Ingenial Fire Protection - Corrosion in Sprinkler Systems

CORROSION IN SPRINKLERS SYSTEMS

Microbiologically Influenced Corrosion of Fire Sprinkler Systems

The updated 1999 edition of NFPA 13 addresses MIC concerns.

by Dana Haagensen

In the past few years, the sprinkler industry has become increasingly aware of incidents in which micro biologically influenced corrosion, or MIC, has accelerated corrosion in t the metallic piping of sprinkler systems leading to leaks, blocks, and sometimes failure Recently, the industry responded to concerns about MIC by participating inthe revision of the 1999 edition of NFPA 13, Installation of Sprinkler Systems, and by creating products and services designed to prevent and mitigate MIC in fire protection systems.

Most metallic piping systems are subject to various forms of corrosion, and fire sprinkler piping is no exception. Traditionally, NFPA 13 has addressed this problem by providing conservative friction factors to be used when performing hydraulic calculations and by specifying minimum pipe sizes.¹

MIC, however, is a unique form of corrosion that can destroy piping in a few years by corroding the pipe wall, creating pinhole leaks, and causing corrosion prod- ucts to become attached to the piping's internal walls.² This corrosion further weakens the pipe wall in the affected areas.³

MIC isn't a new problem, but the relatively recent discovery of MIC in fire sprinkler installations has heightened the fire protection industry's concerns.^4,5,6,7 The discovery of MIC in sprinkler piping in industrial facilities, nursing homes, and in various areas across the country indicates that MIC isn't an isolated problem.^8,9,10 In fact, a National Fire Sprinkler Association (NFSA) study conducted between 1996 and 1998 reported approximately 30 cases throughout the United States in which MIC had affected the sprinkler systern.³

How MIC develops

As its name implies, MIC is caused by several different types of microorganisms that live on nutrients in the water and react with the products of other microorganism reactions and with piping material.^2,3,11 These microorganisms, which arc classified by the reactions and products on which they live, can be aerobic, requiring the presence of oxygen, or anaerobic, which don't require oxygen.¹¹

The microorganisms initially introduced into the fire sprinkler piping system through the water supply are aerobic and develop communities that live off the oxygen in the water or air in a dry-pipe system. Once local communities develop, anaerobic organisms continue to grow in the stagnant water without oxygen.³

Periodically, system tests and activations introduce oxygen into the water, rejuvenating the oxygen-dependent MIC organisms.³ And each time water is introduced into the system, the amount of MIC microorganisms and nutrients increase, as well.

Because MIC communities develop under specific conditions, corrosion is localized and can occur in multiple areas throughout the system. Therefore, treating the water and replacing the piping in one section of a system won't necessarily resolve the problem.

MIC and NFPA 13

Before the 1999 revision of NFPA 13, a task group was formed to look into the issues surrounding MIC and fire sprinkler systems. The task group presented a report to the Technical Correlating Committee on Automatic Sprinkler Systems that resulted in a proposal to add requirements to the standard.¹² This proposal was revised and adopted, and is now Section 9-1.5 of NFPA 13.

Section 9-1.5 doesn't require that all systems be treated for MIC. Rather, it stipulates that water supplies known to cause MIC be tested and treated appropriately. Since a variety of mechanisms can cause MIC, Section 9-1.5 doesn't specify a particular form of treatment, leaving that decision, based on the results of the testing, to the facility.

Where treatment is necessary, Section 9-1.5 requires that all water entering the system be treated, regardless of whether it's used to test or fill the system. Since Section 9-1.5 doesn't per-mit violation of any health regulations pertaining to additives in water-based systems, local regulations need to be examined, and any treatment must be documented in the sprinkler system plans, according to Section 8-2.2.

Treating MIC depends on the specific types of microorganisms causing the corrosion, so it isn't practical to require a universal treatment. For example, introducing chlorine into a system may destroy some of the microorganisms, but it may also promote other forms of corrosion. To determine which microorganisms are causing the corrosion, it's necessary to get a sample of both the sprinkler piping and the water in the system.

