Calcium Naphthenate precipitation is often initiated by a rise in solution pH, as produced fluids are
degassed. It can cause severe problems during the separation of oil and water, forming very
stable emulsions and/or insoluble deposits in separators or crude dehydration/desalting vessels.
Acetic acid injection is widely employed to maintain a low pH and prevent solids precipitation.
This has significant implications for the integrity of the process pipework and vessels.
The impact of acetic acid on weld-corrosion under typical oilfield conditions is reviewed and data
presented to demonstrate its effect on corrosion rates. Typically, this increased threat to system
integrity is mitigated by corrosion inhibition. Laboratory test data demonstrated the importance of
selecting the correct inhibitor chemistry in order to eliminate preferential corrosion of the weld or
heat affected zones. The effects of acetic acid concentration and weld metallurgy on corrosion
rates are discussed. The development of an environmentally acceptable alternative to the
existing inhibitor chemistry is also described.
Keywords: acetic acid, weld corrosion, corrosion inhibition, pH control, naphthenate
precipitation, environmentally acceptable chemistry