Technical Bulletin: FP-03
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Premature Failures
| Major Misconceptions Within The Fire Protection Industry |
Prehistoric cavemen likely figured out how to put a fire out with water long before they learned how to create it. In the millions of years since, and especially within the past four or five decades, major improvements and innovation within the fire protection industry have dramatically reduced this threat and saved countless lives
With the ever increasing sophistication of today’s fire protection systems, however, corrosion problems not entirely recognized, not understood, or simply not addressed, have emerged. The failure of fire protection systems due to corrosion is growing in terms of frequency, severity, cost, and in a few very tragic examples – in human lives.
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Corrosion Is Enemy # 1
The primary threat to the longevity and proper operation of all fire protection systems is corrosion. Add water to steel pipe and it will attack the steel to produce an iron oxide rust product. It is an unstoppable electro-chemical act of nature as reliable as gravity. Allowed to continue at an advanced rate and only two results are possible – corrosion will deteriorate the pipe resulting in a leak, or the iron oxide corrosion product will build-up sufficiently to reduce or stop water flow during a true fire emergency. Failure may take a few years to many decades, with this threat entirely hidden from view.
This threat of fire pipe corrosion has not been adequately addressed by the fire protection industry on multiple levels; with other interests and concerns taking priority. As the same mistakes continue, the corrosion threat and its related losses increase.
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The Obvious Problems
Ironically, the mandated testing and re-filling of fire protection systems is the primary act most responsible for their destruction. Fill a section of steel pipe with water, cap it tight, and a small amount of corrosion will occur until the oxygen is depleted and the corrosion process essentially stops. But introduce fresh, oxygenated water on a regular basis, as mandated by current fire codes, and the corrosion process not only continues, but typically accelerates.
This example of fire sprinkler main from 1928 perfectly illustrates the issue, with current wall thickness still at new schedule 40 specifications after 82 years of service. Only minor surface rust is present primarily due to a complete lack of water flow testing and no introduction of fresh water into the system. An ultrasonic investigation had shown the entire fire sprinkler system in near new condition.
This is why corrosion activity is highest at the very beginning of a fire system closest to the source of fresh water – such as city water feeds or at the outlet of active fire reserve tanks. While pipe failures at the beginning of a fire system are common, failures at the final run-out lines to the sprinkler heads are typically low. Fire standpipe risers show the least corrosion problems, while dry fire systems show the greatest. The relationship is clear and well documented.
Modern fire protection systems, most of which are actually quite simple in design, are constructed of high quality components rigidly inspected. Steel pipe, although typically thin wall and of lower quality and corrosion resistance today, still offers high strength and no possibility of physical or pressure related failure. Yet, on the first day after a new fire protection system is installed, an assumption is made that it will fail to perform and water flow testing is initiated on a regular basis to inadvertently guarantee its ultimate ruin.
Many fire systems will provide very long service, with failures at others commonly related to their physical design, construction, material selection and quality, and of course, the volume of flow testing performed.
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Material Weakness
Poor pipe quality is a common issue and concern for fire protection as well as all piping systems – whether black steel or galvanized. Since fire protection systems are bare pipe filled with untreated fresh water, this threat becomes even more pronounced.
Foreign pipe is especially susceptible to corrosion, and often of poor quality. Installing pipe from Korea, Thailand, China, and most foreign sources, for still unexplained reasons, is an almost 100% guarantee of future trouble. Yet, it is found at over 60% of the fire systems we investigate. The deteriorating quality of American made pipe further reduces available options.
Seamed or ERW welded pipe introduces another vulnerability – with incomplete or defective weld seams a common source of failure. Any corrosion condition, and especially MIC, will typically focus its attack at this most vulnerable area. Add in thin wall schedule 10 pipe, and the threat of failure escalates dramatically. Schedule 10 pipe has roughly half the wall thickness of schedule 40 – a major factor where higher corrosion is present. Drop down to thinner schedule 7 pipe or less, and that threat further increases.
