paper no. 709 - hvac-talk

Paper No.

709

CORROSION FAILURES OF COPPER/COPPER ALLOY PIPING IN BUILDING PIPING SYSTEMS

Richard A. Hoffmann, P.E. Hofhnann & Feige, Inc.

Croton River Executive Park 3-40 Fallsview Lane, Route 22

Brewster, New York 10509

ABSTRACT

The focus of this paper is on copper and copper alloys. Next to steel, copper pipe and tubing are the most widely used materials in building water systems. Its usage in these applications is based on its excellent corrosion resistance, high conductivity and excellent formability. This paper presents three separate case histories that deal with copper/copper alloy piping failures in buildings. Two represent failures in which the pipe or tube product was the primary containment boundary, and the third occurred in copper tubes which were part of an evaporator section in a freon chiller. In every case, an unexpected external influence caused the failure.

The first case is a copper tube failure from a high-rise hotel in which the tubes acted as expansion loops in the hot water portion of HVAC equipment at the individual guest room. The piping was 2Sinch (6.35 cm) copper tubing which split axially and leaked. These failures took place before the facility was in service.

The second case involves externally finned and internally enhanced copper tubes used in the evaporator section of a chiller; the tubes failed through extensive corrosion after a winter lay-up following the first season of chiller operation.

In the tfiird case, a brass pipe failed through stress corrosion cracking. This pipe was in hot water service, which was an inappropriate usage of this pipe product. The pipe experienced external damage from pipe hangers attached to support other pipes running beneath this hot water pipe.

Keywords: copper, copper alloys, stress corrosion cracking, failures, corrosion, copper tubes

INTRODUCTION

The need to understand piping and materials failures is as essential in high-rise building systems as it is in power or process plants. The metals used are essentially the same and the ramifications of piping failures can be equally significant. If a high-rise facility loses its HVAC capabilities because of a materials failure, or if several floors are flooded or trading floors are shut down, the impact in terms of dollar loss could easily be comparable to the loss of production in a power plant or processing facility.

Copyright 01998 by NACE International. Requests for permission to publish this manuscript in any form, in part or in whole must be made in writing to NACE International, Conferences Dwision, P.O. Box 218340, Houston, Texas 77218-8340. The material presented and the views expressed in this paper are solely those of the author(s) and are not necessarily endorsed by the Association. Printed in the U.S.A.

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CASE I: LEAKAGE OF 2%INCH COPPER TUBES FROM HVAC HEATING WATER SYSTEM

This problem involved a complex axial splitting failure of insulated 2Minch (6.35 cm) copper tubing purchased as CDA 122 alloy in accordance with ASTM-B-88. The contractor had completed this installation in a new high-rise hotel complex. The tubing, which was appropriately marked so there was no question of its origin, was supplied by two separate manufacturers. It was completely insulated with black foam insulation.

The tubes were used in a brazed U-joint configuration expansion loop (Figure 1) for the hot water portion of the room HVAC system. Failures were observed in the tubes soon after the first hot water was introduced during system testing, before the facility was open to the public. The need for this analysis was critical because the contractor and the owner were subject to significant penalties if the facility did not open on time.

The tubes were oriented horizontally in the ceiling: the failures occurred as axial splits in the tube. The axial splits ranged from essentially nothing to 2 feet (0.61 m) in length. The fracture mode was readily identified as intergranular cracking; however, the cause of these cracks had to be established as well as the reason for the variations in crack length. Four of the failures were described as follows:

1. Failure 1 was initially characterized as a series of straight, axial splits approximately 0.16 inch (0.41 cm) wide and 6+ inches (l&24+ cm) in length - Figure 2. Penetrant examination revealed additional axial cracking away from the main split. The entire circumference of the tube was discolored and dark in appearance. The failure was located in the bottom side of the top section of the expansion loop.

2. Failure 2 was characterized by fine axial cracking which was limited to black-appearing areas. This failure was located in the top side of the bottom section of the expansion loop approximately 19 inches (48.26 cm) from the elbow.

