Warehouses / Manufacturing Facilities

Large Scale Structures Having Potentially Large Scale Corrosion Problems

Large warehouse and manufacturing  facilities are primarily affected by corrosion problems at their fire sprinkler systems.  In sizes of up to 1 million square feet and greater, tens of thousands of linear feet of fire sprinkler pipe typically exist.  In most examples, office space is limited, and does not contain any significant piping other than domestic water.  Fire sprinkler pipe, however, holds the potential to cause not only water damage to inventory and production lines, but also threatens enormous replacement costs.

The potential for such damage is primarily dependent upon the type of fire system installed.

Dry Fire Service

“Dry” fire or preaction systems are unquestionably the greatest source of corrosion related failures for all building properties simply due to the fact that they are never actually dry.  Once filled with water for testing, substantial water remains behind having abundant air and oxygen to greatly accelerate the corrosion process.  Draining, even where the pipe is inclined to specifications, does not sufficiently remove the water.  In most indoor fire pipe installations, little to no incline or elevation of the pipe exists.

The raised rolled groove at every single pipe section and tee or elbow, common to all fire systems, itself produces multiple internal obstructions to water flowing back to its source.  And the larger the warehouse, in some examples having branch or distribution lines 300 ft. or more in length, the more impossible it is to remove the water.  Each quarterly test of the fire system unavoidably introduces fresh new oxygenated water into the system to perpetuate the problem.  Certainly they can be called “dry” and referenced as such, but unless no water has ever been introduced into the fire piping, a dry fire system is never actually dry.

Results From Remaininig Water

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Water Lines – A common finding at “dry” fire systems due to water remaining at horizontal lines.  Here, we show a water line at the 4 o’clock and 8 o’clock positions and straight line corrosion activity at its air / water interface.  Water level can vary dramatically for any dry fire system, and except for vertically oriented pipe, some water almost always exists.

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Bottom Failure – Water remaining in this section of dry fire pipe focused its impact directly at the bottom, and in specific areas to produce pinholes through the pipe wall.  In comparison, this approximately 5% coverage of water within the rolled groove barrier has the remaining 95% of the pipe volume of air and oxygen to aggressively drive the corrosion mechanism.

Failures at dry fire sprinkler systems at warehouse locations are typically at the bottom and lower sides of long horizontal runs, regardless of how it is pitched.  This is where water remains; fed toward higher corrosion and pitting activity by the abundant air and oxygen above it.  Galvanized pipe suffers similar deterioration; in fact often greater than carbon steel piping due to more aggressive localized pitting.

Vertical risers and smaller vertical sections of pipe typically show little corrosion loss.  Fortunately, dry fire sprinkler systems are less common to warehouse and manufacturing facilities, and are more likely to be installed at data centers, and at outdoor locations.

Wet Fire Service

Wet fire sprinkler systems at warehouse facilities, although technically wet or water filled in their design and installation, can exist dry in many areas to produce very similar failures to an actual dry or preaction system.  Except for the dry or preaction valve, its discharge and activation controls, and any additional incline provided to a dry fire system, dry and wet fire sprinkler systems are constructed similarly.

A critical fault for large warehouse facilities is the requirement to place the fire sprinkler head within a short distance from the absolute roof of the structure.  This in turn creates two major design flaws strictly from a corrosion perspective:

1.  Sprinkler heads directly threaded into long 2 in. or 2-1/2 in. branch or distribution lines must be fed from below in order to place the sprinkler heads close to the roof.  This in turn defines that air will be trapped in this area of pipe as all water is supplied from below.  Without carefully placed air vents at each and every high point, and a fire piping system designed to route the air to those vents, such areas of pipe remain airbound and partially water filled.  In effect, the wet fire system becomes a dry fire system in some areas, and therefore subject to the same higher corrosion activity.

2.  A large warehouse or manufacturing structure will have a bowed or concave roof profile along its length in order to shed the volume of rain water its large surface area will capture.  This in turn exacerbates the angle of the fire sprinkler pipe required to follow that roof bowed roof profile.  For most fire sprinkler systems at warehouses, the branch or distribution fire pipe is directly attached to the roof beams, thereby establishing the same upward curvature.  For a large facility, a difference of 10 ft. is possible between the side wall and center supports; producing an unavoidable sharp incline in fire piping profile.

For a dry fire piping system, such a steep incline is highly advantageous to the removal of water from its horizontal branch lines, but for a wet fire system, such design is negative, and only results in additional trapped air at the building’s peak.  Without air vents to each distribution line, (not the lower main feed line), accelerated corrosion activity is guaranteed.

