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May 2001Page 1 of 19

PREVENTION AND CONTROL OFINTERNAL CORROSION IN AUTOMATIC SPRINKLER SYSTEMS

Table of ContentsPage

1.0 SCOPE ................................................................................................................................................... 31.1 Changes .......................................................................................................................................... 31.2 Superseded Information .................................................................................................................. 3

2.0 LOSS PREVENTION RECOMMENDATIONS ....................................................................................... 32.1 Introduction ...................................................................................................................................... 32.2 Operation and Maintenance ............................................................................................................ 3

2.2.1 Existing Sprinkler Systems .................................................................................................... 32.3 Protection ......................................................................................................................................... 4

2.3.1 New Sprinkler Systems ......................................................................................................... 43.0 SUPPORT FOR RECOMMENDATIONS ............................................................................................... 5

3.1 Microbiologically Influenced Corrosion (MIC) .................................................................................. 53.1.1 What is MIC? ......................................................................................................................... 63.1.2 How MIC Affects Sprinkler Systems ..................................................................................... 63.1.3 Telltale Signs of MIC in Sprinkler Piping ............................................................................... 83.1.4 Industry Position and NFPA Requirements ........................................................................... 8

3.2 Test Data ......................................................................................................................................... 83.3 FM Global UT Protocol for In-Situ Examination of Pipe Internal Corrosion ................................... 93.4 Loss History ................................................................................................................................... 123.5 Illustrative Losses .......................................................................................................................... 12

3.5.1 Sprinkler Leakage Due to Corrosion in Pipe Coupling ....................................................... 123.5.2 Pinhole Leaks From Sprinkler System Over Data Processing Center ............................... 12

4.0 REFERENCES ..................................................................................................................................... 124.1 FM Global ...................................................................................................................................... 124.2 NFPA .............................................................................................................................................. 12

APPENDIX A GLOSSARY OF TERMS ..................................................................................................... 12APPENDIX B DOCUMENT REVISION HISTORY ..................................................................................... 12APPENDIX C ADVISORY GUIDELINES FOR MIC MITIGATION ............................................................ 12

C.1 Mitigation Plan ............................................................................................................................... 13C.2 MIC Prevention: Advice for New Sprinkler Systems .................................................................... 13

C.2.1 STEP 1 Diagnosis of water supply .............................................................................. 13C.2.2 STEP 2 Assessment of possible alternatives ............................................................. 14C.2.3 STEP 3 - Treatment of the local water with disinfectants or biocides ....................... 14C.2.4 STEP 4 Installation of clean pipe and care during system acceptance .................. 15

C.3 MIC Control: Advice for Existing Sprinkler Systems ..................................................................... 15C.3.1 STEP 1 Diagnosis of the corrosion and of the condition of the piping .................. 15C.3.2 STEP 2 Assessment of possible alternatives ............................................................. 16C.3.3 STEP 3 Cleaning of piping ........................................................................................... 16C.3.4 STEP 4 Treatment of local water with disinfectants and biocides .......................... 17C.3.5 STEP 5 Recharging of the system and acceptance .................................................. 17

C.4 Some Currently Available Mitigation Tools ................................................................................... 17C.4.1 MIC Test Kits ....................................................................................................................... 17C.4.2 Chemical Treatment Automatic Delivery Systems .............................................................. 17C.4.3 Chemical Cleaning of Pipe ................................................................................................. 19

FM GlobalProperty Loss Prevention Data Sheets 2-1

2001 Factory Mutual Insurance Company. All rights reserved. No part of this document may be reproduced,stored in a retrieval system, or transmitted, in whole or in part, in any form or by any means, electronic, mechanical,photocopying, recording, or otherwise, without written permission of Factory Mutual Insurance Company.

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List of FiguresFig. 1. Sample arrangement of wet sprinkler piping to prevent air accumulation in branchlines

and other high points of the system. ................................................................................................. 5Fig. 2. Schematic development of MIC. ....................................................................................................... 7Fig. 3. Corrosion at roll groove in a wet pipe system. ................................................................................. 7Fig. 4. Pinhole leak site in cut-away section of pipe. ................................................................................... 8Fig. 5. Pinhole leak site on outside surface. ................................................................................................ 9Fig. 6. Localized nodule formation below water line. ................................................................................. 10Fig. 7. Heavy tubercle formation in a 8 in. (200 mm) sprinkler pipe. ......................................................... 11Fig. 8. MIC test kit and automatic delivery system courtesy of Bio Industrial Technologies Inc. ........... 18

List of TablesTable 1. Guideline for Retaining Pipe Based on Extent of Corrosion Damage ............................................ 4

2-1 Internal Corrosion in Automatic Sprinkler SystemsPage 2 FM Global Property Loss Prevention Data Sheets

2001 Factory Mutual Insurance Company. All rights reserved.

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1.0 SCOPE

This document addresses prevention and control of corrosion in automatic sprinkler system piping withparticular emphasis on Microbiologically Influenced Corrosion (MIC).

1.1 ChangesThis is a new document.

1.2 Superseded Information

The guidelines for MIC provided in Data Sheet 2-8N, Installation of Sprinkler Systems, and Data Sheet 2-81,Fire Safety Inspections and Sprinkler System Maintenance, are superseded by this new document.

