Most of the Naphtenic crude is believed to have the chemical formula R (CH2) nCOOH where R is a cyclopentane ring and n is typically greater than 12. The naphtenic crude corrosivity is not only dependent of TAN number. Some crude of high TAN is some times less corrosive than crude with low TAN. The carboxyl molecule arrangement within the hydrocarbon ring determines the corrosivity of naphtenic crude. If the carboxyl is located inside the hydrocarbon ring, even with a high TAN, such naphtenic crude arrangement will be less corrosive than a low TAN with the carboxyl located on the extremity of the hydrocarbon ring.

1-Is the above statement correct?

2-What is the experience of the forum in the processing of Naphtenic crude?

3-To make metallurgy up grading?

4-To inject corrosion inhibitors?


Thanks in advance  



Luis Marques           

 

I use the following criteria:
- when steell is not of series 300, max TAN 0.3/0.5 the first in case no protective additive addition;
- in case of steell series 300, accepted TAN up to 1.5;
- in some case this formula is also used for assessment: S>2*TAN.
Crude recutting is requested in order to check compliance between stream TAN and piping metallurgy. This is also useful in order to blend HAC with traditional ones in order to dilute acidity;
Bottom Fe/Ni ratio vs crude has to be monitored (increase suggests corrosion in progress)
Additive suppliers are able to make a risk assessment on the unit in order to define critical zones and doping necessity, if any

Luis, I've been looking into the subject of no direct correlation between TAN and corrosivity, since your great contribution to thread124-214862: High TAN Crudes.

I doubt that there could be cycle internal carboxylic groups, for the simple reason that the cycles' conformation is not of planar polygons: cyclopentane appears as an envelope and cyclohexane as a chair.

The only "possible" alternative would be a carboxylic group attached to hydrocarbons in the adamantane (tricyclodecane) series in which three cyclohexane rings share non-adjacent carbons creating some kind of partly closed volumes, but have never found any written confirmation of the existence of such a naphthenic acid.
I found an interesting article by nacecalgary titled: "The influence of naphthenic acid an [pdf]" that can be found by googleing "nacecalgary study on naphthenic acidity".