Sprinklersystems

Casestudies Endures 'Sprinklersystems'

Casestudie: fire protection systems of a parking garage

Problem:

Two leakages at different spots in the piping system

Extra information:
Location: fire protection system of a parking garage
Type of system: dry system
Material used: galvanized steel (both sides)

Investigation:

Two pipe pieces were cut out of the system and the following analyses were done:

  • Visual inspection
  • Microscopic investigation
  • SEM-EDS analysis
  • Measurements on the zinc layer

Results:

  • Bowl shaped pits with a flared depth were found
  • Precipitations and corrosion products clearly showed signs for permanent presence of water inside the pipes
  • SEM-EDS: mostly iron, oxygen and zinc, small amounts detected of calcium, magnesium, chloride, sulfur and silicium
  • Zinc layer:
    1) intact parts of the pipe : 80 – 100 µm
    2) damaged parts : no zinc layer found
    3) values according to EN-ISO 1461(1999) for material with wall thickness between 1.5 – 3 mm:  minimal zinc layer 45 µm and average thickness of 55 µm zinc.

Conclusion:

Pits are formed due to oxygen corrosion of the steel. This corrosion process occurred after the initial zinc layer was dissolved completely due to the fact that the pipes were partly filled with water and air. Normally the system should have been fully dry.

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Recommendation

The presence of water in the pipes resulted in a very large number of corrosion pits spread out over a large surface area. On the long run these corrosion spots will give leakages. Setting the system dry immediately will probably not help preventing leakages because the water has been present too long. Remaining water will be held back in the tubercles and underneath these structures the corrosion process will continue. Furthermore, on the damaged spots the steel is not protected anymore by a zinc layer, leading to much faster localized corrosion. So it is recommended to exchange the parts of the system that show tubercles and have been in contact with water too long.