2.0 LOSS PREVENTION RECOMMENDATIONS

2.1 Introduction

The following recommendations are intended to:

Provide proper diagnosis of corrosion cases involving sprinkler systems;

Attempt to keep existing sprinkler systems affected by corrosion free of piping obstructions;

Minimize the exposure from possible water leakage losses resulting from MIC affected sprinkler systems;

Provide advisory guidance on possible corrosion prevention measures that can be considered for any newwet, dry and preaction sprinkler system. Recommendations for new systems should be considered basedon the occupancy and exposure present.

Locations wishing to pursue further corrosion mitigation than what is being recommended in sections 2.2and 2.3 should follow the guidelines given in Appendix C of this document; these guidelines are advisoryin nature and provide a systematic approach to corrosion mitigation. While these advisory guidelines mayincrease the chances of success in mitigating corrosion, and in particular MIC, they are not intended to rep-resent a complete solution to the problem. Their primary goal is to ensure that the integrity of the sprinklersystem is not further compromised and to prevent loss of protection or further impairments to the sprin-kler system.

2.2 Operation and Maintenance

2.2.1 Existing Sprinkler Systems

2.2.1.1 Investigate for possible corrosion problems and obstructed waterways any sprinkler system exhibit-ing pinhole leaks, or other signs of corrosion (such as scale, tubercles and other deposits) in pipes, valvesor sprinkler heads. Investigate possible waterway obstructions caused by biological growth (typically in theform of tubercles and biofilm) in accordance with Data Sheet 2-81, Fire Safety Inspections and Sprinkler Sys-tem Maintenance. Include in this investigation any piping leading to waterflow alarms and water motor gongs.Conduct obstruction investigation promptly as the adequacy of the sprinkler system is in question.

1. Flush sprinkler systems where investigation reveals obstructions of the waterway in accordance with theprocedures outlined in Data Sheet 2-81.

2. Replace any section of piping that contains obstructions that cannot become removed by flushing

procedures.

Note: Replacement pipe also may eventually corrode if the causes for corrosion are not addressed. In the par-ticular case of MIC, where a proven and universally acceptable solution is not yet available, replacementof pipe and monitoring of corrosion progress is a suitable and less costly alternative to more complex miti-gation options, such as cleaning and treatment, for most occupancies until a better solution is devised.

If galvanized pipe is used in an otherwise black steel pipe system, di-electric unions should be used at theblack steel/galvanized steel interface. This will prevent galvanic corrosion between the black steel and thegalvanized steel pipe.

3. Reinvestigate systems for waterway obstruction annually. This will help to monitor the condition of thesprinkler system and the regrowth of slime, tubercles, and scale in the system.

Internal Corrosion in Automatic Sprinkler Systems 2-1FM Global Property Loss Prevention Data Sheets Page 3


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2.2.1.2 Conduct metallurgical examination on a sample of the affected component to determine the typeand extent of corrosion mechanism involved.

2.2.1.3 Where the extent of corrosion damage to remaining pipe needs to be determined, use the FM Glo-bal protocol for in-situ UT examination of piping given in section 3.3 below. Consider replacement of any

section of pipe exhibiting pit sites with remaining wall thickness less than shown in Table 1.

Table 1. Guideline for Retaining Pipe Based on Extent of Corrosion Damage

Pipe Schedule % Wall Remaining in Any Single Pit

Schedule 40 25 or more



Hybrid Schedule 75 or more

Note: The information in Table 1 provides a working guide for determining whether piping should be retained or replaced. It is based onengineering judgement and on several cases of corrosion examined by Factory Mutual Research. This guidance is intended to identify thosesections of pipe which, because of the depth of the pit, a pinhole leak could develop in a relatively short period of time. However, it doesnot reflect the remaining useful life of a pipe.

2.2.1.4 Further mitigation in the form or cleaning of the piping or treatment of the water is not presently beingrecommended. However, in locations where these are being considered, follow the MIC Mitigation Guide-lines in Appendix C.

2.3 Protection

2.3.1 New Sprinkler Systems

2.3.1.1 Use new, clean pipe for all new sprinkler system installations and retrofits. Over occupancies deemedsensitive to leaks, consider the use of Schedule 40 pipe for wet, dry and preaction systems.

1. Where pipe undergoes fabrication, disinfect the internal surfaces of the pipe at the fabricator with a solu-tion of IPA (Isopropyl Alcohol) or equivalent disinfectant. After fabrication and disinfecting, cap pipe endsto prevent dirt and other residue from entering the clean pipe.

Caution: Do not use chlorine for disinfecting purposes. While under carefully monitored conditions weak chlo-rine solutions have been prescribed as biocide for wet systems, a solution of chlorine applied directly to pipeawaiting installation may induce corrosion.

2. Do not to leave open pipe exposed where it could accumulate dust, dirt, water and other residue priorto installation. Store pipes on pallets or blocks so that they are at least 1 to 2 in. (25 to 50 mm) above theground to prevent foreign material from entering the pipe prior to installation.

3. Certify disinfecting methods and procedures, as well as the pre-assembly storing condition of pipe in theAdditional Explanations and Notes section of the Contractors Material and Tests Certificate for Above-ground Piping.

2.3.1.2 In wet pipe systems:

Avoid repeated cycles of system shutdowns where the system is drained and recharged. This is espe-cially needed during renovations and maintenance in the system. Establish a work plan to minimize

sprinkler system shutdowns. Keep the systems charged as much as possible and keep impairments to aminimum.

