What Does Dry Fire Pipe Mean?
A dry fire pipe is a pipe used in fire sprinkler system to automatically extinguish fire. Dry fire pipe sprinkler systems are installed in areas where wet fire pipe systems may be inappropriate, such as areas where freezing temperatures might be expected.
They are most often used in unheated buildings, parking garages, outside canopies attached to heated buildings or refrigerated coolers.
Within the fire protection industry, the greatest threat of corrosion is generally to dry fire pipe systems since the potential exists for sufficient rust product to completely block water flow during a fire emergency.
Corrosionpedia Explains Dry Fire Pipe
A dry fire pipe sprinkler system has pressurized air or nitrogen inside the piping. This keeps a dry valve closed, and water out of the system. When a sprinkler fuses (opens), it allows the air to escape; then the dry valve opens and allows water to enter the system. Wherever there is an opened sprinkler, water flows through it to put out the fire.
Air escaping from the pipe causes a time delay for water to reach sprinklers, which allows the fire to grow larger than it would with a wet pipe system of similar design. To compensate for the delay, more sprinklers in the fire area actuate in response to expanding fires. When it is critical to speed operation of the dry pipe valve, a quick-opening device can be used to rapidly remove air from the system.
Dry fire pipe systems are very susceptible to various types of corrosion, including:
- Microbial corrosion
- MIL loss
- Rust scaling
- Wall loss
Water pockets are often found in dry systems. This water then collects in one or more low spots within the system, and accelerates corrosion. These low spots exist in pipes due to poor installation practices and typically have accelerated corrosion rates compared to the rest of the system.
Oxygen from the compressed air attacks the pipe at areas where there are trapped pools of water. Corrosion in dry fire pipe sprinkler systems is much more aggressive than in wet fire pipe sprinkler systems.