Gasket Materials Chemical Compatibility and Resistance: What are They?05 March 2019
Fluid temperatures and pressures are linearly applied. When that force hits a gasket, it strikes as either positive or negative energy. Vacuum or outward force, steam or cryogenic, the energies rise and fall. Sudden transient forces or cycling effects are a little different, of course, but they still impact system seals as energy. For chemical compatibility concerns, though, the situation changes completely.
Of Chemical Compatibility Matters
Granted, chemical causticity affects gasket materials. Beyond such singular cause-and-effect outcomes, however, there’s at least one additional causal factor functioning in a chemically incompatible gasket. A seal material’s backbone is susceptible to selected chemical formulations. Caustically aggressive or apparently material benign, it doesn’t matter. The fluid may even be a harmless oil, which feels slippery to the touch. No, what really matters is how a gasket’s molecular backbone reacts to the presence of a stated chemical.
Assessing Chemical Reactivity
Different materials react to chemical attacks in different ways. With certain alloys, the metal will break down and corrode. That’s why some fuels, ethanol among them, require special pipe metals. Aluminium and brass cannot be installed in ethanol-based fuel depots. Likewise, they don’t use cork-based gaskets and/or natural rubber seals. Yet these fuels don’t cause harm to biological tissue, not unless they’re ignited. Again, it’s the susceptibility of a particular gasket materials’ backbone that creates the threat here. To prevent gaskets from being eaten away by these seal-incompatible chemicals, a system designer has to know exactly how a specific chemical family affects a particular gasket material.
Gasket Design: Chemical Resistance
While one seal elastomer staunchly holds its form and features, an almost identical gasket dissolves into a useless ring of broken rubber. The material has lost its form, so it’s no longer capable of creating a reliable seal. Apparently, an acidic reaction has broken down the seal material. In truth, the chemical could just be performing as a catalyst. The molecular structure, covalent bonds and all, are then broken down as a consequence of this entirely natural action. To prevent such bond-breaking reactions, chemically resistant gaskets must be selected. These sealing materials stay inert and reactance-free when attacked by known fluids.
And that’s the crux of the matter, the fact that the fluid carrier must be a known chemical. Only then can the designer select a gasket material, one that’s chemically compatible and reactance resistant. Essentially, the seal material’s structure-retaining bonds stay inert when impacted by a known family of chemical agents. Best case scenario, a selected gasket substance should provide broad-spectrum chemical compatibility so that it has a better chance of resisting the many oils, solvents, and caustic chemicals that exist in this industry.
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