Corrosion has become a hot button issue in recent years, as aging fire sprinkler systems are beginning to develop leaks. Building owners turn to their fire sprinkler contractor for answers, who in turn often look to the governing standards for the industry to help in determining the next steps to take.
However, because of the long development process of updating standards, a lag is beginning to develop between the current standards and the best practices used today as they relate to corrosion monitoring. An overview of some current standards covering corrosion testing and investigation in the fire sprinkler industry are discussed below.
NFPA 25 – Inspection Testing and Maintenance of Water-Based Fire Protection Systems
NFPA 25 is typically the first resource for a fire sprinkler contractor when trying to find guidance on what testing should be performed on a fire sprinkler system. Chapter 14 covers two primary investigations that can help in determining the effects of corrosion on the fire sprinkler system: the Assessment of Internal Condition of Piping (formerly referred to as the Five-Year Investigation) and the Obstruction Investigation.
The Annex for this chapter provides several options for how these testing requirements can be met:
- Opening up the system at select locations to look for signs of corrosion/obstruction
- Using video inspection equipment to get a better look at the internal conditions
- Using ultrasonic testing technology
- Laboratory analysis of water samples from the system
FM Global Property Loss Prevention Data Sheet 2-1 – Corrosion in Automatic Sprinkler Systems
FM Global’s Data Sheet 2-1 provides a good overview of corrosion in fire sprinkler systems, as well as some information on monitoring corrosion in water-based fire sprinkler systems.
In terms of inspection and testing, the Data Sheet makes several recommendations for systems experiencing leaks:
- Inspect pipe using a video camera-based borescope, looking for signs of obstructions. If obstructions are found, flush the systems to remove obstructive material
- Perform metallurgical examination on a sample of affected pipe to determine the type and extent of the corrosion mechanism involved. This allows for a corrosion prevention plan to be put in place
NFPA 13 – Standard for the Installation of Sprinkler Systems
While NFPA 13 covers the requirements for the installation of new sprinkler systems, it does touch on some testing requirements for corrosion. Specifically, Sections 184.108.40.206 and 220.127.116.11 require that source waters be evaluated for conditions that could lead to Microbiologically Influenced Corrosion (MIC) and other unusual corrosive properties.
Based on our experience with testing for corrosion and obstructions in water-based fire sprinkler systems, we've found that some of these testing methods are more effective and beneficial than others.
- Opening only select locations on a sprinkler system can lead to a false sense of security.
- Corrosion is often highly localized to discrete areas within a fire sprinkler system. In wet systems corrosion is most severe at system high points near pockets of trapped water, while dry and preaction systems experience corrosion at system low points, where trapped water is present. Careful consideration should be given to where the piping is opened for inspection.
- Testing of source and system water samples for indications of corrosion are often focused at identifying the presence of bacteria that can contribute to MIC.
- This testing completely ignores the effects of primary corrosive factors which play a much larger role in the corrosion of the system piping, namely oxygen corrosion.
- While ultrasonic testing can be used to determine the amount of wall loss that has occurred at a given point, the highly localized nature of corrosion in fire sprinkler systems makes finding the most severe metal loss extremely difficult with this non-destructive method.
- Obstruction potential and risk can not be quantified by ultrasonic testing alone.
The ECS recommended method of monitoring systems for corrosion and obstruction risk includes the use of a video scope in conjunction with removing pipe samples at the most severely corroded areas. The hard data gathered from these two exercises allows us to determine both the location and severity of corrosion within the system, as well as obstruction potential. This hard data can be used by the building owner/service contractor to make informed decisions on mitigating these risks.
Have specific questions about industry regulations or corrosion control? Ask our team below.