Technical Bulletin # P-13


Changes In Piping Trends Which Have
Occurred Over The Past Few Decades



THE PROBLEM:

     One of the first comments frequently expressed by property managers and engineers suddenly faced with a pipe corrosion problem is that they wouldn't expect to see it at a property of such young age. A failed section of 45 year old condenser water pipe they might expect; a similar problem at a 7 year old property or new renovation is almost beyond belief.

      In recent years, ECI 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 the test results a remarkable demonstration of how environmental concerns and government restrictions, combined with cost cutting and less tolerant engineering practices, have greatly reduced the life expectancy of most new piping installations.


THE SOLUTION:

     Some generalizations regarding some pipe related changes that have occurred over the past few decades are offered below, and may help to shed not only some light on the underlying reasons for certain operating problems, but how to avoid them in the first place.

Pipe Quality

     First and foremost is the obvious superiority in quality and corrosion resistance of pre World War II pipe to that manufactured today - whether foreign or domestic. Our testing of steam systems from 1909 have shown a minimal loss of only perhaps 40% from the original wall thickness. Testing of some galvanized steel domestic water risers from 1920 have shown little if any wall loss. 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.

     Condenser water systems from the early 1940's have been documented to corrode at well below 1 MPY and offer many decades 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, monitoring, and physical 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 absolutely mandatory. Yet, ultrasonic and metallurgical testing at new installations has revealed corrosion rates typically in the 3 - 5 MPY range, with some examples exceeding 15 to 20 MPY even in cases where the chemical water treatment has been extremely well maintained.

     We have either directly seen or have been advised of condenser water piping systems which have been entirely replaced after only 10 years in service, and have found large diameter 8 in. and 12 in. main risers repaired throughout using emergency pipe clamps. The use of copper in smaller diameter distribution piping has become the standard practice today in the effort to avoid the effects of corrosion against carbon steel. Larger diameter 8 in. and 12 in. condenser water piping systems running the height of buildings have been entirely replaced using extra heavy copper, ceramic or plastic lined pipe, and even 304 or 314 stainless steel - such extraordinary expense solely in the effort to avoid the increasingly destructive effects of corrosion.

     Wrought iron pipe, which is well recognized and documented to provide extremely long 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 American production in 1968 and is no longer available. In examples where we have investigated 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 wrought iron pipe surviving 50 or more years of outdoor weathering with only a fine layer of surface rust and the original ASME stamp 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 American produced carbon steel pipe product of significantly higher quality. Aside from the obvious net effects of stringent environmental 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 chemical and physical factors exist beyond the ASME fabrication specification itself - which we believe play a key role in the corrosion susceptibility or resistance of any carbon steel pipe.

     In addition to pipe quality, other changing factors acting against steel pipe produced today obviously exist. For those many reasons, ECI strongly recommends that a higher corrosion rate should be anticipated regardless of any corrosion control measures planned. 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 scale, are available, and offer an excellent prediction or warning of potential corrosion problems. Laboratory testing can also verify whether ASTM A53 Grade B labeled pipe is actually that.

     In response to such observed increases in corrosion, many property managers and engineers have turned to the use of Type L copper tubing (commonly termed pipe) for all smaller diameter runout distribution piping, and in some cases even for main risers. This, however, is only a short term solution to the often more complex problem, 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 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./in., B 88 copper pipe only offers 6,000 lb./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 higher temperatures.

     It is generally recognized that the minimum acceptable wall thickness for copper pipe under any conditions is 0.049 in. At higher pressures, this minimum value increases - thereby allowing for little physical wall loss to occur before being judged unsuitable for further service. Copper pipe, since it exhibits far less physical strength than steel, will fail sooner than steel at the same wall thickness and under the same internal pressure - making it obvious that the greatest threat for any copper components exists at the higher operating pressures.

     While the corrosion rate against copper is commonly believed to exist below 0.5 MPY under all conditions, ECI has well documented a relationship between high steel and copper corrosion rates. In fact, once the average corrosion rate against carbon steel exceeds 10 MPY, the copper corrosion rate will often increase about 10 times its normal value as well. In many of our previous examinations of condenser water systems which have shown a high corrosion rate against carbon steel, we have also measured elevated corrosion attack against 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 corrosion rate has already been established. For those contemplating the use of copper piping as an alternative to carbon steel, a few recommendations worthwhile to remember:

System Engineering

     For older pre-1970's building properties, it is unlikely to find anything but Schedule 80 or Extra Heavy black pipe in use for condenser, steam or steam condensate service. We have even found Extra strong or Schedule 80 pipe installed for chill water and closed secondary systems of older properties. However, today, much thinner Schedule 40 has become standard.

     Contrasted to a 0.322 in. wall thickness for an 8 in. Schedule 40 pipe, Schedule 80 provides a significantly greater 0.500 in. of available steel. For larger diameter Standard pipe of 0.375 in. wall thickness, Extra Heavy again offers 0.500 in. thickness. With internal operating pressures rarely a deciding factor on pipe selection within the commercial building 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 engineering for piping systems assumed a reasonable 1 MPY corrosion rate over an intended life expectancy of about 65 years for the typical property - therefore a theoretical 65 mil corrosion rate or "corrosion factor" was normally added into piping calculations for open water condenser applications. In other words, consulting engineers assumed a total loss of only 65 mils of pipe over the assumed lifetime of the property. Any additional pipe wall thickness exceeding the corrosion factor and that needed to contain the internal pressure and stresses was simply extra insurance against anticipated corrosion and operating problems.

