Reducing metal ion leaching

Reducing metal ion leaching

Maintaining optimal water quality with the right filler metals

Leaching of metal ions into drinking water is a common problem, as metal ions can be introduced to water in a number of ways before it reaches our taps. The ions can be present in groundwater, or they can come from apparatus used to process and clean the water due to corrosion. Access to safe and clean drinking water is recognised by the UN as a human right, so it is essential to take the necessary steps to minimise the amounts of metal ion leaching into drinking water.

Brazed components can unfortunately introduce metal ions to water, but Höganäs has discovered that using certain brazing filler metals can all but eliminate leaching issues in drinking water applications.

Global regulations

Regulations around acceptable metal ion content in drinking water vary from region to region, which you can see in this table. The NSF/ANSI 61 is applicable for USA and Canada.

Ion EU directive 
2020/2184

WHO guideline
2017

 NSF/ANSI 61
2016
Fe 200 µg/L - -
Cr 50 µg/L 50 µg/L 100 µg/L
Cu 2000 µg/L 2000 µg/L 1300 µg/L
Ni 20 µg/L 70 µg/L 100 µg/L
Mn 50 µg/L - 300 µg/L

Proven results

There is a clear industry trend towards improving circularity and reducing environmental impact, which promotes the transition from Cu-brazed heat exchangers to Ni- or Fe-brazed ones. This has been the case even for applications where metal ion leaching behaviour or corrosion resistance technically allows use of Cu-brazed components.

Höganäs has tested the amount of metal ion leaching from various brazing filler metals that are relevant for drinking water applications, particularly for brazed plate heat exchangers. The tests highlighted that Höganäs’ iron-based brazing filler metals BrazeLet® F300-20 and BrazeLet® F86 offer significant technical advantages in terms of lower or no significant metal ion leaching to drinking water.

The conclusions from the tests enable Höganäs to make better material recommendations to existing and potential new customers. This deepened knowledge will also help Höganäs’ customers to meet the applicable regulations for metal ion leaching to drinking water in the markets they serve.

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Results in brief

    • The results are from stagnant immersion trials with local drinking water from Höganäs, Sweden. The samples are vacuum brazed with AISI 316L austenitic stainless steel brazed plate heat exchanger plates. For full details, read the technical paper here
    • Cu-foil showed the highest levels of Cu- and Ni-ion leaching, mainly from the Cu-rich surface layer. No passivation effect at room temperature, while at 80 °C passivation occurs by Cu2(OH)2CO3 formation
    • AWS A5.8 BNi-5 (ISO 17672 Ni650) showed moderate Ni-ion leaching at room temperature and high Ni-ion leaching values at 80 °C due to severe corrosion of the eutectic structure by micro-galvanic corrosion. Low or insignificant leaching of other ions, noting that Si was not measured
    • BrazeLet Ni613 (AWS A5.8 BNi-15) showed very low metal ion leaching values at room temperature and insignificant leaching amounts at 80 °C due to fast passivation
    • Fe-base brazing filler metals (BrazeLet F300-20 (patented) and BrazeLet F86) show significantly lower metal ion leaching compared to standard Ni-base brazing filler metals, with the lowest metal ion leaching measured for BrazeLet F300-20

  
     

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Reducing metal ion leaching
Technical paper: Brazing filler metals for low metal ion leaching in drinking water applications
Iron-based stainless brazing filler metals
Iron-based stainless brazing filler metals
Nickel-based brazing filler metals
Nickel-based brazing filler metals