The CorrView ® corrosion monitor is a new product specifically designed in response to the inherent inaccuracy of corrosion coupons, and to the need to measure pipe wall loss under real world conditions. That is, under the same conditions as exist for the pipe metal itself. CorrView ® is also designed to provide long term and low cost wall loss monitoring where conditions or interests do not allow for any form of regular corrosion testing, and where no corrosion monitoring would be otherwise performed.

     Unfortunately, corrosion coupons, the most common form of corrosion monitoring used today, fall far short of providing accurate corrosion rate data, and often produce wall loss estimates dangerously lower than actually exist. Other testing methods, such as spool pieces and LPR electronic monitoring, are often not practical on the scale necessary to produce sufficient statistical information.


     A history of comparison between corrosion coupon results vs. actual pipe wall loss, as confirmed by ultrasonic wall thickness testing, consistently shows an under reporting of metal loss using corrosion coupons by 5 to 10 times - and in some examples by as much as 200 times or more. For building operators or plant engineers responsible for millions of dollars of mechanical equipment and infrastructure, a total reliance upon questionable corrosion coupon results can spell disaster - and often does. See Technical Bulletin # C-14 for a case history of how a total reliance on corrosion coupons concealed a major corrosion problem for years.

     This is not due to failure of the metal coupon per se, which well represents the corrosion potential of the liquid itself, but due to its placement externally to the piping system. The coupon rack testing configuration inherently eliminates most of the normal corrosion effects found within the pipe, and therefore less effect is shown by the coupon under lab analysis. Corrosion coupons often represent no relationship between the corrosion occurring at their surface, and the corrosion occurring at the pipe surface. Read more about the limitations of corrosion coupons.

     Our own corrosion studies have documented the similarity in wall loss between corrosion coupons and common mild steel pipe samples under a controlled salt spray environment. Side by side testing has shown a general similarity in corrosion rate when under similar conditions - the key factor missing when coupons are installed in an isolated side stream loop. View corrosion testing reports

     In effect, CorrView ® functions as the direct opposite of standard corrosion coupon monitoring in two very important aspects. First, its wear surface is located directly within the piping system, whereas the coupon wear surface is located externally.

     Second, time period of exposure is decided in days or months for corrosion coupons, and the amount of material lost through any corrosion activity is measured following that exposure. With CorrView ®, the thickness of material to corrode away is predetermined, and depending upon the existing corrosion activity, the time that it takes to wear away will change. Fixed time vs. varying metal loss for corrosion coupons, as opposed to fixed metal loss vs. varying time for CorrView ®.


     Adequately monitoring a piping system for corrosion activity is generally prohibitive using any of the previously available testing methods.


Installed in an isolated loop, corrosion coupons never suffer the same environmental effects as the pipe itself, and rarely provide accurate test results. Hardened deposits, electrical activity, under deposit corrosion, micro biological buildup, flow effects, and other common environmental factors typically do not exist for corrosion coupons.

A flow requirement, by definition, prevents their installation in precisely those locations traditionally showing the highest corrosion threat.

In addition, installing corrosion coupon racks at multiple points throughout a circulating system is not practical and is almost never performed - thereby forcing the unlikely assumption that the test results shown for one specific location are representative over the entire piping system.



Periodically cutting out samples of pipe for metallurgical analysis is extremely expensive, usually requires a system shutdown, is rarely carried out for large diameter piping, and for any critical or 24/7 operation - is virtually impossible to perform. Combined maintenance and metallurgical costs can easily exceed $4,000 per sample.

Metallurgical analysis does offer valuable information unavailable through any other means, and is especially useful in order to identify the cause of a corrosion condition, but is generally limited in use due to its cost and inconvenience.

Metallurgical analysis usually plays an inportant role in defining a corrosion problem, rather than discovering one.



Spool pieces, which are nothing more than removable sections of actual pipe within the system, provide valuable information regarding the actual net effect of corrosion activity against the pipe surface. Unfortunately they are only applicable for smaller diameter piping separate from the main lines.

Properly installed, spool pieces offer a true inside look at deposits, surface pitting, inhibitor and cleanout effectiveness, as well as provide samples for micro biological cultures. Like corrosion coupon racks, however, they are rarely installed throughout a piping system and enjoy limited use.



Ultrasonic wall thickness testing provides the greatest volume of reliable data, and will typically produce a thorough corrosion evaluation as long as a sufficient number of test points are taken.

Ultrasound is often used as a prerequisite to other testing methods due to its low cost and wide coverage, or as a confirmation that wall thickness conditions known to exist in one area do or do not exist elsewhere within the piping system.

