How to Choose Chemicals for Scaling and Corrosion in Cooling Water Systems

Why Scaling and Corrosion Are the Two Biggest Threats to Cooling Water Systems

In industrial cooling water systems, scaling and corrosion are not just maintenance problems — they are direct causes of production downtime, equipment failure, and rising operational costs. Scale deposits act as thermal insulation on heat transfer surfaces: even a 1 mm layer of calcium carbonate scale can reduce heat exchange efficiency by up to 10%, forcing equipment to work harder and consume more energy. Corrosion, on the other hand, silently degrades metal pipes, heat exchangers, and cooling towers, leading to leaks and unplanned shutdowns that can cost tens of thousands of dollars per incident.

Both problems share the same root cause: unmanaged water chemistry. As water circulates and evaporates, dissolved minerals concentrate, pH shifts, and microbial activity accelerates fouling. Without a targeted chemical treatment program, every industrial cooling system — whether in a power plant, steel mill, petrochemical facility, or pharmaceutical plant — is vulnerable to the same cascade of damage.

The good news is that both scaling and corrosion are highly controllable. But control requires choosing the right chemicals for your specific system — and that decision is far from one-size-fits-all.

Understanding the Different Types of Scale and Corrosion Inhibitors

Effective chemical treatment starts with understanding what each product class does and where it fits. The main categories used in industrial circulating cooling water systems include:

Scale Inhibitors and Dispersants

Scale inhibitors work by interfering with the crystal growth of mineral deposits — primarily calcium carbonate, calcium sulfate, and silica — on metal surfaces. Dispersants keep suspended particles from agglomerating and settling into hard deposits. In many systems, a combined scale inhibitor and dispersant is used to handle both mechanisms simultaneously. Typical dosage for circulating water treatment ranges from 15 to 40 ppm with continuous addition, though this must always be calibrated against actual water quality analysis.

Corrosion Inhibitors

Corrosion inhibitors form a protective film on metal surfaces, reducing the electrochemical reactions that cause material degradation. Formulations vary significantly depending on the metals present in the system — carbon steel, copper alloys, and stainless steel each respond differently to inhibitor chemistry. Dosage typically ranges from 5 to 15 ppm with continuous feeding, adjusted based on the system's water quality parameters.

Combined Corrosion and Scale Inhibitors

For most open recirculating systems, a multifunctional product that addresses both corrosion and scaling simultaneously is the most practical and cost-effective solution. These products are especially suited to systems where simplified chemical management is a priority, or where space for multiple dosing points is limited.

Closed-Loop Corrosion Inhibitors

Closed-loop systems — such as those used in secondary cooling circuits or HVAC chiller loops — require dedicated corrosion inhibitor formulations. Because there is no blowdown and water is continuously recirculated, inhibitor concentration must be carefully maintained, typically in the range of 30 to 100 ppm, and replenished only to compensate for system losses.

Phosphorus-Free vs. Low-Phosphorus: A Decision Driven by Regulations and Water Quality

Historically, phosphate-based corrosion and scale inhibitors dominated the market due to their proven performance and relatively low cost. However, tightening environmental discharge regulations — particularly limits on total phosphorus in wastewater — have fundamentally shifted the selection criteria for many industries.

Today, the choice between phosphorus-free and low-phosphorus inhibitors is one of the most consequential decisions in system design. Here is a direct comparison:

The shift toward phosphorus-free formulations is accelerating across industries. If your facility operates under strict effluent phosphorus limits or is located in an environmentally sensitive area, selecting a phosphorus-free corrosion and scale inhibitor is no longer optional — it is the baseline requirement. For systems with more flexibility, low-phosphorus formulations remain a viable and often cost-competitive choice.

Four Key Factors That Determine the Right Chemical Selection

No chemical program can be designed in isolation from the system it protects. The following four factors must be evaluated before finalizing any treatment approach:

1. Water Quality Analysis

This is the non-negotiable starting point. The hardness, alkalinity, chloride content, sulfate levels, pH, and total dissolved solids of both makeup water and circulating water directly determine the scaling tendency and corrosion risk of the system. The Langelier Saturation Index (LSI) or Ryznar Stability Index (RSI) are commonly used to quantify calcium carbonate scaling potential and should inform inhibitor selection and dosage before any chemicals are purchased.

