of molten iron and slag at high velocity, posing severe safety risks to personnel and equipment. Prevention through proper slag emptying procedures is the only reliable solution.
Q: What is the primary chemical mechanism behind blowing process splashing?
A: The primary mechanism is sudden FeO accumulation followed by a rapid decarburization surge. When FeO builds up in the slag beyond a critical concentration and then suddenly participates in the carbon-oxygen reaction, the CO gas generation rate increases explosively, creating a pressure wave that ejects slag and steel from the converter.
Q: How does oxygen pressure affect splashing tendency?
A: Insufficient oxygen pressure (equivalent to excessive lance height) produces a weaker oxidation reaction, causing FeO to accumulate in the slag. When FeO concentration exceeds its threshold, it suddenly accelerates decarburization, triggering splashing. Maintaining proper oxygen pressure within specification ensures a controlled, steady-state carbon-oxygen reaction throughout the blow.
Q: Why does bath temperature fluctuation trigger splashing?
A: A sudden temperature drop slows the carbon-oxygen reaction rate, allowing FeO to accumulate. When temperature rebounds above ~1470°C, the accumulated FeO reacts explosively with carbon, generating large CO gas volumes instantaneously. This is why addition timing of slag materials — which cause temperature changes — must be carefully managed.
Q: What role does the furnace volume ratio play in splashing?
A: A larger furnace volume ratio provides more space for CO gas to dissipate, reducing splashing tendency. Converters with smaller volume ratios have less gas accommodation capacity, making them more susceptible to pressure buildup and splashing events during high-intensity decarburization periods.
Q: How does audio-based slag monitoring predict splashing?
A: The audio slag analyzer measures acoustic emissions from the converter. As slag foaming becomes excessive or FeO accumulation reaches dangerous levels, the acoustic signature changes characteristically. When the curve crosses a predefined warning threshold, operators receive an advance alert that allows preventive action before splashing occurs.
Q: Is lowering the lance always the correct response to splashing?
A: Not always. The appropriate response depends on the splashing type and blowing stage. For early-stage low-temperature foam slag, lowering the lance intensifies the reaction and can eliminate the condition. For mid-blow foam slag at high temperature, raising the lance is preferred to reduce reaction intensity and disperse foam.
Internal & External Reference Links
The following links provide additional technical context for the topics covered in this guide:
Internal: Rolling Mill Rolls Product Page
Internal: Copper Mould Tube Product Page
Internal: Graphite Electrode Classification
External: Basic Oxygen Furnace — Global Energy Monitor
External: Numerical Study: Slag Splashing in BOF (ResearchGate)
External: BOF Equipment Technology (SMGS)
Conclusion — Splashing Prevention Is a System Discipline
Converter splashing is not an unavoidable operational hazard — it is the result of identifiable root causes that can be managed, prevented, and properly treated when they occur. The Basic Oxygen Furnace process at modern integrated steel plants relies on rigorous process control at every stage. The key to eliminating splashing incidents lies not in reactive parameter adjustments during the blow, but in upstream process control: proper hot metal charging procedures, stable bath temperature management, controlled slag formation, and continuous monitoring of warning indicators.
Steel plants that maintain the lowest splashing incident rates share common characteristics: rigorous pre-charge slag emptying procedures, disciplined addition timing for slag-forming materials, well-maintained oxygen lance systems, and operators trained to recognize flame-based premonition signals. These are system disciplines, not individual operator heroics.
Investing in operator training, installing audio-based slag monitoring systems, and enforcing proper charging procedures are among the highest-ROI investments a steel plant can make in safety and productivity. For more on steel manufacturing best practices, explore our technical resources or contact our engineering team.