3. Failure 3 was characterized by fine axial cracking around the exterior of the tube in the black-appearing areas in the bottom section of the expansion loop. Leakage took place in two cracks approximately 17 and 25 inches (43.18 and 63.5 cm) from the brazed elbow.

4. Failure 4 was a tube which had not yet leaked but which also exhibited extensive cracking in the discolored area on the outer surface - Figure 3.

Numerous additional samples of tubing were received and evaluated in order to perform a total review of the 2Wnch-diameter (6.35 cm) copper tubing installed by this contractor.

Metalluraical Examination

Examination of the samples revealed the presence of intergranular cracking originating from the outer diameter surface of the tube (Figure 4), not from the inner, product side of the tubing. These cracks were filled with corrosion product, indicating they were “okt” cracks. In order for this intergranular cracking to occur on the outside of the tube, a corrodant had to have contacted the tube surface. Once this occurred, the cracking initiated and the tube wall breached with or without any visual, external evidence of corrosion-induced degradation. In order to establish the cause of the cracking, the corrodant had to be identified.

Chemical Analvsis

The chemical composition requirements for CDA alloy 122 as stated in ASTM - !388 - 88 is 99.9% for the copper + silver. The limits governing the phosphorus content are 0.015% minimum to 0.040% maximum, with no tolerances on these numbers.

The results of the chemical analyses of the tube samples revealed that of 46 samples tested, 23 samples were rejectable because of low copper + silver content (results ranged from 99.40% to 99.84%) high or low phosphorus content (between 0.010% and 0.071%). or both. The four failed tubes were all rejectable based on their low copper content, their phosphorus content (high or low), or both. However, in our opinion, the chemical differences observed were not significant to the cause of the failure. This opinion is based on:

1. The lack of any correlation between the out-of-specification chemical composition in the samples that failed and the unfailed samples, and

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2. The existence of cracking in only the blackened area of all the failures.

The out-of-specification results were associated with both manufacturers, thereby reducing the probability that the out-of-specification conditions represent a mill problem and increasing the probability that this condition was the result of analytical techniques.

No mechanical property testing was performed on any of the samples received because this was clearly a corrosion-induced failure and not a mechanical overload or fatigue type of failure.

Identification of Corrodant

In order to identify the corrodant, it was necessary to attempt to identify the black film present on the outer diameter of the tube samples and on the crack surfaces. This was done on samples from Failures 2 and 3.

The crack surfaces of Failure 3 were examined using the scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), Auger spectroscopy (AS), and electron scanning chemical analysis (ESCA). A sample from Failure 2 was subjected to Fourier transform infra-red analysis (FTIR).

Scanninq Electron Microscoov ISEM) and Enerov Dispersive Spectroscopy (EDS)

SEM examination of the fracture surface of Failure 3 revealed an intergranular fracture mode. EDS data on the fracture surfaces indicated the presence of iron, calcium, chlorine, silicon, aluminum and magnesium. Because of the limitations of the equipment, elements below fluorine could not be detected. No evidence of mercury was detected.

The intergranular cracking or stress corrosion cracking of copper is most commonly caused by exposure of the copper or brass alloys to mercury, ammonia and/or some sulfur compounds. The elemental limitation of the SEM required that additional testing be pursued.

Auaer Spectrosconv and Electron Surface Chemical Analvsis

Auger spectroscopy and electron surface chemical analysis were performed on the fracture surface of Failure 3. The surfaces which were examined by AS and ESCA were:

1. The uncleaned crack half which was exposed to SEM analysis.

2. A nearly through-the-wall crack which was unexpectedly discovered during the sectioning of Failure 3.

The Auger spectroscopy on the fracture surfaces and on the outer diameter surfaces of the tube revealed the presence of nitrogen and carbon on the fracture surfaces and carbon in the black areas on the outer diameter of the tube.

The ESCA work on the fracture surfaces and on the outer diameter surfaces of the tube revealed that nitrogen was present in an energy state representative of an ammonia compound.

These discoveries resulted in the conclusion that the corrodant contained significant amounts of carbon and probably an ammonia compound. The only data still needed was the identity of the black film.

