Where do pilot plant leaks actually start?

Three joints account for most of them: sight-glass and instrument fittings (dissimilar materials, thermal cycling), pump seal flush lines, and valve gland packing. The vessel shell - the thing everyone specifies carefully - almost never leaks. Specify the gasket and seal package against the liquor with the same care as the vessel, and the leak rate drops more than any shell upgrade could achieve.

Which gasket material for which duty?

EPDM for steam, hot water and amine service (but it swells in hydrocarbons and solvents); FKM for most acids and solvents (but not ketones or amines); PTFE envelopes for the most aggressive and least defined duties, at the cost of needing careful bolt torque. And torque matters as much as material: gaskets creep after the first thermal cycle, so a re-torque schedule is part of the specification, not an afterthought.

Gaskets, Seals and Valves: Where Most Leaks Actually Start

By Jingli WangProcess Equipment ManagerUpdated Oct 21, 2026

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.

Torque, creep and the re-torque schedule

Most leaks that appear months after commissioning are not gasket failures but loss of bolt preload. PTFE creeps under load, so a joint torqued to specification at ambient temperature loses 20 to 40 per cent of its preload after the first thermal cycle. A re-torque schedule at first heat-up, then at one week and one month, prevents the majority of weeping flanges, and it costs a fraction of what a shutdown for a failed joint costs.

The second avoidable failure is mixing materials in one joint: a PTFE envelope gasket against a stainless flange with a galvanic couple to a carbon steel support will corrode the support, not the gasket, and the leak appears somewhere nobody inspected. Specifying the gasket and the bolt material as one package, with the torque values and the re-torque intervals written into the maintenance schedule, is the difference between a specification and a hope.

Equipment for this step

Tell us your feed assay, flow rate and target recovery and we will size the unit: request a quote.