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Home > Fire Sprinklers > Policies > Dry Pipe

Dry Pipe Policy

“Dry pipe” in this policy also includes all types of preaction systems

(This policy does not apply to deluge systems)

Dry pipe failures have a variety of causes.  This policy is meant to address the most blatant causes in a manner that offers options to those who bid, design, and install dry pipe systems and it is meant to provide clarity in these options so as to establish an even bidding field so that the life of dry pipe systems may be extended.

Nothing in this policy is intended to prevent the use of systems, methods, or devices of equivalent or superior quality, strength, fire resistance, effectiveness, durability, and safety over those prescribed by this policy.

For background, the predominant cause of internal dry pipe disintegration in Maine appears to be from the process of rusting.  In order for this process to occur there must be the presence of a ferrous metal, moisture, and oxygen.  Plastic pipe materials are not listed for dry pipe systems and copper is not practical.  Stainless steel to be effective needs to be the “316 grade”, not the “305 grade”, and is exorbitantly expensive. That pretty much leaves black steel or galvanized steel pipe for the dry pipe options, both of which contain ferrous material.  It is therefore important in safeguarding these systems to minimize the internal moisture and/or the oxygen.

Rule #1.  (Avoid Dry Pipe)  As a guideline, don’t use a dry pipe system if the space can be readily heated without creating a hardship, or if the space can be designed to meet a fire sprinkler exception for the space, or if an antifreeze system can be used. (Antifreeze systems are not practical for large-volume systems due to maintenance problems and high costs.  There are also other challenges associated with antifreeze. See our "Antifreeze Policy" for those details.)

Rule #2.  (Limit Dry Pipe)  When using a dry system, limit the system to the unheated area, (see NFPA 13, 2010 edition, section A.7.2).  For example, when doing the attic space, don’t use this to feed the top heated floor unless using dry pendents, (section 7.2.2).  Provide coverage for that top heated floor from a wet system.  Exceptions may be granted from our office to extend the dry pipe system coverage to heated areas when those portions are very minimal.

Rule #3.  (Loops)  Loops will only be allowed in dry pipe systems when there is proper pitch for all of the pipe in the loop or unless a nitrogen-generation system is used, or unless it can be clearly documented that the building life is to not exceed 5 years, or if conversion to a wet system is scheduled to be done in less than 5 years.

Rule #4.  (Pipe Type)  Galvanized pipe is discouraged because it has been shown that it tends to fail faster than black steel.  This is because the internal oxygen within a black steel system is spread over a large area, whereas in galvanized pipe, there is plenty of oxygen for the few cracks/chips in the internal galvanization that are created in the fabrication process.  Pin-hole leaks often occur within just a few years in galvanized pipe.  Galvanized pipe is allowed when nitrogen is used instead of air, or when it can be clearly documented that the life span of the building will not exceed 5 years, or if conversion to a wet system is scheduled to be done in less than 5 years. Special consideration will be given for galvanized pipe without nitrogen when the pipe is hot-dipped galvanized after fabrication. (It is interesting that the testing shows that galvanized pipe with nitrogen will typically outlast black steel pipe with nitrogen by about 20 extra years.)

Rule #5.   (Steel Pipe Wall Thickness)  Pipe thinner than schedule 40 may be used however schedule 40 pipe (or greater) is suggested on both mains & branch lines unless the pitch is excessive, (more than 1/2" per 10 feet), nitrogen is used, or when it can be clearly documented that the building life span is to not exceed 5 years, or if conversion to a wet system is scheduled to be done in less than 5 years.  This is not meant to limit new & improved technology pipe with prior approval from our office. Note also that good industry practice avoids having the pipe seam at the bottom since this seam is more susceptible to corrosion because the bottom of the pipe is where moisture tends to collect. This rule does not require anything different from NFPA 13, (which is a minimum standard as stated in section 1.1.1), but provides a "best-industry-practice recommendation".

Rule #6.   (Joint Types)  Roll-grooved joints are allowed, however it should be noted that threaded or cut-grooved joints are also allowed and that they minimally trap water.  When roll-grooved joints are used then it is suggested to use nitrogen to help minimize rust that occurs with the presence of trapped water at the joints. It is recognized that cut-grooving is largely a thing of the past due to the extreme expense in equipment and labor plus having field installation limitations, and that these three limiting factors often apply to large threaded pipe as well.  Nitrogen systems are the preference but the initial extra cost of the nitrogen setup can deter some clients from using this option.   Note however that if the system is very tight and bottled nitrogen is used, then an air compressor isn’t needed, which is a cost savings that may balance the cost of using nitrogen.  

Rule #7.  (Seals)  Whenever grooved joints are used, the seals must be flush seals or tri-seals. The seals must be listed/approved for use in dry pipe systems.  The old “C-shaped” seals will not be allowed since they trap water.