Fourier Transform Infrared (FTIR) Analvsis

The section of Sample 2 on which FTIR analysis was performed contained axial cracks in two circular black spots approximately % to l/i inch (0.95 to 1.27 cm) in diameter. The cracks were limited to the black areas. One crack extended beyond the circular black area. That crack propagated &jjy along the length of the tube approximately % inch (0.32 cm) beyond the circumference of the black spot. The “channel” in which it propagated was black, indicating the exterior corrodant flowed out of the initial spot where it contacted the outer diameter of the tube and filled this exterior surface line on the tube, which allowed the cracking to propagate outside of the initial spot.

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The FTIR testing indicated that the black-appearing contamination was an organic material. No match was found when the “fingerprint” of this material was compared with that of other known materials using a computerized database. The closest similar was achieved by a compound known as ethanolamine. This contaminating material was found in the dark-appearing areas of the tube surface. Dark areas were also found on the crack surface extending about halfway through the sample. FflR spectroscopy of the cross section showed evidence of organic contamination in the dark area and not in the “clean” area.

Residual Stress Measurement of All Tube Samoles

In order to understand the differences in the extent of cracking exhibited by these failures, the residual stresses were evaluated. This work revealed that the residual stresses on tube samples examined ranged between 3000 and 20,000 psi. Copper can stress corrosion crack/lntergranular crack at stress levels as low as 3000 to 5000 psi.

The differences in the degree of crack propagation in the failures were explained by the differences in the residual stresses exhibited by Failure 1 (which split axially for a distance of more than 6 inches (15.24 cm) and had a residual stress level of approximately 18,000 psi) and Sample 2, (which exhibited only fine axial cracking and had a residual stress level on the order of 3000 psi).

Summarv of Test Results and Observations

1.

2.

3.

4.

Location of Crackinq. All cracking observed on the these tubes was initiated on the outside surface and was essentially limited to discolored areas on the outer surfaces.

TvDe of Cracking. Cracking was intergranular and representative of stress corrosion cracking. Newly formed stress corrosion cracks would be clean and open, because this cracking mechanism occurs quickly. This is true even if there is a corrosion residue on the outer surface where the corrodant contacted the metal surface. Because even the smallest branch crack off the main crack on these failures was filled with a reaction product, it is our opinion that these cracks were present for a long time.

Residual Tube Stress Levels. Residual stresses on tube samples were between 3000 and 20,000 psi. Copper can stress corrosion crack/tntergranular crack at stress levels on the order of 3000 to 5000 psi. The residual stress level in tubes is not governed by the ASTM specification.

The allowable stress levels for CDA 122 drawn copper tube material as stated in ANSI 831.9, Suilding Services Piping is 9,000 psi for temperatures up to +25O”F. Using Equation 2 of that document, the maximum pressure the 2%inch-diameter, Type L tube can be exposed to in order to meet the 9,000 psi stress (assuming it is attributable to pressure only) is 480 psi. This is well above the approximate 235 psi maximum system operating pressure to which the tube would be exposed in this installation.

Conclusions

The following conclusions resulted from the work described above:

1.

2.

3.

4.

The corrodant was a nitrogen-containing product, possibly an amine compound/ammonia, which is known to both intergranularly and stress corrode crack copper.

Based on the presence of filled cracks, this corrosion was not a recent occurrence. We could not establish if it took place after the tubes were fabricated, but still at the mill, while in transit or storage at the warehouse, or at the job site.

The high level of carbon together with the presence of chlorine on the outside of the tubes in the blackened areas suggests that a carbon-chlorine containing solvent or equivalent contacted the surface of the tubes, The lower concentration of nitrogen on the crack surfaces cannot be addressed by us. It could represent an accurate level of the product in the corrodant, or it could be lower because of aging or weathering of the corroded surfaces. The escaping hot water altered the chemistry of the fracture surface; this means that any residue still present on the break surface is one that is not highly soluble in water.

The cracking is not related to the insulation adhesive. This is based on the fact that no cracking was observed,

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either visually or by penetrant examination, in other areas of the tubes exhibiting traces of adhesive.

