Naphthenic Acid Corrosion & Material Selection

[ben]

What are the factors which are required to be considered when Naphthenic acid corrosion is likely to occur?
And how should be the right material be selected?
Found an aggressive case, where this requires to be evaluated.

[mechcolor]

You remember these:
Temperature
NAC becomes significant mainly in:
220–240 °C (430–465 °F) begins
240–400 °C (465–750 °F) increasingly severe
> 400 °C NAC subsides, but sulfidation usually dominates
Worst region: 240–380 °C.

TAN
TAN < 0.5 generally low NAC risk (not zero)
TAN 0.5–1.5 possible risk, depends on other factors
TAN > 1.5 high concern
TAN > 3.0 aggressive crudes, high vigilance
BUT - TAN alone is not predictive:

Sulphur
Low sulfur (<~0.5 wt%) → little protective film → NAC accelerates
Moderate sulfur → sometimes reduces NAC (protective sulfide film)
High sulfur → sulfidation dominates and can be more damaging overall
So: high TAN + low to medium sulfur = prime NAC scenario.

Velocity
NAC is erosion-corrosion driven:
elbows, reducers, tees
pump suction/discharge
nozzles, orifices, control valves
high vapor fraction regions

[ben]

Thank you master,

[mechcolor]

I had this NAC registered with me.
But be careful, things even happen outside all these parameters.