Selecting the correct descaling pressure is one of the most misunderstood decisions in rolling mill engineering. Too often, mills assume that higher pressure automatically means better descaling. In reality, descaling pressure must be chosen based on steel grade, section size, mill configuration, scale characteristics, and downstream process sensitivity.
Hot steel descaling is not a one-pressure-fits-all application. A 150-bar system that performs well in one mill may fail completely in another. Conversely, a 400-bar system installed without justification may create more problems than it solves—thermal loss, excessive water consumption, and maintenance stress.
This article explains how to technically and practically select the right descaling pressure—150, 200, 300, or 400 bar—based on real rolling mill conditions, drawing on application experience from industry specialists such as PressureJet Systems Pvt. Ltd., known for engineering descaling systems across a wide range of steel plants.
Why Descaling Pressure Selection Matters?
Descaling pressure determines the impingement force of the water jet on the oxide scale. That force must be sufficient to:
- Break the oxide–metal bond
- Fracture the scale layer
- Lift and evacuate the scale before deformation
If pressure is too low, scale remains partially attached and enters the rolling stand.
If pressure is too high, unnecessary water impact leads to billet cooling, erosion of mechanical components, and higher operating costs.
Correct pressure selection is therefore a balance between:
- Scale adhesion strength
- Jet impact energy
- Thermal and mechanical limits of the process
Key Factors That Decide Descaling Pressure
Before comparing pressure levels, it is important to understand the variables that actually govern descaling effectiveness.
1. Steel Grade and Chemistry
- Mild steels form relatively soft, loosely bonded scale
- Alloy and micro-alloy steels form dense, adherent oxide layers
- Higher alloy content generally requires higher pressure
2. Section Size (Billet, Bloom, Slab)
- Smaller sections need concentrated jets
- Larger sections need higher total energy (pressure × flow)
3. Furnace Conditions
- Higher furnace temperatures and longer soaking times increase scale thickness
- Oxidizing furnace atmospheres produce harder scale
4. Mill Layout and Stand Position
- Descaling before roughing requires different energy than pre-finishing descaling
- Space constraints affect nozzle stand-off distance
Pressure selection must always be considered along with flow rate and nozzle design, not in isolation.
150 Bar Descaling: Where It Works—and Where It Doesn’t
Typical Applications
- Light descaling duties
- Mills rolling clean mild steel
- Applications with short furnace residence times
What 150 Bar Can Do
At 150 bar, water jets can remove loosely bonded surface scale, especially on mild steel billets that have not developed thick oxide layers. The impingement force is sufficient for breaking fragile outer scale but not for deep, adherent layers.
Limitations
- Ineffective on alloy steels
- Partial scale removal leads to scale re-embedding
- High risk of roll surface damage downstream
150 bar systems are often used in older or low-speed mills, but in modern rolling environments, they are increasingly inadequate as standalone descaling solutions.
200 Bar Descaling: The Practical Entry Point
Typical Applications
- Mild steel rolling mills
- Bar and section mills
- Mills with moderate furnace temperatures
Why 200 Bar Is Widely Used
At 200 bar, jet velocity and impingement force increase significantly compared to 150 bar. This pressure range allows:
- Consistent removal of most mild steel scale
- Better fracture of magnetite layers
- Acceptable performance without excessive water usage
For many general-purpose rolling mills, 200 bar represents the minimum practical descaling pressure for reliable operation.
Engineering Consideration
At this pressure, flow rate matching becomes critical. Without sufficient flow, even 200 bar can fail to evacuate broken scale effectively.
300 Bar Descaling: The Industry Workhorse
Typical Applications
- Alloy steel rolling
- TMT, bar, and structural mills
- Mills with long soaking furnaces
Why 300 Bar Is Often the Optimum
300 bar systems deliver jet velocities high enough to:
- Penetrate dense oxide layers
- Overcome strong oxide adhesion
- Remove scale in flakes rather than powder
This pressure level has proven particularly effective for:
- Alloy and micro-alloy steels
- Mills suffering from roll wear and surface defects
- Operations aiming for longer roll life and lower rejection rates
In real rolling mill conditions, well-engineered 300 bar descaling systems have consistently delivered:
- Improved surface quality
- Reduced burs and scale-related defects
- Noticeable improvement in roll life
Practical Insight
300 bar is often the best balance point—high enough for effective descaling, but still manageable in terms of pump life, piping stress, and maintenance.
400 Bar Descaling: When Is It Justified?
Typical Applications
- Very hard scale conditions
- Special alloy or stainless steel rolling
- Plate mills with extremely thick scale
What 400 Bar Brings
At 400 bar, impingement force is extremely high. This allows removal of:
- Very dense, strongly bonded oxide layers
- Scale formed during long, high-temperature soaking
Engineering Trade-Offs
While effective, 400 bar systems introduce challenges:
- Higher capital cost
- Increased stress on piping, valves, and nozzles
- Greater sensitivity to water quality and filtration
- Higher maintenance discipline required
400 bar should be selected only when lower pressures are demonstrably insufficient. Using it without need often increases cost without proportional benefit.
Pressure Alone Is Not Enough: The Flow Rate Reality
A critical mistake in descaling system selection is focusing only on pressure.
Descaling energy = Pressure × Flow × Jet Efficiency
- High pressure with low flow → scale cracks but stays on surface
- High flow with low pressure → billet cools but scale remains
This is why PressureJet systems are designed with:
- Billet-size-specific flow calculations
- Precision nozzle orifice sizing
- Stable volumetric efficiency under continuous duty
Pressure selection must always be validated against actual jet energy delivered at the steel surface.
The Role of Nozzles and Stand-Off Distance
At higher pressures, nozzle selection becomes increasingly critical:
- Incorrect spray angle wastes energy
- Excessive stand-off distance reduces impact force
- Eroded nozzles reduce effective pressure
Even a well-sized pump cannot compensate for poor nozzle engineering. This is why descaling performance often degrades over time if nozzle wear is not monitored.
Common Pressure Selection Mistakes in Rolling Mills
- Selecting pressure based only on competitor mills
- Ignoring billet size and steel chemistry
- Over-sizing pressure to “be safe”
- Underestimating flow requirements
- Neglecting long-term maintenance impact
Experienced mills select pressure based on process need, not marketing numbers.
Why PressureJet’s Approach Is Different?
PressureJet is widely respected because it approaches descaling pressure selection as an application engineering problem, not a catalogue choice.
Its systems are designed by:
- Studying steel grade and furnace conditions
- Matching pressure and flow to section size
- Engineering nozzles and headers as a system
- Ensuring long-term reliability and serviceability
This is why PressureJet descaling systems perform consistently across varied rolling mill environments.
Contact our experts today for a customized descaling solution.
- Visit: www.pressurejet.com
- Specialized Portal: www.steeldescaling.com