In industrial recirculating cooling water systems, copper and copper alloys are widely used in heat exchangers, condensers, and piping components due to their excellent thermal conductivity. However, under conditions of oxygen presence, water quality fluctuations, and biocide addition, copper materials are highly susceptible to pitting and uniform corrosion. Benzotriazole (BTA), as a classic copper corrosion inhibitor, is widely used in copper-containing recirculating water systems.
1. Corrosion Inhibition Mechanism and Characteristics of BTA in Copper-Containing Recirculating Water Systems
The corrosion inhibition effect of BTA on copper mainly stems from its chemical adsorption and complexation reaction on the copper surface. When BTA is added to the circulating water, the triazole ring in the molecule coordinates with the copper surface, forming a dense and stable protective film. This film effectively isolates dissolved oxygen, chloride ions, and other corrosive media from direct contact with the copper substrate, thereby significantly reducing the corrosion rate of copper.
In actual circulating water systems, BTA exhibits the following typical characteristics:
♠ Selective protective effect on copper and copper alloys
BTA mainly acts on copper and its alloys, and has almost no corrosion inhibition effect on carbon steel and stainless steel. Therefore, in multi-metal systems, BTA is usually used as a “copper-specific corrosion inhibitor” and needs to be used in conjunction with other corrosion inhibitor components.
♠ Faster film formation speed, but stability is significantly affected by water quality
Under relatively stable water quality and moderate pH conditions, BTA can quickly form a protective film on the copper surface. However, high chloride ion concentration, high redox potential, or frequent water quality fluctuations can damage the formed adsorption film.
♠ Relatively sensitive to temperature and flow rate
In high-temperature, high-flow rate heat exchanger areas, the BTA film is more prone to local damage, and the corrosion inhibition effect needs to be maintained by reasonably controlling the addition concentration.
2. Key Points for the Use of BTA in Copper-Containing Recirculating Water Systems
In engineering applications, the corrosion inhibition effect of BTA depends not only on the product itself but also on the addition method and system operating conditions.
♠ Addition location and method
BTA is usually added continuously or intermittently in the form of an aqueous solution. To ensure even distribution in the system, it is generally recommended to add BTA to the circulating water return line or at a location where the chemical mixing effect is good, avoiding direct addition to high-temperature or stagnant areas.
♠ Concentration Control
In most industrial circulating cooling water systems, the effective concentration of BTA is usually controlled at 1–5 mg/L (based on active ingredient).
- For new systems or systems that have just undergone chemical cleaning, a higher initial dosage is recommended to accelerate the film formation process.
- After the system operation stabilizes, the dosage can be gradually adjusted to the maintenance concentration.
Too low a concentration will not form a complete protective film, while long-term excessive dosing not only increases operating costs but may also cause compatibility problems with other chemicals.
♠ Synergistic Relationship with Other Water Treatment Chemicals
In copper-containing circulating water systems, BTA is usually not used alone but in conjunction with the following chemicals:
- Zinc salts, phosphonate corrosion inhibitors: Used to protect carbon steel and low-alloy steel.
- Non-oxidizing biocides: Relatively good compatibility with BTA.
It should be noted that strong oxidizing biocides (such as free chlorine, chlorine dioxide) may damage the BTA adsorption film when added in high doses. The frequency and intensity of addition should be reasonably controlled.
3. Common Problems and Cause Analysis of BTA in Circulating Water Systems
Although BTA is widely used, unsatisfactory corrosion inhibition effects are still frequently encountered in actual operation, mainly in the following aspects:
♠ Severe copper corrosion after addition
This problem is usually related to the following factors:
- High chloride ion concentration in the system, which destroys the stability of the BTA film layer
- Insufficient initial dosage, failing to form a complete protective film
- A large amount of suspended solids or oil in the water, affecting the effective contact between BTA and the copper surface
♠ Abnormally fast consumption rate of BTA
In some systems, a significant decrease in the residual concentration of BTA is detected. Common reasons include:
- Frequent use of oxidizing biocides, leading to the oxidation and decomposition of BTA
Large system make-up water volume, resulting in a significant dilution effect - Frequent water quality fluctuations, leading to repeated destruction and reconstruction of the protective film
♠ Uneven corrosion inhibition effect in multi-metal systems
BTA only works on copper. If carbon steel corrosion is not well controlled in the system, it will often indirectly affect the corrosion environment of copper components. Therefore, in multi-metal systems, BTA must be considered as part of a comprehensive corrosion inhibition system, rather than a standalone solution.
In copper-containing circulating water systems, benzotriazole remains one of the most mature and reliable copper corrosion inhibitors. However, its corrosion inhibition effect is not “effective simply by adding it,” but rather highly dependent on the system water quality, dosing strategy, and synergistic relationship with other water treatment chemicals. Only with a thorough understanding of its mechanism of action and application limitations can BTA deliver its intended corrosion inhibition value in practical engineering applications.
