Flange Gaskets

Overview

Essential sealing for flange assemblies

Flange gaskets are the workhorses of industrial piping — every flanged joint in petrochemical plants, water treatment facilities, power generation, and industrial plumbing relies on a gasket to maintain system integrity under operating pressure, temperature, and vibration.

ELASFOR specializes in ASME/ANSI compliant rubber and aramid fiber gaskets. The rubber component provides elasticity and conformability — allowing the gasket to fill microscopic surface irregularities on the flange face — while the aramid fiber reinforcement provides the structural strength needed to resist blowout under pressure and bolt load.

We supply rubber and aramid gaskets in every imaginable size and composition, with 100% inspection on critical sealing applications. Non-standard flanges, odd configurations, and urgent requests are handled regularly.

Measurement Guide

How to measure a flange gasket

Correct measurement is critical — a gasket that doesn't match the flange face geometry will not seal properly regardless of material quality. Use the measurement method that matches your gasket type.

Full face flange gaskets — ID, OD, and bolt holes

Full face gaskets cover the entire raised or flat flange face, including the bolt holes. They are used on flat-face flanges and cast iron flanges where the full surface contact distributes bolt load evenly.

Dimension	What to Measure	Notes
ID (Inner Diameter)	Bore diameter of the pipe — must match the pipe ID	Do not confuse with the flange bore, which may be slightly larger to accommodate weld bevels.
OD (Outer Diameter)	Overall gasket outer diameter — matches the flange OD	Full face gasket OD equals the flange OD including the bolt circle area.
PCD (Pitch Circle Diameter)	Circle diameter on which bolt holes are centered	Required to position bolt holes correctly. Measure from center to center of opposing bolts.
Bolt hole diameter	Bolt hole diameter in the gasket	Typically bolt nominal size + 3 mm clearance. Confirm from flange drawing or standard table (ASME B16.5).
Number of bolt holes	Count the bolt holes	Must match flange standard exactly. Rotational position of holes relative to split line must be confirmed.

Gasket Technicals Tool

Ring-type gaskets — ID and OD only

Ring gaskets fit inside the bolt circle and contact only the raised face of the flange. No bolt holes — simpler to measure, easier to center.

Dimension	What to Measure
ID	Pipe bore diameter. The gasket ID must match or be slightly larger to avoid flow restriction.
OD	Must be smaller than the bolt circle diameter (PCD) to fit inside the bolts. Standard raised-face OD tables per ASME B16.20 and EN 1514-1.
Thickness	Measured uncompressed. Specify the compressed thickness you need if critical — compression depends on bolt load and gasket material.

Gasket thickness — guidelines

Flange Condition	Recommended Thickness	Notes
New flanges, good surface finish	1.5 mm	Minimum creep, maximum bolt load transfer. Preferred choice for new installations.
Standard industrial flanges	3.0 mm	Most common specification. Accommodates minor surface irregularities.
Corroded, pitted or irregular faces	4.5 mm or custom	Thicker gasket fills deeper surface defects. Consider face repair instead — a gasket is not a substitute for proper flange maintenance.

Why thinner is stronger under pressure: A thicker gasket has more material to creep and relax under bolt load — over time, this allows the joint to lose seating stress and leak. A thinner gasket transfers bolt load more directly to the sealing surfaces, creeps less, and maintains seating stress through thermal cycles and pressure pulsations. The image shows how a thin gasket stays in uniform compression across the full flange face, while a thick gasket develops uneven stress distribution — highest at the bolt holes, lowest at the bore — which is where blowout initiates.

Gasket Selector Tool ↗ Durlon Gasket Manual 2023 (PDF)

Materials

Rubber and composite gasket materials