EPDM or FFKM on SIP and steam duty: how to choose on a sterile line

This page sets out how I choose between EPDM and FFKM when a seal has to survive steam and SIP cycles, and what the certificates on the datasheet do and do not tell you.

The short answer

What SIP actually does to a seal

A typical SIP cycle holds saturated steam at around 121°C, and some sites run hotter, up to about 135°C. Then the line cools, often under vacuum, and goes back to process or CIP.

So the seal does not just see heat. It sees:

• Steam and hot water, which attack some compounds that handle chemicals well
• Repeated heating and cooling, hundreds of cycles a year
• CIP chemistry in between, usually caustic and acid washes
• Compression the whole time

The failure is rarely a seal that melts. It is a seal that slowly takes a permanent set, stops pushing back, and leaks when the line cools down.

Compression set is the number that matters

Compression set is how much of its squeeze a seal loses permanently after being held compressed at temperature. A seal with high compression set still looks fine when you take it out. It has just stopped sealing.

On SIP duty, check compression set data tested at your steam temperature, not at room temperature and not in dry air. A compound that holds up in hot air can behave very differently in steam.

EPDM on steam duty

EPDM is naturally strong in hot water, steam and most CIP chemicals. The cure system matters a great deal:

• Sulphur cured EPDM is usually limited to around 120°C continuous. That is right at the edge of a 121°C SIP cycle.
• Peroxide cured EPDM can be used up to around 150°C, with low compression set reliably held to around 130°C and short peaks higher.

For SIP duty, specify a peroxide cured pharmaceutical grade. Do not accept "EPDM" on a drawing as a full specification.

Where EPDM is the wrong choice: oils, fats, hydrocarbons and many solvents swell it badly. If the product or the cleaning regime includes them, EPDM is out, however good it is in steam.

FFKM on steam duty

FFKM has the widest chemical resistance of any elastomer. That does not make every FFKM good in steam.

Some FFKM grades made for high temperature chemical duty are marked by their own maker as not recommended for hot water and steam. Others are made for exactly that duty. Pharmaceutical FFKM grades are made for Water for Injection, SIP and FDA compliance, and are rated well above SIP temperatures.

So when FFKM is the answer, the question is which FFKM. A cross reference by brand name alone can put a chemical grade into a steam duty.

FFKM costs many times more than EPDM. It is worth it when the process chemistry demands it. It is not worth it as a cure for a seal that failed for another reason.

Related: FFKM guide, FFKM chemical compatibility and Kalrez alternative cross reference.

What USP Class VI proves, and what it does not

USP Class VI is a biological reactivity test. Extracts of the material are tested in vivo to show the compound is not acutely toxic. It is a baseline for pharmaceutical contact and a sensible requirement.

What it does not prove:

• That the seal survives your steam temperature or number of cycles
• That compression set stays low on your duty
• That extractables stay low in your product, at your temperatures, over time
• That the part in your hand is the same compound that was tested, unless there is batch traceability

A Class VI certificate tells you the material is not toxic. It tells you nothing about whether it will seal.

What FDA 21 CFR 177.2600 proves, and what it does not

21 CFR 177.2600 covers rubber articles for repeated use in contact with food. It sets which ingredients may be used in the compound and limits on extractives, for example with distilled water at reflux for aqueous foods.

It is a food contact rule. It is not a pharmaceutical standard and it says nothing about steam life or sealing performance.

Also check how compliance is claimed. Some FFKM compounds show FDA compliance through a Food Contact Notification rather than 177.2600 itself. Both can be valid. Your QA team will want to see which one the declaration relies on.

And remember: the FDA does not approve seals. It sets rules for materials. Any datasheet that says "FDA approved seal" needs a closer look.

The failure I see most: duty drift after a like for like swap

This is the pattern behind a lot of repeat failures on product contact seals.

A seal worked for years. It gets replaced like for like, same part number, same size, same "EPDM" or "FFKM" on the paperwork. Then it starts failing.

Usually one of two things has changed:

• The seal changed. Same material family, different compound or cure. A sulphur cured EPDM where there used to be peroxide cured. A chemical FFKM grade where there used to be a steam grade.
• The duty changed. SIP was added or made hotter or longer. The CIP chemistry changed. Cycles went up with production.

Nobody changed the seal spec, because the seal "was fine". The paperwork still passes. The seal does not.

The fix is not a more expensive material by default. It is going back to the real duty, temperature, steam, chemistry and number of cycles, and choosing the grade to match.

How I choose, step by step

1. Write down the real duty: product, CIP chemicals and concentrations, SIP temperature and time, cycles per week, and cool down conditions.
2. Rule out materials on chemistry first. If oils, fats or solvents are present, EPDM is likely out.
3. Check temperature against the grade, not the family. Sulphur or peroxide cure for EPDM, steam grade or chemical grade for FFKM.
4. Ask for compression set data in steam at your temperature.
5. Match the compliance paperwork to the application: USP Class VI for pharmaceutical contact, 177.2600 or a Food Contact Notification for food contact, with batch traceability.
6. Choose the lowest cost material that meets all of it.

Questions I get asked