By Lukeron Lubricants · Last updated
Steam turbine oil does one quiet job all day: it keeps the shaft bearings of a turbine alive. It runs for months or years without a stop, under heat, steam and a little water. This guide explains in simple words what the oil must do, which grade is usual, what to check while it runs, and when to change it.
What does steam turbine oil do?
- It lubricates the bearings that carry the turbine shaft, so metal does not touch metal.
- It carries heat away from the bearings.
- In many turbines it is also the oil of the control and governing system.
- It protects steel parts from rust, even when a little water gets in.
Because the same oil does all of this for a long time, a turbine oil is made to last. It is not the same as an ordinary hydraulic or gear oil.
Which viscosity grade is usual?
Most steam turbine bearing systems use ISO VG 32 or ISO VG 46. Some turbines with a gearbox between the turbine and the generator use a thicker grade, often VG 68 or above. The right grade is the one in the turbine maker's manual. If the manual gives a grade, use that one.
If you want to know what the VG number means, read our short guide on ISO VG grades for industrial oils.
What a good turbine oil must do
Resist oxidation
Heat and air slowly age any oil. A good turbine oil is built to age slowly, so it stays clean and keeps its properties for a long time. Oil that ages fast makes sludge and varnish, which block small passages and coat the bearings.
Separate quickly from water
Steam can leak into the oil system at the shaft seals. The oil should let the water drop to the bottom of the tank quickly, so it can be drained. Oil that holds water in a cloudy mix is a risk for the bearings.
Protect against rust
Where there is water, there is a risk of rust. Turbine oil carries additives that coat steel parts and slow rust.
Release air and avoid foam
Air bubbles in the oil weaken the oil film and can upset the control system. A good turbine oil lets the air out fast and does not build foam.
Some turbine makers and standards set test limits for these properties. For example, you may see ISO 6743-5 (turbine family) or DIN 51515-1 named in a maker's manual. Ask your supplier for the data sheet and which tests the oil is actually reported against. Do not assume.
What to check while the oil is running
The best turbine oil still needs watching. A simple routine is enough for most plants.
- Look at the oil. It should be clear and bright. Cloudy oil often means water. Dark oil or a burnt smell can mean heat or ageing.
- Drain a little from the bottom of the tank. Water collects there first.
- Send a sample for testing at regular times, often every few months, and sooner if something changes. Typical checks are water content, acid number, viscosity and cleanliness.
- Keep the filters in good order, and change them when the maker says.
- Look for the cause of any water. A steady rise often points to a leak at the shaft seals.
The numbers and limits you should use are the ones from the turbine maker and your oil test report. A change over time matters more than one single reading.
When to change the oil
Turbine oil is not changed on a fixed calendar in most plants. It is changed by condition. A clean, dry system with good filtration can run a long time on the same oil. The sample results tell you when it is time: for example, when the acid number has risen a lot, the viscosity has moved, or the oil will not shed water any more.
When you do change oil, drain the tank, clean it, and flush if the maker asks for it. Fill with clean oil through a filter. New oil from a drum is not always clean enough for a turbine, so filtering it as it goes in is good practice.
Can I mix turbine oils?
Do not mix casually. Different brands and types can have different additives. Mixed oil may foam, hold water or make sludge. If you plan to change from one brand or type to another, check with the maker and the new supplier, and flush the system first.
Common problems and what they usually mean
- Cloudy oil: water in the oil. Check the shaft seals and drain the tank bottom.
- Foam on the oil: air in the oil, a wrong oil, or too low a level. Check the level and the return lines.
- Dark oil, sludge, varnish on parts: oil that is too old or too hot. Test it and plan a change.
- Rust spots in the tank: water has stayed in the system for a long time.
What to ask a turbine oil supplier
- Which grades do you have (VG 32, VG 46 or higher)?
- Can I have the data sheet and a recent test report for the batch?
- What pack sizes do you supply (for example 20 litre pails and 210 litre drums)?
- Can I have a sample before I order?
- Who do I call if the oil test shows a problem?
Lukeron turbine oil
Lukeron makes a turbine oil in ISO VG 32 and VG 46 for steam, gas and hydro turbines, and for related bearings and hydraulic systems. It is made to resist oxidation and to separate quickly from water. It is supplied in 20 litre and 210 litre packs, and free samples are available. Our team replies within 1 to 2 business days.
Open the Lukeron turbine oil page from the box below this guide for the grades, pack sizes and data sheet. For the bigger picture of power plant lubricants, read our power plant lubrication guide, and for choosing a viscosity grade for hydraulic systems, read our hydraulic oil VG 32, 46 or 68 guide.