Interim Report on the Examination of

Corrosion Damage in Homes

Constructed with Imported Wallboard

I. Examination of Samples Received

September 28, 2009

D. J. Pitchure

R. E. Ricker

Report prepared for the

U.S. Consumer Product Safety Commission

Directorate for Engineering Sciences

Bethesda, MD 20814

NISTIR 7652
 

NISTIR 7652

Interim Report on the Examination of

Corrosion Damage in Homes

Constructed with Imported Wallboard

I. Examination of Samples Received

September 28, 2009

D. J. Pitchure

R. E. Ricker

Materials Performance Group 

Metallurgy Division 

Materials Science and Engineering Laboratory 

November 2009

U.S. Department of Commerce 

Gary Locke, Secretary 

National Institute of Standards and Technology 

Patrick D. Gallagher, Director 
1 

Interim Report on the Examination of Corrosion Damage in 

Homes Constructed with Imported Wallboard 

I. Examination of Samples Received September 28, 2009 

D. J. Pitchure and R. E. Ricker 

Materials Performance Group 

Metallurgy Division 

Materials Science and Engineering Laboratory 

National Institute of Standards and Technology 

US Department of Commerce 

Gaithersburg, MD 20899-8553 

ABSTRACT

 Since many household systems are fabricated out of metallic materials, changes to the 

household environment that accelerate corrosion rates will increase the frequency of failures in 

these systems. Recently, it has been reported that homes constructed with imported wallboard 

have increased failure rates in appliances, air conditioner heat exchanger coils, and visible 

corrosion on electrical wiring and other metal components. At the request of the Consumer 

Product Safety Commission (CPSC), the National Institute of Standards and Technology (NIST) 

became involved through the Interagency Agreement CPSC-1-09-0023 to perform metallurgical 

analyses on samples and corrosion products removed from homes constructed using imported 

wallboard. This document reports on the analysis of the first group of samples received by NIST 

from CPSC. 

 The samples received by NIST on September 28, 2009 consisted of copper tubing for 

supplying natural gas and two air conditioner heat exchanger coils. The examinations performed 

by NIST consisted of photography, metallurgical cross-sectioning, optical microscopy, scanning 

electron microscopy (SEM), and X-ray diffraction (XRD). Leak tests were also performed on 

the air conditioner heat exchanger coils. The objective of these examinations was to determine 

extent and nature of the corrosive attack, the chemical composition of the corrosion product, and 

the potential chemical reactions or environmental species responsible for accelerated corrosion. 

A thin black corrosion product was found on samples of the copper tubing. The XRD analysis of 

this layer indicated that this corrosion product was a copper sulfide phase and the diffraction 

peaks corresponded with those for the mineral digenite (Cu9S5). Corrosion products were also 

observed on other types of metals in the air conditioner coils where condensation would 

frequently wet the metals. The thickness of the corrosion product layer on a copper natural gas 

supply pipe with a wall thickness of 1.2 mm ±0.2 mm was between 5 m and 10 m. 

 These results indicate that a chemical compound that contains reduced sulfur, such as 

hydrogen sulfide (H2S), is present in the environment to which these samples were exposed. The 

literature indicates that these species strongly influence corrosion rates of most metals and alloys 

even at low concentrations. None of the samples examined were failed components, and no 

evidence of imminent failure was found on any of the samples examined. All of the corrosion 
2 

damage observed to date is consistent with a general attack form of corrosion that will progress 

in a uniform and relatively predictable manner. No evidence of localized attack was found, but 

these forms of attack typically require an incubation period before they initiate. Therefore, the 

number of samples examined to date is too small to draw a conclusion on the relative probability 

of these forms of corrosion being able to cause or not cause failure. Samples from failed systems 

or from laboratory tests conducted over a wide range of metallurgical and environmental 

conditions will be required to assess the probability of these other forms of corrosion causing 

failure. 
3 

Examination of Corrosion Damage to Metallic Materials 

Removed from Homes Constructed with Imported Wallboard 

I. Results of the Examination of Samples Received October 1, 2009 

 D. J. Pitchure and R. E. Ricker 

I. INTRODUCTION

 Metallic materials in home construction are subject to corrosive attack by the normal internal 

atmosphere of homes as well as the other environments they encounter during service in the 

home. The corrosion resistance of the metals in these environments is a major factor in 

determining the normal deterioration of the performance of household appliances, switches, 

safety systems, and water, electrical, and gas supply systems. When these systems deteriorate 

more rapidly than normal, there is a high probability that accelerated corrosion is the cause. 