Rule #8.  (Pitch)  Pitch is to be at least ½” per 10’or better for mains as well as branch lines for non-refrigerated spaces whenever this can be achieved.  This is the minimum NFPA 13 standard for refrigerated spaces. Only where this cannot be achieved, either physically or by violating other requirements such as required proximities to ceilings, then the mains can be no less than ¼” per 10’ but branch lines must still be at least ½’ per 10’ to be in compliance with NFPA 13 .  When the minimum pitch requirements of NFPA 13 cannot be met, then nitrogen must be used, and extra low-point drains may be needed for questionable areas susceptible to trapping water. Exaggerate the pitch during installation wherever possible.

Rule #9.  (Drains)  Low-point drains must be installed for every area susceptible to trapping water.  This must be done according to section of the 2010 edition of NFPA 13.  Note that these drains must be readily accessible and that there must be a sign at the dry pipe valve that indicates the number and location of every low-point drain so that the system can be serviced properly.  The total number of low-point drains with their locations must also be indicated on plans submitted for a fire sprinkler permit.  Specify the type of low-point drain in each case, since 2-valve drains are required when the trapped water could exceed 5-gallons. As-built info is required to be submitted to this office when this changes in order to update the job file for future reference. There will be no fees for submitting the as-built info.

Rule #10.  (Heads)  Upright heads should be used where possible.  Pendent heads must be dry-pendents, not regular pendents for areas subject to freezing.  Return bends are not recommended, but they are allowed by NFPA 13 for heated areas. Return bends in heated areas are more acceptable when it can be clearly documented that the building life is to not exceed 5 years or if nitrogen is used or if conversion to a wet system is scheduled to be done in less than 5 years or if heads in this area are scheduled to be eliminated in less than 5 years, (such as a ceiling change that would switch the pendents to uprights).  Horizontal sidewalls must be dry horizontal sidewalls unless fed from below with vertical pipe, or otherwise are installed in a manner so as to not trap water or when they have low-point drains where they do trap water.  Return bends can be used when the return bend and the head are both in a heated area.  (NFPA 13, section (3) already specifies that they are limited to heated areas, but it is noted here as an important point).

Rule #11.  (Nitrogen)  There are two basic options for nitrogen.  One is to use bottled pressurized nitrogen.  These tanks are typically leased, serviced, & refilled for a very minimal expense. The other is to use an air compressor with an oxygen-nitrogen separator with reserve tank(s) and auto-purge, (and preferably with a leak detection system).  The latter type of nitrogen systems may be phased in, which is more practical when the dry system is more than 750 gallons since the air compressor is a separate unit on the larger systems.  For example, phase 1 may include the dehydrating compressor with the after-cooler & filters, and then phase 2 may include the nitrogen generator, storage tank, & auto purge. The acceptable time span between phases will be standardly about a year from the end of phase 1 to the beginning of phase 2, but may be longer if warranted.  Systems of this type are so effective that even with schedule 10 pipe, roll-groove joints, and the minimal pitches given in NFPA 13 they last for about 48 years according to test data. Nitrogen systems may do a full-flow trip test once every 5 years rather than once every 3 years, based on NFPA 25, 2011 edition, section 4.6 when it is documented that the system has otherwise been inspected, tested and maintained according to the prescriptive requirements of the currently adopted edition of NFPA 25.

Rule #12.  (Acceptance Testing)  NFPA 13 requires that all dry pipe systems be initially tested with water to check for leaks, (section 24.2 in the 2010 edition).  When cold weather does not permit this, then it allows testing with air until warm weather permits the testing with water.  The testing with air does not negate the requirement to test with water.  The testing with water is mandatory by all installers and must be completed before the permit can be signed off by the licensed Responsible Managing Supervisor.  All leaks must be repaired.  This is imperative because a leaky system will cause the air compressor to come on more frequently to maintain pressure, which will pump warm air into the system from which moisture will condense, thereby creating an enhanced environment for internal corrosion.

Rule #13.  (Plans)  Submittals for fire sprinkler permits must indicate all items above that apply. This info must be summarized on the plans.  Dry pipe systems will be scrutinized in the plan review for compliance to this policy before a permit will be issued.  Missing information will hold up the processing of issuing the fire sprinkler permit.  Field inspections by our office will prioritize the inspection of dry pipe systems for compliance to this policy.

Rule #14.  (Start of Policy)  This policy will go into effect Monday, November 12, 2012, (The first business day after 30 calendar days after posting onto our web page and notification by email to the licensed fire sprinkler industry.  It will not apply to jobs that were bid previous to the issuance of this policy.  We will fine-tune this policy as new technology and information becomes available.  Any change will be accompanied by an update to our web site and by email notification to the licensed fire sprinkler industry.


[First posted 10-6-12.]