System Dependent Corrosion

For many cooling water loops, and especially for open recirculating systems, dramatically different corrosion conditions can exist at various points throughout the piping layout. Often, the actual causes of such corrosion differences, such as at low flow areas or at long horizontal runs, are unavoidable. Similar differences in corrosion activity can exist at different areas of a fire protection system – for totally different reasons.

Following 30 years of experience in chemical water treatment and ultrasonic pipe testing, we have been able to predict problem corrosion areas simply based upon the physical configuration of the piping system. Some commonly recognized problem areas are summarized below:

Piping System

Corrosion characteristics are so different between different piping systems that they can never be evaluated as one. Condenser water has much higher corrosion than chill water, steam condensate higher than steam, and dry fire significantly greater than wet fire pipe. Pipe materials and their age also play a significant role.

Corrosion activity is typically related to a combination of pipe quality, water quality, chemical inhibitor quality, and water movement. Other issues play a less important role.

Corrosion monitoring for any piping system therefore requires a basic knowledge of its common corrosion problems, combined with an understanding of the system design.

Physical Location

Lower floor areas of the same piping system typically suffer a far greater degree of corrosion and pitting activity simply due to the settling of dirt, iron oxide, organic material, and particulates.

For many larger layouts, flow velocity decreases furthermost from the circulating pumps to allow settling of even the finest particulates.

Ultrasonic testing results showing a 4 MPY corrosion rate at the upper floors of a condenser water system, will often indicate higher rates at the bottom of the system. This higher wall loss in many cases also exists where piping has been reduced in size and therefore having less available wall thickness.

A seemingly reasonable and moderate corrosion rate of 5 MPY will actually produce tremendous volumes of iron oxide each year which will settle to produce secondary corrosion problems if not removed.

Pipe Orientation

Horizontal sections of pipe typically show a higher degree of sediment and deposit buildup, corrosion, and pitting than vertical sections – for the obvious reason.  Where a higher than normal corrosion rate exists, ultrasonic testing of horizontal lines will typically document significantly greater wall loss and pitting along its bottom surface.

Coupled with low flow conditions or the periodic loss of flow, as might occur with individual HVAC package units, horizontal piping can suffer at significantly higher corrosion rates.

Random Pitting

The net result from various corrosion mechanisms is often deep and random pitting which can only be defined through metallurgical analysis.

The presence of a microbiological agent or MIC condition is especially effective at producing random areas of extremely high wall loss often exceeding 25 mils per year (MPY). This produces often devastating results and is extremely difficulty and costly to correct.

Drained Conditions

Piping which is drained down over the winter months, or which is shut down and drained periodically, can suffer up to 10 times greater wall loss than other filled areas of the system.  Such corrosion loss is often directly proportional to the proximity to the open atmosphere.

This is a common problem for many Northern climate properties regardless of the standard lay-up precautions taken.

Supply and Return

Return side piping at a condenser or cooling water system often shows a higher degree of corrosion and pitting than for the supply side simply due to the slightly higher return water temperatures which favor corrosion activity and promote microbiological growth.  Higher temperatures accelerate most chemical reactions.

Higher return side corrosion may also be due to the secondary effect of rust particulates originating from the supply side pipe, or other factors.

Pipe Quality

Due to the generally lower quality of steel pipe today in comparison to that manufactured 50 years ago, higher average corrosion rates are common.  Where 1 MPY corrosion rates once existed many decades ago for condenser or open water service, 3-5 MPY corrosion rates are now expected, and 10 MPY rates are not unusual.  Pipe produced outside the United States seems especially more corrosion susceptible.

For reasons not fully understood, new piping additions and renovations will often show a higher corrosion rate than for the original piping itself.  Speculation is that rust deposit existing at the older pipe quickly migrate to the new pipe to initiate higher corrosion conditions.

Any new pipe should therefore always be monitored equally or even more closely than older areas of the system.

Low Flows

Stagnant areas can often develop severe pitting from the settlement of particulates and/or a lack of chemical protection.  The lower flow rates existing in the distribution and run-out piping to individual A/C or package units will often show accelerated corrosion in those smaller lines which can least afford it.

Pipe leading to rarely used plate and frame heat exchangers are especially vulnerable to this effect, and have been documented with as much as a 0.200 in. wall loss along the bottom due to particulate deposition.

Dead ends, by-pass lines, futures, lead and lag equipment, mud legs, and other no flow areas can produce corrosion rates well exceeding 15 mils per year, and accelerate pipe replacement decades before the rest of the system.  Any bottom take-off from a main service life is especially vulnerable.

Pipe Assembly

Rarely a corrosion related factor in the early stages of a piping system, pipe construction does play a critical role in an aged system.  End gaps of a Victaulic, Grinnell or other clamped type piping system often accumulate with particulates and microbiological agents to produce localized high corrosion and pitting losses.

Threaded pipe will almost always leak or fail prior to other areas due to the 50% or greater wall loss produced in the threading process, among other factors.

Cutting the groove into pipe used in clamped pipe assembly, rather than rolling or swaging it, has the similar effect of significantly reducing pipe wall life.  This wall loss, coupled with a high corrosion rate, will typically produce advanced failures.

Further Examples

articles corrosion galleryCorrView International, LLC offers a series of photo galleries taken from 18 years of past ultrasonic piping investigations, which address the above and additional corrosion conditions.  A review of the different types of corrosion is often helpful in initially determining the likely corrosion cause.

In many cases, however, a combination of conditions will exist within the same piping system.  View our extended Corrosion Photo Gallery of 27 different corrosion types and failure conditions.

The issue of corrosion is complex; typically relating to issues of maintenance, chemical treatment, pipe quality, engineering design, as well as less significant factors.  Rarely is just one issue responsible for a piping failure.  Investigating to the point of defining all aspects of a corrosion problem, and most importantly not excluding any area of interest, is the key to a successful resolve.

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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