Identification of the factors responsible for accelerated corrosion can be done through three 

ways: (i) identification of the unique characteristics of the homes with accelerated deterioration, 

(ii) identification of the differences in the environments encountered in the homes with 

accelerated deterioration, or (iii) identification of failure modes, corrosion product compositions, 

and responsible chemical reactions. 

 Of immediate concern is the accelerated deterioration of systems in homes constructed with 

imported wallboard. Due to the very large number of complaints from the owners of homes 

constructed with imported wallboard, the Consumer Product Safety Commission (CPSC) has 

become concerned that this product contains chemical species that alter the internal atmosphere 

of the home and accelerate corrosion and the deterioration of systems that rely on metals to 

perform critical functions. As a result, the CPSC has instituted a large multitasked program to 

look at this product and how it influences the health of occupants, the performance of critical 

household systems, and the prevalence of this product in homes in the US. As part of this 

program, the Materials Science and Engineering Laboratory (MSEL) of the National Institute of 

Standards and Technology (NIST) became involved through the Interagency Agreement CPSC1-09-0023 to examine metallic samples removed from service in homes constructed using 

imported wallboard. The objective of these examinations is to identify potential corrosion 

related failure modes, corrosion product chemistry, and potential chemical reactions. This 

document reports on the findings of the examinations performed on the first group of samples 

provided to NIST by CPSC. All findings reported here should be considered preliminary, as 

more examinations are planned. None of the samples provided to NIST in the first group were 

failed components. Therefore, none of the conclusions drawn here can address the mechanisms 

of the reported failures. 

II. EXAMINATIONS

A. Sample Selection and Delivery
4 

 The samples were selected by CPSC staff and transported and hand delivered to NIST. The 

samples were received on September 28, 2009 and immediately cataloged for recording and 

tracking the examinations. All of the samples received were identified with a number assigned 

to the sample by CPSC. These numbers consisted of eleven digits, starting with: 09-302-####-

##. NIST used the last six unique digits of the samples to track them during the examinations. 

The samples received consisted of a number of lengths of copper tubing used as natural gas 

supply lines and two air conditioner heat exchanger coils. 

B. Visual Examination and Photography

The lengths of copper tubing were discolored to varying degrees. This discoloration, which is 

illustrated in Figure 1, was found to be due to the presence of a thin adherent layer of a black 

substance. This is clearly illustrated in Figure 2 where the sample number has been scribed into 

the sample exposing fresh bare copper. The contrast in this figure is obvious. While this film 

adhered to the surface, physical contact would result in the transfer of a small quantity of a fine 

black powder from the film. In some cases, the discoloration was found to be very uniform, but 

in other cases it was irregular. The extent of discoloration varied with the thickness of the layer. 

Figure 1 – Photographs of two representative samples of copper natural gas supply tubing. 

Figure 2 – Scribe marks illustrating the contrast between the color of bare copper and a sample 

of copper natural gas line tubing. 

 The air conditioner evaporator coils were also examined, Figure 3. From the two coils in this 

figure it can be seen that all exposed copper surfaces have turned dark. These coils are 

constructed out of parallel lines of copper tubing placed through thin sheets of aluminum that 
5 

serve as the heat transfer fins. The copper tubing is linked together by soldered U-bends to the 

ends of adjacent lengths of copper tubing. The end plates that hold this assembly in place are 

made out of galvanized steel. Copper manifolds and valves complete the assembly. Figure 4 is a 

close-up of the end plates and the U-bend region. In this figure, brown and orange corrosion 

products can be seen on the galvanized end plates, while black and green corrosion products can 

be seen on the copper tubing. The normal patina that forms on copper in the cyclically wet and 

dry environment of an air conditioner evaporator coil would be expected to contain copper (I) or 

copper (II) ions in oxides (black to brownish-red), carbonates (green to blue), sulfates (bright 

blue), and chlorides (greenish white to blue-green) [1,2]. Again, the black color was found to be 

due to the presence of a thin layer of a loose black powder. 

