Sprinkler systems

Case studies Endures 'sprinkler systems'

Case study: sprinkler pipes in a parking garage

Customer question / problem:

Two leaks in different segments of the sprinkler system

Extra information:
Type of system: dry system.
Material: hot dip galvanized steel (two-sided)

Research:

Two pipe samples were taken and further examined in the laboratory using:

  • Visual inspection
  • Microscopic examination
  • Analysis of material and corrosion products using SEM-EDS
  • Thickness measurements on the zinc layer

The results:

  • Cup-shaped wells with different pit depths
  • light brown deposits and layers of corrosion products at the location of both leaks; clearly visible that the pipe has been (long) wet
  • SEM-EDS: mainly found iron oxide and zinc; also found small amounts of salts and minerals such as calcium, magnesium, chlorine, sulfur and silicon that normally also occur in tap water.
  • Zinc layer thickness:
    1) on the undamaged pipe section: 80 – 100 µm
    2) on the damaged pipe section: no zinc layer present
    3) According to NEN-EN-ISO 1461 (1999), a pipe with a wall thickness between 1.5 and 3 mm must have a zinc layer with an average thickness of 55 µm and no thinner than 45 µm.

Final conclusion:

The damage and leakage was caused by oxygen corrosion: this could occur due to the permanent presence of water together with air in the galvanized steel sprinkler pipe. Since this is a dry sprinkler system, the aerated water should not have been present (permanently).

Recommendation

The long-term presence of water in the pipes has created a very large number of corrosion pits spread over a large surface. All these corrosion wells will (could) lead to leakage in the long term. Even immediately drying the installation will not do much to prevent contamination because the process has been going on for a long time and water will remain in the layer of tubercles and corrosion products. In addition, the steel at the wells is no longer protected by a zinc layer. Any condensation formed there will therefore lead to ongoing corrosion. As a result, the only solution to the problem remains to replace the parts of the pipe network that have been corroded in the form of a well.