It is most often used as a tool to identify the extent of an already recognized leak or rusting problem, and long term corrosion monitoring using ultrasound requires establishing specialized testing procedures. Read more about ultrasonic pipe testing.



A wide variety of electronic techniques eixst to produce an estimate of corrosion rate generally based upon the principal of Linear Polarization Resistance, or LPR.

LPR provides the benefit of an immediate corrosion measurement that can be routed to monitoring electronices, or data logged for download, and offers an extremely useful corrosion measurement tool.

LPR is generally expensive to install and maintain. Regular celaning and calibration is often required, and even then, results may not approximate true corrosion activity - expecially if underdeposit corrosion or MIC is active.



The insertion of a remotely controlled camera into the pipe offers a valuable thought very limited inspection option. Its use requires the system to be out of service and drained, and is greatly limited by access into the piping system. Pipe size, physical configuration, internal conditions, and length of travel offer further restrictions in its use.

Remote Video Inspection (RVI) cannot provide any wall thickness data, but can quickly locate those internal indications that wall loss has occurred - such as tubercular deposits, deep pitting, or suspected MIC growths.

Combined with ultrasound or metallurgical testing, RVI can quickly and cost effectively document whether similar problem conditions exist in other areas of a piping system.



X-ray offers limited application for a piping evaluation primarily due to its high cost and safety concerns. While x-ray can provide the wall thickness values necessary for a true pipe condition analysis, it is most often used for the inspection of weld integrity or for identifying cracks, voids, or a major localized deterioration in a pipe material.

Cost, health, and environmental issues severely restrict its use in all but the most critical of applications.



  Similar technology also exists for an excellent but rarely used tool in measuring a wide variety of piping related problems. Its use of safe, low powered gamma radiation rapidly identifies areas of higher wall loss - quickly locating those areas in need of further investigation.

By detecting variations in metal density, this hand held device can also detect pipe blockages, identify wet insulation, show liquid level, or confirm pipe schedules, etc.



     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 20 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:


 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.

Ultrasonic testing results showing a 4 MPY corrosion rate at the upper floors of a condenser water system, will often indicate substantially 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 in available wall thickness. See Technical Bulletin C-14 showing where a 6.5 MPY corrosion rate at the roof increased to a 22 MPY rate at its lowest point.

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 problems if not removed. See Technical Bulletin # C-1 for the actual pounds of metal lost and deposits created at various corrosion rates.



Horizontal sections of pipe typically show a higher degree of sediment and deposit buildup, corrosion, and pitting than vertical sections - for the obvious reason.

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.



Within horizontal sections of pipe, and often depending upon flow rate, the bottom and lower side wall areas often show significantly higher metal loss - again due to the settlement of rust and particulates.

Even under 24 hour moderate flow conditions within large diameter main riser piping, ultrasonic testing has often documented the presence of under deposit activity - as suggested by a randomly elevated corrosion rate and in some cases deep pitting.

The presence of significant differences in wall thickness from top to bottom of any same section of horizontal pipe should always provide a warning of an interior deposit problem.



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 micro biological 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 difficuly and costly to correct. See Technical Bulletin C-5 regarding the MIC threat.



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 properties regardless of the standard lay-up precautions taken. See Technical Bulletin C-3 about this well documented problem.



Return side piping at a condenser or cooling water system often shows a higher degree of corrosion and pitting than for the supply side - this may be due to the slightly higher return water temperatures which favor corrosion activity and promote micro biological growth.

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



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, 3-5 MPY corrosion rates are now expected. Pipe produced outside the U.S. 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. Any new pipe should therefore always be monitored equally or even more closely than older areas of the system.



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.

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.



  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 micro biological 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. See Technical Bulletin P-1 regarding the inherent weakness of threaded pipe.

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. See Technical Bulletin P-3 about the threat created by cutting the groove for clamped pipe construction.


     Obviously, pipe corrosion activity is a complex mechanism which cannot be reliably predicted by any one means. It is therefore necessary to establish a corrosion monitoring program that will not only provide accurate and relative information to what is actually taking place at the pipe, but to also address those areas of the system where elevated corrosion activity is likely to take place.


     It is important to remember that while the variance in wall loss, corrosion rate, and pitting will fall within a certain range of values for most piping systems, that range of values will widen substantially when a serious corrosion problem exists. As corrosion rates and pitting activity increase, so does the probability that random piping areas may produce sufficient weakness in the pipe to cause a leak or operating problem.

     This greater fluctuation in corrosion rate simply increases the existing danger of having a corrosion rate determination based upon only one monitoring technique, and at only one monitoring location.

      It was with the interest to address such concerns that the CorrView ® corrosion monitor was invented. CorrView ® has been awarded Honorable Mention in the 2004 AHR Expo Innovation Award Competition.



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