5. Cracking occurred for the most part in the areas of the tube which were stained with black-appearing material.

In conclusion, this analysis demonstrated a distinct linkage between crack length and residual stresses of the tubing and showed that an unidentified external corrodant was the source of the stress corrosion cracking of the copper tubing.

CASE II: CORROSION OF ENHANCED COPPER EVAPORATOR TUBES

Case II involves the corrosion failure of internally enhanced, externally finned copper tubes in a new chiller. These tubes failed after the first lay-up.

Svstem Historv

The chiller was installed and used for one cooling season. The system was drained in late fall for winter lay-up. The system piping (steel) and copper tubes (believed to be alloy CDA 122) were not dried at that time. Two months later extensive leaks were discovered in many of the evaporator tubes,

No water treatment was used in either the old chiller system or the new replacement chiller system. No corrosion problems were reported in the past in the evaporator tubes or carbon steel system piping. Glycol was used to rinse the air handler coils at the end of the cooling season. The glycol was added to provide freeze protection for any residual chilled water which remained in the air handler coils after the drain-down. The type of glycol was not known.

This analysis consisted of:

1. Examination of two failed %-inch-diameter (1.91 cm), lBfoot-long (3.66 m) copper evaporator tubes which were internally enhanced and had integral fins on their external surfaces, and

2. Analysis of five water samples: two incoming city water samples and three residual chilled water system samples taken from the chiller system after draining for the winter.

Visual Examination

The external surfaces of these tubes did not exhibit any signs of leakage in the as-received condition, Longitudinal sectioning of Sample 1 revealed that one half of the internal surfaces of these tube sections was covered with a blue deposit: the other half had a green deposit over most of its surface with a yellow-orange deposit in random areas. No corrosion tubercles were observed on the internal surfaces and no pits were observed.

Sample 2 was pressure tested with approximately 5 psig of nitrogen gas. Numerous leaks were detected during this pressure test. Longitudinal sectioning of Sample 2 revealed numerous small-diameter pits over the internal surfaces of these tubes. Cracks initiated at many of these pits when they were bent open.

Enerav Dispersive Soectroscoov Examination of Deposits

A semi-quantitative elemental EDS analysis was performed on the blue, green and orange-yellow deposits on the internal surfaces of these tubes. EDS was also performed locally on the internal tube surfaces immediately adjacent to the pits and also in the pits. Table 1 presents the results of the EDS analysis on the green, blue and orange-yellow deposits. These results indicate the following:

1. The high iron contents indicate that significant corrosion has occurred on the carbon steel piping in the system and iron oxide is being carried to these copper tube surfaces from the steel piping.

2. The silicon and phosphorus were probably carried in with the system water.

3. The copper is from the copper and copper alloys in the system (predominantly from these copper evaporator tubes).


Metalluraical Examination

Metallurgical mounts were made of several longitudinal cross sections from Sample 1. Many pits were observed in these sections. The propagation of these pits confirmed that this pitting was caused by formicary corrosion which initiated on the internal surface of the tube. The appearance of these pits resembles the tunneling in an ant hill. These pits initiated both on the peaks of the internal fins and in the valleys between the fins; the majority of the pits lnltlated on the peaks of the Internal flns - Figures 5, 6, and 7.

Scannina Electron Microscooe

SEM examination of the pits which were exposed upon bending of the tube sections from Sample 2 confirmed that the pitting proceeded from the inside to the outside of these tubes - Figure 8. The physical appearance of these pits identified the corrosion mechanism as formicary corrosion.

Water Analvses

The analyses of the water samples showed that the incoming city water had an approximate neutral pH and very low hardness, alkalinity and dissolved solids. The Langelier Saturation Index (LSI) was -1.0 and -2.74 for the two makeup water samples. These LSI values indicated that the water was not scale forming. Untreated water with this general composition is known to be corrosive to copper.

