Impact of Acetic Acid on Weld Corrosion and its Mitigation

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.  Test data will demonstrate 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 also discussed.