Base number in Engine Lube Oil

It depends - is this for a mobile equipment or stationary engine? What fuel are you using or gas such as methane on a genset? Do you check the TAN as well and look at the wear metals and wear rates? Bearing material such as lead can be susceptible to attack by organic acids etc...

for some engine oil TBN is raised by using TBN Booster (calcium sulphonates), which deutoriates very fast and hence decreasing TBN fast.

If the oil manufacturer was using TBN booster, and as per the facts, the TBN will drop easily, how can they get API certificate?

There are typically 4 parameters for change of engine oil.
1. Change/drop of TBN ( by 50%)
2. Presence of water ( not moisture)
3. Change/drop in KV 40 (by 50%)
4. Drop in flash to below 160 C (result of fuel dilution/dribbling)

TBN can be boosted by adding "higher TBN oil." Similiarly KV 40 can be boosted by higher SAE number.

However if you water in oil, there is drop of FP, oil needs to be changed/replaced.

Hussam Adeni