At a design temperature of 85 °C the material is the design. Every wetted alloy, plastic, lining, coating and elastomer is chosen with a temperature rating safely above the duty — and against the chloride and chemistry of the actual stream.
Indicative continuous-service limits for water/wastewater duty. Final selection depends on chloride, pH and chemistry — not temperature alone.
| Material | Typical continuous limit | Notes for hot duty | Reference |
|---|---|---|---|
| 304 / 304L stainless | ≤ 60 °C (low chloride) | Pitting and chloride stress-corrosion-cracking risk climbs with heat — usually stepped up to 316L for hot streams. | EN 10088 / ASTM A240 |
| 316 / 316L stainless | 85 °C+ (moderate chloride) | The workhorse for hot wastewater; molybdenum improves pitting resistance. Watch chloride × temperature. | EN 10088 / ASTM A240 |
| Duplex 2205 / super-duplex | 85 °C+ (high chloride) | For hot, chloride-rich or saline effluents where 316L would crack; higher strength allows thinner sections. | EN 10088 / ASTM A240 (S32205) |
| GRP (vinyl-ester resin) | ≤ ~90 °C | Excellent for corrosive hot streams; resin system, not glass, sets the limit. UV-stable gelcoat for outdoor hot climates. | EN 13121 / BS 4994 |
| GRP (isophthalic resin) | ≤ ~65 °C | Lower-cost option for milder hot duty; vinyl-ester preferred at or above 70 °C. | EN 13121 / BS 4994 |
| HDPE (PE100) | ≤ ~40–45 °C (pressure) | Allowable design stress derates steeply with temperature; suitable for warm gravity/low-pressure duty only. | ISO 4427 |
| Polypropylene (PP-H) | ≤ ~60–80 °C | Better heat tolerance than HDPE for tanks and ducting; still derated for pressure. | EN 1778 / DVS 2205 |
| Rubber-lined / ebonite-lined steel | ≤ ~80–90 °C (lining-dependent) | Carbon-steel strength with a temperature-rated elastomeric barrier; lining compound chosen to the peak. | BS 6374 / manufacturer data |
Chloride content and temperature must be assessed together: a stainless grade fine at 85 °C in low-chloride water can crack at the same temperature in a saline stream.
The most common cause of premature failure on a hot duty — matched to the peak temperature and the chemistry.
| Elastomer | Typical max | Use on hot duty |
|---|---|---|
| NBR (nitrile) | ~100 °C | Good oil resistance but hardens with heat; avoided as a primary seal on the hottest streams. |
| EPDM | ~120–130 °C | Excellent for hot water and many chemicals; a default for 85 °C aqueous duty (not for oils/fats). |
| FKM (Viton) | ~200 °C | For hot oily, fatty or aggressive-chemical streams where EPDM is unsuitable. |
| PTFE / FEP-encapsulated | ~200 °C+ | Near-universal chemical and temperature resistance for the most demanding seals. |
| Silicone (VMQ) | ~180 °C | Wide temperature range; chosen where flexibility at temperature matters more than abrasion. |
| System | Typical max | Notes |
|---|---|---|
| Vinyl-ester (glass-flake) | ~90–100 °C | Tough chemical barrier for hot, corrosive immersion service. |
| Epoxy novolac | ~80–90 °C (immersion) | High chemical and temperature resistance; immersion grade selected for the stream. |
| Soft / hard rubber lining | ~80–90 °C | Proven immersion barrier; compound graded to the peak temperature. |
| Standard epoxy | ~50–60 °C (immersion) | Cost-effective for warm duty; upgraded to novolac or vinyl-ester above ~60 °C. |
Plastics do not just have a temperature limit — their allowable design stress falls continuously as temperature rises. An HDPE or PP line rated for a given pressure at 20 °C may be derated to a fraction of that at 60 °C. We apply the manufacturer’s temperature-derating factors to wall thickness, pressure rating and support spacing — and switch to metal or GRP where the derated plastic no longer carries the duty.
Wetted materials supplied with EN 10204 3.1 inspection certificates — full traceability from mill to finished plant.
Welding procedures and welders qualified to ISO 15614 / ISO 9606, with correct pickling and passivation of stainless to restore corrosion resistance.
Where the stream is saline or sour, selection follows the appropriate guidance (e.g. NACE MR0175 for sour service) — not temperature in isolation.
Tanks and vessels designed to the relevant code with a full design dossier. See our standards & codes.
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