Avoid air gaps (pockets) within the system, which can expose piping to dry/wet conditions. This is particu-larly important for branchline piping where air pockets tend to form in high points of the system as thesystem is charged. Air gaps can be avoided by providing means for air release at the highest point of eachbranchline as shown in Figure 1. Connect the highest points of branchlines to a minimum 12 in. (13 mm)gang air drain which is pitched and routed to a safe location outside the building. Provide the gang airdrain with a manual ball valve that can be opened for bleeding air out of the system. This arrangement alsowill serve as a possible re-circulation loop in case treatment of the water is desirable per the advisory miti-gation guidelines below.

When systems are provided with air release valves in conjunction with the gang air drain shown in Fig-ure 1, provide a pressure relief valve of not less than in. (6.4 mm) in size or an auxiliary air reservoir



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to absorb pressure increases caused by thermal expansion. Set the relief valve to operate at pressuresnot greater than 175 psi (12.1 bars) or 10 psi (0.7 bars) in excess of the maximum system pressure whenthe maximum system pressure exceeds 165 psi (11.4 bars).

2.3.1.3 In dry-pipe and preaction systems:

Avoid the use of roll grooved joints. Roll grooved joints in a dry sprinkler system promote water accumu-lation that can result in preferred corrosion sites.

Install pipe with proper pitch to promote drainage of all testing water and water vapor condensate within

piping. For additional corrosion protection, pressurize the system using dry Nitrogen (from cylinders or plant sup-

ply) and provide air supply as back up. Alternatively, install an air drying system so that the dew pointtemperature of the supply air is 20F (-6C) below the lowest expected room temperature for the loca-tion where the systems will be installed. Check air-drying systems at regular intervals as needed, to preventsaturation of the drying media and excessive humid air from entering the system.

Keep low point drains clean and drain condensate as needed to prevent water accumulation.

Fix air leaks to keep system as tight as possible.

2.3.1.4 Further mitigation in the form or cleaning of the piping or treatment of the water is not presently beingrecommended. However, in locations where these are being considered, follow the MIC Mitigation Guide-lines in Appendix C.

3.0 SUPPORT FOR RECOMMENDATIONS

3.1 Microbiologically Influenced Corrosion (MIC)

Over the past years an increasing number of leaks and other corrosion related problems have been associ-ated with microbial or bacterial activity in fire protection piping.

Corrosion influenced by the action of bacteria is a widely recognized phenomenon in the oil, nuclear, chemi-cal and sewage industry. This type of corrosion also occurs in domestic water systems. MIC is not a newcorrosion mechanism; however, its association to fire protection piping is relatively new.

Because of its nature and the complexity of fire protection piping, MIC is not easily controlled in fire protec-tion systems. Until very recently, except for pipe replacement, no other mitigation or treatment options wereavailable that could be viably applied to fire protection systems. In the last few years, the emergence of new

Fig. 1. Sample arrangement of wet sprinkler piping to prevent air accumulation in branchlinesand other high points of the system.



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alternatives in cleaning of pipe and a better understanding of treatment options have made MIC mitigationattempts possible. However, mitigation efforts in fire protection systems are still evolving and remain largelyempirical at present with no conclusive available field data on their long-term success. Conversely, severecases of MIC left unchecked in sprinkler systems can progress over time leading to an increased number ofleaks and possible obstruction of pipes and sprinkler heads.

3.1.1 What is MIC?

MIC is one of the many forms of corrosion that can affect sprinkler systems. In MIC, the onset of corrosioncells and/or the corrosion rate are influenced by the activity of different types of aerobic and anaerobic bac-teria and microbes within the piping system. Some of the bacteria and microbes related to MIC include: SRB(Sulfate Reducing Bacteria), SOB (Sulfur Oxidizing Bacteria), APB (Acid Producing Bacteria), IRB (IronReducing Bacteria), and LNB (Low Nutrient Bacteria). These types of bacteria are naturally occurring andcan be found in ground and surface waters; they also are found in soils, particles, oils and other sub-stances that can be present in the piping system prior to installation or that can be carried into the pipingsystem by the local water supply.

MIC almost always occurs concurrently with other corrosion mechanisms, and it is virtually impossible to sepa-rate them. This is in part due to the fact that microbes help create conditions under which other corrosionmechanisms can occur, such as crevice corrosion, pitting, and under-deposit corrosion. However, there are

major differences between the corrosion induced by bacteria and uniform corrosion within the piping sys-tems. Some of these differences are as follows:

MIC is usually localized and damages piping through progressive pitting corrosion. General corrosion usu-ally results from the oxidation of the iron on the piping and does not tend to be localized; the corrosionrate also will diminish once a layer of iron oxide (rust) is formed on the piping wall.

MIC affects almost all types of metals, including black and galvanized steel, copper, stainless steel andother steel alloys, with the possible exception of Titanium. General corrosion usually is associated withblack steel pipe.

MIC creates nodules and biofilms, while general corrosion will develop scales within the piping.

Once within the piping system, the bacteria and microbes tend to settle and attach themselves to preferen-tial regions within the pipe wall, such as small imperfections or crevices. The bacteria will thrive only wherenutrients and a favorable environment are available. Their activity in the initial stages is typically localized

within the piping system. Once established, the bacteria start reproducing and, very quickly create large colo-nies. A schematic of the development of MIC is shown in Figure 2 below.