Although NFPA Chapter 13 defines the use of heavier schedule 40 pipe where threaded, it does allow thinner materials if approved. Less cost always means it will be installed, with the result being even more advanced failures. For 2 in. schedule 7 pipe having an initial wall thickness of 0.084 in., an outer thread cut of 0.070 in. leaves only 0.014 in. of pipe wall remaining at the threads – barely half the thickness of a common credit card. This may be sufficient to hold the pipe assembly together, but it will likely fail unless strict threading protocols are followed using special dies, leaving zero allowance for the corrosion guaranteed to occur.
Amazingly, many fire systems are designed and constructed using such thin materials; seemingly under the absurd assumption that corrosion doesn’t exist.
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Undersized Pipe
ASTM, the American Society For Testing And Materials, allows a 12.5% manufacturing tolerance for steel pipe. In past decades, almost all pipe manufacturers produced pipe at or above that ASTM factory wall thickness. Today, however, most new pipe is found to be below its published wall thickness; with manufacturers seemingly taking advantage of this tolerance to their benefit.
For 6 in. Schedule 40 pipe, a 10% shortage will still provide long service life assuming that corrosion activity is low. But for 2 in. thin wall schedule 10 and 7 pipe, the impact is dramatic. No, its not the 0.084 in. thin wall schedule 7 pipe you believe you have used in your design or have installed, but 0.074 in. or even less. And that is on day one before corrosion even begins!
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Galvanized Steel Pipe
The most obvious solution to the problem of corrosion within fire protection systems, one might reasonably think, would be to use galvanized steel pipe instead. In fact, that would be true if galvanized pipe was of the quality made decades ago. Although a common sense alternative, galvanized steel piping will often fail far in advance of its black steel counterpart.
Galvanized pipe corrodes quite differently than black or carbon steel pipe. Whereas a corrosion attack against black steel pipe is generally widespread and uniform against its entire circumference, the attack against galvanized pipe is typically very random, severe, and localized. Shown in the photos below, all corrosive potential focuses its attack against any slight weakness in the galvanizing finish – similar to a magnifying glass focusing the sun’s energy. Drill bit style holes are a common corrosion characteristic to galvanized steel pipe.
Given the noticeably lower quality of today’s galvanized pipe, both foreign and domestic, no real benefit exists in its use over black pipe except that it will not produce the high volume of rust deposits prior to its failure. As one manufacturer of schedule 10 galvanized pipe stated to us:
“The real benefit of thin wall galvanized pipe is that it will fail long before internal corrosion products can build-up enough to clog it up.”
Very true, but not quite a selling point to advertise!
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Dry Fire Sprinkler Systems
An enormous corrosion threat exists to all dry fire systems. First and foremost, a dry fire system is “dry” in name only, and always contains some volume of water. Abundant water typically remains after testing to ensure the highest level of deterioration of any fire system – regardless of the efforts used to remove it.
Most dry systems we investigate are installed dead level, and even if installed having the ½ in. per 10 ft. pitch defined by NFPA Chapter 13, have a grade still entirely inadequate to remove the water. Significant water always remains, with a water line up 50% to 75% of the pipe wall not uncommon.
This was obviously the condition at the below “inclined” sections of “dry” fire sprinkler pipe; opened for inspection. For any fire piping system of known dimensions, design programs will precisely calculate the volume of water it contains when full. Removing less than 25% of that amount is an important first clue to the corrosion problems which will soon appear.
For any roll grooved fire system, the groove itself becomes a primary barrier to drainage. Dry fire pipe installed parallel to parking garage down ramps having a steep 10° decline have still produced severe localized wall loss due to trapped water immediately above the rolled groove – proving the impossibility of draining a dry fire system constructed to current grade requirements.
Unlike wet fire systems, where the oxygen required for corrosion to occur is gradually depleted, dry fire systems have an abundant supply of air and oxygen to maximize corrosion activity. Regular draining and testing then replenishes the system with new fresh water and more oxygen to guarantee the highest level of pipe wall deterioration.
