Elsevier

Chemosphere

Volume 236, December 2019, 124329
Chemosphere

Corrosion of upstream metal plumbing components impact downstream PEX pipe surface deposits and degradation

https://doi.org/10.1016/j.chemosphere.2019.07.060Get rights and content

Highlights

  • PEX pipe degradation in metal-plastic hybrid plumbing networks was examined.

  • CuO, Cu(OH)2, FeOOH, Fe2O3, and MnO2 were found on exhumed PEX pipe surfaces.

  • Moderate water at 55 °C resulted the greatest metal loading on plastic surfaces.

  • PEX pipes exposed to hot water released more organic carbon than cold water.

  • PEX pipes connected to copper and brass had the greatest plastic surface oxidation.

Abstract

Plastic pipes have been and are being installed downstream of metal drinking water plumbing components. Prior research has suggested that such pipe configurations may induce plastic pipe degradation and even system failure. To explore the impact of upstream metal plumbing components on downstream plastic pipes, field- and bench-scale experiments were conducted. Six month old galvanized iron pipes (GIPs) and downstream crosslinked polyethylene (PEX) pipes were exhumed from a residential home. Calcium, iron, manganese, phosphorous, and zinc were the most abundant elements on both GIPs and PEX pipes. Black and yellow deposits were found on some of the exhumed PEX pipe inner walls, which were mainly copper, iron, and manganese oxides (CuO, Cu(OH)2, Fe2O3, FeOOH and MnO2). Follow-up bench-scale experiments revealed that metal levels in the drinking water did not always predict metal loadings on plastic pipe surfaces. The pH 4 water resulted in a greater amount of metals released into the bulk water, but the pH 7.5 water resulted in a greater amount of metals deposited on the PEX pipe surfaces. Hot water (55 °C) induced a greater amount of organics released and higher metal loadings on PEX pipe surfaces at pH 7.5. ATR-FTIR analysis showed that at 55 °C, PEX pipes connected to copper and brass components had the greatest oxidation functional group peak intensity (COOC, CO, and COC). This study highlights potential downstream plastic pipe degradation and metal deposition, which may cause plumbing problems and failures for building owners, inhabitants, and water utilities.

Introduction

Plastic drinking water pipes are being increasingly installed for building water service lines and commercial/residential plumbing (Whelton and Nguyen, 2013). A survey of 59 U.S. homeowners who replumbed their homes documented that 54% preferred to install crosslinked polyethylene (PEX) pipes, instead of applying an epoxy coating to the existing pipes or installing metal plumbing materials (Lee et al., 2013). When buildings are renovated sometimes only part, not all, of the existing metal plumbing is replaced with new plastic pipes (Kimbrough, 2007; Rhoads et al., 2016; Salehi et al., 2018). As a result, these buildings contain metal-plastic hybrid plumbing networks, where released metals may interact with plastic materials. Such hybrid plumbing networks can also be observed at the service line, where the utility installs a new plastic pipe and the customer does not replace the older piping material. PEX piping can also be located downstream of metal service lines and water distribution system pipes. Even when building owners install PEX piping throughout the household plumbing, metal fittings such as brass valves and couplings can be present.

While studies have investigated metal leaching into water from metal plumbing components (Edwards et al., 2002; Lasheen et al., 2008; Tam and Elefsiniotis, 2009; Elfland et al., 2010), few studies have investigated metal fate within plastic plumbing (Kimbrough, 2007; Inkinen et al., 2014; Salehi et al., 2018). Brass leaching has been identified as a major source of metals release within plastic plumbing systems, and can be influenced by the product’s composition (Lytle and Schock, 1996; Pieper et al., 2016), drinking water characteristics (Boulay and Edwards, 2001; Edwards et al., 2002; Edwards and Dudi, 2004; Pieper et al., 2017), water temperature (Sarver and Edwards, 2011), galvanic current (Dudi, 2004; Triantafyllidou et al., 2012), and hydraulic conditions (Lytle and Schock, 1996; Zhang, 2009; Sarver and Edwards, 2011). For example, compared to incoming building water metal concentrations, brass-related metals such as copper, lead, and zinc were higher in the plastic household plumbing water (Salehi et al., 2018). Another study examined metal deposits on indoor PEX plumbing pipes from a 1 year old single family U.S. home, and surface analysis revealed orders of magnitude different metal loadings on the exhumed pipes (Salehi et al., 2017). Calcium (Ca), iron (Fe), magnesium (Mg), manganese (Mn), lead (Pb), and zinc (Zn) were the most abundant metals observed, which were hypothesized to have originated from the source water, water treatment chemicals, and plumbing components. Researchers also found abundant Fe deposits on a high-density polyethylene (HDPE) residential service line (Campbell et al., 2008), Fe, Ca, and Zn deposits on PVC water mains (Lytle et al., 2004), and Ca, Mn, and Zn deposits on HDPE water mains (Friedman et al., 2010). In contrast, a PVC water main exhumed from a U.S. water distribution system had “no or very small corrosion deposits” (Tang et al., 2006). In Honduras, Mn deposits on exhumed PVC water mains were about 1.8 times greater than on iron water mains from the same distribution system (Cerrato et al., 2006). In response to more than 100 black and yellow water complaints received by one utility in China, PVC and polyethylene (type not specified) water mains were exhumed and found to contain high loadings of aluminum (Al), silicon (Si), Mn, and Fe (Li et al., 2018). Thus, metal loading on plastic plumbing materials have been observed and the composition and amount of metal deposits present on plastic pipe surfaces likely originated from the drinking water source, water treatment processes, and water distribution system materials. Further research is needed to characterize deposition throughout the piping network, in particular, building plumbing.

