Copper is familiar, rigid, malleable, and well understood. But why do Australia’s most trusted plumbers, HVAC installers and fridgies keep coming back to copper piping systems over the “alternatives”?  

When looking at a piping solution for water and gas transfer, we need pipes that tick the boxes. We need them to be strong, durable, and easy to work with. Engineers need to be satisfied with the performance properties but also are cognizant that our customers need a solution that is cost-effective and seamless.  

When 316L stainless steel comes into the equation, it’s often due to short-term cost factors, with some perceived positive material benefits in corrosion-resistance, durability, and favorability for flexible routing. Respect where respect is due. PEX is self-proclaimed the cheaper, flexible, quick plastic pipe that also loves to throw itself into the ring. 

Record high copper prices might lead you to think about substitution, but price is momentary, it is more productive to consider longer-term cost factors, the durability and reliability of the material and its source, as well as the health implications of said material before considering substitution.  

The Underrated Seamless Advantage

Most stainless-steel tube for water applications in 316/316L is manufactured by roll forming stainless steel sheet and joining the sheet with a longitudinal weld along the length of the tube. The variation in types of welding (laser welding vs TIG welding) and its integrity can vary significantly from manufacturer to manufacturer. Welded stainless steel tubes possess a heat affected zone (HAZ) along the seam that can act as a location for galvanic micro-cells, preferential corrosion, cervice corrosion (especially in chlorinated water or stagnant conditions), exposing a weakness point at any area across the entire length of the piping system. 

On the other hand, Kembla copper plumbing tube is extruded and drawn seamless, eliminating the longitudinal weld and its associated HAZ, thus maintaining integrity and reducing piping vulnerabilities. Over an entire piping system, that is significantly reducing your risk to corrosion around a weld or seam. This means there is no weld bead, no change in metallurgy along the seam and a uniform wall thickness and grain structure. Copper naturally forms a protective cuprous oxide (Cu2O) patina in potable water. This oxide layer is self-healing, stable across a broad pH range (6.5 – 8.5), and results in uniform, predictable wear rates.  This stable, self-healing layer provides predictable corrosion behaviour across a broad range of water conditions.  Across an entire piping system, this removes one potential source of corrosion, metallurgical variation, and manufacturing defects from the equation. 

Built to Handle the Pressure 

Unfortunately, it has been a common occurrence for stainless steel to be supplied without post fabrication annealing as per the requirements of AS 5200.053. Molybdenum content can vary, and if it is not properly annealed or pickled, chromium carbides can form near the weld. Intergranular corrosion on the weld seam leads to premature cracking, porosity, and splitting along the longitudinal axis under hydraulic shock or stress.    

Stainless steel also depends entirely on an oxygenated passive chromium oxide layer. In low-oxygen stagnant water, dead ends, or under deposits (crevice conditions), or in water with high chloride concentrations, stainless steel suffers from pitting and stress corrosion cracking (SCC) – often leading to sudden pinhole leaks without warning. The weld and parent metal can also behave differently electrochemically, creating potential for differential corrosion. 

Conversely, copper has no seam and has a lower elastic modulus allowing it to absorb and dampen pressure fluctuations more readily than stiffer materials, helping reduce the impact of hydraulic shock, protecting backflow prevention devices, solenoid vales and inline meters from destructive pressure peaks. 

A simple way to think about it: a shirt might look great, but the seam is often where it can split and fall apart. 

Therefore, when it comes to tube eccentricity, material knowledge, testing and the technical expertise required to form the tube that performs, facts need to be checked. This is especially relevant in lower-cost imported tubing or tube that is not manufactured to high hygienic standards. 

Thermal Conductivity and Superior Heat Transfer

Where they diverge is thermal conductivity. Copper is an exceptional thermal conductor, boasting a thermal conductivity of roughly 330-340 W/m·K. By comparison, 300-series stainless steel sits at around 14-16 W/m·K – less than 5% that of copper.  Meaning, in mechanical heating and cooling loops, copper’s rapid heat exchange minimises thermal lag and lowers operating energy consumption, inevitably saving cost and improving system performance, ideal particularly for HVAC refrigerant lines. 

