Gaskets, Seals and Valves: Where Most Leaks Actually Start
In pilot plants, most leaks come from gaskets, valve seats and instrument fittings rather than the vessel shell. The reason is simple: the vessel gets specified against the liquor, while the fittings get whatever was on the shelf.
Gasket selection by duty
| Duty | Suitable | Avoid |
|---|---|---|
| Dilute acid, < 80 °C | PTFE envelope, EPDM | Natural rubber, cheap fibre sheet |
| Concentrated H₂SO₄ | PTFE, Viton for lower concentration | EPDM (swells), silicone |
| Chloride with titanium flanges | PTFE envelope with a metallic core | Graphite (galvanic couple) |
| Caustic | PTFE, EPDM | Viton at high temperature |
| Solvent / organic | PTFE, Viton | EPDM (swells badly) |
The three joints that fail most
1. Agitator shaft seal. Mechanical seals need a clean, cool flush. Running dry or with solids in the flush destroys the faces in hours. Specify a flush plan and a pressure gauge you actually read.
2. Instrument tappings. Small threads with tape instead of a proper gasket, in a vibration field, will weep. Use welded bosses with PTFE gaskets and support the instrument.
3. Valve seats in slurry. Soft-seated ball valves in slurry service lose their seat to erosion. Use pinch or diaphragm valves for slurry, and reserve ball valves for clean liquor.
Galvanic pairs to avoid
Graphite gaskets against titanium or stainless flanges create a strong galvanic couple in conductive liquor, and the flange faces corrode preferentially. The same applies to stainless bolts on titanium flanges without insulating washers.
Specify the package, not the vessel
Ask for a wetted-parts schedule: shell, internals, gaskets, seals, valve bodies, seats, instrument wetted parts. If a supplier only quotes the vessel material, the rest will be decided by whoever assembles it.
Send your P&ID and liquor analysis and we will return a wetted-parts schedule with the exceptions flagged.