The Total Acidity Number (TAN) in lubricants and why is it so important

Measuring the quality and condition of a lubricant is essential to ensure that equipment operates correctly. One of the most important metrics for this task is the Total Acidity Number (TAN), which allows for the identification of the presence of acidic compounds in the oil. 

This indicator helps assess the level of lubricant degradation while also playing a key role in preventing damage to engines and industrial systems. In this article, you will find a detailed explanation of what the TAN is, how it is measured, and why it is so important for maintenance.

What is the Total Acid Number (TAN)?

The Total Acidity Number (TAN) is a metric that reflects the amount of acidic components present in a lubricant. These acids can be organic or inorganic and, in many cases, are by-products of the oil oxidation process during use. The TAN is expressed in milligrams of potassium hydroxide (KOH) needed to neutralize the acids present in one gram of oil. 

When a lubricant is new, its TAN is usually low, as it contains few acidic compounds. However, over time and with use, the TAN tends to increase due to factors such as oxidation, contamination, and depletion of oil protective additives. 

How is the TAN measured?

The TAN is measured by chemical analysis in specialized laboratories. This procedure consists of adding a potassium hydroxide solution to the oil until all the acids present are neutralized. The amount of potassium hydroxide used determines the Total Acidity Number value.

This analysis is particularly useful when comparing the TAN of a used oil with the initial TAN of the same product, as it allows us to evaluate the degree of degradation of the lubricant and determine if it is still suitable for use or if it needs to be replaced.

Why the TAN is important in lubricant performance

The TAN is also a key tool for preventing major issues with engines and industrial systems:

• Identification of oil degradation. A significant increase in the TAN indicates that the oil has undergone oxidation or contamination processes. This can lead to the formation of deposits, sludge, and varnishes that affect the system’s performance.
• Corrosion prevention. The acids present in the oil can attack the metal surfaces of the components, causing corrosion and premature wear. 
• Maintenance optimization. Knowing the TAN allows you to plan oil changes at the right time, avoiding both the excessive use of a degraded lubricant and the waste of a still functional oil.
• Cost reduction. Keeping the TAN within acceptable limits contributes to prolonging the useful life of the lubricant and equipment, reducing expenses in repairs and unscheduled shutdowns.

Factors influencing the increase in TAN

There are several conditions that can accelerate the increase of TAN in a lubricant, among which the following stand out: 

• High temperatures. Heat accelerates the oxidation of the oil, which generates more acidic compounds.
• External contamination. The entry of water, dust, or chemicals into the system can alter the composition of the oil.
• Depletion of additives. Lubricant antioxidant and detergent additives are consumed over time, leaving the oil more vulnerable to degradation.
• Presence of metals. The metals present in the system can act as catalysts, intensifying the chemical oxidation reactions.

How to manage the TAN effectively

To keep the TAN under control and ensure the proper functioning of your equipment, consider the following recommendations: 

• Establish a regular test schedule. Perform periodic TAN tests to identify any changes in the lubricant condition.
• Use high-quality oils. Lubricants formulated with advanced additives have higher oxidation resistance and maintain a stable TAN for longer.
• Minimize exposure to pollutants. Implement measures to prevent water, dust, and other external agents from entering the system.
• Follow the manufacturer's specifications. Change the oil according to the recommended intervals and use products compatible with your equipment.

The Total Acidity Number (TAN) is a valuable tool to ensure the efficiency and durability of lubricated systems. By properly monitoring and managing the TAN, you can prevent damage, optimize the performance of your equipment, and reduce operating costs. Do not underestimate the importance of this indicator and make sure to include it in your maintenance strategy.

At Repsol Lubricants, we are committed to helping you take care of your equipment. We offer products designed to withstand the most demanding conditions and lubricant analysis services so you always make informed decisions.