Figure 3 – Photograph of the two air conditioner evaporator coils showing the black 

discoloration of the copper U-bends and corrosion of the end plate. 
6 

Figure 4 – Close-up photograph of the U-tubes and end plate of an air conditioner evaporator coil 

showing that there appears to be 5 colors associated with the corrosion products: white, brown, 

orange, green, and black. 

C. Identification of the Black Corrosion Product by X-Ray Diffraction

 The black substance observed on the surfaces of the copper components was identified by Xray diffraction. This was accomplished by scraping the black substance from the surface of one 

of the sample of copper natural gas line tubing using a razor blade. The powder removed in this 

manner was accumulated on double stick tape and attached to a glass slide as shown in Figure 5. 

A powder diffraction pattern was then obtained from this sample of scrapings using Siemens 

D500 X-ray diffractometer with a Cu K radiation source operated at 40 kV and 30 mA using a 

step size of 0.03 degrees, and a dwell time of 5 s.

Figure 5 – Photographs of the scraped copper natural gas supply line and the slide holding the 

sample for X-ray diffraction. 

 Figure 6 shows the results of these measurements in red along with the peak locations in 

black for copper metal (Figure 6a), copper (I) oxide (Figure 6b) and copper (I) sulfide (Figure 

6c) as listed in the International Crystal Structure Database (ICSD). This figure shows that peaks 

corresponding to all three of these phases are present in the sample of scrapings from the surface 

of the copper natural gas supply line. Given that the sample was collected by scraping the 

surface of copper metal with a sharp razor blade, the peaks for copper and copper oxide were 

expected since copper is a soft metal compared to the steel of the razor blade and will normally 

form copper oxide when exposed to air. The third phase, copper sulfide (Cu2S) is not a typical 

atmospheric corrosion product as the concentration of the reduced sulfur species, such as H2S, 

required to form this product is usually very low under normal atmospheric conditions. [1, 3-5] 

Figure 7 is a summary of the XRD results showing that all but two small peaks, indicated by 

question marks, are accounted for by these three phases. 

 

The identification of any commercial product or trade name does not imply endorsement or 

recommendation by the authors or NIST.
7 

Figure 6 Powder diffraction patterns for the sample of corrosion products scraped off a copper 

natural gas supply line (red) with, identified in black, the peaks for (a) copper, (b) copper (I) 

oxide (ICSD #38233), and (c) copper (I) sulfide (ICSD #95395). 
8 

Figure 7 – Summary of peaks found in the corrosion product sample and their identification for 

showing that only two small peaks were unidentified by the three phases. 

D. Air Conditioner Evaporator Coil Leak Testing

 Leak testing was performed on the air conditioner heat exchange coils by attaching air tight 

fittings to the ends of the copper lines and connecting these to a helium gas detector. The inside 

of the coil was evacuated and helium gas passed over different regions of the coils. No leaks 

were found by this method. Then, the coils were pressurized with helium and a solution of soapy 

water was squirted onto different regions of the coils. This method also failed to find any leaks in 

these coils. 

E. Air Conditioner Evaporator Coil Sectioning

 To evaluate the possibility of corrosion damage occurring between the aluminum heat 

transfer fins and the copper tubing inside them, the heat exchanger unit was sliced with a band 

saw as shown in Figure 8, to expose these internal surfaces for examination of the copper. No 

evidence of localized attack was found, and the black corrosion product layer was not detected 

by visual examination. 
9 

Figure 8 – Air conditioner evaporator coil after slicing to allow for examination for corrosion 

damage between the aluminum sheets and the copper tubing. 

F. Measurement of Corrosion Product Layer Thickness

 The thickness of the black corrosion product was measured using optical microscopy of 

samples prepared in cross section. For this analysis, samples of natural gas supply lines were 

cut, mounted in epoxy, and polished using standard metallurgical practice, exercising care to 

maintain the edge of the sample with the corrosion products in place. Figure 9 shows optical 

micrographs of this sample where the corrosion product layer varied from 5 m to 10 m thick. 

