Why steam is hard
Steam hydrolyses some polymers (polyurethane, ACM, some FKM), swells others, and combined with heat accelerates oxidation and compression set. Pressure steam at 170 degrees C or higher is among the harshest elastomer duties.
Material guide
| Material | Steam suitability |
|---|---|
| EPDM, peroxide cured | Good to about 150 degrees C continuous, up to 180 degrees C with premium grades |
| FEPM | Good at 200 degrees C, better chemical range |
| FFKM | Excellent, expensive |
| FKM | Standard grades poor; special steam-resistant bisphenol or peroxide grades are better |
| HNBR | Limited, suitable for hot water at moderate temperature |
| Silicone | Poor to fair |
| PTFE / spring-energised | Excellent but creeps |
EPDM formulation for steam
- Peroxide cure with coagents, not sulphur.
- Low-metal filler system with carbon black N550/N990 or non-hydrating minerals.
- Minimal plasticiser.
- Zinc oxide avoided (use alternative acid acceptors if needed).
- Long post-cure to reduce volatiles.
Design guidance
- Keep squeeze at 20 to 25 percent for static seals, so the ring still recovers after set.
- Leave groove void for swell.
- Avoid dead legs where condensate collects.
- Control water chemistry. Amine-treated boiler water is aggressive to some compounds; FEPM or EPDM cope better.
- Plan replacements by cycles and hours.
Test
Autoclave ageing at the actual pressure and temperature, with compression set measured afterward, is the most reliable test. ISO 1817 (liquid immersion) and ASTM D471 do not capture steam pressure, so supplement with autoclave tests.
Common failures
Blistering at depressurisation, hardening and cracking from oxidation, shrinkage from filler leaching and extrusion caused by softening at temperature.
About this article. It is original writing prepared from public sources, standards and general industry practice. It is not a copy of any book or standard and it is not engineering advice. Confirm values against the current edition of the standard and test in your own application. Only analyse material you own or are entitled to analyse.