The high iron levels and the low pH in the chilled water samples indicated a probable corrosion problem on the mild steel piping in the system. The high copper levels indicated attack on the copper components. Copper corrosion usually occurs beneath deposits and propagates by deep pitting attack. The results of the analyses of the two water samples are reported in Table 2.

Discussion

Formicary corrosion is a type of pitting corrosion which propagates in copper in a manner similar to the way ants tunnel through dirt/sand. These corrosion pits are very small in diameter and often branch. The precise cause(s) of formicary corrosion have not been identified as yet. However, 1 .l .l - trichloroethane has been shown to produce corrosion pitting similar to formicary corrosion. Trichloroethane has been used as a solvent in removing oils (which are introduced during manufacture) from the tube surfaces. The trichloroethane can break down to hydrochloric acid and phosgene and these are believed to be responsible for formicary corrosion.

Glycol was reportedly used for freeze protection of the water remaining in the air handlers after the chilled water was drained. If the glycol did not contain oxidation inhibitors to help prevent oxidative degradation of the glycol, oxidation of the uninhibited glycol could have occurred to form organic acids and it is believed that many of the organic acids can produce the formicary corrosion pattern.

Uninhibited glycol can also allow microbiological activity which can result in low pH levels. Regardless of the reason for the low pH, the result will be high corrosion rates on the steel and copper in the system.

Conclusions

The leakage in the tubes was caused by a failure mechanism known as formicary corrosion. The morphology

of these pits and the possible presence of organic acids in the chilled water support this conclusion.

Two possible sources of the organic acids are:

1. Trichloroethane solvents which are known to produce formicary corrosion. Hydrochloric acid and phosgene, byproducts of trichloroethane, are believed to be responsible for the corrosion. The use of trichloroethane would have occurred at the mill. It is not possible to detect the presence of trkchloroethane after the evaporator tubes were on-line for several months.

2. The breakdown of uninhibited glycol. Glycol was used during the lay-up of this system, but information regarding the type of glycol was not available.

The acidic pH levels in the chilled water system samples could have been caused by organic acids formed

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from decomposition of ethylene glycol during the lay-up of this system.

The lay-up procedure used for this chiller could have created a corrosive environment for the copper tubes. When a system lay-up leaves the tubes wet and open to the air, carbon dioxide absorption can occur, forming carbonic acid in the water.

The extremely high levels of iron oxide on the internal surface of the two evaporator tube samples indicated that significant corrosion, most probably caused by the strongly acidic pH levels, has probably occurred on the internal surfaces of the iron-containing components in this system.

CASE Ill: STRESS CORROSION FAILURE OF A BRASS PIPE FROM STRESS CORROSION CRACKfNG

Case Ill involves the failure of a full-hardened red brass pipe removed from a high-rise building where it supplied 14O’F potable hot water at 90 to 100 psig. This pipe which was 1 5/16 inches (3.33 cm) in diameter, 0.125-inch (0.32 cm) wall thickness, and approximately 12 feet (3.66 m) in length, had been in service for approximately 5 years. This pipe failed suddenly, causing leakage damage to two floors in the building and to the ceiling in a third floor. The leakage was discovered when water was seen coming out of the lobby mail chute, many floors below.

Visual Examination

Post-failure examination revealed that the pipe had split axially for a total of 68 inches (1.73 m) of the total 144inch length (3.66 m). The width of the crack opening at the widest point was approximately 0.020 inch (0.51 cm). Examination of the area where the crack originated revealed the presence of a 3/8-inch-diameter (0.95 cm) embossed circular mark, 7 inches (17.78 cm) from the threaded elbow end of the pipe - Figures 9 and 10. This damage area was located at the bottom position of this horizontal pipe.

The Initial crack extended approximately 2.95 inches (7.49 cm) in length on each side of that embossed area (Figure 11) and failed catastrophically for a distance totaling 68 inches (1.73 m) - Figure 9. There was a second embossed area observed on the other end of this 12-foot-long (3.66 m) pipe; however, no cracking was associated with this area - Figure 12. We learned that pipe hangers had been installed at these two locations to support other pipes running beneath this brass hot water pipe. The pipe hangers were screwed very tightly to the brass pipe, creating the embossing described above.