In hot water recirculation systems, high thermal efficiency means copper systems maintain predictable temperature gradients throughout domestic hot water (DHW) loops. In DHW systems, copper allows rapid heat transfer from heat exchangers into storage and distribution lines, eliminating prolonged burner or heat pump run times caused by thermal lag. 

Continuous Surface Disinfection and Antimicrobial Properties

Copper’s brings an additional layer of defense through its inherent antimicrobial activity, providing a real hygiene advantage in drinking water systems compared with 316L stainless steel, particularly in situations where water stagnation or biofilm growth (slimy microbial layers that can develop inside pipes) are a concern. 

Unlike stainless steel, copper is not a passive surface. Whilst, 316L stainless steel does offer a smooth, hard passive oxide layer, which can make microbial attachment more difficult, coppers oligodynamic effect, continuously occurring on the copper surface, can inhibit microbial growth and reduce the ability of bacteria to establish and maintain biofilms.  

Copper tends to disrupt and slow biofilm growth better than stainless steel, especially at moderate temperatures in low-flow conditions and in dead legs or stagnant pipework, helping reduce bacterial colonisation, odors and microbiologically influenced corrosion (Tomboulian et al., 2004). Through copper ions released from the pipe surface, copper actively disrupts and damages bacterial cell membranes, proteins , enzymes and microbial DNA. While highly cleanable, stainless steel lacks intrinsic biocide action. 

This is why material selection matters.   

Example 1 — Copper recorded the lowest biofilm formation potential

A 2010 study compared biofilm formation potential across six pipe materials, including copper (Cu), stainless steel (SS), steel, zinc-coated steel and plastics.

Copper recorded the lowest biofilm formation potential, while stainless steel was among the materials with the highest. The study measured biofilm using ATP concentration, with copper recording approximately 20 pg ATP/cm², compared with around 100–120 pg ATP/cm² for stainless steel under the tested drinking-water conditions.

The researchers also found that pipe material influenced not only the amount of biofilm formed, but also the diversity and composition of the microbial communities living within those biofilms.

This supports the role of copper as more than simply a durable pipe material. Copper’s durability and inherent antimicrobial properties can actively influence microbial growth and biofilm development, whereas stainless steel primarily relies on its highly passive, corrosion-resistant surface (Yu et al., 2010).

Better Control of Legionella 

In hot water systems, copper has historically shown lower Legionella colonisation rates than many plastic systems and, under some conditions, lower than stainless steel systems. This is why copper has long been favored in hospitals, aged care, healthcare plumbing, and potable hot water reticulation.  

Safe trace levels of copper ions act as the secondary sanitizer within internal plumbing lines. Copper kills more than 99.9% of bacteria (including Legionella pneumophila) within two hours of exposure. Also reducing the survival of organisms such as E. Coli, Pseudomonas and Staphylococcus. So, while 316 stainless steel is highly corrosion resistant and hygienic, it does not actively kill bacteria in the same way copper does. 

Micro organism  Inactivation on Seamless Copper   Survival on 304/316 Stainless Steel 
Legionella pneumophila  >99.9% kill within 2 to 3 hours   Persists indefinitely inside biofilms 
Escherichia coli   Total clearance within 90 minutes   Forms stable, resilient colonies 
Pseudomonas aeruginosa  Suppressed; biofilm formation inhibited   Rapid attachment to passive oxide layer 
Example 2 — Copper vs 316L Stainless: Legionella

A two-year study compared copper (Cu), stainless steel (SS) and PEX pipework in a warm-water system under conditions designed to simulate domestic water use. The results showed lower median Legionella concentrations in water from copper pipework — approximately 1,500 CFU/L — compared with around 4,300 CFU/L for both stainless steel and PEX.

Water ATP levels, an indicator of overall biological activity, were also lower in copper (2.1 ng/L) than stainless steel (2.5 ng/L) and PEX (4.5 ng/L).

While Legionella was ultimately detected across all three materials, the study found that copper temporarily limited Legionella growth under the conditions tested, demonstrating the potential antimicrobial advantage of copper in warm-water systems where microbial growth is a concern (Silhan et al., 2006).

The Corrosion Resistance Argument  

Both materials will corrode under inadequate water chemistry, design, and installation. The difference is how wide the safe operating window is. Coppers long service history and durability, with a service life of around 50–70 years when correctly designed and installed under suitable water conditions, has proven corrosion resistance and high-temperature performance have made it a long-standing choice for the harsh Australian conditions (attach Chels' article – Built for Here). 

