How We Solved the Problem of Scale Formation in Cooling Circuits: Practical Procedure and Prevention

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In one of the industrial plants, we encountered a recurring problem of hard scale formation in cooling circuits, which led to clogging of heat exchangers and a reduction in cooling efficiency by up to 30%. Analysis revealed that the cause was not only the high amount of dissolved salts but also an improperly selected combination of corrosion inhibitors and dispersing agents. The problem was further exacerbated by seasonal fluctuations in raw water quality. In this article, we describe how we proceeded with diagnostics, what water treatment adjustments we chose, and what preventive measures ensured long-term system stability without the need for frequent shutdowns.

Scale problem: How we identified it and why it occurred

Incrustations in cooling circuits represent a common operational problem that reduces heat transfer efficiency, increases energy demands, and can even lead to equipment damage. In our case, we noticed the issue during a routine inspection of heat exchangers, when we observed a gradual decline in cooling performance and an increase in pressure drop across the filters. Water sample analysis revealed a high content of calcium and magnesium ions, which precipitated as carbonate and sulfate deposits at elevated temperatures. Another important factor was the water pH, which ranged in the alkaline region (pH 8.5–9.2), promoting the precipitation of insoluble salts.

The formation of incrustations was caused by a combination of several factors: insufficient treatment of make-up water, the absence of crystallization inhibitors, and inadequate control of concentration cycles. The water used in the circuit came from a local source with high hardness (over 30 °dH) and was not pre-treated to remove dissolved salts. Additionally, operating temperatures in some parts of the circuit exceeded 60 °C, accelerating the formation of deposits. Without regular water quality monitoring and preventive measures, the problem gradually worsened.

Diagnostics and Analysis: Key Steps to Understanding the Problem

The first step toward resolving the issue was a detailed assessment of the cooling circuit’s condition. We conducted a comprehensive water analysis using standard methods, focusing on hardness, total dissolved solids (TDS), pH, alkalinity, and the concentration of specific ions (Ca²⁺, Mg²⁺, SO₄²⁻, HCO₃⁻). We also reviewed operational parameters such as inlet and outlet temperatures of the exchangers, flow rates, and pressure losses. The collected data were compared with historical records to identify trends and critical points where the most intense deposition occurred.

Subsequently, we conducted an inspection of the internal surfaces of the piping and heat exchangers using endoscopic equipment. The identified incrustations were collected and subjected to laboratory analysis, which confirmed their composition—primarily calcium carbonate (CaCO₃) and calcium sulfate (CaSO₄). This information allowed us to determine the optimal strategy for deposit removal and propose preventive measures. It was also important to assess the compatibility of the circuit materials with the planned chemical treatments to avoid damaging the equipment.

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Problem solution: Chemical and mechanical removal of incrustations

Based on the analysis, we selected a combination of chemical and mechanical cleaning. To dissolve carbonate deposits, we used an acidic cleaning agent based on organic acids (e.g., citric acid or amidosulfonic acid), which is gentle on the circuit materials while being effective at a pH of 2–3. Sulfate incrustations were addressed with a special chelating agent that binds calcium ions and prevents their re-precipitation. The chemical cleaning was carried out in a closed circuit for 12–24 hours at a controlled temperature (40–50 °C) and flow rate to ensure maximum efficiency.

After chemical cleaning, we proceeded with mechanical removal of the remaining deposits using a high-pressure water jet and rotary brushes. This step was essential, particularly in areas with a thick layer of incrustations where the chemical agent did not achieve sufficient penetration. Upon completion of the cleaning, we thoroughly flushed the circuit with demineralized water to remove any residual chemicals and loosened particles. Control water analysis and visual inspection confirmed the successful removal of incrustations and the restoration of the original flow profile of the piping.

Prevention: How to Prevent the Recurrence of Incrustations

To prevent the problem from recurring, we implemented a comprehensive preventive maintenance system. The foundation is regular monitoring of water quality, including measurements of hardness, pH, conductivity, and inhibitor concentration. Make-up water is now treated using a softener that reduces the content of calcium and magnesium ions to an acceptable level (below 5 °dH). To maintain water stability in the circuit, we use a combination of crystallization inhibitors and dispersing agents, which prevent salt precipitation and keep particles in suspension.

An important part of prevention is also the optimization of operational parameters. We reduced the maximum operating temperature to 55 °C and introduced regular circuit desludging to minimize the accumulation of undissolved substances. Operators are trained to recognize the first signs of incrustation formation, such as pressure changes or temperature differences. Furthermore, we implemented an automatic dosing system for inhibitors, which ensures their constant concentration in the circuit. Thanks to these measures, we have managed to keep the cooling circuit in optimal condition and significantly extend the intervals between necessary cleanings.

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Optimizing Inhibitor Dosage: How to Find the Right Balance

After removing incrustations from the cooling circuit, ensuring the long-term stability of the system is crucial. Corrosion and scale inhibitors are among the most effective tools, but their efficiency strongly depends on precise dosing. Too low a concentration will not provide sufficient protection, while overdosing can lead to undesirable side effects, such as foaming or the formation of new types of deposits. In our case, we started with the recommended dose of 5–10 mg/l but gradually adjusted it after analyzing water quality and operating conditions.

The optimization process involved regular water sampling and measurement of key parameters, such as pH, conductivity, calcium and magnesium content, and inhibitor concentration. We used standard colorimetric methods to determine residual inhibitor levels and monitored corrosion rates using metal coupons placed in the system. After three weeks, we found that the optimal dose for our circuit was 7.5 mg/l, ensuring effective protection without the risk of overdosing. This approach reduced chemical consumption by 15% while maintaining full protection against incrustations.

Impact of Operating Parameters on Incrustation Formation: Temperature, Flow Rate, and Water Quality

Incrustation formation is not solely caused by the chemical composition of water but also by the operating conditions of the cooling circuit. In our case, we identified key factors such as water temperature, flow rate, and fluctuations in makeup water quality. For example, in areas with lower flow rates (below 0.5 m/s), solid particles deposited more quickly, while in regions with temperatures above 50 °C, the crystallization rate of minerals, particularly calcium carbonate, increased.

To address these issues, we adjusted the operational parameters: we increased the minimum flow rate to 0.7 m/s to prevent sedimentation and implemented a continuous temperature monitoring system at critical points in the circuit. Additionally, we introduced pretreatment of makeup water using a softener, which reduced calcium and magnesium content by over 80%. These modifications led to a significant decrease in the rate of scale formation and extended the intervals between necessary system shutdowns for maintenance from the original 3 months to 8–10 months.

Economic Impact of the Solution: Costs vs. Savings and Return on Investment

Addressing scale issues in cooling circuits is not just a technical matter but also an economic one. In our case, we first quantified the direct costs associated with production shutdowns, increased energy consumption (due to reduced heat exchanger efficiency), and the costs of mechanical cleaning. We found that the annual losses caused by scale reached approximately 1.2 million CZK, with the largest shares being energy costs (45%) and losses due to downtime (35%).

The investment in preventive measures, including the installation of an automatic inhibitor dosing system, water pretreatment, and a monitoring system, amounted to roughly 850,000 CZK. Thanks to these measures, we managed to reduce annual maintenance and operating costs of the circuit by 70%, resulting in savings of approximately 840,000 CZK per year. The return on investment was thus achieved within the first 12 months. This example demonstrates that a systematic approach to solving scale issues can bring not only technical but also significant economic benefits.

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