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Study of lead leaching from copper-alloy water pipe components into potable water

Project Title: metallurgical impact due to thermo-mechanical processing of copper-alloy pipework components

Research Impact Fund (RIF) project 2020/21 by Professor A.H.W. Ngan

The problem of lead leaching in potable water has been a serious concern in different jurisdictions. Although copper-alloy components used in potable water pipework must be of the nominally "lead-free" grade in most jurisdictions including Hong Kong, incidents of excessive lead leaching, such as that occurred in Kai Ching Estate in 2015, are still reported from time to time.

Conventionally, people use electrochemistry to explain the phenomenon of lead leaching from copper alloy components. However, our recent research shows that this approach of explanation is inadequate. Instead, thermal and mechanical treatments in common engineering practice can significantly increase the lead content on copper alloy surfaces, thus causing leaching to above the acceptable threshold.

This project aims at finding a science-based solution to lead leaching. First and foremost, the susceptibility of the large variety of approved plumbing products typically available in the Hong Kong market to the thermo-mechanically induced lead leaching will be studied by high-throughput experimentation. The mechanisms of lead segregation and leaching will also be investigated by microscopic techniques. Based on the gathered database, data analytics methods will be used to devise codes of practice and guidelines for proper processing of plumbing components during installation to avoid lead leaching, and the provision of sufficient immersion of newly installed components to ensure complete leach out of lead before usage.

The impact of this project will include a scientific understanding of the metallurgical mechanism of lead leaching from plumbing alloys, a new sets of engineering guidelines and standards for plumbing installation works, and, in the longer run, revision in legislation, to solve the lead leaching problem.

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