The impact of metal deposition on plastic pipe service life has received little scrutiny, but field and laboratory evidence suggest there may be a relationship. In 2018, the Plastic Pipe Institute described concerns regarding use of copper pipe with polypropylene (PP-R) pipe. They claimed that “dissolved copper levels below 0.1 mg/L will not adversely affect PP-R piping materials,” but copper concentration at or above 0.1 mg/L could have negative impacts on PP-R pipe integrity (Plastic Pipe Institute, 2018). That same year, a PP-R pipe manufacturing company stated that copper ions could attack downstream PP-R pipes and PEX pipes (Aquatherm Technical Bulletin, 2012). In 2014, bench-scale experiments demonstrated that polyethylene (PE) exposed to “copper ions” at > 60 °C increased crystallization and surface roughness (Tanemura et al., 2014). In 2012, a researcher observed that copper salts deposited on the surface of PP-R, PEX, and polybutylene water pipes and catalyzed plastic pipe degradation (Graeme, 2012). It was reported that copper ions and high temperatures for a hot water recirculation system depleted PP pipe stabilizers. Unfortunately, data were not found to support these claims. A 2001 study reported that copper ions in a hospital’s hot water PP pipe system catalyzed system failures after 4–5 years of installation (Wright, 2001). As far back as 1974, carbonyl functional groups (CO) were found to be caused by the exposure of low density polyethylene to polished copper plates at high temperature (>55 °C) (Chan and Allara, 1974). Because PEX piping is increasingly being installed downstream of metal plumbing components and metal deposits can accumulate on plastic pipes, understanding metal-plastic interactions is warranted.

Field- and bench-scale tests were conducted to further understand metal deposits on PEX piping installed in a residential building and deposition caused by upstream metal plumbing components. Specific objectives were to: (i) characterize scales from GIPs and downstream PEX drinking water pipes exhumed from the residential building (ii) examine the influence of water conditions, temperature, and pipe apparatus on metal leaching and metal deposition, and (iii) evaluate potential plastic degradation phenomenon.

Section snippets

Characterizing metal scale and deposition on exhumed pipes

On May 10, 2018, six GIPs connected to six PEX pipes (i.e., total length was 0.9–3.7 m) were exhumed from a single family home in West Lafayette, Indiana, USA. This home had a total area of 204 m2, with 4 bedrooms and 1.5 bathrooms. All sections were removed from the basement ceiling by a plumbing contractor and separated into hot and cold water sections. The exhumed PEX pipes were approximately 6 months old, while the GIPs were originally installed in 1928 (90 years old). One GIP-PEX pipe

Chemical composition of exhumed residential plumbing pipe surface deposits

Metal deposits were found on both GIP and PEX pipe inner walls (Fig. SI-2) (Table 1). The most abundant metals on GIPs scales were Fe (48.0–86.7 wt%), Ca (3.1–27.2 wt%), Mn (0.3–21.0 wt%), and Zn (1.0–10.6 wt%) (Tables SI–2). Fe is a major GIP component, the water supplier reported 0.05 mg Fe/L water entering their distribution system, and ductile iron water mains conveyed water from the treatment plant to the service line (Gonzalez et al., 2013; Salehi et al., 2017). Ca likely originated from

Conclusion

  • Fe, Ca, Mn, Zn and P were the most abundant elements found on the six exhumed GIPs and six PEX pipes. These compounds likely originated from plumbing components, water distribution materials, the source water, and/or thewater treatment plant.

  • CuO, Cu(OH)2, Fe2O3, FeOOH, and MnO2 were identified as the major metal species on exhumed PEX pipe surfaces using XPS analysis.

  • While the aggressive water induced greater aqueous metal concentrations, the moderate hot water resulted in greater metal

Declarations of interest

None.

Acknowledgements

This work was funded by the United States Environmental Protection Agency (USEPA) (grant number: R836890). The authors thank Xingtao Liu (Birck Nanotechnology Center-Purdue University) for his assistance to the SEM-EDS measurement. The authors appreciate support provided by Dr. Chloe De Perre (Purdue University College of Agriculture) for conducting ICP-OES measurements. Additional thanks are extended to Nicholas Salts (Mechanical Engineering, Purdue University) for collecting exhumed plumbing

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