How to Monitor Alkaline Cleaning Tanks

After machining parts, manufacturers have to clean them. Once clean, the parts may be painted, assembled, or stored with a rust inhibitor coating. That makes cleaning crucial. Poor cleaning could lead to rust, uneven painting or failure in assembly. Many manufacturers do not have the time or budget to rapidly change out (1-day to 1-week intervals) cleaning tanks; if you are fortunate to have short intervals, little maintenance is required as there is limited time for problems to arise. However, you should still perform basic tests to ensure your cleaner is working properly.

For manufacturers with longer tank life, there are 2 main properties to monitor to ensure the performance of your alkaline cleaner: pH and concentration. When the pH and concentration change, the efficacy of the cleaners can decline and lead to more frequent change-outs and greater cleaner consumption. Basic monitoring can prove to be highly cost effective and extend tank life. 

pH Testing

The ability to remove soils declines as the cleaner’s pH drops. The recommended pH for cleaning non-aluminum parts is > 9.0 and > 9.5 for aluminum parts. Additionally, many corrosion inhibitors have a pH-dependent solubility curve. As the pH drops, less inhibitor is incorporated into the solution and the more likely corrosion on cleaned parts can occur. These inhibitors start to drop around 10.2 pH, but do not cause significant issues until the pH drops below 9.5.

Maintenance programs typically attempt to adjust the pH back into range after falling out rather than monitoring the pH for remaining in range. We recommend the latter method as this ensures the pH does not drop dangerously low and potentially renders the solution unusable. Trying to keep the pH between 9.5 (or higher) and 10.5 is ideal. Adding a caustic to boost pH could cause problems as you will get a false concentration reading. If you plan to adjust the pH, have a qualified on-site analytical chemist perform the adjustments.

To measure the pH, pull a sample of agitated solution and wait for it to cool to room temperature. Once cooled, use a narrow range pH strip to test the pH. Higher temperatures can render pH tests unreliable and measuring in the tank could capture the pH of contaminants on the strip.

Concentration Testing

The other key test involves testing the concentration using titration. Titration is used to find the tank strength (concentration). Titration involves adding an acidic reagent to a know volume of tank solution until a defined pH is reached. This can be done simply by adding drops of a reagent to the tank solution. This process involves a dye that changes colors at the defined pH endpoint. This is useful for finding the concentration with a +/- 2% tolerance.

This method is rather crude, but can be highly refined by having a trained chemist use lab equipment to run the test. Lab equipment is required for tests that require tighter tolerances than +/- 2%. Look for a constant concentration over time. If the concentration drops, some likely suspects are: cleaner carry-out, leaks, overly aggressive oil skimming, pH degradation by contaminants, and excessive raw material stripping. If the concentration increases, some likely suspects are: excessive add-back of cleaner or the presence of metalworking fluids. Sometimes soil could affect the strength reading and could indicate rising concentration or stable concentration when the strength is actually dropping.


The pH and concentration tests should be conducted each shift in the manner described above. Investing in lab equipment may prove worthwhile if you have stringent tolerances. If the concentration is too low, add some cleaner to put the solution in the proper range. If too high, add water to bring solution within the proper range. pH adjustment is not recommended unless you have a trained chemist on-site. For more information on cleaner management, contact Twin Specialties and ask about our “Coolant Management Guide” that includes tips and information for aqueous cleaners.

Case Study: Recreational and Commercial Marine Components

Products: Twin Industrial Cleaner 2458-B and Twin Soluble Rust Preventative 110

Product Types: Liquid Alkaline Cleaner and Water Soluble Rust Preventative

Customer: Manufacturer of Recreational and Commercial Marine Components

The Problem: The customer manufactures parts for recreational and commercial boats, but was starting to encounter rust on some of their parts after running them through a cleaning tank. Specifically, the rust was appearing on a ductile iron piece, which is difficult to prevent as iron is a very porous metal and absorbs moisture easily. The cleaner and rinse solution the customer was using did not effectively prevent rust and left spots on the parts after cleaning.

The cleaning tank was running at 180⁰ F and a concentration of approximately 1.5%, this was both too hot and too weak for an effective cleaning process. The higher temperature resulted in “flash drying” which leads to more rust than regular drying. This occurred in between the cleaning cycle and the rinse cycle. The higher temperatures and weak solutions caused greater evaporation and rusting.

The Solution: After evaluating their cleaning process, Twin Specialties determined that adjustments were needed for the cleaning process, cleaner, and rinse solution. In the cleaning process, the first issue to address with the temperatures for the cleaning and rinse cycles. The cycles ran at 180⁰F and 100⁰F, respectively. After consulting the manufacturer and technical data sheets, we determined the proper temperatures for the cleaning and rinse cycles should be 140⁰ F and 75⁰ F, respectively. This reduced evaporation of the cleaner and rust preventative and alleviated the “flash drying” issue.

Secondly, we increased the concentration of both the cleaner and rust preventative. Originally, both were running around 1-2%. Based on the manufacturers recommendations and previous results, we determined that running both the cleaning and rinsing solutions at 3% will improve performance of both chemicals. This allowed for a thorough cleaning and application of the rust preventative.

Finally, we set up the system with our high-performance products. For the cleaning cycle, the customer is using the Twin Industrial Cleaner 2458-B. This is a heavy-duty liquid alkaline cleaner that has some of the Twin Soluble Rust Preventative 110 included in the product’s chemistry. For this specific application, this helps fight the “flash drying” that occurs in between the cleaning and rinse cycles. In the rinse cycle, the customer is using the Twin Soluble Rust Preventative 110 as an additive to the rinse solution. This synthetic product is non-foaming and provides a dry film for short term rust protection in typical indoor storage conditions.

Using this formula for cleaning operations, the customer eliminated rust from parts and reduced service needed on its products. Coupling this with Twin Industrial Cleaner 2458-B and the Twin Soluble Rust Preventative 110, the customer is able to fulfill its orders and deliver pristine parts to its customers. The lower temperatures also reduced energy consumption and produced further cost savings.