An Alaskan school district learned the hard way about corrosion in metal sprinkler pipes, as school buildings in Petersburg, Alaska, had corroded metal pipes found during a special inspection for the interior workings of the fire sprinkler system in the high school and middle school.
As part of the NFPA (National Fire Protection Association) code 25, pressure tests are required every three years. The schools passed those tests with no issues, as well as the inspections done annually by a certified technician. Specialized investigations of the fire suppression system are required every three and five years, but the school had not had a five-year inspection done in at least 10 years, according to district maintenance director Dan Tate, as reported in an article posted on KFSK.org by Joe Viechnicki on October 14. The five-year borescope inspection is a requirement in NFPA25. By not following NFPA guidelines, the school district takes on all liabilities of the system.
The problems were found during a special inspection that included an examination of pipe interiors. During that inspection, bacterial growth, sludge and sediment were found.
All of the damage was said to have been caused by condensation in the pipes, as reported in Viechnicki’s article. Corroded sprinkler heads and a valve were also found in the school buildings, which were constructed in 1985 and 1986. The district already had to replace corroded pipes in the elementary school in 2014.
Corrosion can lead to pinhole leaks, limited effectiveness of fire sprinkler design, loss of property, loss of production, temporary shutdowns, total system replacements and personal injury. Corrosion in the sprinkler system may cause it to not operate correctly in a fire.
“This was just one small section of the entire expansive pipe system for the sprinkler system, which means five years from now they’re going to go look at somewhere else,” said Tate. “They might find similar problems.” In the article, he estimated that it would cost $25,000 to replace the damaged pipes.
Corrosion was listed by FM Approvals as the fourth-most common cause of sprinkler leakage losses from 2001-15, behind freezing, mechanical injury and defective equipment.
VdS, a German fire safety firm, found that 73 percent of dry systems have significant corrosion issues at 12.5 years old and 35 percent of wet systems have significant corrosion issues at 25 years after installation. For that reason, VdS guidelines specify that wet systems be thoroughly inspected after 25 years and dry systems after 12.5 years, adding that the inspections include an internal examination with an endoscope and a check of the residual wall thickness with ultrasonic measurement. That’s more relaxed than the NFPA recommendation of inspections every five years.
According to FM Global Reason Magazine, “There is no widely accepted strategy either within the fire protection industry or the National Association of Corrosion Engineers (NACE International) to effectively mitigate these types of problems in fire protection systems.”
An alternative to the above is using CPVC pipe rather than metal. Unlike metal, CPVC has a natural immunity to MIC (microbiologically influenced corrosion) and is not susceptible to oxygen corrosion. CPVC will remain corrosion-free for the life of the system. CPVC is approved for light hazard applications as defined by NFPA, such as schools, offices, hotels, long-term care facilities, and residential facilities.