What hygienic seals must do
- Contain no harmful extractables.
- Resist cleaning (CIP/SIP) with caustic, acid, hot water and steam.
- Not harbour bacteria in crevices.
- Stay stable over thousands of cycles.
Approvals to ask for
| Area | Reference |
|---|---|
| US food contact | FDA 21 CFR 177.2600 (rubber articles for repeated use) |
| EU food contact | Regulation (EC) 1935/2004, plus national rules |
| Pharma | USP Class VI, USP <87> and <88> |
| Biopharma | ISO 10993, extractables and leachables reports, animal-derived-ingredient statements (TSE/BSE) |
| Hygienic design | EHEDG, 3-A Sanitary Standards, ASME BPE |
| Drinking water | NSF/ANSI 61, WRAS, KTW, ACS |
Approvals are for a specific compound. A change of formula needs a new declaration.
Material choices
- EPDM (peroxide cured): best all-round for steam, hot water, caustic and acid cleaning. Not for oils and fats.
- Silicone (platinum cured): wide temperature range, used in pharma and biotech; weak in steam beyond limited cycles, and tears easily.
- FKM: for oils, fats and flavours; weak in hot caustic and amines unless specially formulated.
- FFKM: premium for broad chemicals, high-temperature SIP.
- PTFE and PTFE-encapsulated: inert, but stiff and prone to cold flow.
- Thermoplastic elastomers: economical for disposable assemblies, with temperature limits.
Design
- Use gland designs without dead legs. Hygienic seals often have specific profiles (tri-clamp gaskets, bevel seat).
- Surfaces Ra 0.8 micrometres or finer, electropolished for biopharma.
- Avoid sharp edges that cut the seal.
- Choose colours that show contamination (blue, white) for food.
- Provide metal detectable or X-ray detectable seals where required.
Quality documents
Certificate of conformity, material safety data, extractables report, lot traceability, cleanroom packing, and for biopharma a change-control agreement with the supplier.
Common failures
Steam-induced compression set in EPDM, silicone tearing, swelling in fats, fouling in crevices and swell by sanitiser. Validate with real CIP/SIP cycle counts, not just short tests.
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.
