How to choose gasket material by fluid and temperature

A flange joint does not fail by chance. It fails because the elastomer cannot handle the fluid the line carries, or because it was asked for a temperature outside its range, or because nobody asked whether there was steam. The material is decided by three data points — fluid, temperature and pressure — and none of them can be guessed at the counter.

The four everyday elastomers

The vast majority of industrial lines in Panama are solved with four materials. Knowing what each is for avoids 90 % of specification errors.

Nitrile (NBR)

The hydrocarbon material. It stands up to mineral oils, fuels, greases and petroleum-based hydraulic fluids, across a temperature range that covers ordinary plant service.

Its weak point is ozone and prolonged weathering: a nitrile gasket left in sun and open air cracks before a neoprene one. It is also not the material for steam or hot water.

Neoprene (CR)

The all-rounder. Good against weathering, ozone and ageing, with moderate oil resistance. It is the logical choice for water, air and general service lines, and for exposed joints where nitrile would degrade.

It is not a demanding process material: with aggressive hydrocarbons or high temperature it falls short.

EPDM

The material for hot water, low-pressure steam and much of the chemical side. Excellent against dilute acids and bases, treated water and cleaning solutions.

And one warning that costs outages: EPDM does not resist hydrocarbons. An EPDM gasket in an oil line swells and loses the seal. It is the most common substitution error, because EPDM is cheap and close to hand.

Viton / fluoroelastomer

The expensive material that turns out cheap when it is the right one. It covers high temperatures and a chemical compatibility none of the others reaches: aggressive hydrocarbons, solvents, concentrated acids.

It is not specified out of habit: it is specified when the service demands it. Putting Viton where nitrile was enough is money thrown away; putting nitrile where Viton was needed is a leak.

When an elastomer is not enough

Above a certain pressure and temperature, no elastomeric sheet holds the seal. That is where the spiral wound gasket comes in, combining a wound metal strip with a soft filler and an outer retaining ring.

It is the joint of serious process lines: it recovers elastically as the flange cycles thermally, it tolerates pressures that would crush an elastomer, and its centring ring prevents the off-centre assembly that ruins a flat gasket.

Size matters as much as material

A gasket that is right in material and wrong in dimension does not seal. The joint is cut to the flange dimensional standard, not to whatever the old flange measures after years in service.

To order it properly you need the nominal line diameter, the flange pressure class and the facing type. If they are not to hand, the flange itself or a photo of the gasket being removed is usually enough to identify it.

What to have ready before requesting a quote

• The fluid the line carries, with its concentration if it is a chemical.
• Operating temperature and, if any, peak temperature.
• Working pressure and flange class.
• Nominal diameter and facing type.
• Whether service is continuous or cyclic: thermal cycling changes the recommendation.

With those five data points the right gasket gets quoted. Without them, what gets quoted is an equivalent — and the equivalent shows itself with the system running.

Frequently asked questions