2. System Metallurgy

The metals in your heat exchangers, pipes, and cooling towers are not all the same. Carbon steel, galvanized steel, copper, and cupronickel alloys each have different corrosion mechanisms and respond differently to inhibitor chemistry. A formulation optimized for a steel system may be incompatible with copper components, causing accelerated rather than reduced corrosion. Always confirm the metallurgy of the entire wetted circuit before selecting a corrosion inhibitor.

3. Cycles of Concentration

As water evaporates from an open recirculating system, dissolved minerals concentrate. The number of times they concentrate relative to makeup water is called the cycles of concentration (CoC). Higher CoC means better water efficiency but higher scaling and corrosion risk. Your chemical program — both product selection and dosage — must be designed around the target CoC of your system, which typically ranges from 3 to 6 in industrial applications.

4. Environmental Discharge Requirements

Blowdown from cooling systems is regulated in most jurisdictions. Phosphorus limits, heavy metal restrictions, and COD (chemical oxygen demand) standards all constrain which chemical formulations can be used legally. Understanding local discharge regulations before selecting any treatment program is essential to avoid compliance risk and potential penalties.

Dosing Methods: Continuous vs. Shock Dosing

Beyond product selection, the method of chemical addition has a significant impact on treatment effectiveness and operating cost.

Continuous dosing is used for corrosion inhibitors, scale inhibitors, and dispersants. These products need to maintain a stable residual concentration in the circulating water at all times to provide consistent protection. Dosing pumps calibrated to feed at a rate proportional to makeup water flow are the standard approach.

Shock dosing is the standard method for biocides and algaecides, including both oxidizing types (such as active bromine) and non-oxidizing types. Intermittent high-concentration doses are more effective at controlling microbial populations than low continuous additions, which can promote resistance over time. A typical program alternates oxidizing and non-oxidizing biocides to prevent adaptive resistance, with non-oxidizing agents added 1–2 times per month at 50–100 mg/L.

For systems experiencing existing biofilm or heavy fouling, a stripping agent may be needed as a first step before the routine treatment program can deliver its full effectiveness. Our non-oxidizing sterilizing stripping agent is specifically formulated to break down and remove established biofilm in circulating water systems before regular maintenance dosing resumes.

Industry-Specific Considerations: One System Does Not Fit All

While the general principles of scaling and corrosion control apply across industries, the specific demands of each sector shape the treatment approach significantly:

• Power plants operating large-capacity units — including 1,000 MW class — require treatment programs that can maintain stable water chemistry across very high circulating water volumes, where even minor scaling significantly impacts thermal efficiency and turbine performance.
• Steel and metallurgy facilities deal with high heat loads and water containing elevated levels of iron and suspended solids, making dispersant selection and blowdown management particularly critical.
• Petrochemical and chemical plants may have cooling water that comes into contact with process hydrocarbons, requiring inhibitors with oil-tolerance and programs that account for organic contamination of the water.
• Pharmaceutical and food-grade facilities face strict constraints on which biocides can be used, particularly where cooling water is in indirect contact with product streams or where regulatory approval is required.
• Waste incineration and paper mills operate with cooling water that may contain elevated levels of chloride or organic contamination, accelerating both corrosion and biofouling beyond typical industrial baselines.

For a complete overview of industrial circulating cooling water treatment chemicals suited to these industries — including scale inhibitors, corrosion inhibitors, biocides, dispersants, and antifoam agents — our product range covers more than 100 formulations across ten series, designed to meet the demands of both standard and highly challenging water conditions.

Working with a Supplier Who Provides More Than Just Chemicals

Selecting the right chemicals is only half the equation. The other half is having the technical support to implement a program correctly — including water quality testing, on-site dosage verification, and the ability to adjust treatment as water conditions change seasonally or as system parameters evolve.

This is where the difference between a chemical distributor and a technical service partner becomes apparent. A supplier who has direct experience operating and optimizing cooling water systems — not just selling into them — brings a fundamentally different level of accountability to the relationship. With over 30 years of experience and an active portfolio of more than 200 operating cooling water systems across the power, steel, and chemical sectors, we provide technical service as a core part of what we deliver, not an optional add-on.

If you are evaluating treatment options for a new system, troubleshooting performance issues in an existing one, or looking to transition from a phosphate-based program to a phosphorus-free or low-phosphorus alternative, we can help you build a program that works — starting with a water quality assessment and a clear set of product recommendations matched to your system's specific conditions.