The feeding, or metabolic, cycle of the bacteria produces different by-products, such as acids, sulfates,biofilms (slime) and nodules, depending on the type of bacteria involved. As these by-products accumulatethey foster conditions that make the growth of other types of bacteria possible, and influence the develop-ment of localized corrosion cells on the pipe walls. Corrosion cells resulting from MIC are typically coveredby nodules or by biofilm created by the metabolic bacterial process. Under a nodule, the pipe wall progres-sively deteriorates by pitting or other corrosion processes, until the wall is finally perforated and a pinhole leakdevelops.

Although there have been regions of the United States, such as the Phoenix, Arizona area, where a large num-ber of MIC cases have been reported and documented, there is presently no indication that MIC is confinedto any specific geographical area. Reports of MIC have been received from throughout the United Statesand also from abroad.

3.1.2 How MIC Affects Sprinkler Systems

MIC can affect any piping within the sprinkler system, however branchlines and risers seem to be moreseriously affected. In branchlines, the presence of air gaps in wet systems or undrained water in dry pipe sys-tems is believed to be a contributing factor. This is shown on Figure 3. In risers, the higher exposure tooxygenation compared to other parts of the system is believed to be a contributing factor.

Pitting corrosion is one of the most common MIC characteristics. This can happen throughout the system(see Figures 4 and 5).



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Fig. 2. Schematic development of MIC.

Fig. 3. Corrosion at roll groove in a wet pipe system.



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Given the nature of some of the aerobic bacteria, MIC generally results in the growth of biofilms and nod-ules within the piping. The biofilm produced will generally present itself as a black slime that, in certain cases,can be flushed out. Nodules, on the other hand, are hard, well adhered to the pipe wall, and will not flushout. Nodules and biofilm may result in increased friction loss, and affect the ability of the pipe to carry the nec-essary flow. Figures 6 and 7 show typical nodules and tubercles formation in a sprinkler pipe sample.

In addition to the above, MIC also may affect sprinklers and valves, and block water motor gongs and alarmlines and other components of a fire protection system.

3.1.3 Telltale Signs of MIC in Sprinkler Piping

Pinhole leaks, reduced flow capacity, nodules or slime deposits in pipes, sulfur like smell, and other relateditems are among the telltale signs of MIC. It is important for these signs to be recognized and investigated.

3.1.4 Industry Position and NFPA Requirements

MIC is now an industry wide concern and has gained the attention of groups such as NACE (NationalAssociation of Corrosion Engineers), NFPA (National Fire ProtectionAssociation), AFSA (American Fire Sprin-klers Association) and the NFSA (National Fire Sprinkler Association). NFPA 13 introduced new languagein paragraph 9-1.5 of its year 2000 code. These provisions require that in areas with water supplies knownto have contributed to MIC of sprinkler system piping, water supplies to be tested and appropriately treatedprior to filling and testing of metallic pipe systems.

3.2 Test Data

For the period between 1994 and 2000, the FM Global Metallurgical Laboratory has examined approximately155 cases involving failed sprinkler system components. These ranged from pipes of several diameters,materials and pipe schedules as well as other components such as fittings, sprinkler heads and valves.

Fig. 4. Pinhole leak site in cut-away section of pipe.



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Evidence of MIC was present in about 40% of all the cases involving sprinkler system components. The datacollected shows no indication that MIC is restricted to a particular geographical area, as MIC was evidentin components sampled from different geographical areas within North America and abroad. Also, there is noevidence that MIC is restricted to certain types of pipes or sprinkler components. MIC was found in corro-sion cases involving both black steel pipe and galvanized pipe of different pipe schedules as well as in cooperpiping. MIC also has been found in some cases involving corrosion of sprinkler heads, flexible steel hosesand other sprinkler components.

3.3 FM Global UT Protocol for In-Situ Examination of Pipe Internal Corrosion

Objective: Nondestructive, in-situ investigation of both wet and dry pipe systems with the objective of iden-tifying potential sites within the piping systems with advanced pitting corrosion.

Ultrasonic Thickness (UT) surveys of wet and dry pipe systems in-situ should be conducted in accordance

with the following protocol:

1. Make Ultrasonic Thickness surveys of sprinkler piping systems with Ultrasonic (UT) Examination Systemsthat incorporate a cathode ray tube or similar display.

These UT instruments are regularly referred to as Flaw Detectors. They are designed to detect small flawswithin a material. They are capable of displaying information from a reflector that enables an experiencedoperator to judge the shape, depth, and size of the flaw.

2. Do not use UT thickness devices that display thickness measurements only as a digital numerical reading.

These instruments cannot be relied upon to detect and measure pits in a sprinkler pipe. Digital thicknessgauges that display only a numeric reading are suitable only for thickness surveys where there is an over-all thinning of the piping wall. Such overall thinning can be caused by erosion, or corrosion. However in the

Fig. 5. Pinhole leak site on outside surface.



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case of corrosion in sprinkler pipes, the condition of the affected surface is more irregular, and usuallyinvolves pitting. In sprinkler piping, corrosion pits are usually localized, and can sometimes be quite deepin relation to their diameter. The evidence of pits is indicated by a numerical digital UT thickness gauge (if atall) as instability of the numerical read out. Because the UT beam is being reflected irregularly by the shapeof a pit, a numerical digital thickness gauge does not receive a coherent reflection. In such cases, the read-ing by an experienced operator of such a device might strongly suspect that a pit is being indicated. Thereis no information obtainable regarding the size, shape, or depth of the pit, unless it is quite large or largeareas of the surface are affected.

