Filtration 101

The Most Common Mistakes of Water Filtration Representatives and HVAC Design Engineers


A past client hires CorrView International, LLC to perform ultrasonic pipe testing at one of their older properties.  The pipe was installed in the early 1950’s using extra heavy steel.  They do not perform corrosion monitoring and have hired many different chemical water treatment companies over their history.  The quality of their past chemical treatment is questionable.

A common operational problem for the building is large pieces of rust which break off to produce flow restriction for the pump strainers.  Rust has sufficiently accumulated in the chiller heads to impact their operation, and have forced mid season condenser water tube cleaning.  Some examples of rust they have saved exceed 1 in. in diameter.  Frequent manual removal of the pump and chiller strainer elements are required for cleaning.  Their condenser water is also tinted a light brown color and has some turbidity.


Ultrasonic testing shows moderate corrosion activity of near 2-3 MPY, with moderate pitting activity but no severe wall loss.  Investigation identifies that the pipe has uniformly deteriorated down from an original 0.500 in. thickness to near or slightly below ASTM schedule 40 and standard specifications – the wall thickness that would today be specified were pipe replacement required.

Over 55 years of service has deteriorated the pipe significantly but it still offers many decades of additional service life.  Although they are removing higher than normal volumes of rust, we explain that approximately 18 times more iron oxide is produced from its original volume of steel.  A very common misunderstanding, the thickness of the rust lost does not represent an equal amount of pipe wall loss.

We recommend a review of the chemical treatment program for opportunities for improvement.  We also recommend the installation of a water filter combined with an effective dispersing agent to loosen and remove the rust back into the water flow for capture.  A centrifugal separator is recommended given the very large particles present.

One year later we receive a call from the building chief engineer requesting further ultrasonic testing at the domestic cold water main galvanized steel riser.  While on the property, we begin discussing their actions taken at the condenser water system and are told that they had a water filter installed and operating for approximately the past 9 months.  The filter was selected by their mechanical engineer based upon its very low sub-micron rating.

The building chief engineer relates that the filter turned their condenser water crystal clear, but that they are still plagued with rust in their strainers.  Further inspection shows the installation of a very popular sand filter capable of 0.6 micron removal efficiency at an approximate 120 GPM flowrate.  The filter is located at the roof level mechanical equipment room (MER).  Refrigeration machines are located in the basement.  No chemical cleaning or dispersing agent has been applied as the filter manufacturer states it is unnecessary.

The 2 in. inlet to the sand filter is located 12 o’clock on the top of the 12 in. diameter horizontal condenser water return line to the cooling tower and approximately 1 ft. after a wide sweep 90 degree elbow.  Filter blowdown is run to a large holding / settling thank.  The engineer relates that the filter worked great for the first few weeks and cleaned up the water as intended.  Shortly after, however, the filter slowed to a minimal backwash.  Although they suspect the filter is not operating correctly, service visits by the manufacturer claim it is working properly.  There is approximately a 2 lb. coffee container size volume of rust or other debris which has settled in the backwash holding tank, which has never been cleaned.

As installed, only the smallest particles of smallest mass can be sucked into the filter inlet line.  Located on the top of the 12 in. diameter return pipe, the filter inlet is directly opposite where any heavier particulates would likely exist – at the bottom.  Located downstream immediately after a 90 degree horizontal elbow further defines that any heavier rust or particulates will be forced to the outer wall of the elbow by inertia, velocity, and centrifugal force.  In short, it is virtually impossible for this filter to provide any real benefit to the system.

The filter had been viewed as a tremendous success by everyone involved.  Yet no one recognizes that there has been a very limited benefit of removing only those particles small enough to remain in solution long enough to be captured.  An interpretation of total success based upon the color of the water was unfortunately wrong.  In reality, only those smallest micron size particles having no possibility of producing a flow blockage were removed.


CorrView International, LLC reiterates our original recommendation that a Lakos style 12 in. full flow centrifugal filter would better control their problem, but they have already expended their capital budget.  We provide a written recommendation for the building to relocate the sand filter to the bottom of the supply riser where the pipe makes a 90 degree transition from its vertical shaft horizontally across the ceiling to the chiller plant.  Operating pressures at the base of the riser are within the limits of the equipment.

We recommend removing the existing 12 in. elbow and replacing it with a 12 in. tee to create a new dead leg.  We further recommend to extend this dead end approximately 4 ft. downward and then gradually reduce and valve it to 4 in. gate valve.  Following the valve, the line would be then further reduced to the 2 in. size required for the filter.  In this way, all rust particulates will be influenced by their own velocity, their inertia based upon physical size, and the force of gravity directly into this dead leg area.  Water will continue to turn as it always has, as a higher volume of particulates are captured.

The mechanical engineer (PE) for the building contacts CorrView International, LLC to question our recommendation, and to inform us that the current location of the sand filter and choice of inlet location was not only their recommendation after significant consideration, but also the recommendation of the sand filter manufacturer and local representative.  He suggests that we have provided no proof to any benefits of this filter relocation and that there is no cost justification for the shutdown and modification to a 12 in. condenser water riser.

We relate other experiences with the same issue but the design engineer disagrees and holds firm against relocating the filter.

Many months later, and after strugglles with management, the building’s chief engineer is finally successful at having the sand filter relocated.  He contacts CorrView International, LLC to thank us for the help, and to relate that they have almost resolved their rust deposit problem.  Large volumes of rust material are now collected in the backwash holding tank, which requires frequent emptying.

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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