Quick answer: for the purity-critical Technology Cooling System (TCS) loops that feed direct-to-chip cold plates, stainless steel remains the benchmark for coolant cleanliness, pressure headroom and design life. Polymer systems (PP-H, PP-RCT, HDPE) are a credible, lighter-weight option for larger facility water loops. Many new builds use both — stainless closest to the chip, polymer further out.
As AI rack densities push past 100 kW, direct-to-chip (DTC) liquid cooling has moved from niche to necessity — and one of the first questions a design team faces is what to make the pipework from. Here’s how the two material families compare on the criteria that matter.
1. Coolant purity — the deciding factor near the chip
Cold plates on modern GPUs use microchannel geometries that a single flake of corrosion product or weld debris can obstruct. That makes the internal condition of the pipework a reliability issue, not a cosmetic one.
Hygienic-grade stainless tube is manufactured to controlled internal surface finishes — the same specifications (e.g. ASME BPE SF1/SF4) developed for pharmaceutical process lines, where sub-micron cleanliness is the whole point. A smooth, passive chromium-oxide surface gives particulate and biofilm nowhere to take hold, and it survives the aggressive flush-and-clean regimes loops undergo at commissioning.
Quality polymer systems are also clean-bore, but they carry different considerations: leachables from the material itself, permeation over long service life, and joint integrity that depends heavily on fusion-weld workmanship.
2. Pressure, temperature and design life
Data centres are designed for 20+ years of continuous operation. Stainless steel offers large pressure and temperature safety margins, is immune to UV and creep, and its mechanical properties don’t degrade with age or thermal cycling. Polymer pressure ratings de-rate as temperature rises — a real design constraint as DTC loops trend toward warmer water (supply temperatures of 30–45 °C are now common to enable free cooling and heat reuse).
3. Chemical compatibility
Single-phase DTC loops typically run treated water or a propylene glycol mix (commonly PG25). Both material families handle these fluids well; 316L stainless adds headroom for biocides, inhibitor packages and any future change of coolant chemistry without requalifying the pipework.
4. Installation and programme
Polymer’s genuine advantages: lighter weight, faster fusion jointing on large bores, and no hot works permits. Stainless requires TIG/orbital welding and purge control — but that skill base is exactly what hygienic-industry fabricators already have, and prefabricated spools can compress site time dramatically. On fast-track builds, the constraint is usually material availability, which is why early engagement with a stockholder matters more than the jointing method.
5. Fire, mechanical damage and insurability
Stainless is non-combustible and shrugs off site knocks that would gouge or stress-crack thermoplastic. Some insurers and end-client standards specify metallic pipework in white space for exactly this reason — always check the basis of design.
Where each one wins
| Criterion | Stainless steel | Polymer (PP-H / PP-RCT / HDPE) |
|---|---|---|
| Coolant purity at the chip | ✅ Benchmark | Good, workmanship-dependent |
| Pressure/temp headroom | ✅ Large margins | De-rates with temperature |
| 20-year design life | ✅ Proven | Proven in lower-temp duty |
| Weight & handling | Heavier | ✅ Lighter |
| Jointing speed, large bore | Orbital/TIG weld | ✅ Fast fusion |
| Fire performance | ✅ Non-combustible | Combustible (varies) |
| Heat-reuse-ready (warm loops) | ✅ | Check de-rating |
The pragmatic answer
Most new-build AI facilities land on a hybrid: stainless steel for the TCS loop, CDU connections and anything close to the IT hardware; polymer or carbon steel further out on the facility water side. If the end client’s standard specifies metallic throughout, stainless is the straightforward compliant path.
Neumo UK stocks hygienic-grade stainless tube from ½” to 8″, fittings, flanges and pressure-rated AWH butterfly valves for data centre liquid cooling loops — with EN 10204 3.1 certification and next-day availability on stock lines. See our liquid cooling infrastructure for data centres page.
Talk to us about your project
Kevin Windsor — Product Manager, Data Centre Liquid Cooling
kw@neumo.co.uk · 01952 583 999