3. Remove outside paint from the pipe prior to UT scanning.

4. Scan the entire circumference of the pipe in search for pits, with particular focus on the bottom of thepipe between three oclock and nine oclock position.

5. Use any of the following modes of UT flaw detector display: A SCAN, B SCAN or C SCAN.

Ultrasonic examination instruments with cathode ray tubes, and more recently developed digital screens,can display the information from a reflector in a variety of ways.

Modes of UT Flaw Detector Display:

A SCAN

A SCAN displays are the most commonly used with portable UT flaw detectors. Ultrasonic reflectors are dis-played on the rectangular screen as base line deflection spikes. The horizontal axis represents materialthickness, and the vertical axis represents the amplitude of the reflected energy. Other controls and optionsenable an operator to precisely locate and measure small flaws.

Fig. 6. Localized nodule formation below water line.



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B SCAN

B SCAN displays are becoming very popular for monitoring thickness of tank and pressure vessel walls.The rectangular screen displays a profile view of a walls thickness, and the shape and depth below the sur-face of a flaw. In tank and vessel examinations, ultrasonic reflection data from all points scanned are recordedand usually stored electronically.

C SCAN

C SCAN displays data in a plan view. Images of pits would be displayed as round shadows on a flat sur-face, similar to a radiograph.

Any one of these flaw detector displays would be sufficient for sprinkler pipe thickness survey/pit detectionexaminations.

6. While using a flaw detector system to scan a section of piping, continuously monitor its relative thick-ness and search for pits. Once pits are detected, stop and measure the pit depth, diameter and theconcentration of pits in a given area. Mark the location of the pit in the pipe with an indelible marker or paint.

7. Prepare a final report with the results of the survey indicating regions of the pipe scanned; location anddepth of the pits in the sprinkler plan.

Fig. 7. Heavy tubercle formation in a 8 in. (200 mm) sprinkler pipe.



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3.4 Loss History

A study of sprinkler leakage losses for the period between 1988 and 1997 shows corrosion as the fifth larg-est cause of sprinkler leakage losses by dollar loss, preceded by mechanical injury, freezing, defectiveequipment and accidental discharge. While loss history has been favorable, it shows internal corrosion of

fire protection piping is a potential source of sprinkler leakage losses and a potential factor aggravating firelosses.

3.5 Illustrative Losses

3.5.1 Sprinkler Leakage Due to Corrosion in Pipe Coupling

A bolt for a 2 in. (50 mm) grooved pipe coupling rusted to the point that the 75 psi city water pressure causedthe bolt to break. This resulted in wet down of 71 pallet loads of pharmaceutical products in a warehouse.The suspected cause for the bolt rusting was a leak in the rubber seal onto the bolt for an extended periodof time.

3.5.2 Pinhole Leaks From Sprinkler System Over Data Processing Center

Pinhole leaks developed in a schedule 10 sprinkler piping system protecting a data processing center. The

leaks damaged records and computer equipment. This location was not insured with FM Global.

4.0 REFERENCES

4.1 FM Global

Data Sheet 2-8N, Installation of Sprinkler Systems.

Data Sheet 2-81, Fire Safety Inspections and Sprinkler System Maintenance.

4.2 NFPA

NFPA 13, Installation of Sprinkler Systems.

NFPA 25, Standard for Inspection, Testing and Maintenance of Water-based Fire Protection Systems.

APPENDIX A GLOSSARY OF TERMS

MIC: Microbiologically Influenced Corrosion.

XRD Analyses: X-Ray Defraction Analyses.

APPENDIX B DOCUMENT REVISION HISTORY

This document does not have any revision history.

APPENDIX C ADVISORY GUIDELINES FOR MIC MITIGATION

MIC mitigation is complex. While different companies and groups are presently undertaking considerableeffort to come up with a solution for the problem, mitigation activities remain largely experimental. Proper diag-nosis of the problem and a sound evaluation of the condition of the affected piping are key to the developmentof a mitigation plan with clear, attainable objectives. For the success of any mitigation activities it also is

important to constantly monitor the conditions inside the pipe and take corrective action promptly.

Factory Mutual Research is actively investigating possible detection, damage assessment and mitigationstrategies. Research in this area is expected to produce some preliminary results within the next few years.In the interim, advisory prevention and mitigation guidelines are included in this appendix. These are intendedas a source of guidance through the many steps of MIC prevention and control for those locations wish-ing to pursue further mitigation than what is recommended above. The goal of these guidelines is to helpsuch locations select technologies that will not cause further damage to sprinkler systems; they do not rep-resent a complete solution to MIC corrosion problems.

Mitigation guidelines are divided into two distinct groups. The first group includes those activities intendedto prevent MIC from developing in new sprinkler systems, particularly for those systems to be installed in areas



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where the water supply is known to be contaminated with MIC-causing bacteria and microbes. The secondgroup includes those activities to help mitigate or control MIC in existing sprinkler systems that are sus-pect or known to have MIC-related problems.

C.1 Mitigation Plan

All mitigation efforts should be under the direction of a registered professional engineer and performed inaccordance with a detailed work plan addressing:

Complete diagnosis of the corrosion problem.

Overall objectives of the mitigation effort.

