Ask the Experts

"Do you have any suggestions for problems with the solubility of oxidation products in turbine oil at low temperatures?"

Recently, my clients have had a problem with the solubility of oxidized products in turbine and hydraulic oils. At operating temperatures (60-80 degrees С), they are dissolved, but in stoppage (i.e., temperatures below 25 degrees C), they become insoluble and begin to deposit on working surfaces. This is a problem with the hydraulic piston pumps, and it does not matter the type of turbine (gas/steam/etc. or manufacturer) or the working hours."

Based on your comments, you may be dealing with varnish formation, which is a frequent problem in high-temperature and high-pressure systems such as steam turbines or high-performance hydraulic systems.

Varnish is the accumulation of oil oxidation and degradation compounds on machine surfaces or components. It can be the result of several possible root causes, including high temperatures, electrostatic discharges, lubricant degradation and microdieseling. Varnish can produce a number of problems related to machine operation, such as valve stiction, lubricant flow restriction, clogged filters, etc.

Varnish begins as dissolved impurities. When these impurities accumulate and reach the saturation point, they migrate to the surfaces of the lubrication system. If these deposits remain on the surfaces, they cure (harden) with time, causing failure of the lube system and lubricated components.

Oxidation resistance and solubility are two important lubricant properties to consider. Oxidation resistance refers to how molecules resist the chemical reaction with the oxygen in the air. Oxidation degrades oil and is one of the main reasons to change it. The greater the oxidation resistance, the longer the oil life.

Solubility is the property that allows a lubricant to hold polar substances like varnish in suspension without damage to the machine. Oil solubility increases at higher temperatures. Group III oils also have lower solubility than Group II and Group I oils. There have been many instances of machines experiencing varnish deposits due to lower solubility of the oil after switching from a Group I oil to a Group II or III oil.

If you are facing varnish deposits, two actions are recommended to control it. First, identify the root causes. This will require a systematic study of the possible factors supported by oil analysis. Next, remove the existing varnish in the machine. This can be achieved by adding solvent or detergent additives to the oil, using a synthetic product with high natural solvency or installing varnish removal systems. In cases of hardened varnish, the solution will be mechanical and may simply involve changing the components.

"Why aren't more machine shops using natural biodegradable oils? Is it the cost, availability or marketing? Don't they outperform the others? I am confused why more machinists don't use them."

Much of the reason for this may be due to old practices and mindsets. If your mineral oil worked for you yesterday, why would you want to change to a vegetable-based oil today and take a chance that the new product won't perform as well?

People often fall into a routine, and unless something upsets that routine, the current practices tend to stay the same. It's usually not until an event like a discharge, government agency involvement or new personnel entering the facility that old practices are questioned and new ideas are considered.

Many machinists may not even be aware of the other products on the market. In today's economy, it seems as if no one wears just one hat on the job anymore. The pressing issues at hand must be addressed, so the thought of looking for new products frequently gets pushed aside. Of course, there are those who are constantly looking for the best-performing products on the market and taking proactive steps to save the environment.

The other issue is that biodegradable oils usually have a higher cost than mineral oils. This hinders smaller shops from changing to environmentally friendly lubricants. The cost not only involves the oils but also ensuring that all equipment is cleaned out completely before making the switch, since most vegetable oils and mineral oils don't mix well.

Changing to biodegradable oils can be costly and take time away from production. Obviously, additional costs and downtime are two things most plants never want to hear and will be put off until absolutely necessary unless financial justification can be made.

Biodegradable oils have many advantages over mineral-based oils. Anyone working in a machine shop knows of the dreaded oil mist. This mist consists of harmful volatile organic compounds (VOCs) and can cause dermatitis. With biodegradable oils, the oil misting is lessened, which means fewer VOCs entering the air and minimal skin-related issues. Using a vegetable oil may also improve lubricity.

When deciding which lubricant is right for you, consider the application as well as your company values. Some industries may have sticker policies on environmental impacts or be forced to adhere to government regulations. The process might even demand a biodegradable fluid. Whatever the case, be sure to evaluate all of your options.