Left to continue, sufficient rust product can and has accumulated to reduce or completely stop water flow. In the below photo taken at a “dry” parking garage 4 in. fire main, sufficient rust had accumulated in many areas to totally envelop the side branch port lines. No water would have ever reached the sprinkler heads, and the condition never been known to exist except for a leak and subsequent investigation.
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Cleaning & Flushing
This internal dry fire pipe photo was taken from a system which was regularly tested, flushed, inspected, and certified as suitable for service. Our archives alone contain hundreds of additional examples. As an extended tree root like network of one way piping, it is virtually impossible to flush any fire system of debris using currently employed procedures. Similarly, it is impossible to sterilize a system against MIC, clean it of cutting oils, eliminate trapped air, or completely drain it of water.
Codes can exist, and procedures followed under the pretense to accomplish such functions, but in reality, a wet or dry fire system’s inherent design prevents any truly effective success to the above.
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Design Induced Failure
The design of fire protection systems has unfortunately not caught up with the reality and inevitability of future corrosion problems which ultimately destroy them. The demand to install fire sprinkler heads at the very top of a warehouse ceiling, for example, ignores the obvious fact that air rises. With water fed from below mains to the above branch lines, air is trapped in every line, and will produce high corrosion losses, high rust deposits, and advanced failures equal to dry fire systems.
Designing a galvanized fire system should mean an entire galvanized fire system, and not just the straight pipe. The combination of black steel fittings and galvanized pipe ignores the potential for galvanic attack against the zinc finish by the black steel. Welding black steel branch couplings to galvanized pipe burns away the internal zinc protective coating to immediately initiate higher localized pitting. Cold galvanizing the outside only improves its appearance; ignoring this newly created internal source of failure and now establishing a zone of high corrosion activity opposite the welded area. Advanced failures along welded seams is the common result.
Galvanizing the pipe after port welding is required, yet rarely performed. Fabricated fire sprinkler pipe is rarely galvanized after welded on modifications so that the internal surface is protected as well. In some instances, as shown below, common silver spray paint was found in the attempt to simulate a galvanized steel sprinkler run-out line at a fully galvanized steel pipe dry fire system. The bottom right photograph shows an example before cold galvanizing, which has corroded due to minor humidity.
Carbon Steel to Galvanized Outside Protection Only
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Basic Mistakes
Very common errors in the design, construction, or maintenance of a fire protection system are often the source of failure. A minor packing seal leak and minor drip at a fire pump, insignificant in terms of the volume of water lost and usually ignored, becomes immensely important due to the volume of fresh oxygenated water introduced into the system. This leads to the advanced deterioration of the inlet line; with all pipe after the pump and check valve often untouched.
Installing thin wall schedule 10 pipe at any city water inlet line, in close proximity to the city feed having flow and therefore saturated oxygen content, will mean its advanced failure in only a few years. Fire pipe which is sweating means there is a downstream leak bringing in cold fresh water. This is a sign that higher corrosion activity is occurring and the need to find and repair the leak – not insulate the pipe, as we have seen in multiple examples.
Concern to the vulnerability of clamped or threaded fire pipe located within critical areas such as computer data centers and electrical switch-gear rooms has produced the totally absurd recommendation to weld together galvanized steel dry fire pipe. This action immediately initiates an aggressive corrosion condition along the interior weld seam. Coupled with schedule 10 pipe, often of foreign origin, and failure within a few years is virtually guaranteed.
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Changes Needed
As we have often stated:
A fire system that fails after 50 years is a result of natural forces and old age. One that fails after two years is someone’s fault.
Our investigation of a wet fire standpipe system in San Francisco, installed after the great earthquake and fire of 1906, showed it in still new condition after providing over 100 years of service. Yet many new fire systems may last only 10 years, and often less.
Today, major shifts in the fire protection industry toward thinner materials, more complex designs, and greater testing has had a dramatic effect in reducing the protection such efforts were intended to provide. Across the United States, a significant amount of false security exists due to a hidden enemy that has, in many ways, been unknowingly enabled.
You can view and download our two page handout on this subject below.
© Copyright 2023 – William P. Duncan, CorrView International, LLC