In recent years, CorrView International has performed numerous ultrasonic investigations of either very old pipe installed in the early 1900's, or at properties where a combination of old and new pipe exist. We have found our test results a remarkable demonstration of how environmental concerns and government restrictions, combined with less tolerant engineering practices and cost cutting, have greatly reduced the life expectancy of most new piping installations.

     First and foremost is the obvious superiority in quality and corrosion resistance of much older pre World War II pipe to that manufactured today - whether foreign or domestic. Our ultrasonic testing of steam systems from 1911 have shown a minimal loss of only perhaps 20% from the original wall thickness. Testing of some galvanized steel domestic water risers from 1920 have documented little if any wall loss and no loss of the zinc coating.

     We have certified 80 year old steam condensate pipe, which traditionally suffers from the acidic conditions of condensate requiring frequent replacement, as useful for another 50 years of service. CVI has documented condenser water systems from the early 1940's to corrode at well below 1 mil per year (MPY) and offer hundreds of years of future service - even at building locations where chemical treatment was poor or non-existent.

     In contrast, we find few new properties able to control corrosion to below 5 MPY today without expending extraordinary cost, supplemental filtration, close monitoring, and greater maintenance effort. Chemical treatment programs costing $10,000 only 15 years ago now reach almost 10 times that expense. Fully automatic chemical feed and bleed systems are no longer a convenience, but mandatory.

     Yet, most piping evaluations performed at newer building or plant installations using ultrasonic and metallurgical testing typically reveal corrosion rates in the 3 to 5 MPY range - with some examples exceeding 15 to 20 MPY. Such high rates often exist even in cases where the chemical water treatment has been extremely well maintained. See Technical Bulletin C-2 for recommendations on maintaining good corrosion control.

     We have either directly seen or have been advised of condenser water or process piping systems which have been entirely replaced after only 10 years in service or less. We have also found large diameter 8 in. and 12 in. main risers repaired throughout some facilities using emergency pipe clamps.

     The use of more expensive copper in smaller diameter distribution HVAC piping and process loops has become almost standard practice today in the effort to avoid the damaging effects of corrosion against carbon steel. Larger diameter 8 in. and 12 in. condenser water piping systems running the entire height of large commercial office buildings have been entirely replaced using extra heavy copper and even 304 or 314 stainless steel - such extraordinary expense applied solely in the effort to avoid the destructive effects of corrosion rarely seen decades earlier.

     Wrought iron ASTM A 72 pipe, which is well recognized and documented to provide extremely long service life due to its internal grain structure and inherently high corrosion resistance, can be found at many older pre-1970 properties. However, it was removed from U.S. production in 1968 and is no longer available.

     In examples where we have investigated building properties having both new carbon steel and older wrought iron pipe, we have consistently provided remaining service life estimates in the hundreds of years for the wrought iron, as opposed to a few decades or less for the newly installed carbon steel. In many examples, we have found unpainted and un-insulated wrought iron pipe surviving 50 or more years of outdoor weathering with only a fine layer of surface rust and the original ASTM markings still intact.

     While foreign produced pipe from Japan, Korea, Mexico, South America, and Eastern Europe has traditionally shown the greatest susceptibility to corrosion, we have not found recently produced American carbon steel pipe products of significantly higher quality in terms of corrosion resistance.

     Aside from the obvious net effects of stringent U.S. environmental controls and government over-regulation, and the competition of low cost foreign steel, we have not been able to establish suitable explanation for the obvious difference in new vs. old American pipe products. Other changing factors acting against steel pipe produced today obviously exist.

     For those many reasons, CVI strongly recommends that higher corrosion rates should be anticipated regardless of any corrosion control measures planned or implemented. It should be noted that standardized corrosivity tests, laboratory methods capable of measuring the susceptibility of a metal to a typical corrosive environment and rating that metal according to an established numerical standard, are available, and offer an excellent prediction or warning of potential corrosion problems. Please contact CVI for further information about this evaluation service.

     As mentioned, in response to such observed increases in corrosion, many property managers, operating engineers, and plant managers have turned to the use of Type L copper tubing (commonly called pipe) for all smaller diameter run-out distribution lines, and in some cases even for the main risers. This, however, may only be a short term solution to an often more complex corrosion condition, and in some cases may actually complicate an existing corrosion problem with additional and unseen threats.

     Important to consider in the substitution of copper pipe for carbon steel is the significant difference in initial wall thickness. Standard Type L B 88 copper for 3 in. diameter pipe has a standard wall thickness of only 0.090 in., whereas 3 in. A 53 schedule 40 carbon steel has a wall thickness of 0.216 in. Compared to steel pipe having a stress efficiency (a strength rating, not pressure rating) of 15,000 lb./sq. in., B 88 copper pipe only offers 6,000 lb./sq. in. - a physical decrease in strength of 60%. Copper pipe has less than half the tensile strength of steel, and quickly loses that strength at high temperatures.

