A mock sink supply configuration was created using commonly employed materials in United States residential construction. Each supply pipe was terminated with a compression supply valve and metal braided supply line, in an effort to simulate water supply connections to a common sink. The far end of the metal braided supply line was capped (Figure 1). Low-volume leaks were intentionally created at each copper pipe to supply valve connection and from each supply valve to supply line connection (Figure 2). Leaks were ensured by not tightening compression fittings entirely and not using thread sealant putty or tape between connections. Component specifications were provided for reference (Table 1).

Five individual plumbing pipes were placed in a linear configuration along a common incoming pipe, and consequently subjected to the same internal pressure. The five specimens were numbered 1 through 5 from left to right, with Specimen 4 serving as the control (Figure 3). The control sample was subjected to the same internal pressures and external temperature and humidity exposure, in an effort to separate normal weathering from usage and moisture induced conditions. The specimens were mounted on a wood frame with 100 to 150 mm between specimens, above a clear, plastic container, measuring 40.1 cm wide by 65.5 long by 17.5 cm deep. The container retained the leaked water and was manually emptied on a daily basis. Suspended supply line components were never submerged below the water line.

Water supply was provided by the Town of Davie, Florida municipal water supply, under common city service conditions. Water temperature ranged from

21.1˚C to 25˚Celcius (˚C). Ambient room temperature in the conditioned environment ranged from 23.3˚C to 25.8˚C. Ambient relative humidity (RH) ranged from 52 to 79 percent. Internal water pressure remained a constant 482 kilopascals (kPa) throughout the study.

Due to manufacturing variations and hand assembled components, the multiple drips did not have the same flow rates. Additionally, flow rates diminished with time and leaks continuously self-sealed, necessitating drips to be manually re-created on a weekly basis. The average flow rate was taken weekly by collecting and measuring the retained water for one hour and dividing by eight, the number of individual leaks. Due to the inability to provide uniform leaks, the average flow rate varied widely from 1.1 to 23.75 milliliters per hour.

On a weekly basis, specimens were analyzed for corrosion and patina, and the locations were noted. Observed corrosion and patina were rated on a 1 through 10 color scale, with higher numbers corresponding to deepening shades of orange and green, respectively (Figure 4). Pipes and supply components were measured initially with a micrometer and measurements were recorded. Measurements were recorded at the same locations periodically to assess dimensional changes associated with corrosion and/or deposits.

By week 3, all specimens exhibited light widespread patina spots with an average of color depth 3.25 (Figure 9). Specimens 1 and 3 first exhibited minute specks of patina on the pipe adjacent to the supply valve connection leak on week 8, with color depths of 6 and 4, respectively (Figure 10). By week 16, the widespread, minute spots circularly increased slightly in area and deepened in color. Patina at the leaking connections progressed to an average of 6.25 by the end of the study on week 15 and remained locally concentrated around the leaks (Figure 11 & Figure 12).

Widespread patina spots represented atmospheric and usage induced patina and were also observed on the control specimen. This is a vital observation, as detailed observations distinguished patina caused by a leak from that which is caused by general service conditions.

The localized patina on the supply pipe was largely concentrated adjacent to the engineered leak from the angle stop compression fitting. The concentrated area represented the surface which was directly wetted by the leak and did not greatly expand outside of this limited area.

Figure 13 depicts the control specimen and data average with corresponding trendlines. The solid green line represents the increase in color depth plotted against time, while the dotted green line provides the best fit trendline data average. The best fit equation is depicted above. The corresponding R² value depicts the accuracy of the best fit equation as compared to the recorded data. Generally, above 0.9 is considered an accurate fit, while above 0.99 is considered ideal.

The control specimen data and trendline is also depicted by the solid and dotted blue lines, respectively. The intent and effect of the control sample data was to separate normal humidity or usage induced patina from the patina created by the direct water exposure.

As both specimen and control data trends gradually increased with time, one may conclude that the difference in color depth between the exposed specimens and data specimen reflects the direct water exposure. This is an erroneous assumption, as in actual practice, the patina induced from direct water exposure occurred concentrated to the limited area of contact with water leaks, while the control specimen patina formed over the general surface area of the pipe. Wetted specimens also exhibited similar patina over the surface area of the pipe, but patina was not accurately represented by data as the area exposed to direct water exhibited a deeper color and was consequently recorded as the deeper shade.

Notable corrosion of average color depth 2.25 first appeared on the copper pipe adjacent to the supply valve connection on week 2 (Figure 14). Corrosion gradually advanced to an average color depth of 6.75 by the end of the study, remaining concentrated around the supply line connection, while streaking downward onto the supply line on one specimen (Figure 15). The area of downward streaking denoted the surface of the supply line wetted by the engineered leak.

The angle stop valve itself was in contact with both leaks and did not itself exhibit corrosion or patina, while adjacent components exhibited progressive corrosion and patina. Please refer to Table 1 and note that the angle stop valve body is brass which may exhibit patina as a copper containing metal alloy.

Figure 16 illustrates the physical data gathered depicted as the solid orange line, and corresponding trendline as the dotted orange line. The color depth was plotted against time and illustrates a gradual increase, which correlated to length of exposure time. A scaled logarithmic equation offered the best fit equation, which indicated that the data followed an initial sharp increase in color depth followed by a period of tapering toward asymptotic behavior. A longer period of data gathering would further illustrate this trend. Consequently, it may be concluded that deepening colors of corrosion require extremely extended time periods to occur and the ultimate color depth of 10 may never be reached.

The control specimen data and trendline were also depicted for comparison, by the solid and dotted blue lines, respectively. Corrosion on the control specimen may have been limited to initial oxidation of the outer protective layer of metal. The fact that the corrosion color depth leveled off at week 8 illustrated this phenomenon.

No accumulated deposits were observed nor measured throughout the duration of the study.