That said, although stainless steels lifespan is only 20-25 years, having a high flow velocity up at 6m/s, compared to copper's max of 3m/s and it's chromium oxide passive layer provides broader resistance to certain aggressive environments, making it appropriate for combatting high seawater and chemical exposure, alongside high-volume water movement, adequate for processing plants like desalination and distilleries. 

Molybdenum is a rare element and price volatile 

Creating potential supply issues means exposure to significant price fluctuations. For 316 stainless steel, molybdenum is required at levels of up to 2.5%, with current prices around $65,000/tonne — with prices up to 50% higher in 2023. 

Molybdenum is officially recognised as a critical mineral by countries including Australia, Canada, Japan and China, roughly 50 times rarer than copper in the Earth's crust.  

Mineable operations are concentrated within a relatively fragile supply chain making supply vulnerable to geopolitical factors, shifts in copper production and declining global ore grades. 

You best believe it, Molybdenum supply is heavily dependent on copper mining, with the vast majority produced as a by-product of copper operations, meaning that if copper production or supply falls, molybdenum prices can rise significantly.  

Molybdenum is mined at only around 76 projects globally, with more than half located in China. As the world's largest producer and consumer, China's tighter environmental permitting and strong domestic demand have contributed to a more constrained global supply. Additionally, strong domestic consumption has led to supply rigidity, with producers limiting sales and holding firm on higher tender base prices. With few new primary molybdenum mines in advanced stages of development or permitting, the global market remains tight, highlighting that alternative materials are not immune to price volatility. 

Scrap Value, On-site Cost Saving and Flexibility 

Copper can provide significant end-of-life value, with scrap worth up to 10 times more than stainless steel depending on market conditions, and recovered copper tube often commanding more than 90% of the current copper price. For plumbing businesses, this can help recover costs when systems are replaced or removed, with potential annual scrap returns of $20,000–$30,000, depending on the volume recovered.  

Copper's workability also allows fast field modifications, manual bending and potentially lower labour-hour requirements per joint, adding value throughout the installation and replacement lifecycle.  

Material selection should therefore be driven by environment, pressure requirements, lifecycle cost and installation method, not just upfront price. 

Copper is proven and material substitution has hidden dangers 

Copper remains the proven all-rounder. It combines durability, high-temperature performance, malleability, excellent thermal conductivity, recyclability and, importantly, inherent antimicrobial properties. Stainless steel has genuine advantages in certain aggressive environments and high-flow applications, but it is not automatically the better material for all applications. 

The Australian plumbing market has also established a long history of training and education around the use of copper tube in installations, such design and installation knowledge is not as prevalent with other materials. 

The strongest choice is usually the one that reduces hidden joints, protects water quality, handles real building routes, and gives confidence over decades. For decades, copper has been the default for domestic and commercial plumbing across Australia. Millions of copper systems are still operating reliably, and copper remains the stronger choice. 

Kembla. Copper. Unrivalled.

Sources & Further Reading 

  • van der Kooij, D., Veenendaal, H. R., & Scheffer, W. J. H. (2005). Biofilm formation and multiplication of Legionella in a model warm water system with pipes of copper, stainless steel and cross-linked polyethylene. Water Research, 39(13), 2789–2798.  
  • Silhan, J., Corfitzen, C. B., & Albrechtsen, H. J. (2006). Effect of temperature and pipe material on biofilm formation and survival of Escherichia coli in used drinking water pipes: A laboratory-based study. Water Science & Technology, 54(3), 49–56. https://doi.org/10.2166/wst.2006.487 
  • Yu, J., Kim, D., & Lee, T. (2010). Microbial diversity in biofilms on water distribution pipes of different materials. Water Science & Technology, 61(1), 163–171. 
  • Tomboulian, P., Schweitzer, L., Mullin, K., Wilson, J., & Khiari, D. (2004). Materials used in drinking water distribution systems: Contribution to taste-and-odor. Water Science and Technology, 49(9), 219–226. https://doi.org/10.2166/wst.2004.0575 
  • International Copper Association Australia — copper.com.au