Analysis of Degraded Brass Plumbing Fittings

Case Studies

Background

Two 90-degree brass plumbing fittings were received by the Rimkus Materials Testing and Investigation team for a corrosion investigation to determine the extent of deterioration and leakage. The fittings were reported to have been installed in an occupied residential home during a two-year restoration project. Excessive corrosion deposits, stains, and discoloration were visually observed on the outer surfaces of the fittings.

Services Provided

To evaluate the cause of corrosion, the brass plumbing fittings were subjected to a series of testing and analytical techniques including visual and stereoscopic examinations, scanning electron microscope (SEM) examinations, elemental analysis, metallography/microstructure evaluation, chemical composition analysis, and hardness testing.

Results indicated the fittings were severely degraded due to “plug-type” dezincification corrosion. The dezincification was due to the high concentration of internal deposits, hot water temperature, water pH, water chloride content, stagnant or low flow conditions, and the use of a brass material susceptible to this form of corrosion (copper alloy C36000, leaded brass).

Zinc was found to be completely leached from the brass alloy (normally +/-34% zinc), leaving a porous matrix through the entire wall thickness of the fitting. Leakage was determined to be imminent at all locations with comparable fittings in the hot water line where similar flow velocities were found.

Rimkus experts performed energy dispersive x-ray spectrographic (EDS) microanalysis to identify the elemental composition of localized corrosion cells that occurred as a result of heavy internal deposits, which was determined to be zinc oxide. The corrosion-attacked regions were essentially made up of pure metallic copper, with only traces of zinc remaining. The heavy internal deposits were also mainly zinc oxide, due to the corrosion, as well as aluminum oxide. The source of aluminum oxide, without significant levels of calcium carbonate or silicon oxide, was unusual and may indicate corrosion of an aluminum component in the hot water system.

Conclusion

The Rimkus team recommended that all similar fittings should be replaced with dezincification-resistant brass alloy fittings. In addition, it was recommended that the home’s water be tested and treated for pH and chlorine content, and that the maximum hot water temperature be decreased to help reduce corrosion. Additionally, any aluminum components in the hot water system should also be inspected for corrosion damage.

Photos

The above image shows the two brass elbow plumbing fittings in the received condition for analysis. Significant deposits and various stains were observed on the outer surface of the fittings.
Figure 1: The above image shows the two brass elbow plumbing fittings in the received condition for analysis. Significant deposits and various stains were observed on the outer surface of the fittings.

 

As seen in the close-up view above, heavy internal deposits were observed on the interior surface of the fittings.
Figure 2: As seen in the close-up view above, heavy internal deposits were observed on the interior surface of the fittings.

 

A cross-section cut through one of the fittings revealed heavy orange and white internal deposits. The deposit morphology indicated low flow velocity or a stagnant condition over an extended period of time.
Figure 3: A cross-section cut through one of the fittings revealed heavy orange and white internal deposits. The deposit morphology indicated low flow velocity or a stagnant condition over an extended period of time.

 

EDS elemental analysis of the internal deposits indicated they were mainly comprised of zinc corrosion products and aluminum oxide. Sulfur and chlorine were also noted. The source of aluminum oxide indicates likely corrosion of an aluminum component within the water system.
Figure 4: EDS elemental analysis of the internal deposits indicated they were mainly comprised of zinc corrosion products and aluminum oxide. Sulfur and chlorine were also noted. The source of aluminum oxide indicates likely corrosion of an aluminum component within the water system.

 

A low magnification SEM image of the cleaned surface showed localized patches of corrosion pitting.
Figure 5: An increased magnification SEM view of the fitting’s internal surface showed the pitting effects from localized corrosion cells.

 

An increased magnification SEM view of the fitting’s internal surface showed the pitting effects from localized corrosion cells.
Figure 6: A high magnification SEM view of a corrosion cell pitting location on the fitting’s internal surface.

 

EDS elemental analysis of the localized corrosion site shown in Figure 6 identified nearly 100% copper with only a trace of zinc. Evidence of dezincification was revealed, as zinc had leached from the matrix.
Figure 7: EDS elemental analysis of the localized corrosion site shown in Figure 6 identified nearly 100% copper with only a trace of zinc. Evidence of dezincification was revealed, as zinc had leached from the matrix.

 

A low magnification photomicrograph of a cross-section through the fitting nipple tube. The un-attacked brass is observed as a bright yellow color while the copper-colored areas are indicative of dezincification. The dezincification attack had penetrated 100% through the tube wall.
Figure 8: A low magnification photomicrograph of a cross-section through the fitting nipple tube. The un-attacked brass is observed as a bright yellow color while the copper-colored areas are indicative of dezincification. The dezincification attack had penetrated 100% through the tube wall.

 

A high magnification photomicrograph of the attack of the zinc phase along the internal surface of the fitting cross-section. The un-attacked brass is light yellow in color while the attacked area is copper colored and filled with voids where the zinc had leached out.
Figure 9: A high magnification photomicrograph of the attack of the zinc phase along the internal surface of the fitting cross-section. The un-attacked brass is light yellow in color while the attacked area is copper colored and filled with voids where the zinc had leached out.