In Case 2, microbiological
assays were also performed. The total counts of aerobic and anaerobic bacteria and the amount
of sulphate reducing bacteria were analysed by cultivation from the samples taken at site, from
the water inside the pipes as well as from the deposits on the surfaces of the pipes. Samples were
scraped from several places on the surface of the opened pipe. The system had been opened half
an hour before the sampling.
Results
Case 1
The failures of the removed metal pipes (EN 1.4301) occurred in less than three years of usage.
Some pits already perforated the pipe wall. Most of the corrosion attacks detected were either in
the fusion line or in the heat affected zone, Figure1. Although the weld itself was uneven and
partly incomplete in some cases, the corrosion did not occur especially in those areas. Instead,
colourful heat tint areas could be seen on the failed pipes. The heat tint colours ranged from very
dark blue to dark brown.
a) b)
Figure 1.