January 04, 2018
A Q&A with Dan Myrick, Summit’s Chief Technology Officer Transcribed from Tribology Talk Podcast: FAQ: TAN Progression
What is TAN progression and how do you deal with it?
First, we’ll remind everybody that TAN stands for total acid number. You monitor the acid number in your equipment looking for the byproducts of oxidation. We talked previously about oxidation being the biggest determiner in the effective life of the lubricant. One of the byproducts of oxidation is organic acid that increase the acid number. So the acid number is something we really look for in the laboratory to determine the onset of oxidation. When oxidation starts occurring and the acid number starts going up, after a certain period of time of a gradual increase in acid number you start seeing an accelerated increase in acid number. The acid number increase really starts to accelerate at a certain point. You really need to change the oil before it gets to this point. After it starts increasing so rapidly, then you’re in an area where you will have deposit formation and a real negative effect on the equipment. You’re going to reach a situation where you will have a difficult cleaning out of the equipment at that point.
So it gets exponentially worse the longer it goes?
It does. The danger of this is that once it reaches the point of rapid acceleration, if oil analysis is not being used to monitor the condition of the oil, the TAN can increase to a very high level very quickly. TAN typically starts at a value of less than 1.0 for new lubricant, and can easily progress up to 50, 60 or 100 over time, which is tremendously high. We want to try to change the oil when the acid number is about 2.0 to control the potential negative effects of a high TAN on the equipment.
When does this typically happen? If you’re putting oil into a machine when do you need to start worrying about this?
Well it can happen at different rates depending on how oxidative the environment is and how high the operating temperature of the equipment is. As we discussed before, high temperature will increase the rate of oxidation. In a typical rotary screw air compressor, for instance, it’s a very oxidative environment and we anticipate that a petroleum oil that could start oxidizing in the first few hundred hours of operation. In a synthetic you would expect 4,000-6,000 hours of operation before you see oxidation starting to occur. Another issue when we talk about high levels of acid number are the fact that when you drain the oil it is not uncommon to leave 10% of the oil in the machine. So if you allowed the acid number of the product to get up to a level of 50 and you change the oil leaving in 10%, then you will be starting with an acid number of 5.0 which is already well over the maximum recommended level of 2. It then starts increasing rapidly from day one so the problem just compounds on itself. If you are not using a good oil analysis program, it’s kind of the silent killer. It’s almost like building up a blockage in your heart where it is really progressing on itself until you reach a point that the machine shuts down or dramatically decreases in performance.
So let’s say you haven’t been keeping up with oil analysis well enough and you are at 50 and you need to change your oil but you don’t want to leave 10% in there. What’s the process?
If you are lucky enough to actually find that through this period you’ve increased the acid number this much and you haven’t had a shutdown of the equipment, then you can pretty much assume at that point you have some pretty heavy deposit formation in the equipment. You would want to use a compression cleaner or conditioner. Summit manufactures a product called Varnasolv that is formulated to clean out the hydrocarbon deposit from equipment. You run Varnasolv for a period of time and drain it out. It will probably require two or three flushes of the equipment to get all of the acid constituents out to the point where the acid number drops well below 1.0 again which is where your starting point needs to be.
I should mention, if you’re using Summit products you get free oil analysis so it’s almost crazy not to use it.
That’s right, and again we talked about how quickly this can occur. We recommend analysis of non-food grade compressor oil every 2,000 hours of operation. On food grade products it becomes much more critical and we recommend you look at them every 1000 hours. Like you said, it’s free of charge to our customers. Even the best oil in the world, you don’t want to put it in and forget about it. You want to make sure you have a good handle on things that are occurring so that you can capture the problem before it elevates to the point where it is really a much larger situation later.
And as you were saying, it’s the silent killer. So does that mean you won’t really know this is a big problem until it is too late to prevent permanent damage?
You can very well get to a point where the machine locks itself up and you had no idea this was occurring because you weren’t looking at the oil analysis to determine what was going on.