To obtain a sample of the affected piping, the facility may have to dissemble it or introduce a remote camera to help establish the level of pipe degradation, although non-intrusive inspections may also be carried out. Methods of examining the water supply range from using a do-it-yourself sample and analysis kit to having a testing laboratory perform the sampling and analysis.

The proper treatment depends on the type of corrosion and extent of pipe degradation. Water supplies for newly installed systems must be treated before the system is filled, in accordance with Section 9-1.5 of NFPA 13. System designers should consider specifying the installation of components necessary to make treatment connections. Existing systems with small amounts of corrosion or few affected pipes must be cleaned and the corroded portions of piping replaced. The piping and components of systems with a large amount of corrosion may have to be completely replaced.

Corrosion that isn't removed may block the water supply or become dislodged and obstruct waterflow from the sprinklers.² Corrosion can also prevent treated water from reaching the source of the corrosion.4 And because the degradation caused by MIC essentially eats away at the pipe wall, corroded pipe may fail at substantially lower pressures than the rated working pressure.3

Once the pipe has been cleaned and repaired, any water entering the system should be treated.

Products used to treat water supplies for MIC vary. In some cases, a continual treatment system can be permanently installed. In others, connection components can be installed to treat water as it enters the system. Or a source of pretreated water may be used to fill the system. The best solution depends on the arrangement of the system and the nature of the corrosion.

The suggestion that NEC spells the end of fire sprinkler systems is untrue.¹³ There's no indication that MIC will affect all sprinkler system installations, and problems posed by MIC can be prevented, mitigated, and resolved. Fire sprinkler systems remain an effective tool to protect life and property, and NFPA and the sprinkler industry will continue to develop reasonable solutions to deal with the threat of MIC.

1. NFPA 13, Installation of Sprinkler Systems, 1999 edition, NFPA, Quincy, Mass., 1999.

2. Microbiologically Influenced Corrosion in Fire Protection Systems, Altran Technical Notes, Altran Corporation, Boston, Mass.

3. Bsharat, Tariq, Detection, Treatment, and Prevention of Micrvobiologically Influenced Corrosion in Water-Based Fire Protection Systems, National Fire Sprinkler Association, Patterson, N.Y., June 1998.

4. Huggins, Roland J., RE., "Microbiologically Influenced Corrosion: What It Is and How It Works," Sprinkler Age, American Fire Sprinkler Association, Dallas, Texas, July 1997.

5. Borenstein, Susan Watkins, Microbiologically Influenced Corrosion Handbook, Woodhead Publishing, Ltd., Cambridge, England, 1994.

6. Kobrin, Gregory, ed., A Practical Manual on Microbiologically Influenced Corrosion, NACE International, Houston, Texas, 1993.

7. Fleming, H.-C., et al., ed., Microbiologically Influenced Corrosion of Materials: Scientific and Engineering Aspects, Springer, New York, 1996.

8. McReynolds, Gary S., Prevention of Microbiologically Influenced Corrosion in Fire Protection Systems at a Semiconductor Manufaduring Facility, Corrosion Conference, NACE Intrnational, Houston, Texas, 1998.

9. Shenkiryk, Myron, Mitigating MIC: McCarrrn International Airport System Cleaned to Correct for Microbiologically Infuensed Corrosion, www.sprinklernet.org/technical/mic/articles/article2.html, American Fire Sprinkler Association, Dallas, Texas, 2000.

10. Marshall, Roy, Iowa Authorities Suspect MIC: Nursing Home System Plugged With Rust-Colored Material, www.sprinklernet.org/terhnical/mic/articles/articlel.html, American Fire Sprinkler Association, Dallas, Texas, 2000.

11. Pope, Daniel H., Testing For and Treating MIC. Monitor For MIC to Help Prevent Long-Term Effects, vww.sprinklernet.org/technical/mic/articles/article3.html, American Fire Sprinkler Association, Dallas, Texas, 2000.

12. 1999 Spring Association Technical Meeting Report on Proposals, NFPA, Quincy, Mass., 1999.

13. Kammen, Jon, "Bacteria Spell Doom for Fire Sprinklers,' The Arizona Republic, October 24, 1999.