Corrosion behavior of an American Petroleum Institute N-80 grade steel
in 3% sodium chloride (NaCl) in distilled water was studied under a c
arbon dioxide (CO2) partial pressure of 1. 03 mPa (150 psig) at 71-deg
rees-C (160-degrees-F). The pH was maintained constant at 3.4 for some
tests but allowed to fluctuate for other tests. A two-phase, flow-loo
p test facility for studying effects of flow velocity produced two-pha
se flow conditions of CO2 gas and liquid in stratified, slug, froth, a
nd mist flow patterns. A test cell for the flow loop allowed for corro
sion rate measurements by electrochemical and weight-loss methods usin
g removable pipe spools. Iron carbonate (FeCO3) formed only for low-ve
locity, single-phase flows where pH increased above 5. 0. Corrosion ra
tes after scale formation decreased by almost one order of magnitude.
No FeCO3 scale formed in tests involving high-velocity, single-phase f
lows or two-phase flows. Corrosion rates when no scales formed were in
dependent of pH and flow pattern.