Valves for Demineralised Water (DM Water / Deionised Water) Service
Demineralised water (DM water) is ultra-pure water with almost all dissolved minerals removed by ion exchange or reverse osmosis. It is used as boiler feedwater (BFW) in power plants and refineries, process water in pharmaceutical and semiconductor manufacturing, and as cooling tower make-up in critical systems. Its very low conductivity makes it unusually aggressive toward metals.
Pressure Range
3–120 bar (boiler feedwater up to drum pressure)
Temperature
Ambient to 250°C (boiler feedwater at operating temperature)
Industries
Thermal and nuclear power (boiler feedwater), Pharmaceutical API and formulation water, Semiconductor wafer fabrication
Key Properties — Demineralised Water (DM Water / Deionised Water)
- Very low conductivity (<0.5 μS/cm for high-purity grades) — highly aggressive to carbon steel
- pH typically 6.5–8.5 (controlled by ammonia or morpholine dosing in boiler service)
- No scale-forming minerals — allows operation at higher heat flux without fouling
- Dissolved oxygen must be controlled (<7 ppb for high-pressure boiler BFW)
- CO₂ absorption from atmosphere — can cause carbonic acid corrosion
Material Compatibility — Demineralised Water (DM Water / Deionised Water)
Ratings are indicative. Actual compatibility depends on concentration, temperature, velocity, and presence of contaminants. Always consult corrosion tables or a materials engineer.
| Material | Rating | Notes |
|---|---|---|
| Carbon Steel (WCB/A105) | Fair | Corrodes rapidly in aggressive DM water. Acceptable only with pH control and oxygen scavenging. |
| SS 316L | Excellent | Standard material for DM water service — no iron contamination, corrosion-resistant. |
| SS 304 / 304L | Excellent | Acceptable for most DM water service; 316L preferred for hot or higher-purity applications. |
| Duplex SS | Excellent | Overkill for most DM service but used in pharmaceutical ultrapure systems. |
| PTFE-lined | Excellent | Zero contamination — preferred for semiconductor and ultra-high purity DM water. |
| Bronze / brass | Poor | Zinc dezincification and copper leaching — avoid for DM water where purity matters. |
Recommended Valves
Ball Valve (SS 316L, full-bore, PTFE seats)
Standard isolation and on/off service for DM water — zero contamination, low pressure drop.
Diaphragm Valve (SS 316L body, EPDM or PTFE diaphragm)
Preferred for pharmaceutical and semiconductor ultra-pure DM water — smooth bore, no dead leg.
Globe Valve (SS 316L)
Flow control and throttling on DM water supply lines and chemical dosing.
Check Valve (SS 316L piston or swing)
Pump discharge non-return — SS 316L to prevent iron contamination.
Valves to Avoid
Cast iron or carbon steel bodies (iron contamination and rapid corrosion in aggressive DM water)
Bronze or brass valves (zinc/copper leaching into ultra-pure water)
Valves with dead legs or blind spots where stagnant DM water can concentrate corrosion
Special Considerations
Applicable Standards
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