Closer examination of the failed area revealed a stain at the embossed area where the failure originated, while the other embossed zone at the opposite end of the pipe was free from any staining. The nature of this stain deposit was not determined. The interior of the pipe looked satisfactory. There was no evidence of any corrosion deterioration on the interior surface, and metallographic examination of the inner wetted surface did not identify any problems.

Residual stress measurements showed that the pipe had a residual stress level in excess of 17,000 psi. This indicates that the material is hardened to its maximum level through cold working. The chemistry of the pipe was found to be primarily copper (83%) and zinc (17%) and the hardness was found to be Rockwell B86.5 through 88.

These values, along with the residual stress level and the dimensional measurements, indicate that the pipe is NPS l-inch (2.54 cm), fully hardened red brass furnished in the H58 (drawn, general purpose) temper capable of meeting the requirements of ASTM B43.

It must be noted that no markings were observed anywhere on this lBfoot-long (3.66 m) pipe; therefore, no comment can be made regarding the actual applicable specification for this pipe. If this pipe is indeed manufactured to ASTM 843, then this usage as a hot water pipe is inappropriate. Paragraph 1 .l describing the scope of ASTM B43, states:

1 .l ‘Ihis specification covers seamless red brass (Copper Alloy UNS No. C23000) pipe in all nominal pipe sizes, both regular and extra strong. In the annealed temper (061), the pipe is suitable for use in plumbing, boiler feed lines, and for similar purposes. In the drawn general purpose temper (H58), the pipe is suitable for architectural applications, such as guard railings and stair hand-railings.”

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Conclusions and Recommendations

The failure was the result of stress-induced cracking introduced into the pipe because of external damage. This damage was caused by a pipe hanger which was clamped to this pipe at that location by other tradesmen. This pipe happened to be a convenient support for other pipe hanger clamps for piping runs below this pipe. Screwing the pipe hangar clamp onto the pipe apparently created enough additional stress to cause a stress- cracking failure in this fully hardened brass pipe. The stain on this pipe at the crack initiation site indicated that corrosion may also have been a factor in this stress cracking failure.

If the pipe had not been fully hardened red brass, and if the pipe hanger not been placed on the pipe and the screw clamp tip screwed into the pipe, this failure would not have happened. The material which discolored the break origin area was not identified.

Considering the possibility of the inappropriate use of other lengths of red brass in the fully hardened condition, it was recommended that the remaining fully-hardened red brass piping should be changed out as soon as possible because of the following combination of factors:

1. The extreme cold-worked level of this product,

2. The extremely high residual stresses and the obvious commensurately low resistance to crack propagation.

Replacement of this alloy with an annealed grade or very lightly drawn grade of a copper or copper alloy pipe is acceptable. The replacement effort should be sequenced to replace all physically damaged hardened red brass pipe lengths first, since they are the most prone to crack and split. The practice of fastening pipe hangers to copper or copper alloy pipes should be stopped.

SUMMARY

In summary, the three case histories presented above clearly show the versatility of copper and copper alloys. More importantly, these failures would not have taken place had not an externally supplied corrodant initiated the attack in each case.

A second point which must be considered in high-rise building piping is that it is not always the product that the pipe or tube is carrying that causes failure. Therefore, the person responsible for the system must be sure to maintain the copper surfaces clean and free from deposits and to use only approved alloys and installation

TABLE 1 CASE II: CORROSION OF ENHANCED COPPER EVAPORATOR TUBES

SEM/EDS ELEMENTAL CoMPosrnoN OF DEPOSITS

Element’ Blue Green

Deposit Deposit Orange-Yellow

Deposit

Ixygen

>arbon

(0)

(Cl

present

present

present

present

present

present

silicon W 1 not detected I

0.6 I

1.0

‘hosphorus (P) 1 not detected 1 0.7 1 1.4

ron (Fe) 1 5.6 1 16.4 I 44.2

>opper 0’) I 94.4 I 82.1 I 53.4

Note: 1. The oxygen and carbon levels cannot be quantified with this EDS system.