     It is generally recognized that the minimum acceptable wall thickness for copper tubing, under any conditions, is approximately 0.040 in. At higher pressures, this minimum value increases - thereby allowing for less physical wall loss to occur before being judged as unsuitable for further reliable service.

     Copper pipe, since it exhibits far less physical strength than steel, will fail sooner than steel at the same wall thickness dimension and under the same internal pressure - making it obvious that the greatest threat for any copper piping or components installed in a high rise property exists at the higher operating pressures of the lower floors. The joint filler and quality of workmanship is extremely critical for copper installed pipe, and has been documented as the starting point of many failures.

     While the corrosion rate against copper is commonly believed to exist below 0.5 MPY under all conditions, CVI has repeatedly documented that the same corrosive environment responsible for raising corrosion rates against carbon steel past 10 MPY, will greatly increase the copper corrosion rate above its normal value as well.

     In many of our previous ultrasonic examinations of condenser water systems which have shown a high corrosion rate against carbon steel, we have also measured elevated corrosion attack against the copper pipe. In fact, it is not uncommon to identify condenser water systems having both a high steel corrosion rate of 15 MPY and a corrosion rate against copper at 5 MPY or more.

     Having a 5 MPY copper corrosion rate aggressively working against piping which may only have an available 30 mils to 40 mils (0.030 in. to 0.040 in.) of wall thickness over minimum acceptable standards translates to a system which will reach those minimum standards in only a few years. Copper therefore should not be relied upon or viewed as any form of safe or corrosion immune alternative given conditions where a high carbon steel corrosion rate has already been documented, or where a high copper corrosion rate is suspected.

     For older pre-1970's building properties or plant operations, it is unlikely to find anything but schedule 80 or extra heavy black pipe in use for cooling water, steam, or steam condensate service. However, today, schedule 40 is the standard. Contrasted to a 0.322 in. wall thickness for an 8 in. section of schedule 40 pipe, schedule 80 provides a significantly greater 0.500 in. of available steel; for larger diameter standard grade pipe of 0.375 in. wall thickness, extra heavy again offers 0.500 in. thickness. See Technical Bulletin P-5 for the pipe sizes and schedules of different piping materials.

     With internal operating pressures rarely a deciding factor on pipe selection within the commercial building and process cooling market, the previous use of heavier materials, we believe, has been more intended to counteract the known effects of corrosion activity and thereby provide longer service life.

     It is important to realize that decades ago, design engineers for piping systems assumed a reasonable and readily achieved 1 MPY corrosion rate over an intended life expectancy of about 65 years for the typical building property. Therefore, a theoretical 65 mil corrosion rate or "corrosion factor" was typically applied in piping calculations for open condenser water or process cooling applications. (A 25 MPY "corrosion factor" was applied to closed systems such as for chill and how water heating.)

     In other words, consulting and mechanical engineers estimated a total loss of only 65 mils of pipe over the assumed lifetime of a typical condenser water or open process water system. Any additional pipe wall thickness exceeding the corrosion factor and that needed to contain the internal pressure and stresses was simply extra insurance against corrosion and future operating problems.

     Today, it is not unusual to measure the same loss of 65 mils after only 5 to 10 years of service, and sometimes in as little as 2 years. But while corrosion activity has obviously increased, the response to the greater loss of pipe has not been factored into the design and planning of modern piping systems - leaving very little if any tolerance for a system wide corrosion rate exceeding a few mils per year.

     CorrView International has identified many building properties constructed in the 1970's and earlier as benefitting by such engineering decisions. In the many decades since their construction, we have documented the heavier schedule 80 pipe to have worn down to approximately schedule 40 today. Some older properties, due to the original use of better quality schedule 80 steel, actually have heavier and longer lasting pipe than their newly constructed neighbors. It is an amazing paradox that CVI has well documented throughout many years of ultrasonic testing.

     This change in engineering design toward using thinner schedule 40 pipe, and sometimes schedule 20 and schedule 10, is far more obvious and threatening for smaller diameter threaded applications - where the additional loss of metal during the threading process often reduces the life expectancy of open condenser water or process water piping to a decade or less. See Technical Bulletin # P-1 about the effect of wall loss in threaded applications.

     Threading typically reduces the available wall thickness by over 50% - leaving a 0.154 in. thick piece of 2 in. schedule 40 pipe, less its thread cut of 0.087 in., with a true available and working wall thickness of only 0.067 in. beginning at day one. See our thread loss table.

     For piping systems having a typical 5 MPY corrosion rate, total penetration of the threads will occur within 13 years of installation. In reality, failure usually occurs years earlier. In fact, the use of schedule 40 or standard grade pipe in threaded open water condenser applications does not even meet minimum acceptable engineering guidelines for piping systems, and will typically provide only 10-15 years of service life under good corrosion conditions. The failure of a threaded schedule 40 piping system in under 5 years is not unusual, based upon our experience.

