Monitoring Copper Corrosion Inhibitors in Cooling Water Systems Online

Copper and its alloys are often utilized for their superior heat transfer properties to maintain industrial cooling water systems. While useful for this purpose, these materials are often susceptible to corrosion which can lead to failure of the equipment and decreased plant efficiency.

Equipment failure will lead to an inevitable increased cost of replacing the equipment, as well as loss of profit due to the plant’s downtime. Additionally, decreased plant efficiency can result from the loss of heat transfer that can eventually lead to an accumulation of corrosion products within the system.

Corrosion in Industrial Cooling Systems

To protect power plants from all types of corrosion that can occur in their cooling systems, managers can monitor substances and parameters within the system that indicate corrosion. These parameters include conductivity, pH value, as well as the presence of corroding anions and cations. Additionally, power plants can also implement varying amounts of corrosion inhibitors to their systems to prevent equipment failures.

Corroded copper that is produced from the heat exchanger can cause deleterious effects to the environment, as soluble copper is toxic and must be properly controlled when released into any discharge stream. Additionally, soluble copper can also plate out on mild steel surfaces and form galvanic corrosion sites that result in severe localized corrosion, which is also referred to as pitting, and therefore lead to the premature failure of steel heat exchangers. It is therefore imperative that all cooling water systems include a method of monitoring the presence of corrosion inhibitors within the system.

Commonly Used Corrosion Inhibitors

Triazoles (e.g., tolyltriazole, benzotriazole, and 2-mercaptobenzothiazole) are commonly added in the mg/L range to protect copper and its alloys from corrosion. When added to these systems triazoles are placed sparingly as soluble layers on the surface of the metal. Following triazole adsorption, copper-azole complexes precipitate at the liquid-solid interface to protect the metal substrate from further dissolution. Since these complexes are often prone to oxidation and reaction with microbiocides, triazole concentrations must often be replenished, which therefore necessitates regular concentration determinations.

Cooling towers at a power plant. Chromatogram of a spiked cooling water sample containing 1 mg/L benzotriazole, tolyltriazole, and 2-mercaptobenzothiazole; sample volume: 20 μL; wavelength: 214 nm.

Cooling towers at a power plant. Chromatogram of a spiked cooling water sample containing 1 mg/L benzotriazole, tolyltriazole, and 2-mercaptobenzothiazole; sample volume: 20 μL; wavelength: 214 nm.

Quantifying Corrosion Inhibitors

Ion chromatography direct UV/VIS detection can often be utilized to quantify the presence of copper corrosion inhibitors, however there is an urgent need for more precise and reliable trace analysis techniques to automate this procedure. Inconsistent measurements and slower offline analyses can result in fluctuating triazole concentrations in the cooling water. The implementation of constant online measurement of the cooling water additives can therefore result in additional cost savings by optimizing parameters and requiring less chemicals to be added to the systems.

Metrohm Process Analytics offers the Process Ion Chromatograph to solve this issue, as in a single analysis, the Process IC is able to measure numerous ionic and UV-active compounds present within the aqueous media from ng/L to % concentrations. The Process IC analysis system is fed directly and continuously with samples through a bypass in the process.

The use of automated calibration by this system guarantees excellent detection limits, a high reproducibility and excellent recovery rates. Additionally, the Process IC provides an alarm if pre-set warning or intervention concentration limits are reached, which also helps companies to save significant costs in preventing irreparable damage due to corrosion.

The Process IC TWO, which includes two analytical channels, allows for the monitoring of all other corrosion indicators through a conductivity detection that provides users with a comprehensive overview of the chemistry within the water circuit. The Process IC TWO analyzer is capable of running for extended periods of time in less-frequented areas, as this analyzer is capable of storing a larger amount of reagents, canisters of ultrapure water and/or prepared eluent and level sensors to ensure that constant monitoring of the system’s chemical consumption.

With a built-in eluent module and optional PURELAB® flex 5/6 from ELGA® for continuous and pressureless ultrapure water supply, the Process IC can be configured to run trace analyses of elements autonomously. In fact, one Process Ion Chromatograph can be connected to up to 20 sample streams, thereby allowing multiple areas within a plant to be monitored by a single instrument.

Conclusion

The monitoring of corrosion chemistry within industrial cooling systems helps to minimize any loss of efficiency within the system, while also protecting the internal components that come in contact with steam and water against any potential sources of damage.

Constant monitoring of power plant water chemistry in an effective manner is critical for maintaining the efficiency and safety of the instrument. The implementation of online analyzers is ideal for this purpose, as it provides operators with the necessary information to accurately identify trends of the system and any potential operational issues before costly problems arise.

The Process IC is available with either one or two measurement channels, along with integrated liquid handling modules and several automated sample preparation options.

The Process IC is available with either one or two measurement channels, along with integrated liquid handling modules and several automated sample preparation options.

This information has been sourced, reviewed and adapted from materials provided by Metrohm AG.

For more information on this source, please visit Metrohm AG.

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