Two Corrosion Causes

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Inclune – A steep incline for a dry fire system is greatly preferred, but for a wet fire system where the pipe is directly mounted to the curved roof beams, air is trapped at the top to produce an essentially dry fire system subject to the same higher corrosion and pitting activity.  Without air vents, this condition will ultimately lead to premature failure at the higher elevations of the fire system.

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Trapped Air – This standard design for large warehouse fire sprinkler systems, whereby the branch or distribution lines must be mounted to the top of the roof level, invites corrosion problems.  With the water fed from below, as the above photo illustrates, each branch line contains some volume of trapped air.  Abundant air and oxygen in that region then promotes significantly greater corrosion similar to a dry fire system

Some simple calculations illustrate the problem.  For a zoned wet warehouse fire sprinkler system comprising 500 ft. of 6 in. schedule 10 main feed piping, 7,500 ft. of 2-1/2 in. schedule 10 branch lines, and 450 ft. of back feeding 4 in. schedule 10 main, we can calculate an internal volume of approximately 439 cu. ft. of air.  Installed under atmospheric conditions, the piping system is then filled from below typically to 125 psi to 180 psi, which in turn forces the air upward as it is compressed.

Using the universal gas pressure formula known as “Boyles Law,” or (Pressure 1 * Volume 1) = (Pressure 2 * Volume 2), we can calculate the final volume of that 439 cubic feet or 3,282 gallons of air having now been compressed by the introduction of incompressible water at 150 psi.  In this example, we have (1 * 439) = 150 * V 2.  Solving for V 2 produces a result showing that the original 439 cu. ft. of air within the system is compressed down to  2.93 cu. ft. (21.7 gallons) of air remaining above the water line.  A larger volume of air will exist at a lower static pressure, and double this volume of air would eist at 75 PSI.  This trapped air does not simply disappear as often argued, but instead remains to accelerate the corrosion process.

With each linear foot of 2-1/2 in. schedule 10 pipe containing a volume of 0.038 cubic feet, we can then estimate that roughly 300 linear feet of pipe at its uppermost areas of the structure likely exist partially water filled (filled 25%) and therefore exist subject to the higher corrosion activity common to a true dry fire system.  With this mathematical illustration, it is easy to understand how placing the dead ended branch line piping ABOVE its source of water, absent adequate and properly placed air vents,  results in more advanced corrosion problems.

A further seemingly insignificant issue is temperature.  Temperature slightly expands and contracts the pipe as well as the air inside it.  This produces changes or movement in the water level to essentially wash the pipe back and forth at its air / water interface thereby even further accelerating corrosion.  Each release of water from the system and variation in air or water pressure via its jockey pump or air compressor also changes this water line to produce the same result.

Pipe Wall Thickness

Common to both forms of fire sprinkler system is the use of thin or light wall and ultra thin wall piping in today’s installation.  Ultra thin schedule 5 and schedule 7 pipe, however, is not called ultra thin wall, but typically labeled as being capable of flowing more water due to its greater inside diameter, MaxiFlow, for example.  Up front savings in cost, shipping, handling, and installation often has a significant payback, however, in terms of far lower useful service life under any other than extremely low corrosion condition.

Take as an example 4 in. steel pipe having a standard outer diameter of 4.5 in.  For schedule 40 pipe, commonly used for fire sprinkler systems decades ago, the original ASTM wall thickness is 0.237 in., shown at top left.

For thin wall schedule 10 pipe commonly installed today, that wall thickness is 0.120 in. or  approximately half.  Ultra thin wall schedule 7 pipe reduces further to a wall thickness of 0.098 in., with schedule 5 pipe offering even less.  Under equal corrosion conditions, failure is guaranteed far sooner as wall thickness is reduced.

Although the NFPA code calls for the use of heavier schedule 40 pipe where threaded, thin wall schedule 10 and ultra thin wall schedule 7 pipe is acceptable in threaded applications by using special threading dies and handling procedures.  Once again, various initial savings are gained in its original construction, but quickly disappear once failures occur requiring its replacement.

