ABSTRACT
In a sour field, severe corrosion was observed in dead ends (or dead legs) of oily-water lines with total dissolved solids (TDS) up to 250 g/l and pH around 6 – 6.5. At such high TDS and salinity levels, the activity of sulfate reducing bacteria (SRB) and thiosulfate reducing bacteria (TRB) are presumed to be very low, although the organisms may indeed be present. To understand the reason for the experienced severe corrosion, water samples were collected from the dead ends of the oily-water piping system. These analyses confirmed the presence of SRB and TRB. Then few months later three consecutive water samples of 3-4 cm3, each obtained without flushing and one sample after flushing were collected from the same dead ends. Laboratory analysis of these small samples showed that the salinity of the stagnant water at dead ends was one order of magnitude less than the salinity of the bulk fluids. It was also found that the pH of the stagnant water present in dead ends was one unit lower than the pH of the bulk. These observations were confirmed on other water samples analyzed by an independent laboratory. In order to understand the corrosion mechanism and the reasons for the changes in the water chemistry, more samples were collected from dead ends and sent to an independent laboratory for identification of different species. The mechanism of the dead end corrosion was investigated.