Figure 9 – Optical micrographs of the wall of a copper natural gas supply line and the corrosion 

product layer at two magnifications (wall 1.2 mm thick). 
10 

III. DISCUSSION AND CONCLUSIONS

 The copper metal surfaces of the samples provided for examination were covered with a 

black film that appears to be a corrosion product. The X-ray powder diffraction results 

unambiguously identified this substance as a copper sulfide phase. Copper sulfides (CuxSy) can 

have a wide range of stoichiometry ranging from CuS2 to Cu2S with 9 distinctly different phases 

having been identified over this range depending on the stoichiometry. The powder diffraction 

pattern was consistent with the digenite phase of copper sulfide that has a stoichiometry of Cu9S5

or Cu1.8S. The presence of a copper sulfide phase on the surface of the copper indicates that 

reduced sulfur compounds, such as hydrogen sulfide (H2S), sulfur (S8), or mercaptans (thiols), 

are present in the indoor atmosphere of the homes from which these samples were removed. 

 Reduced sulfur compounds generally accelerate the corrosion of engineering metals, as sulfur 

forms stable compounds with most of the parent and alloying elements in these alloys. [3] 

However, copper and silver are reported to have the greatest sensitivity to this environmental 

contaminant. [2,6] Rice et al. [2,6] conducted studies on the sensitivity of indoor corrosion rates 

of different metals to environmental contaminants including hydrogen sulfide. These authors fit 

the rate of mass increase (dm/dt) to the equation 

 (1) 

where A is a constant, [H2S] is the concentration or activity of hydrogen sulfide in the 

atmosphere and n is a measure of the sensitivity of the corrosion rate to changes in the hydrogen 

sulfide concentration. This parameter, n, is also the slope of a log-log plot as 

 (2) 

Table I shows the results of Rice et al. [2,6]. This table clearly shows that copper and silver are 

the most sensitive of these metals to the concentration of hydrogen sulfide. 

Table I - The corrosion rate parameter, n, in equations (1) and (2) for different metals exposed to 

hydrogen sulfide at different concentrations in air specifically formulated to represent a typical 

indoor air environment and air that is purified to remove all contaminants other than hydrogen 

sulfide.[Rice, 1982 #4] 

Metal Cu Ag Co Ni Fe 

Representative

Indoor Air 

0.30 0.55 0.02 0.03 0.05 

Purified 70 % 

RH Air 

0.93 0.14 - - - 

 While the results clearly indicate that a reduced sulfur species is present in the indoor 

atmosphere of the homes that these samples came from, the corrosion product layer observed on 

these samples was less than 10 m thick. This layer makes the copper look dark due to the black 
11 

color and opaque nature of this corrosion product. All of the corrosion damage observed to date 

is consistent with a general attack form of corrosion that will progress in a uniform and relatively 

predictable manner. No evidence of any type of localized attack was found, but these forms of 

attack typically require an incubation period before they initiate. Therefore, the number of 

samples examined to date is too small to draw a conclusion on these forms of corrosion being 

able to cause or not cause failure. Samples from failed systems or from laboratory tests 

conducted over a wide range of metallurgical and environmental conditions will be required to 

assess the probability of these other forms of corrosion causing failure. 

IV. REFERENCES

1. N. de Zoubov, C. Vanleugenhaghe, and M. Pourbaix, Copper, Atlas of Electrochemical 

Equilibria in Aqueous Solutions, M. Pourbaix ed., NACE International, Houston, TX, 1974, 

p. 384-92. 

2. D. W. Rice, R. J. Cappell, P. B. P. Phipps, and P. Peterson, Indoor Atmospheric Corrosion of 

Copper, Silver, Nickel, Cobalt, and Iron, Atmospheric Corrosion, W. H. Ailor ed., J. Wiley 

& Sons, New York, 1982, p. 651-66. 

3. K. Barton, Protection Against Atmospheric Corrosion - Theories and Methods, J. Wiley & 

Sons, New York, 1976. 

4. G. Valensi, J. VanMuylder, and M. Pourbaix, Sulphur, Atlas of Electrochemical Equilibria in 

Aqueous Solutions, M. Pourbaix ed., NACE International, Houston, TX, 1974, p. 545-53 

5. T. E. Graedel and N. Schwartz, Air Quality Reference Data for Corrosion Assessment, 

Mater. Perf., 16(8), 1977, p. 17-25. 

6. D. W. Rice, R. J. Cappell, W. Kinsolving, and J. J. Laskowski, Indoor Corrosion of Metals, 

Journal of the Electrochemical Society, 127(4), 1980, p. 891-901.