Pipe Material Selection for Hydraulic Systems
AS/NZS 3500 / AS 4130 Contractors1. Purpose
This memo gives you a straight comparison of pipe materials for building hydraulic systems. We cover copper, PEX, polyethylene (PE), polypropylene (PPR), and stainless steel. You will find the temperature limits, pressure ratings, installed costs, and the situations where each material works best.
2. Material Properties and Ratings
Copper (AS 1432 / AS 3688)
Copper handles continuous temperatures up to 93°C. Type B tube has a minimum wall thickness of 0.9 mm, and Type A runs at 1.0 mm. A DN15 Type B tube holds 3.5 MPa at 20°C.
Copper lasts 50 to 70 years in normal service. It resists bacterial growth due to natural antimicrobial properties in the copper ions. You can join it by soldering, brazing, compression fittings, or press-fit connections.
Installed cost for DN20 copper runs AU$15 to $45 per metre, depending on the joining method and access conditions. Copper prices have jumped roughly 38% over the past 12 months, so budget accordingly.
Copper remains the required choice in hospitals, schools, and fire-rated structures where code restrictions limit alternatives.
PEX - Cross-Linked Polyethylene (AS 2492 / AS/NZS 4020)
PEX comes in three types: PEX-a (Engel method), PEX-b (silane method), and PEX-c (electron beam). All three meet the same performance requirements, but PEX-a has better shape memory for expanding fittings.
PEX handles peak temperatures of 95°C and runs continuously at 70°C. Working pressure sits between 1.0 and 1.6 MPa depending on the class and temperature.
PEX now accounts for about 60% of new residential plumbing in Australia. Installed cost for DN20 runs AU$5 to $15 per metre. You can buy coils up to 100 m, which means fewer joints through wall cavities and ceiling spaces.
Watch out for brand compatibility - crimp rings, expansion fittings, and press sleeves vary between manufacturers and you cannot mix them. Lifespan runs 30 to 50 years depending on water quality and operating temperature.
Polyethylene - PE100 (AS/NZS 4130)
PE100 pipe is the standard for underground cold water mains. Pressure classes range from PN6.3 through to PN16. All ratings assume a water temperature of 20°C.
When the water runs hotter, you must derate the pressure. At 40°C, multiply the rated pressure by 0.80. At 60°C, multiply by 0.50. Do not use PE above 60°C.
PE100 joints use butt fusion or electrofusion welding. A properly fused PE joint is stronger than the pipe wall itself. This makes PE the best option for ground movement zones and seismic areas.
Installed cost for DN20 sits between AU$8 and $25 per metre. For large-diameter civil mains (DN100+), PE100 beats every other material on combined material and installation cost.
The 2025 update to AS/NZS 3500 now includes higher-pressure PE classes to address shortened life expectancy in northern Australian conditions where ground temperatures run higher.
Expected service life is 50 to 100 years in cold water applications at or below 20°C.
PPR - Polypropylene Random Copolymer (AS/NZS 4020 / EN ISO 15874)
PPR handles 95°C continuous operation and tolerates peaks up to 110°C. That makes it the strongest performer for hot water systems among the plastic options. Pressure rating sits at PN16 (1.6 MPa) at 20°C, dropping to PN10 at 70°C.
PPR joints use socket fusion welding, which creates a single homogeneous piece of material at each joint. No O-rings, no gaskets, nothing to degrade over time.
Installed cost for DN20 runs AU$10 to $20 per metre. PPR is gaining ground in commercial hot water systems where copper costs have become hard to justify.
The 2025 edition of AS/NZS 3500 Part 2 now permits polypropylene pipes for vacuum drainage systems, which expands the material's approved uses beyond pressure applications.
Expected service life exceeds 50 years.
Stainless Steel (AS 4321)
Stainless steel handles temperatures above 120°C and delivers the highest pressure ratings of any pipe material used in building hydraulics. Use it where you have aggressive water chemistry, coastal salt exposure, or high-temperature process connections.
Installed cost for DN20 runs AU$30 to $80 per metre. That price tag limits stainless steel to applications where nothing else will survive the conditions.
Connections use press-fit or welded joints. Expected service life exceeds 50 years even in harsh conditions.
3. Selection Criteria
Pick your pipe material based on five factors:
- Operating temperature. If your system runs above 70°C continuously, copper, PPR, or stainless steel are your options. PEX works up to 70°C continuous. PE stays below 60°C.
