There has been a lot of discussion on the TBN and the different methods of determining it, so we wanted to give you our thoughts on the matter. Blackstone started offering the TBN as a regular test about two years ago. At first, we used Dexsil kits for this test. The Dexsil kits are pretty good and fairly repeatable, though they are expensive and take some time to run. Another drawback is the endpoint. This was determined with a color change, and this method is good only if the same person does the test every time, the same way, and if he/she is not color blind
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About eight months ago, our sample volumes got to the point that it became obvious that we needed to find a better way to run the TBN test. About the only solution to this problem was an auto-titrator. This is basically a computer-controlled syringe that has the ability to add a solution at a very highly defined rate and volume. The titrator also has a meter attached to it that will read either milli-volts or pH.
Once we decided on the auto-titrator (Metter-Toledo) we then had to decide which test method to use to run the TBN. If you have been reading these postings, you know that there are many different ASTM methods for running this test. There are two main problems with these ASTM methods. One, you have to have a good idea of what the value should be before you run the test, and two, the test itself is very slow to complete --ASTM D-4739 can take several hours for one result. (As a side note, all ASTM tests are available at the library, so you can learn about any test method for free.) The slowness of the test makes it uneconomical for a lab to run this method on every sample. So, we chose a method that was fairly simple (ASTM D-974) and modified it. Originally, this test used a color change as an endpoint. We changed it to have the endpoint be a pH of 4.0 on our meter.
This leads us to our next problem: What should the TBN be? There are no standards for the TBN, and there are many different methods for testing. So what do you use? We chose to use virgin oils as our standard, and we adjusted the calculation of the result to read what the virgin oils should be. Our standard oils are Shell Rotella T 15W/40, Shell 10W/30 and Non-Detergent 30W. These were chosen because they are readily available and give us a good range. The virgin Non-Detergent TBN was about 0.5, the Shell 10W/30 was 6.9, and the Rotella T was 11.5 (both stated on their web site). We run these every day, at the beginning and end of every batch of TBN samples, and we get very repeatable results. We have not run any major tests determining the differences between the different ASTM methods or determined the percentage of error between the tests, though we know that when we run the virgin oils, we repeatedly get the results we expect.
As an independent laboratory, the validity of our data is essential to our business and it is also essential to our customers’ confidence. If our TBN results are actually low, then we need to find the reason why; however, if the results just seem lower then they should be for a certain oil type, this is something that we cannot address. This brings us back to the lack of standards for this test. It has been our experience that the repeatability of the test is as important (if not more so) than the actual result, so we are sticking with our new method.
An interesting note: we are not sure exactly how much of a problem a low TBN is – or whether it is even a problem at all. Both ASTM methods D-4739 and D-974 state that “No general relationship between bearing corrosion and acid or base numbers is known.” Does the TBN give good information about the oil? We think yes, though we also think that a low TBN may not necessarily harm the engine or signal the need to get rid of the oil. I hope this helps explain the TBN test from our point of view and answers some of your questions. Please feel free of contact us, or stop by if you are in the Fort Wayne area.
Sincerely,
Ryan Stark and Kristin Huff
Blackstone Labs
About eight months ago, our sample volumes got to the point that it became obvious that we needed to find a better way to run the TBN test. About the only solution to this problem was an auto-titrator. This is basically a computer-controlled syringe that has the ability to add a solution at a very highly defined rate and volume. The titrator also has a meter attached to it that will read either milli-volts or pH.
Once we decided on the auto-titrator (Metter-Toledo) we then had to decide which test method to use to run the TBN. If you have been reading these postings, you know that there are many different ASTM methods for running this test. There are two main problems with these ASTM methods. One, you have to have a good idea of what the value should be before you run the test, and two, the test itself is very slow to complete --ASTM D-4739 can take several hours for one result. (As a side note, all ASTM tests are available at the library, so you can learn about any test method for free.) The slowness of the test makes it uneconomical for a lab to run this method on every sample. So, we chose a method that was fairly simple (ASTM D-974) and modified it. Originally, this test used a color change as an endpoint. We changed it to have the endpoint be a pH of 4.0 on our meter.
This leads us to our next problem: What should the TBN be? There are no standards for the TBN, and there are many different methods for testing. So what do you use? We chose to use virgin oils as our standard, and we adjusted the calculation of the result to read what the virgin oils should be. Our standard oils are Shell Rotella T 15W/40, Shell 10W/30 and Non-Detergent 30W. These were chosen because they are readily available and give us a good range. The virgin Non-Detergent TBN was about 0.5, the Shell 10W/30 was 6.9, and the Rotella T was 11.5 (both stated on their web site). We run these every day, at the beginning and end of every batch of TBN samples, and we get very repeatable results. We have not run any major tests determining the differences between the different ASTM methods or determined the percentage of error between the tests, though we know that when we run the virgin oils, we repeatedly get the results we expect.
As an independent laboratory, the validity of our data is essential to our business and it is also essential to our customers’ confidence. If our TBN results are actually low, then we need to find the reason why; however, if the results just seem lower then they should be for a certain oil type, this is something that we cannot address. This brings us back to the lack of standards for this test. It has been our experience that the repeatability of the test is as important (if not more so) than the actual result, so we are sticking with our new method.
An interesting note: we are not sure exactly how much of a problem a low TBN is – or whether it is even a problem at all. Both ASTM methods D-4739 and D-974 state that “No general relationship between bearing corrosion and acid or base numbers is known.” Does the TBN give good information about the oil? We think yes, though we also think that a low TBN may not necessarily harm the engine or signal the need to get rid of the oil. I hope this helps explain the TBN test from our point of view and answers some of your questions. Please feel free of contact us, or stop by if you are in the Fort Wayne area.
Sincerely,
Ryan Stark and Kristin Huff
Blackstone Labs