Threaded pipe introdues even greater threat where thin wall material is installed.  For 2 in. schedule 40 pipe having a wall thickness of 0.154 in., the loss of 0.070 in. at its outer thread cut still leaves 0.085 in. remaining.  For schedule 7 pipe having an initial wall thickness of 0.084 in., this same thread cut leaves only 0.014 in. at the threads – less than half the thickness of a common credit card.  Long service life is rarely possible; requiring an assumption that in contrast to all fundamental laws of nature, corrosion at such ultra thin pipe will not occur

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Dead Zones

The Leading Cause Of Pipe Failure At Condenser Water Systems

Despite various corrective measure, advanced failures at condenser water systems are on the rise. Many problems are engineered into the system from the start due to the failure to recognize the impact rust deposits and particulates have on producing higher secondary corrosion levels. In addition, most corrective measure, if they are attempted, fail to provide a solution. Here is why.


Undersized Steel Pipe

A Simple Dial Caliper Measurement Of New Steel Pipe May Reveal Surprising Results

In addition to the many corrosion influences negatively impacting piping systems, many new building properties are constructed using carbon steel pipe which is below factory specification. To the surprise of many, an FM or UL approval, like its ASTM stamp, does not define that the pipe actually meets ASTM thickness standards.


Inevitable Corrosion

The Decline In The Quality Of Today’s Piping Products Means Greater Corrosion Problems

A large number of negative influences have comined to produce a higher frequency of corrosion problems – often in spite of all precautionary measures taken. Of those, lower quality pipe, undersized pipe, more complex piping layouts, and generally less effective chemical treatment options have produced a “Perfect Storm” contributing to more piping failures.


Corrosion Threats

When Pipe Corrosion At A Fire Protection System Can Cost Lives

The time to learn of a fire pipe corrosion problem is not during an actual fire emergency. Internal rust deposits can, and have, totally blocked water flow through the sprinkler heads – resulting in the loss of human life. More common at dry systems, internal deposits are a serious threat to all fire protection systems.


Fire System Failures

Major Misconceptions Within The Fire Protection Industry

Ignoring the obvious does have serious consequences when it comes to fire protection systems. From the use of thin wall schedule 10 & 7 pipe, to lower quality pipe products, to frequent flow testing which brings in new fresh water, clear and well documented reasons exist to explain the higher corrosion activity found at today’s fire protection systems.


Fire System Corrosion

The Threat Of A High Corrosion Condition To A Fire Sprinkler Line

Often viewed only in terms of water damage in the case of a corrosion induced pipe failure, far more serious concerns exist, although rarely considered. Unlike HVAC piping systems, corrosion activity at fire related piping can impede and in some cases totally block water flow – a potentially life threatening condition during any fire emergency


Ultrasonic Testing

The Benefits of Ultrasonic Testing in Determining Corrosion Rate and Service Life

Ultrasonic testing provides the most comprehensive, accurate, and cost-effective tool to assess the condition and remaining service life of any piping system. Planned and performed properly, ultrasound offers the first step toward identifying a potential corrosion problem, or for certifying a piping system as fit for service.


Corrosion Influences

Why Not All Pipe Failures Are The Fault Of Your Chemical Water Treatment Provider

Various design elements to any piping system can have dramatic impact upon its corrosion activity. Pipe origin, schedule used, physical layout, and many other unknown factors can produce a pipe failure. And yet they are completely beyond the realm of protection offered by chemical water treatment.


Corrosion By Design

Pipe Corrosion Problems No Water Treatment Program Can Protect Against

Various changes have occurred to mechanical piping designs over the past few decades, with virtually all HVAC, plumbing, and fire protection systems having been affected in some way. Many changes relate to the materials themselves. Major changes in piping design, however, have introduced new corrosion problems no chemical treatment program can stop.


Corrosion Coupons

The Benefits and Limitations of Corrosion Coupons

Relied upon for decades as an indicator of corrosion activity within piping systems, corrosion coupons are highly unreliable in most examples, and totally worthless in others. Many of the most damaging corrosion failures have occurred while at the same time corrosion coupons produced excellent results. Here is why.


Unexpected Failures

If Corrosion Activity Is Only 0.4 MPY, What Is Wrong With The Above Picture?

Corrosion coupons reported a 0.4 MPY corrosion rate for 6 years where the actual rate exceeded 25 MPY. Believed implicitly in contrast to multiple leaks and failures, the slow but total destruction of the entire condenser water piping system was the net result. A case history illustrating the threat from relying exclusively upon this highly flawed testing method.

Dry Fire Sprinkler

Fire Protection Contractor – Antifreeze: The Fine Line Between Hero and Defendant

Antifreeze used in dry fire sprinkler systems may solve one problem, but has also proven deadly. Rated a Class 1 flammable liquid, antifreeze can accelerate a fire, create a fireball, and even cause an explosion. Although now restricted to lower concentrations, antifreeze still adds heat value to any fire and introduces new and unknown liability to any such system.