A complete evaluation of the extent of corrosion damage to the piping, including identification of whatsections of pipe will require replacement.

A detailed description of the processes to be used to mitigate corrosion, identifying suppliers, chemicalsand dosages to be used.

A detailed cleaning and treatment plan as outlined in this guideline.

Expected downtime of the sprinkler system.

Plans for periodic monitoring and expected results at monitoring intervals.

Environmental impact assessment of the proposed effort.

Periodic monitoring reports should be kept on file for review.

C.2 MIC Prevention: Advice for New Sprinkler Systems

New sprinkler systems offer a unique opportunity for cost-effective MIC prevention. Such measures alsoare in line with the requirements of NFPA 13, Installation of Sprinkler Systems, as discussed above.

MIC prevention should include some or all of the following steps:

Step 1 Diagnosis of the water supply.

Step 2 Assessment of possible alternatives.

Step 3 Treatment of the local water with disinfectants or biocides.

Step 4 Installation of clean pipe and care during system acceptance.

C.2.1 STEP 1 Diagnosis of water supply

An analysis of the water will help determine whether there is a tendency for corrosion and whether thereare nutrients that can support the growth of bacteria, hence MIC. It also will help determine whether thereare sufficient residual disinfectants in the water supply or if additional disinfectants need to be added, and thetype of bacteria that can be encountered in the system.

Conduct a chemical analysis of the water to determine how corrosive the water is and whether it can sup-port biological organisms. Important issues to identify in a local water test are alkalinity (pH); suspended solidsor turbidity, total organic carbon, chemicals, including sulfates and residual disinfectant for public water sys-tems. For untreated water it also is important to determine whether SRB and IRB are present in the watersupply.

Information about the local water condition should be obtained directly from the plant or from the contract-ing sprinkler installer. Water authorities normally carry only information about the condition of the water as itleaves their treatment facilities but not necessarily about the condition of the water at the point of use. Infor-mation about the water condition at the point of use remains mostly in the private domain.

In addition, test the local water supply to determine the types of MIC-causing bacteria present in the water sup-ply and in the supply piping at the point of connection to the plant. This test for MIC-causing bacteria isrelatively simple and inexpensive, and can be accomplished by using portable MIC Test kits or by a quali-fied testing laboratory.



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C.2.2 STEP 2 Assessment of possible alternatives

Based on the results of the water supply analysis investigate other possible cost-effective alternative sup-plies for one that is superior. This could include wells, lakes and other reservoirs. Generally, the leastexpensive way of providing water for fire protection is through a direct feed from the public fire main, since pub-

lic fire mains typically carry enough pressure and/or flow to supply the fire protection system without theneed for fire pumps and tanks.

If no superior water supply is available or feasible, consider providing continuous treatment to the water sup-ply with biocides (disinfectants) and corrosion inhibitors as described in Step 3 below.

C.2.3 STEP 3 - Treatment of the local water with disinfectants or biocides

Water, as it enters the sprinkler system, should be treated with disinfectants (to kill or control the growth ofMIC causing bacteria) and with other corrosion inhibitors. The treatment should be evaluated for its corro-sive properties, and a treatment plan should be developed in accordance with the FM Global guidelines givenbelow. All incoming water supply to the sprinkler system should be treated.

One of the challenging aspects of treating water to sprinkler systems is that sprinkler systems are typicallynon-recirculating systems. This makes it difficult for treatment chemicals to reach and maintain prescribeddosages in all pipes within the system.

One of the biocides more commonly used in wet systems is a weak solution of Chlorine (typically no morethan 50 ppm), which is effective against MIC bacteria and can be obtained at relatively low cost. Chorine hasalso been used in several MIC-infected sprinkler systems to date. Other biocides and disinfectant optionsexist.

When biocides are used in a sprinkler system, they may create cross-flow conditions, which require the instal-lation of a back-flow preventer in the fire protection system. The treatment prescription, including the typeand dosage of biocides should be formalized in the MIC Mitigation Plan.

C.2.3.1 FM Global Guidelines for Treatment of the Local Water Supply

Use these guidelines where a preventive or post-cleaning treatment plan for sprinkler system water is beingconsidered.

1. Use only NSF (National Sanitary Foundation) approved, noncombustible, chemicals (biocides, disinfec-tants, corrosion inhibitor or passivating agents).

2. Independent laboratory test data should be provided confirming that the prescribed dosage is effectiveagainst the types of MIC-causing bacteria found in the water supply.

3. Plan should address general corrosion of the piping.

4. Delivery devices used to add treatment chemicals to sprinkler systems should be automatic and capableof delivering the prescribed maintenance dosage based upon flow in the system. Delivery devices shouldbe arranged to sound an alarm in case of trouble or failure, such as low tank. Devices should be providedwith an indicator giving the biocide concentration being delivered.

5. Field test data should be provided showing that with the intended delivery devices the prescribed dosageis met at the inspectors test connection.

6. Data should be provided showing that the type and dosage of the selected treatment chemicals is not dam-aging to any of the materials present in piping, valves, or sprinkler waterways, including any elastomericproducts used in sprinkler piping, such as those used in gaskets, o-rings, valve seats.

7. Plan should include treatment of all incoming water to fire protection sprinkler systems. When conduct-ing an inspector test, allow enough water flow until biocide is coming out at the other end.

8. The application rate of the treatment chemicals should be enough to promote the desired concentrationthroughout the system and to compensate for any decay of biocide concentration over time, anywhere withinthe system.

