I have a problem with the Pielstick Diesel Engine,because TBN Depletion in the Oil. The Engine use Residual Fuel and high sulfur content.Besides the oil just get top up level and never been drained. Can you Explain why the TBN of the Oil keep going lowe.

Jeff,
The additives that are supposed to neutralize formed acids in an engine oil get used-up over time. They are sacrificial in nature. How quickly the additives that consist TBN will drop depend on many factors, ranging from engine status (e.g. blowby), operational conditions (e.g. temps and environment), and quality of fuel (concentration of impurities).
Just occasional top-offs are like putting a drop in a bucket, and will not sufficiently replenish the additives. Therefore, you might want to replace your oil, or drain at least a half of oil and replenish with new oil.

You need to change your engine oil when the TBN has been depleted. As John said, just topping off isn't enough to replenish it to acceptable levels.

As your TBN goes down TAN (Total Acid Number) goes up. It is an indication that your additives are nearing its depletion, once the additives are depleted then it will cause much problems as varnish, sludge, residues, and makes your oil easy to oxidize. Hence, you need to change your oil. Remember that engine oil are the most dirtiest oil with lots of contamination ranging from metals, dust, blow-by, moisture just to name a few. Once oil is contaminated then oxidation results.

As a precaution, TAN should be less than 2.

My Warm Regards,

Rolly Angeles
www.rsareliability.com

Hi Jeffturbo,

It's also important to get both a TBN and TAN done on the new oil. This will give you a base line from which to monitor the oil. Many of the modern formulated diesel engine oils will give an initial TAN reading, I have come across values on new oils ranging from 1 to 3 mgKOH/g. This is just due to the additives reacting with the reagents used in the method to give an initial TAN value.

Hi Jeff

an old tart like the Pielstick should be using enough oil to enable top up oil to maintain TBN TAN ect,
I would be taking this difficulty back to your fuel and lubricant supplier as usually large engines in ships, locos and the like will maintain TBN from the amount of top up required.
This scenario suggests either the alkalinity reserve in the lubricant is not high enough the neutralize the amount of contamination in the fuel or the amount of contamination in the fuel is too excessive for any well made lubricant to cope with,
if the suppliers think their products are OK there may be a combustion difficulty causing this,

Just for interest Jeff, what application is the engine performing,

Best Regards Rob S