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CASE II: CORROSION OF ENHANCED COPPER EVAPORATOR TUBES

TABLE 2 CHEMICAL ANALYWS RESULTS OF WATER SAMPLES’

Parameter AS MW* CHW3

PH’ - 6.54 4.14 Conductivity’ (j.rmhos) - 106 472

Total alkalinity CaCO, 23.7 NSQ“ Total suspended solids - 2.3 NSQ Total dissolved solids - 60 324

Aluminum Al <O.l 0.11

Boron B co.10 2.01 Calcium CaCO, 17.0 44.2 Chromium Cr co.01 0.03

Copper CU 0.01 13.7 Iron Fe 0.04 564 Lead Pb 0.04 0.42

Magnesium CaCO, 5.7 9.96

Manganese Mn <O.Ol 10.7 Molybdenum MO <O.Ol 0.08

ohosphorus, ortho PO, <0.2 <0.2

3hosphorus, total PO, <0.6 3.97

Jotassium K co.5 45.0 Silica SiO 4.56 2.36 Sodium Na’ 13.5 31.8

jtrontium Sr 0.02 0.07 Zinc Zn <O.Ol 1.74

=luoride :I 1.07 <5.0 Chloride 8.10 11.1

rlitrate N 0.09 co.25

Uitrite sulfate 4,

7.34 <0.25 co.05 cl.5

rotal Acidity CaCO, NA5 1279 angelier Saturation Index (at 8O’F) - -2.74 -6.49

3rganic Acids (% by weight) Acetic acid co.oo1 0.13

Notes: 1, Unless otherwise noted, results are reported in mg/L. 2. MW: Make-up Water. 3. CHW: Chilled Water 4. NSQ: Not Sufficient Quantity for Analysis. 5. NA: Not Available

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Figure 1. CASE I. Overall view of typical expansion loop. The overall length of this loop is about 8 feet (2.44 m). The cracking was limited to the straight lengths of the tube.

Figure 2. CASE I. Representative photograph of cracking. Note the poor condition of the outer surface of the tube.

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Figure 3. CASE I. Macrophotograph showing the relationship between the black staining on the outer surface of the tube and the associated cracking. Magnification: 1.5X

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Figure 4. CASE 1. A composite photomicrograph showing intergranular cracking originating on the outer diameter surface of the tube. The left photomicrograph is unetched and the right is the same crack following etching with ammonium persulfate. Magnification: 400X reduced -% for publication.

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Figure 5. CASE II. Photomacrograph of longitudinal cross-sections of enhanced copper tubing. The lower surface of each longitudinal strip represents the form of the internal enhancement. The formicary corrosion was found only in the peaks of the interior enhancement.

Figure 6. CASE II. The formicary corrosion deterioration as seen in the unetched condition. Magnification: 100X reduced -% for publication.


Figure 7. CASE II. This photomicrograph shows the metal laps at the base of the enhancement and the very obvious lack of formicary deterioration. Magnification: 400X reduced -9/o for publication.

Figure 8. CASE II. Scanning Electron Microscope photograph of the interior enhanced surface after it was bent back upon itself. This physical distortion clearly shows the sporadic nature of the deterioration. Magnification: 9X reduced % for publication. -

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Figure 9. CASE Ill. Overall view of the origin area showing the circular damage mark where a pipe hanger was placed. This damage allowed a crack to originate which eventually grew to a critical size and propagated catastrophically, splitting essentially half the pipe.

Figure 10. CASE Ill. Close-up of the exterior damage showing the presence of corrosion discoloration and the split. The black marks onn the pipe show the extent of the crack before it propagated to catastrophic failure.

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Figure 11. CASE Ill. View of fracture surface showing the origin of the crack centered around the external damage present on the pipe. The overall length of this crack was 5.9 inches (14.99 cm) before it propagated catastrophically.

Figure 12. CASE Ill. The other end of the pipe shown in Figures 10, 11 and 12. This end exhibited identical exterior damage, but it did not develop a crack.

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paper no. 709 - hvac-talk

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