9. Treatment plan should identify all necessary periodic monitoring and tests to be conducted as well ascorrective measures during the life of the system.



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10. Plan should identify what measures should be taken when system is flooded with untreated water aftera fire or accidental trip.

11. Records detailing the treatment agents, concentration, injection process for the initial treatment as wellas for all periodic monitoring should be kept on file and on a summary record sheet displayed on the riser

of each system undergoing water treatment.

C.2.4 STEP 4 Installation of clean pipe and care during system acceptance

The last step in MIC prevention for new sprinkler systems is to ensure that all piping installed is disinfected,and that proper hydrostatic test procedures are used. This step should be taken to minimize the possibilitythat bacteria or microbes are present in the new piping to be installed or are introduced into the system acci-dentally during hydrostatic test or other acceptance procedure.

Regardless of the condition of the water supply, all piping to be installed should comply with recommenda-tion 2.3.1.1 above. Piping that is rusted or weathered should not be installed.

Where the water supply is treated, all hydrostatic tests and other acceptance test procedures should be doneusing treated water in accordance with the guidelines established in Step 3 above.

C.3 MIC Control: Advice for Existing Sprinkler Systems

Mitigation of MIC in existing sprinkler systems can be complex and costly. Because nodules, tubercles andother deposits on the internal surfaces of the pipe can shield microbial colonies and corrosion cells, biocidetreatment of the incoming water alone may not suffice to control MIC. Therefore, before treatment is appliedto the water, the piping should be thoroughly cleaned. Cleaning of pipe should be aimed at removing alldeposits to bare metal.

Cleaning existing pipe to bare metal can be challenging depending on the amount and type of deposits. Whereonly partial or non-uniform cleaning of the pipe can be achieved, microbes can re-colonize in the pipe fromthese partially cleaned areas. Subsequent water treatment to partially cleaned pipe may be able to con-trol the bacteria count, keeping the corrosion in check and helping extend the life of the piping system.

Mitigation activities in existing sprinkler systems should include one or all of the following steps:

Step 1 Diagnosis of the corrosion and of the condition of the piping.

Step 2 Assessment of possible alternatives.

Step 3 Cleaning of piping.

Step 4 Treatment of the local water with disinfectants and biocides.

Step 5 Recharging of the system and acceptance.

C.3.1 STEP 1 Diagnosis of the corrosion and of the condition of the piping

The first step involves determining the nature of corrosion in the piping and conducting a corrosion dam-age assessment of the piping to determine extent of corrosion damage and feasibility of further treatment.

Diagnosis of the corrosion should be conducted per recommendation 2.2.1 above. Preferably, piping shouldbe sent in for metallurgical examination in the as removed condition, without any cleaning or removal ofinternal deposits or substances, so that a metallurgical lab can analyze the nature of the residuals found in

the piping.

Assessment of the condition of remaining piping should be conducted per recommendation 2.2.2 above.Any sections of piping that are damaged or that do not meet the criteria given in Table 1 should be replacedprior to cleaning. Remaining piping should then be cleaned as outlined in Step 3 below.



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C.3.2 STEP 2 Assessment of possible alternatives

Similar to what is done with new sprinkler systems, it is important to determine to what extent an existingsprinkler system is exposed to MIC. Information about the local water condition should be obtained directlyfrom the plant or from the contracting sprinkler installer. Water authorities normally provide only informa-

tion about the condition of the water as it leaves their treatment facilities but not necessarily about the conditionof the water at the point of use. Information about the water condition at the point of use remains mostlyin the private domain.

In most cases, however, the condition of the local water supply with respect to MIC is not known by plant per-sonnel or by the installing contractor. In those cases, the local water supply should be tested for the presenceof MIC-causing bacteria. This test is relatively simple and inexpensive, and can be accomplished by usingportable MIC test kits or by a qualified testing laboratory.

If the local water supply is free of MIC-causing bacteria, then it could be used in the existing system. If thelocal water supply is determined to carry the MIC-causing bacteria, then it may become necessary to exploreone or more of the following options:

Option 1 - Investigate other possible cost-effective alternative supplies for one that is free of MIC-causing bac-teria and microbes. This could include wells, lakes and other reservoirs. Normally, the least expensive wayof providing water for fire protection is through a direct feed from the public fire main. This is because pub-

lic fire mains normally carry enough pressure and/or flow to supply the fire protection system without the needfor fire pumps and tanks. For most sprinkler systems, public water supplies can be used directly or in con-junction with booster pumps to increase supply pressure to meet the demand of a fire protection system. Pubicwater supply systems also may require the installation of a back-flow-preventer to eliminate cross connec-tion problems. As other alternative supplies are explored, the cost of providing water for fire protection mayincrease. The increased cost may be offset by the additional costs for the continuous treatment necessaryfor a supply that is known to carry MIC-causing bacteria.

Option 2 Provide continuous treatment to the water supply with biocides or disinfectants to eliminate or con-trol the growth of the MIC-causing bacteria, as outlined above for new systems.

