Mastering Film-Forming Amines: Application in Heating Networks

Abstract

Heating networks face corrosion challenges due to oxygen ingress, mixed metallurgy, and limited water quality control. Traditional treatments, such as oxygen scavengers and pH boosters, often increase conductivity and struggle to protect systems effectively under dynamic conditions. Film-forming amines (FFAs) offer a modern, efficient alternative, providing surface-level protection without elevating salt levels. This article outlines the principles of FFA application in heating networks, focusing on operational guidelines, corrosion prevention, system efficiency, and long-term stability. Case studies from municipal and industrial systems illustrate how FFAs reduce corrosion rates, improve flow efficiency, and support sustainable, low-maintenance operation. Introduction 

In district heating systems and industrial thermal loops, maintaining water quality is critical to avoid corrosion, fouling, and efficiency losses. Factors such as oxygen ingress, fluctuating loads, and the presence of various metals contribute to complex corrosion mechanisms. Standards such as VDI 2035 provide frameworks for managing system chemistry, but modern systems increasingly demand treatment strategies that go beyond pH control and demineralization. Film-forming amines represent one such strategy, enabling passive, long-term protection through the formation of hydrophobic layers on internal metal surfaces.

This article builds on the fundamentals discussed in previous ODACON Insights editions, applying the principles of film formation and analytical control to the specific conditions found in heating networks. Corrosion Risks in Heating Systems 

Heating systems are exposed to multiple corrosion triggers that are often difficult to control. One major contributor is oxygen ingress, which can occur during system filling, through minor leaks, or from poorly degassed make-up water. Once oxygen enters the system, it initiates electrochemical reactions that lead to pitting and surface degradation.

In addition to oxygen, stagnation plays a critical role. In branches or circuits that experience low or no flow—particularly during seasonal standstills—oxygen and corrosion products accumulate, accelerating degradation. Furthermore, many heating networks consist of mixed metallurgy, for example copper in heat exchangers and steel in distribution lines. These dissimilar metals promote galvanic corrosion, further complicating water chemistry control. Pump systems also present a vulnerability, as low-flow erosion and cavitation can damage internal surfaces and release metal oxides into circulation.

Although standard treatments such as softening or demineralization help to prevent scaling, they do not sufficiently address these complex corrosion mechanisms. In contrast, film-forming amines offer a targeted and passive protection mechanism. By adsorbing to metal surfaces, they create a hydrophobic layer that acts as a physical barrier against oxygen. This film is particularly effective in systems with irregular flows or prolonged idle periods, where traditional methods offer limited resilience.

Operational Chemistry and Standards 

Heating networks are generally operated within two established chemical regimes, as outlined in guidelines like VDI 2035. In low-salt operation, conductivity remains below 100 µS/cm and demineralized water is used. In contrast, salt-containing operation permits higher conductivities up to 1500 µS/cm, often relying on softened water.

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Maintaining control over pH and oxygen levels is essential in both cases. Film-forming amines support this stability by not contributing to overall conductivity. Their compatibility with different water chemistries allows operators to apply them flexibly without conflicting with regulatory limits or damaging sensitive components.

In systems containing aluminum—common in heat exchangers or modular radiators—pH management must remain between 8.2 and 9.0. FFAs stabilize such systems by providing a non-aggressive, pH-neutral protective effect. This allows operators to achieve corrosion control even within narrow chemical tolerances.

Mechanism of Action 

FFAs consist of amphiphilic molecules that distribute through circulating water and steam. Upon contact with metal surfaces, these molecules adsorb and align to form a dense, continuous layer. This monomolecular film acts as a physical and chemical shield. It resists oxygen diffusion, balances surface potentials between different metals, and reduces the formation of porous oxide structures.

Even after partial drainage or temperature cycling, the film remains intact. This makes it particularly effective in heating systems that are subject to seasonal shutdowns or intermittent flow conditions. Components retain their protective layer, which prevents corrosion re-initiation during periods of stagnation or ambient humidity exposure.

System Performance Improvements 

The impact of FFAs extends beyond corrosion prevention. Their use in heating systems leads to smoother internal surfaces, which in turn reduce hydraulic friction. Lower resistance improves overall flow efficiency and can reduce the energy demand of pumps.

By minimizing porous oxide formation, FFAs also enhance thermal conductivity. Fewer insulating deposits on heat transfer surfaces result in more efficient heat exchange and improved system responsiveness. Over time, operators observe lower maintenance intervals, cleaner filter elements, and extended component life cycles. Microscopic analysis has shown that rough, uneven magnetite layers transform into compact, uniform films after several weeks of FFA treatment, further confirming the stabilizing effect on internal surfaces.

Application and Dosing Guidelines 

Effective FFA treatment in heating networks begins with a defined dosing protocol. Initial application should be carried out using a dosing pump placed in the main circulation line. A target concentration between 0.1 and 0.3 ppm is sufficient for surface activation.

During the start-up phase, intermittent dosing over a period of four to six weeks allows the protective layer to form gradually without disturbing settled oxides. Weekly concentration checks during this phase help ensure adequate coverage. Once the system has stabilized, quarterly monitoring is typically sufficient. Should the concentration fall below 0.1 ppm, a maintenance dose can be applied.

In older systems with existing corrosion products or oxide deposits, slow and controlled introduction of FFAs is recommended to avoid mobilizing loose materials that could clog filters or interfere with flow.

Implementation Recommendations 

For best results, FFAs should be dosed directly into the main circuit rather than into the make-up water. This accelerates distribution and minimizes dilution. Automated, timer-controlled dosing units help maintain consistent concentration and reduce operator workload.

A baseline water analysis should be performed before introducing FFAs. This provides insight into the system’s initial condition and helps tailor the treatment plan. Where needed, side-stream filtration and softening can be used to support long-term stability.

Case Studies

District Heating Network (Germany) 

A municipal network in Leipzig transitioned from caustic chemistry to FFA treatment. Prior to implementation, iron levels ranged from 600 to 1500 µg/L. Within several weeks of FFA dosing, these levels dropped to below 40 µg/L. The result was improved water clarity, reduced maintenance effort, and fewer flow disturbances during peak heating demand.

Industrial Heating System (New Zealand) 

An industrial thermal loop with high heat load recorded initial corrosion rates of 8.6 mils per year. After three months of FFA treatment, the rate dropped to 0.5 mils, and after six months to just 0.1 mils. Operators also reported clearer water and improved hydraulic response.r.

Conclusion 

Film-forming amines provide a practical and effective method for protecting heating networks from corrosion and efficiency loss. Their ability to form persistent hydrophobic films allows for long-term operation with minimal interference to standard water chemistry.

When integrated with routine monitoring and dosing, FFAs offer a low-maintenance alternative to conventional treatments. Their adaptability to both municipal and industrial systems, along with environmental compatibility, positions them as a future-ready solution for sustainable thermal operations.

Author Bio

Ronny Wagner is the Managing Director at REICON Wärmetechnik und Wasserchemie Leipzig GmbH. As an experienced water treatment professional, he specializes in the application of film-forming amines in water-steam cycles, as well as in closed cooling and heating systems. With over 15 years of experience in the preservation of nuclear, fossil, and industrial power plants, he has played a pivotal role in advancing industry best practices. As an active member of vgbe and the IAPWS Power Cycle Chemistry (PCC) group, he has co-authored several international standards for the safe and effective application of film-forming amines in power plant chemistry.