For any given sealing application, the correct gasket material and flange type are picked by an informed engineer. A fluid-suitable material is high on the features shortlist, for the gasket has to resist heat and chemical attacks. A tough seal structure comes next. It needs to be mechanically tough so that it can withstand great pressure extremes. Still, there must be more to leak management than flange types and gasket materials, right?
Flange and Gasket Geometry
Quite so, contemporary sealing technology is as much about surface contact profiles as it is about material compressibility. The flanges are stationary, although they do absorb massive amounts of kinetic energy as their bolts are tightened. Similarly, the gasket compresses but conforms to the shape of those twin sealing faces. The modulus of elasticity contained within the gasket material assures this essential leak stoppering effect. All the same, there’s always the remotest chance of a leak propagating pathway, behind which a fluid quickly follows. A raised face, followed by a gasket that incorporates a mild steel insert, stops unwanted leaks in their tracks. In effect, that softer steel is pressed beyond its yield point. With extreme bolt loads applied, the mild steel insert deforms so that it occupies every flange imperfection and leak propagation pathway.
Utilising the Correct Sealing Technology
Coming to the rescue, improved engineering practices produce mirror-like finishes. Those flange surfaces exhibit fewer surface imperfections, along with machine-sharpened profiles that tighten exactly against mirror-image gaskets. Like the old apparel makers used to say, “They fit like a glove.” There can be no gaps, no leakage pathways when such a fit is maintained. However, there are a number of real-world seal-attenuating influences that also require a technology-based solution. Thread friction, bolt creep and elasticity issues, these are just a few of the factors that technology can purge. Of course, a healthy measure of high-tech joint analyzing ingenuity also helps.
And that’s the key to this approach, the application of a leak analysis study. CFD (Computational Fluid Dynamics) modelling is of great use, as is the proper application of a pressure distribution simulation. Computers take over when such number-crunching duties beckon. All the same, the practicalities cannot be ignored. Proper bolt loading patterns are essential. Even so, such attention to detail means little if the threads loosen because of vibration or thermal expansion. Heat treated metals mitigate this effect somewhat. At any rate, flange materials, gaskets and fasteners are constantly under scrutiny. Always under development, external flange and gasket arrangements eliminate bend and orientation stresses. Inside those flanges, raised faces and composite rings counteract creep and elasticity changes.
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.