     Today, it is not unusual to measure the same loss of 65 mils after only 5 to 10 years, sometimes in as few as 3 years (Many of the sample corrosion photographs on this site are of pipe less than 10 to 15 years old). But while corrosion activity has obviously increased, the response to the greater loss of pipe has not been applied to the design and planning of modern piping systems - leaving very little if any physical tolerance for a system wide corrosion rate exceeding a few mils per year.

     This change in engineering design toward using thinner Schedule 40 pipe, and sometimes Schedule 20, is far more obvious and threatening in smaller diameter threaded applications - where the additional loss of metal during the threading process often reduces the life expectancy of condenser water piping to a decade or less. 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! View Tables P-13 A&B for a visual thickness comparison of Schedule 10, 20, 40 and 80 pipe.

     For systems having a typical 5 MPY corrosion rate, total penetration of the threads will occur within 13 years of installation - guaranteed! 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.

     It is worthwhile to simply stress that in applications where small diameter piping will be installed, the use of Schedule 80 is very highly recommended. Ample technical and engineering documentation exists to fully support this argument. See Technical Bulletin # P-02 regarding the danger of using Schedule 40 pipe in threaded applications.

Water Treatment

     For decades, building engineers relied solely upon the use of chromate based chemical treatments 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 could 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. Today, molybdate, phosphate, and other approved chemical inhibitors rarely equal the effectiveness of chromate treatments. Though offering impressive corrosion suppression in bench test or laboratory settings, non-chromate programs rarely provide similar results in the field.

     Through our involvement with ultrasonic pipe testing, we have identified multiple examples where the highest corrosion rates have been found exclusively at those areas having the lowest flows. In addition, non-chromate treatments offer no biological or fungal control - thereby placing increased emphasis on the use of alternating biocide chemicals. Yet, biocides themselves have had their effective half-life reduced to about 6 hours by federal and state environmental regulators.

     The result - a legal limitation of the amount of biocide one can apply over a given period of time, as well as a legal limitation of its strength, effectiveness, and time it will remain active. And yet, biological activity has been found to play an increasing role in metal corrosion - MIC being the most serious piping threat known.

     The alternative, oxidizing biocides such as chlorine, bromine and ozone, all offer excellent biological control at the trade off of increased corrosion and pitting. The common overuse of oxidizing agents such as chlorine on a weekly basis have been known to produce severe pitting of metal surfaces, and to quickly remove the galvanizing from cooling tower pan surfaces. Together, the combination of all the above factors has placed a high priority on corrosion control which did not exist 20 years ago, and has raised chemical treatment, and the monitoring of its effectiveness, to new levels of importance within those involved in building engineering, maintenance, and operations. Read Technical Bulletin # M-06 about an extremely effective new biocide.

Free Cooling

     Energy costs to cool any large commercial building are enormous. Extending daily hours and the cooling season, necessary today for many tenants and especially computer oriented operations, can more than double that expense.

     In the interest of eliminating the high cost of operating mechanical chillers when outdoor temperatures are low, the idea of directly routing condenser water through the chilled water piping appeared in the 1950's and 60's, and was widely accepted. Today, many older building properties still have what is known as a "Strainercycle" unit. Patented under the "Strainercycle" cross cooling concept, a high capacity, automatically backwashing filter was the key component thought to prevent the dirt, debris, and biological content, always present in an open water cooling tower system, from entering the closed and generally clean chill water and secondary piping.

     Thirty to forty years later, property owners and operators are learning that the standard 110 micron particle retention of the filter was not quite sufficient to eliminate the type of piping damage one typically finds in condenser water systems. Particle distribution studies generally find the majority of suspended condenser water particulates down in the 40 to 50 micron range. And of course, only a sub-micron filter would be capable of removing microbiological contamination - a known major factor influencing pipe corrosion.

     Ultrasonic wall thickness and metallurgical testing of building properties currently or previously operating cross cooling systems have very well documented similarly higher condenser water corrosion rates and deep pitting throughout their associated closed cooling systems. Unlike condenser water piping, which is generally of large diameter welded piping throughout and, in older properties, often constructed of extra heavy material, closed systems distribute down to small size piping, and ultimately to even smaller cooling coils.

     Furthermore, closed systems are traditionally constructed of standard or Schedule 40 piping which provides less available wall thickness, and have threaded connections further limiting available wall thickness. Dirt, particulates, iron oxide corrosion products, and microbiological contamination entering through the cooling tower, or originating in the condenser water piping, typically pass through a 110 micron screen filtering element and enter the closed system. There, the contamination migrates downward and under a continually lower flow velocity where it eventually settles out and remains.

     While the majority of foreign material does escape again through the cooling tower blowdown, the amount which remains can create substantial secondary problems - most noticeably a loss of cooling or heating efficiency across the fan's coils. As a result, many property owners and operators have replaced their cross cooling filtration with fully isolating plate and frame heat exchangers.

     ECI strongly recommends that properties having once operated as a free cooling system should view their closed systems with the same degree of concern as they would a condenser water system. Due to the large volume of debris and corrosion product likely trapped within a free cooling closed system, we strongly recommend the installation of side stream filtration and additional chemical dispersants in order to gradually resuspend and remove those deposits - thereby reducing under deposit corrosion, decreasing corrosion rates, and extending the life of the piping system. See Technical Bulletin # W-01 regarding the benefits of side stream filtration for closed piping systems.



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