C.3.3 STEP 3 Cleaning of piping

Cleaning may become a key step in mitigating MIC in existing sprinkler systems. Cleaning should be doneso that all internal surfaces within the piping are cleaned to bare metal . Advances in chemical clean-ing methods have now made it possible for piping to be cleaned in place. The following guidelines should applyto any cleaning method:

C.3.3.1 FM Global Guidelines for Cleaning of Sprinkler Piping

1. A written cleaning plan should be developed identifying:

how cleaning will be conducted,

which methods, chemicals or other cleaning agents will be used,

an outline of the process and the process sequence,

the concentration of any chemicals to be used,

the duration of the cleaning process,

disposal of cleaning solutions.

2. A cleaning test should be conducted in at least three sections of pipe, removed respectively from theriser, a mid-system branchline including a riser nipple for a sprinkler and inspector test connection. All pip-ing should be sampled from the actual sprinkler system to undergo cleaning.

3. Metallurgical examination should be conducted on all sample piping subjected to the cleaning test toassess the extent and uniformity of cleaning, the internal condition of the piping with respect to corrosion dam-age including the depth of the pitting and the loss of piping wall during the cleaning process. Wall thicknessprior to testing should be benchmarked by UT or equivalent testing. Results of the analysis should beincluded as part of the cleaning plan.

4. All sprinkler heads should be removed from the system prior to cleaning. Cleaning agents or solutionsshould be circulated through all riser nipples and drops to sprinklers. Used sprinkler heads should not be rein-stalled in the system.



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5. Cleaning agents should circulate throughout the system to promote complete cleaning of all piping, includ-ing all branchlines, pipe drops and sprig-ups, all risers, feedmains and crossmains.

6. After cleaning, metallurgical examination should be conducted on at least three more samples of pipingremoved from the riser, mid-branchlines and inspector test connection. This examination should determine the

extent and uniformity of cleaning performed.7. Chemical cleaning solutions should be NSF approved.

8. Cleaning agents should not result in damage to any of the metals present in sprinkler piping or damageto natural or synthetic rubber, silicone, or any other elastomeric products used in gaskets, valve seats, o-ringsand other nonmetallic parts in a sprinkler system.

9. No residual cleaning agents or solutions should be left in the system after cleaning.

10. Any cleaning should be immediately followed by a treatment of the water. The treatment plan shouldbe in accordance with FM Global Guidelines for Water Treatment for Sprinkler systems, given above.

C.3.4 STEP 4 Treatment of local water with disinfectants and biocides

All systems undergoing cleaning should be treated afterward. Cleaning will leave exposed fresh metal withopen pits. If treatment is not provided promptly and continuously these exposed surfaces will rapidly cor-rode. Hence, it is equally important for the treatment plan to address the MIC problem as well as general andpitting corrosion within the exposed fresh pipe. Treatment plan should follow the FM Global Guidelines forTreatment of the Local Water Supply.

C.3.5 STEP 5 Recharging of the system and acceptance

The last step in MIC mitigation is to ensure that existing system piping is recharged properly. Properhydrostatic test procedures should be used any time sections of piping have been replaced and after clean-ing. In order to minimize the possibility that bacteria or microbes are reintroduced into the new piping duringhydrostatic testing, this test should be conducted using properly treated water.

System should be recharged with water that has been treated following the guidelines established above.Past experience has shown that after cleaning is completed some pinhole leaks were encountered in the pip-ing. This is because the cleaning process is mildly corrosive or abrasive and can open up pits. Leaking pipe

should be replaced. If treatment is effective, pinhole leaks should stop after a few weeks.

C.4 Some Currently Available Mitigation Tools

This section discusses some of the currently available MIC technologies in the United States. The intent ofthis section is to provide information and general comments about technologies available.

Reference to a particular technology does not represent FM Global or Factory Mutual Research endorse-ment of a particular company, procedure or technology.

C.4.1 MIC Test Kits

MIC Test kits and portable kits can be used to test the local water for MIC bacteria. These kits include anumber of small vials with the nutrient for the different bacteria being tested. With a pipette or syringe, a watersample is collected from the sprinkler system injected into the different vials.After an incubation period of sev-eral days, results on the type and count of bacteria are read directly from the vials, by the change in color

of the different vials.

MIC test kits should not be relied on as the sole source of diagnosis for MIC, but as just one of the informa-tion components of the diagnosis. The kits also should not be used as the sole means of monitoring theeffectiveness of mitigation measures in the field.

C.4.2 Chemical Treatment Automatic Delivery Systems

These are new products intended to automatically deliver water treatment solution to a sprinkler system.Delivery systems consist of a reservoir where the chemicals are kept, a small injection pump that starts auto-matically when there is water flow in the system and an alarm to indicate trouble with the unit. Chemicaldelivery systems are typically fixed systems permanently connected to the riser. The system will deliver the



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prescribed dosage of treatment solution to the system automatically upon flow in the system. The cost ofthese delivery systems varies but should be in the range of US $3,500 for well-equipped delivery systemsuninstalled.

Fig. 8. MIC test kit and automatic delivery system courtesy of Bio Industrial Technologies Inc.



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C.4.3 Chemical Cleaning of Pipe

Chemical cleaning is aimed at removing build-up and corrosion scale from the inside walls of the pipe. Theprocess involves the circulation within the piping of chemical solutions at prescribed concentrations. Itrequires establishing a temporary re-circulation loop between the chemical supply unit and the sprinkler sys-

tem. Typically a sprinkler system can be cleaned in one day. The riser as well as the end of branchlinesand sprinkler head outlets needs to be tapped so that re-circulation hoses can be connected to system. Thecost of the procedure varies according to work schedules, occupancy types, quantity and type of system.


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