FKM(Viton)delivers exceptional resistance to high temperatures,oils and aggressive chemicals,establishing it as the sealing material of choice for harsh operating conditions in chemical,petroleum,valve and hydraulic systems.Many specification engineers focus solely on material grade and hardness while overlooking gasket thickness.This oversight frequently results in leakage,extrusion,bolt stress relaxation and premature gasket failure.The core principle for FKM gasket thickness selection is straightforward:select a thickness adequate to compensate for flange surface imperfections,as greater thickness does not equate to superior sealing performance.
Fundamental Impact of Thickness on Sealing Performance
FKM gaskets achieve sealing through compression and resilience,with an optimal compression range of 20%–30%.
•Thin gaskets(1 mm–2 mm):Preferred for finely machined,smooth flange faces.Thin gaskets exhibit low creep,minimal loss of bolt preload and strong blowout resistance.They suit medium-and low-pressure applications,precision flanges,vacuum systems and valve face sealing.Limitation:limited compensation capability.Partial insufficient compression and leakage may occur where flanges have corrosion,deformation or surface irregularities.
•Medium-thickness gaskets(3 mm–5 mm):The industry standard.Balanced compression and resilience compensate for minor flange corrosion,surface unevenness and slight equipment warpage.Well suited for most chemical pipelines,pumps and heat exchanger flanges.Ample elastic reserve maintains consistent sealing contact when flange gaps shift under thermal cycling,making this the primary option for most corrosive service conditions.
•Thick gaskets(6 mm and above):Offer strong compensation capacity,intended for aged equipment,rough cast flanges,heavily distorted flanges and inconsistent sealing gaps.They carry notable downsides:under the same bolt load,creep and stress relaxation are more likely,and the risk of lateral extrusion rises sharply at elevated pressures,alongside higher material costs.Avoid arbitrarily specifying thick FKM gaskets for high-pressure service.
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Key Factors for FKM Gasket Thickness Selection
1.Condition of flange sealing face(primary consideration).Precision-machined flat flanges:1–2 mm.Regular cast flanges with light corrosion:3 mm.Aged equipment,warped or pitted flanges:4–5 mm.Severely deformed flanges with highly variable gaps:above 5 mm;back-up rings are recommended where necessary to prevent extrusion.
2.System pressure rating.Low-pressure and vacuum service:1–3 mm preferred.Medium pressure(≤1.6 MPa):2–3 mm typical.High-pressure service:thinner gaskets paired with higher-hardness FKM grades are preferred.Thick gaskets require back-up rings to prevent extrusion into flange clearances.
3.Thermal cycling and media properties.Under high-temperature and thermal cycling conditions,flange gaps change due to thermal expansion and contraction.A modest increase in thickness leverages FKM’s resilience to accommodate these gap variations.For highly corrosive media,apart from selecting the correct material grade,a suitable thickness extends resistance to media permeation,though excessive thickness should be avoided.
4.Flange nominal size.Small-bore flanges DN15–DN50:1.5–2 mm typical.DN65–DN200:3 mm standard.Large-bore flanges DN250 and above have lower rigidity and tend to deform;3–4 mm gaskets are recommended.
FKM is a relatively costly material.Appropriate thickness selection protects sealing integrity while controlling procurement and maintenance costs.A properly specified gasket eliminates fugitive emissions,extends service life,cuts maintenance downtime,and provides dependable sealing for stable operation in high-temperature corrosive environments.
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