- Water chemistry. Acidic water (pH below 6.5) attacks copper. Chloramine-treated supplies can degrade some PEX products over time. Aggressive or saline water demands stainless steel.
- Location. Underground services favour PE100 for flexibility and corrosion resistance. Internal risers and branches suit copper or PEX. Exposed outdoor runs require copper, PE (with UV-stabilised grades), or stainless steel.
- Fire rating requirements. Copper and stainless steel maintain integrity in fire-rated compartments. Plastic pipes need fire collars at every penetration through fire-rated construction, and some authorities reject plastics entirely in certain fire-rated applications.
- Budget. PEX delivers the lowest installed cost per metre. Copper costs 3 to 4 times more than PEX but lasts longer and holds resale value through recycling. Balance the capital cost against the expected building life.
4. Installation Requirements
All pipe materials require compliance with AS/NZS 3500 and WaterMark certification. Beyond that:
Copper
Allow for thermal expansion - copper expands 17 mm per 10 m run for a 100°C temperature rise. Support intervals: 1.2 m horizontal for DN15, 1.8 m for DN25. Keep dissimilar metals separated to prevent galvanic corrosion. Use dielectric unions between copper and steel.
PEX
Protect from UV at all times, including during storage on site. Support intervals: 300 mm horizontal for DN16, 500 mm for DN25. Allow expansion loops - PEX expands roughly 10 times more than copper. Do not mix fittings between brands.
PE100
Fusion welding requires a qualified operator. Butt fusion machines must be calibrated, and joint records should be kept. Lay PE pipe on a sand bed (75 mm minimum) in trenches. Minimum cover: 300 mm where there is no vehicular loading, 450 mm under footpaths, 600 mm under sealed carriageways, 750 mm under unsealed carriageways.
PPR
Socket fusion requires clean, dry pipe ends and a calibrated fusion tool set to 260°C. Insertion depth marks are mandatory - under-insertion weakens the joint. Support intervals: 500 mm horizontal at 70°C, 750 mm at 20°C.
Stainless Steel
Press-fit tools must match the system manufacturer. Confirm the grade - 316L for coastal and aggressive environments, 304 for general building services.
5. Common Mistakes
We see these errors regularly on hydraulic projects:
Every single penetration needs one. Missing even one fails the fire inspection.
PE is a cold water material. Even at 40°C your pressure rating drops by 20%. At 60°C it drops by half. We have seen failures where PE was connected directly to solar hot water outlets.
A Rehau expansion fitting does not work with a Rifeng crimp ring. The crimping tools are different, the ring dimensions are different, and the failure mode is a slow leak inside a wall cavity.
A 30 m hot water riser in copper will grow by roughly 30 mm between cold fill and operating temperature. Without expansion provision, the pipe forces loads onto fittings and branch connections.
Connecting copper directly to galvanised steel or a steel water heater creates a galvanic cell. The steel corrodes at an accelerated rate. Every copper-to-steel transition needs a dielectric fitting.
Cheap imported PPR floods the Australian market. If it does not carry the WaterMark, it has not been tested to AS/NZS 4020 for drinking water safety and you cannot legally install it.
6. Recommendation
No single pipe material suits every application. Use this as your default approach:
| Application | Recommended Material | Why |
|---|---|---|
| Underground cold water mains | PE100 (AS/NZS 4130) | Best flexibility, corrosion resistance, and cost for buried services |
| Internal cold water branches | PEX | Lowest installed cost, fast installation, fewer joints |
| Internal hot water (below 70°C) | PEX or copper | PEX for cost; copper where codes require it |
| Internal hot water (above 70°C) | Copper or PPR | Both handle continuous high-temperature service |
| Hot water circulation loops | Copper | Proven performance, handles erosion-corrosion at continuous flow |
| Hospitals and healthcare | Copper | Antimicrobial properties, code requirements |
| Fire-rated risers | Copper or stainless steel | Maintains integrity without additional fire protection |
| Aggressive or saline water | Stainless steel 316L | Only material that survives long-term |
| Solar hot water connections | Copper | Handles stagnation temperatures above 100°C |
Get the material right at the design stage. Changing pipe material after rough-in costs 3 to 5 times more than getting it right the first time.
This memo reflects current requirements under AS/NZS 3500 (2025 edition) and AS 4130. Check with your local authority for jurisdiction-specific adoption dates of the 2025 standards. All products must carry WaterMark certification.