Determinants of Gasket Thickness in a Flange System

02 April 2019

In an ideal world, an engineer would select an overly thickened gasket. Then the flange bolts would tighten until even the slightest leak pathway was filled by the incredibly compressed material. That’s not a real-world option, not when there are physical constraints to evaluate. For starters, all of that flange pressure, as applied by the ring of bolts, would create great stress along the flange faces.

A Deterministic View Of Flange Stressors

Again, thicker gaskets do a better job of filling flange face irregularities, so shouldn’t this thicker-than-average seal be used as the preferred solution to any fluid sealing issue? Not so fast, new problems crop up as the ring of compressive material thickens. Unless the gasket material is exactly as wide as the flange face, then the diameter difference will produce loading stress. The faces will actually deform and warp as the flange bolts are tightened. Furthermore, that stress won’t stay at the faces, it’ll propagate to a weak spot, perhaps a weld seam, where a hairline fracture could pop into existence.

Follow The Seal-Attenuating Determinants

It’s just common sense, the fact that a thicker gasket equals more gasketing material. Now the seal begins to suffer in other ways. Sure, the additional material provides more material plasticity, which means the tiniest leak-propagating irregularity is blocked. That feature comes at a cost, though. Thicker gaskets suffer from creep relaxation after their bolts are fully tightened. As a result of this issue, seal compressibility plummets. Viewed side-on, another dangerous problem makes itself apparent. There’s more material exposed to the open air, so a blow-out risk becomes likelier. Just to prove things aren’t all bad, though, thicker gaskets do work better in systems that have damaged flange faces.

Assessing The System-Prevailing Benefit

That’s right, thinner gaskets are not the preferred fixture when flange faces are uneven or poorly finished. Perhaps those surfaces are aging badly, or maybe they’re not perfectly aligned. Whatever the reason is, a thicker gasket acts as a force compensating device. If such unevenly applied forces or irregularity-plagued surfaces were handled by a 1-mm thick gasket, it wouldn’t counteract such flanging deficits. Switching to a 3-mm thick substitute, the thicker gasket fills the surface discontinuities while it also compensates for the unequally applied bolt loading forces. However, there’s still the blow-out factor and creep relaxation issue to consider.

A repaired gasket, fully realigned and milled flat, is the best answer here, but that solution isn’t always possible, not under real-world conditions. When such conditions transpire, a thicker gasket is the workable option, but it should use a reinforced material backbone, one that’ll resist creep, blowout hazards, and other such performance-altering determinants.

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