The moment nobody plans for
It usually happens during a routine changeout. A technician goes to remove a gasket from a tri-clover connection on a lyophiliser or process vessel. It doesn’t come away cleanly. It’s bonded to the ferrule face, not dramatically, not visibly cracked or perished, just stuck. And getting it off requires force.
A screwdriver between the flanges. A lever. Something.
And then the pressure transducer diaphragm gets scored. Or the ferrule face gets damaged. Or worse, a fragment stays behind in the process line.
What just happened? And more importantly, why does it keep happening?
What vulcanisation actually does
EPDM starts as a liquid rubber compound, a flowing, sticky, gum-like material. Vulcanisation, the curing process, is what transforms it into the solid, elastic gasket that ends up in your tri-clover connection.
During curing, cross-links form between the polymer chains. These cross-links are what give the material its elasticity, its resilience, and its ability to compress and recover. They are also what stop it from behaving like gum.
The problem is that those cross-links are not permanent. Heat, aggressive chemical exposure, and time all work against the cured state. The material doesn’t announce this. It just slowly, quietly, tries to return to what it was before it was cured.
A gasket that has been in service too long, or was poorly formulated to begin with, is essentially reverting to its original state. Which is basically a gum.
Why formulation matters more than people realise
Plasticisers
- Added to make the rubber easier to process during manufacture
- Not bound into the polymer matrix, so they migrate out under heat and pressure
- As they leave, they act as a bonding agent between the gasket face and the ferrule
- This is the primary driver of sticking
Inorganic Fillers
- Used as a cheap substitute for carbon black to reduce material cost
- Unlike carbon black, inorganic fillers don’t reinforce the polymer matrix, they weaken it
- A weaker gasket deforms more under clamp load, flows into ferrule surface texture, and bonds more aggressively
Quality Formulation
- No plasticisers, appropriate carbon black levels
- Holds its structure, compresses and recovers, releases cleanly
- Can achieve service life of up to three years without re-torquing
- Compliance doesn’t tell you which type you have
The chewing gum test
Leave a piece of chewing gum on a warm surface for a few days. It flows into every imperfection. It bonds. When you try to remove it, you tear it, or you take the surface with it.
That’s your EPDM gasket after repeated SIP cycles with the wrong formulation, or simply in service past its useful life.
The connection doesn’t fail dramatically. There’s no leak alarm, no obvious event. It just gets progressively harder to maintain, until someone reaches for a screwdriver, and then the downstream consequences begin.
The two-part fix
Material Selection
- Specify silicone or high-grade EPDM with no plasticisers and correct carbon black content for any application with regular SIP exposure
- The upfront cost difference is minimal
- The operational cost difference is significant
Replacement Intervals
- Don’t wait for a gasket to stick before you change it
- Define a replacement programme based on service conditions and material specification
- This is a planned maintenance decision, it should never be a reactive one
- The gasket is one of the lowest-cost components in a hygienic process system, it is rarely the lowest-cost failure
Want to talk process reliability?
Pure Transfer Ltd works with pharma and biotech facilities on high-purity process reliability, from gasket selection and clamp standards to ASME BPE-aligned installation practices and connection integrity monitoring.
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