Case Study: 32% HCl for Steel Rust Removal — 15% Cost Savings
1. Background
The Vietnamese steel industry is experiencing strong growth, driving significant demand for pickling chemicals used on hot-rolled coil (HRC) prior to cold rolling or galvanizing. The pickling process is an essential step: the layer of iron oxide (rust) that forms on the steel surface during hot rolling at high temperatures must be completely removed before the steel can undergo further processing. HCl is the most commonly used pickling agent due to its fast reaction rate, lower corrosion of the steel substrate compared to H₂SO₄, and the ability to regenerate spent acid.
A steel mill in the Bà Rịa–Vũng Tàu region has a rust removal capacity of 30,000 metric tons of steel per year and uses HCl (hydrochloric acid) as its primary rust removal agent. The mill’s descaling line is a continuous pickling line, where steel coils are pulled through a series of pickling tanks at a speed of 80–120 m/min, requiring very precise control of acid concentration and temperature.
For many years, the plant used 20% HCl purchased from a local supplier. As production increased and cost-competition pressures grew, the plant’s management decided to review all chemical costs—and discovered that the 20% HCl was quietly “eating into” the plant’s profits more than they realized.
2. The Problem
A detailed analysis revealed that the use of 20% HCl was causing significant losses:
| Issue | Details | Consequences |
|---|---|---|
| Low concentration, long cleaning time | 20% HCl requires 25–30 minutes per batch to achieve the required cleanliness | Reduced production line capacity, production bottlenecks |
| High chemical consumption | ~18 kg of 20% HCl per metric ton of steel | Total consumption of ~540 metric tons of 20% HCl per year |
| High transportation costs | 20% HCl contains 80% water — transportation consists mainly of… water | 25% increase in logistics costs |
| Suboptimal pickling tank temperature | 20% HCl struggles to reach the operating temperature of 60–70°C, requiring additional heating | Auxiliary energy consumption |
| Waste acid tank management | Large volume of waste acid; FeCl₂ concentration in the tank rises rapidly | High tank replacement frequency; neutralization costs |
The plant estimates the descaling cost at ~420,000 VND/metric ton of steel, of which chemicals account for 35% (147,000 VND/metric ton)—15–20% higher than the industry average.
3. Solution
Loc Thien Chemicals proposes switching to 32% HCl (higher concentration, diluted on-site) along with optimizing the descaling process:
Technical Solution:
- Use 32% HCl as the base material — the high concentration reduces transport volume; dilute it at a 1:1 ratio with recycled water from the treatment system to achieve a working concentration of ~16–18%
- Install an automatic dilution system — use a metering pump for 32% HCl + water, and precisely control the concentration via an online density sensor
- Optimize the cleaning tank temperature — 32% HCl releases heat during dilution; utilize this reaction heat to raise the tank temperature to 65–70°C without external heating
- Acid recirculation — the bleaching tank is designed for partial recirculation, extending the solution’s service life and reducing the frequency of acid replacement
| Technical Specifications | 20% HCl (old) | 32% HCl (new) |
|---|---|---|
| Purchase concentration | 20% | 32% |
| Working concentration | 18–20% | 16–18% (after dilution) |
| Pickling tank temperature | 50–55°C (heating required) | 65–70°C (utilizes dilution heat) |
| Pickling time per batch | 28 minutes | 18 minutes |
| HCl consumption (equivalent to 100%) (kg/metric ton of steel) | 3.6 | 3.2 |
4. Results
After 4 months of implementation, the plant reported:
| Parameter | 20% HCl (old) | 32% HCl (new) | Improvement |
|---|---|---|---|
| Actual HCl consumption (metric tons/year) | 540 | 300 | ↓ 44% |
| Bleaching time (minutes/batch) | 28 | 18 | ↓ 36% |
| Production line capacity (metric tons/day) | 85 | 105 | ↑ 23% |
| Chemical costs (VND/metric ton of steel) | 147,000 | 110,000 | ↓ 25% |
| Logistics costs (million VND/year) | 420 | 280 | ↓ 33% |
| Total descaling cost (VND/metric ton of steel) | 420,000 | 357,000 | ↓ 15% |
- Total descaling cost decreased by 15%, saving ~1.89 billion VND/year
- Production line efficiency increased by 23% thanks to shorter descaling time
- Steel surface quality after descaling improved — uniform surface roughness, no remaining rust streaks
- Reduced the amount of HCl requiring transport by 44%, significantly cutting CO2 emissions from logistics
5. Lessons Learned
- Purchasing high-concentration HCl and diluting it on-site is always more cost-effective than buying pre-diluted, low-concentration HCl — saving on both chemical and transportation costs. For the same 100% HCl content, the price per kilogram of 32% HCl is always about 10–15% lower than that of 20% HCl due to reduced packaging and water transportation costs
- Utilize the heat of reaction when diluting HCl — the process of diluting HCl is a strongly exothermic reaction that can raise the solution’s temperature by 15–20°C. Utilizing this heat significantly reduces the heating energy required for the neutralization tank, a dual benefit that is often overlooked
- Automated dilution system with a density sensor — a one-time investment (approximately 150–250 million VND) offers long-term benefits in terms of accuracy, safety, and chemical savings. An online specific gravity sensor allows concentration control with an error margin of less than ±0.5%.
- Recirculating waste acid extends the service life of the pickling tank — instead of replacing the entire acid batch when FeCl₂ concentrations become too high, a partial recirculation system combined with supplemental 32% HCl helps maintain stable pickling performance and reduces the volume of waste acid requiring neutralization by 30–40%
🔰 Do you need high-quality 32% HCl for your steel descaling line?
Loc Thien Chemicals supplies industrial-grade 32% HCl with fast delivery from 6 warehouses nationwide.
📞 Hotline: 0979 891 929
🏭 Warehouses: Ho Chi Minh City, Ba Ria-Vung Tau, Dong Nai, Da Nang, Can Tho, Bac Ninh