Photo Gallery F5: Dry / Pre-Action Fire Sprinkler
Unquestionably, the most troublesome fire protection systems are of dry and pre-action type design for a multitude of reasons. The common threat is due to the fact that they are “dry” in name only. As soon as hydrostatic testing is performed, some water will remain to initiate higher corrosion activity. Water remaining along the bottom and with abundant air and oxygen above it produces a far greater corrosion condition than if the pipe were completely filled with water and left stagnant. With industry and government regulations mandating regular flow testing of such systems, new fresh oxygenated water is constantly introduced to replenish and advance high corrosion conditions. The most common reaction to a failure of such fire sprinkler system is that it could not occur due to corrosion given that they are dry.
Most such systems are not installed with an incline or grade to help remove the water, with the specified grade still inadequate to remove water even if applied. The internal bump created by roll-grooving the pipe itself prevents full draining under anything except a steep vertical orientation. As many of the below photographs prove, clearly defined water lines remain showing the amount of previously trapped water, and the dramatic difference in corrosion conditions above, below, and at the water line. Rust deposits ranging from mild to severe are directly proportional to the amount of corrosion having taken place.
Add to this scenario the fact that virtually all such systems are now constructed of thinwall schedule 10 pipe, and even ultra thinwall schedule 7 in some examples; 50% or less than the wall thickness of the previous schedule 40 standard. Change in code requirements now allow threading of thinwall schedule 10 pipe further explain the advanced failure of such systems.
The threat of leaks and failures are, however, far secondary to the true threat at such systems being the volume of rust product created, and for the potential of that rust product to reduce to stop water flow through the sprinkler heads during a true fire emergency – as has resulted in deaths in many examples. A small sampling of examples of such are provided below. Our own field experiment, documented on this Internet site, proved that as little as 1/4 cup of rust product is capable of completely stopping water flow through an activated sprinkler head.
Today, most dry and pre-action systems have a reliable service life of 25 years or less under the most favorable of conditions. While previous industry recommendations to install galvanized steel pipe as a solution to such corrosion issues made sense, even lower service was realized due to the generally poor quality of today’s galvanized steel pipe.