Corrosion Trends

American Welding Society – Understanding Pipe Corrosion Problems

A piping system that satisfies service life demands, requires the recognition of piping design vulnerabilities, effective corrosion monitoring, and the adoption of corrective measurements. With corrosion related failures on the rise, and with generally lower quality pipe being installed, advanced planning and an awareness of potential threats becomes more important.


Testing Procedures

World Pipelines – Investigation vs. Procedure

Substantially different findings are likely where ultrasonic pipe testing is approached as a forensic investigation based upon known system problems and vulnerabilities, rather than simply a linear based measurement procedure. A critical importance is understanding the inherent corrosion related problems to various piping systems. An adapting investigation will also produce a more definitive answer to any piping problem.


Fire Pipe Corrosion

Fire Protection Contractor – When Pipe Corrosion In a Fire Protection System Can Cost Lives

The time to first learn of a pipe corrosion problem is not during a true fire emergency when lives are in jeopardy. Thinner pipe, more corrosive steel, lower quality galvanizing, foreign pipe, dry systems, MIC – all such negative factors are driving toward higher internal corrosion deposits to render your fire protection system worthless.


Ultrasonic Testing

Fluid Handling Systems – Finding The Remaining Service Life

Ultrasonic testing is, by far, the most informative diagnostic method available for determining pipe status, as well as extremely cost effective. An effective piping analysis is much more than a spreadsheet of a few wall thickness measurements – requiring careful statistical analysis and practical interpretation of the data.


Pipe Corrosion

World Pipelines – Multiple Metering And Monitoring Needs

With no single form of corrosion monitoring capable of proving full coverage to the many different forms of pipe corrosion possible, multiple testing methods are always advised. These should include ultrasonic testing, spool pieces, LPR, regular internal inspection, and a close observance to the often obvious but missed signs of a problem.

A 30+ Year Knowledge Base










Unfortunately, the above is a very common progression of events for many of our clients. Often, greater attention to chemical corrosion control and corrosion monitoring could have saved the system and avoided the problem. In others, a decades prior design flaw or poor choice of pipe supplier may be traced back as the primary fault.

During the 20 years that we have been involved in the field of ultrasonic pipe testing / corrosion monitoring, we have authored various Technical Bulletins for the benefit of our clients. These Technical Bulletins address frequent problem issues to any building owner or operator, and offer both insight as well as reasonable and proven solutions.

We offer below the various categories available, and continue to add new bulletins as time permits.

Current Categories

Interior Rust Deposits, Common Threats, Corrosion Types, Winter Lay-Up, MIC, Corrosion Monitoring and Testing, CUI, Corrosion Coupon Failures, Rust Removal, Reducing Corrosion Threats, Roof Level Corrosion, Drained Pipe, Corrosion Trends, Fire Sprinkler Corrosion, Corrosion At “Free Cooling” Systems

The Impact Of Flow Rate To Higher Corrosion, Inadequate Water Filtration, Piping Layout Design, “Green” Piping Designs

Corrosion Threats, Design Misconceptions, Interior Rust Deposit Threat, Dry Fire System Corrosion, Schedule 10 Pipe, Premature Failures, Clogged Fire Systems, Chemical Control Options, Remediation Choices

Condition Assessment, Due Diligence, Preparation Prior To Renovation, System Evaluation, Expert Witness

Heat Exchangers, Benefits of UT Testing, High Pressure Water Jet Cleaning, Filtration Errors, Chemical Treatment, Condenser Tube Coating, Mold Concerns, Chromate Removal, Growing Threat of Corrosion, Heat Exchanger Tub Coating, Nondestructive Testing

Schedule 40 Limitations, Piping Trends, Hidden Corrosion Threats, Dielectric Insulators, Clamped Grooved Piping, Piping Schedules, Pipe Testing Specification, Roof Pipe Draining, Low Corrosion Guidelines, Dual Temperature Piping Failure

Cold Water Threats, External Corrosion Issues, Fire Reserve Tanks, Interior Pitting, Protective Coatings, Rehabilitation

Improving Heat Transfer Efficiency, Improving Filtering Efficiency, Filter Placement, Poor Performance Causes, Filter Selection Considerations

Chemical Treatment Challenges, Limitations to Water Treatment, Corrosion Coupon Reliance