Microbiological Influenced Corrosion

Mitigating MIC

McCarran International Airport System Cleaned to Correct for Microbiologically Influenced Corrosion

by Myron Shenkiryk, h.e.r.c. Products

The effects of corrosion, especially Microbiologically Influenced Corrosion (MIC), in fire protection systems are costly and potentially disastrous. Pinhole leaks are one obvious indication that MIC is present. The cost of lost time and damage to products and equipment from the leaks is often many times that of the necessary repairs. Another MIC problem is the buildup, or "tuberculation," inside the piping impacts the hydraulic characteristics of the pipe and can break off into pieces that could plug a sprinkler. In recent years the industry has recognized and begun to focus on MIC.

A Case Study

A terminal at the McCarran International Airport, Las Vegas, Nev., was experiencing an unusually high number of pinhole leaks in its fire sprinkler system. During the course of repairing these pinhole leaks in the less than 10-year-old system, airport technicians noticed a significant amount of internal buildup of tuberculation nodules in the system piping. This internal buildup caused concern over the system's ability to perform to its hydraulic specifications. Additionally, the possibility of the buildup breaking off and plugging the sprinkler heads in an emergency event led the airport authority to investigate methods of correction.

In July 1996, McCarran International Airport personnel decided to use the PIPE-KLEAN® fps (patent pending) cleaning process to chemically rehabilitate the standpipe system in the International terminal. The laboratory results from testing the internal buildup of the pipe samples sent to HERC Products showed Microbiologically Influenced Corrosion (MIC) was the culprit. High levels of iron, as well as aerobic and sulfate reducing bacteria were present in the system.

The project started with the standpipe system. Due to the non-uniformity of the internal buildup in the system, an isolated circulation loop was designed using a HERC patented Mobile Recirculation Unit (MRU) to pump the PIPE-KLEAN C cleaning solution through the standpipe system. The chemistry was circulated for approximately two hours to remove the MIC and internal buildup. The PIPE-KLEAN fps process calls for the monitoring of specific gravity, pH and total dissolved solids during the cleaning process to track the cleaning progress. A CCTV system was then employed to scan the pipe interior to ensure that all the buildup had been dissolved and removed. The spent cleaning solution was then evacuated from the system, neutralized, and discharged to the sanitary sewer with the appropriate local regulatory approvals. HERC's PIPE-KLEAN C chemistry is a low pH, aqueous organic biocleaner with dispersants and inhibitors that has been certified to ANSI/NSF Standard 60 for the use in potable water systems and applications.

With the successful cleaning of the standpipe system, the airport then engaged the services of HERC's PIPE-KLEAN fps to clean the entire wet sprinkler system in the International terminal in March 1998. A joint effort of Grinnell Fire Protection Systems Company's Las Vegas, Nev. office and HERC Products was planned to clean the fire protection system of the terminal, which consisted of four separate systems with a combined total of over 1600 sprinkler heads. Due to the passenger traffic, the cleaning schedule was limited to a 48-hour window, beginning Monday at midnight and concluding Wednesday at midnight each week.

After draining the system and protecting the work area, each sprinkler head was removed and replaced with a valve assembly attached to plastic hose with connections to a series of manifolds. These manifolds were connected to the patented MRU, which pumped the PIPE-KLEAN® C cleaning solution through the isolated system. Over 300 sprinklers were removed during each 48-hour cleaning schedule. Once the cleaning process was complete, the sprinkler heads were cleaned and reinstalled.

In order to control MIC, some type of post cleaning water management is necessary. McCarran opted to work with their contracted chemical supplier to treat the water used in their fire protection system with a non-oxidizing biocide.

This is one case in which the effects of MIC have been mitigated. Using HERC's process, McCarran was able to remove the MIC presence from the entire fire protection system in their International terminal in only 240 hours over a five-week period.

Editor's Note: HERC Products Inc. is based on Phoenix, Ariz., and can be reached a 602-492-0336.