Vega consists of three separate gas-condensate accumulations, Vega Nord, Vega Sør and Vega
Sentral. The field is developed by subsea wells tied in to a host facility, Gjøa, with a 51 km multiphase
pipeline. Internal corrosion control of the carbon steel pipeline shall be done with a combination of pHstabilization
and film forming corrosion inhibitors.
The aim of the present work has been to qualify a method for internal corrosion control of the Vega
pipeline. The main parameter to determine was the concentration of pH stabilizer required for
controlling the internal corrosion in the pipeline. The tests have been done using MEG / water mixtures
corresponding to the conditions in the pipeline at 115°C. Some tests have also been done at 80 and
40°C, and the test solution has been modified accordingly. The effect of back production of formate
completion fluid has also been tested. The requirements have been set to maximum 0.10 mm/year in
corrosion rate and maximum 10 µm local corrosion depths after 3 days testing.
The results showed that a pH-stabilizer concentration of 30 mmole/kg lean MEG (24 to 34
mmole/kg rich MEG) was required to control the corrosion (general as well as localized corrosion).
Furthermore, with the film forming corrosion inhibitors tested herein, a concentration of 290 ppm in the
lean MEG (100 to 200 ppm in rich MEG) was needed. These values were determined in MEG /water
mixtures with scale inhibitor. The scale inhibitor caused higher corrosion rates and also more localized
corrosion. The same values were also valid when formate was present. No negative effect of the wax
inhibitor on the corrosion control was found.
Keywords: gas condensate, carbon steel, corrosion control, pH-stabilization, inhibition