     A growing concern is the recent increase in the use of Victaulic or clamped constructed schedule 10 pipe in fire sprinkler service and even for condenser or open water systems. While providing adequate wall thickness initially, schedule 10 pipe has approximately half of the thickness of schedule 40, leaving virtually no tolerance for corrosion to occur.

     Where the pipe is filled and left stagnant over extended time, a small amount of corrosion takes place, oxygen is depleted, and the corrosion process virtually stops. However, where the system is frequently drained, or where service extensions, leaks, or repairs bring in fresh water, corrosion rates can reach the level of open water systems, and premature failure is inevitable. Combined with the use of thin wall schedule 10 pipe, a fire sprinkler system having any influx of fresh water is almost guaranteed to experience premature failure.

     For a section of 8 in. condenser water pipe that would have provided an extra heavy wall thickness of 0.500 in. for a 1950's property, or 0.322 in. at a facility constructed of schedule 40 in 1985, the frequently seen use of schedule 10 now provides only 0.188 in. of available wall thickness under substantially higher corrosion conditions.

     Advanced failures are therefore quite frequent where schedule 10 is employed, and easy to understand in viewing the above relative illustration of different pipe wall thickness schedules for 8 in. pipe. View a more detailed comparison of various wall thickness values for carbon steel pipe.

     CVI overwhelmingly recommends using heavier schedule 80 steel pipe in all small diameter applications calling for threaded joints. We also recommend using no thinner than schedule 40 pipe for fire sprinkler or condenser water systems - whether using threaded, welded, or Victaulic or grooved clamped construction.

     For decades, building and plant engineers relied solely upon the use of chromate based chemical additives to provide the required corrosion protection of steel piping systems. With even the most inferior application methods, often nothing more than an unmeasured scoop of chromate powder dumped into the cooling tower sump at irregular intervals, corrosion rates could often be maintained at or below 1 MPY.

     Biological fouling was a rarely encountered problem due to chromate's inherent toxicity. Such trouble free operation ended, however, in the mid-1980's - with the prohibition of all chromate use in open water circulating systems in the United States.

     Today, molybdate, phosphate, and other U.S. EPA approved chemical inhibitors rarely equal the effectiveness of past chromate treatments. Though offering impressive corrosion suppression in bench test or laboratory settings, non-chromate programs rarely provide similar results under real world conditions. They are documented as being substantially ineffective in stagnant, low flow, or dead ended piping areas. During many years of ultrasonic pipe testing, CVI has identified numerous examples where the highest corrosion rates have been found exclusively at those areas having the lowest flows.

     Non-chromate treatments offer no microbiological or fungal control - thereby placing increased emphasis on the use of alternating biocide chemicals. Unfortunately, biocides themselves have had their effective half-life reduced to about 6 hours by U.S. federal and state environmental authorities. The result - a legal limit of the amount of biocide one can apply over a given period of time, as well as a legal limitation over its strength, effectiveness, and the time it will remain active.

     And yet, microbiological activity has been identified as playing an much greater role in metal corrosion then previously thought - MIC being the most serious piping threat known. See Technical Bulletin # C-5 for more about the threat of MIC.

     The alternative, oxidizing biocides such as chlorine, bromine and ozone, all offer excellent microbiological control at the trade off of increased corrosion and pitting. The common overuse of oxidizing agents such as chlorine and bromine on a weekly or daily basis have been known to produce severe pitting of steel and copper pipe, and to quickly remove the galvanizing coating from cooling tower pan surfaces.

     Together, the combination of all the above named factors has placed a higher priority on corrosion control which did not exist 20 years ago, and which has raised the issue of chemical treatment, and the monitoring over its effectiveness, to new levels of importance within those involved in building and plant engineering, maintenance, and operations.

     Virtually all advanced piping failures we have seen have been traced back to an ineffective or lacking water treatment program at some point in the building's history - most notably due to poor initial cleanout and start-up procedures. Quite clearly, the first six months of operation are critical for any building or plant facility.

     To the inherent limitations of the chemicals must be added the experience and reputation of the water treatment professional. A lack of knowledge, experience, and professionalism, or a primary interest for profits, can be equally as damaging to a piping system as a lack of chemical protection entirely.

     A less reputable water treatment company may be discovered and replaced, but the effects of even six months of sub-standard service can initiate a lifetime of corrosion troubles for a building or plant operation. A further limitation may also be the budget constraints of the property or plant itself, or the need to meet a contract limit established by a previous water treatment vendor.

     Ultimately, some building property owner or plant operator is faced with with not only the difficult task of correcting or replacing a piping system, but perhaps the responsibility for the actions or inactions of those years prior as well. Constant attention, and a thorough and accurate corrosion monitoring program is therefore they key to trouble free operation.

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