Warum Flanschdichtungen niemals wiederverwendet werden sollten

Technische NeuigkeitenBewertet: 27 August 2026Von SASA FLANGE Team für technische Inhalte

Direkte Antwort

For most pressure-boundary flange joints, a gasket removed after service should not be reinstalled. Initial bolt load permanently changes its thickness and contact pattern; Temperatur, pressure and the process fluid may further reduce recovery. Reuse should occur only when the gasket manufacturer and the governing engineering procedure explicitly allow it—not because the removed gasket still looks intact.

A flange gasket is part of a loaded sealing system made up of two mating flange faces, the gasket, Verbindungselemente, lubricant and the assembly method. During tightening, bolt load compresses the gasket so it conforms to the flange finish and blocks potential leakage paths. The installed gasket is therefore no longer identical to the unused component that was originally selected.

When the joint is opened, stored elastic recovery is released but permanent deformation remains. Reinstalling the same gasket rarely recreates the original contact stress at every point around the circumference. The risk is especially important where leakage could expose personnel, release a hazardous fluid, interrupt production or damage nearby equipment.

Wichtige Erkenntnisse

A used gasket may have hidden compression loss, chemical attack or thermal damage even when its surface appears acceptable.
The flange faces, Dichtung, Schrauben, lubricant and tightening procedure must be treated as one engineered joint.
RTJ rings, spiral-wound gaskets and many soft-cut gaskets rely on deformation that is not reliably repeatable after removal.
A new gasket is not a substitute for cleaning, Ausrichtung, face inspection and controlled bolt loading.

Why a flange gasket changes during its first installation

Permanent compression and a joint-specific contact pattern

The gasket must be compressed enough to seat against the flange surface and maintain sealing stress during operation. Part of that deformation is elastic, but part is permanent. Serrations, waviness, local flange rotation and small alignment differences create a contact pattern unique to the assembled joint. Once removed, the gasket cannot be expected to return to its original thickness or reproduce the same pattern in a second assembly.

A second installation may also rotate or shift the gasket relative to the original imprint. High and low contact areas then occur at different locations. Applying more torque does not guarantee correction: it may overload the gasket, fasteners or flange while other areas remain below the stress needed for sealing.

Relaxation, creep and loss of recovery

Gasket stress normally decreases after tightening as the gasket relaxes and embeds into the flange finish. Soft materials can creep under sustained temperature and load. Spiral-wound constructions can lose recovery if the winding is compressed beyond its intended operating range. Metallic rings are plastically seated into matched grooves. These mechanisms are useful during first assembly, but they make an unknown used gasket a poor reference point for a controlled second assembly.

Service exposure changes material condition

Heat can harden, embrittle or oxidize some filler and facing materials. Process fluids can cause swelling, dissolution, corrosion or deposit formation. Thermal cycling and pressure cycling change load distribution, while vibration can produce fretting at the interfaces. The most important damage may be internal or microscopic and cannot be cleared by a quick visual inspection.

Reuse risk by common gasket type

Dichtungstyp	What happens during seating	Why reuse is unreliable	Normal maintenance approach
Spiral-wound gasket	Metal windings and filler compress while guide and inner rings control geometry	Recovery and winding condition may be reduced; local over-compression may be hidden	Install a new, correctly specified gasket after joint opening
RTJ metal ring	The ring plastically deforms against the matched flange grooves	The seated contact band is joint-specific and may not reseat uniformly	Use a new ring of the specified number, profile and material unless an approved procedure explicitly states otherwise
Compressed fiber or graphite sheet	The sheet fills flange finish and local surface variation	Thickness loss, kriechen, cracking or surface adhesion can remain after removal	Cut or obtain a new gasket to the required dimensions and material specification
PTFE-based gasket	The material flows under compression to conform to the faces	Creep and cold flow can reduce thickness and dimensional stability	Replace and verify temperature, chemical compatibility and seating stress
Elastomeric gasket	Elastic compression creates the seal	Compression set, swelling, hardening or cracking may reduce resilience	Replace according to the equipment and gasket manufacturer procedure

Damage that visual inspection can miss

A removed gasket should still be examined because it can provide evidence about the previous joint. Uneven compression may indicate flange misalignment, pipe strain, incorrect tightening or flange rotation. Local blowout or discoloration can point to insufficient seating stress, chemical incompatibility or a leakage path. A damaged inner ring may suggest excessive compression or installation interference.

That examination is diagnostic; it does not qualify the gasket for reuse. Internal filler damage, reduced spring response, small cracks and chemical degradation may not be visible. Cleaning a gasket can also remove evidence needed for a leakage investigation. Photograph and document the joint condition before scraping, grinding or discarding components when the leak has safety or reliability significance.

The flange faces require equal attention. Check for radial scratches, Lochfraß, distortion, Einlagen, Beschichtung, embedded gasket material and damage to RTJ grooves. Confirm that the replacement gasket matches the flange standard, gegenüber, Größe, Druckklasse, material and service—not simply the outside diameter of the removed item.

Flange-joint reassembly checklist

1. Confirm the specification

Identify flange standard, NPS oder DN, Klasse oder PN, gegenüber, Dichtungstyp, Abmessungen, filler or material, ring number where applicable, und die erforderliche Standardausgabe.

2. Inspect both flange faces

Clean by an approved method and evaluate finish, scratches, Korrosion, Ebenheit, groove condition and remaining gasket material before assembly.

3. Check alignment and pipe strain

Do not use the bolts to force a severely misaligned joint into position. Verify the site procedure and engineering limits.

4. Inspect fasteners and lubrication

Confirm bolt and nut specification, Thread-Zustand, washer requirement, lubrication and any replacement criteria in the joint procedure.

5. Install one new gasket

Keep it clean, dry and centered. Do not stack gaskets or apply unapproved compounds to compensate for poor fit.

6. Apply controlled bolt load

Use the approved tightening method, Muster, passes, tools and target load. Record critical-joint assembly data where required.

Replacing the gasket addresses only one component. Reassembly can still leak if the wrong gasket is selected, the faces are damaged, the joint is misaligned or the target bolt load is not achieved. For a broader failure review, see our guide to the common causes of flange leakage and the explanation of gasket stress in bolted flange joints.

Primary standards and references

ASME PCC-1 — Pressure Boundary Bolted Flange Joint Assembly: industry guidance for developing flange-joint assembly procedures, Inspektion, Ausrichtung, tightening and troubleshooting.
ASME B16.20 — Metallic Gaskets for Pipe Flanges: dimensional and marking requirements for ring-joint, spiral-wound and other metallic gasket constructions within its scope.
ASME B16.21 — Nonmetallic Flat Gaskets for Pipe Flanges: Typen, Größen, Materialien, Abmessungen, tolerances and markings for nonmetallic flat gaskets.

Use the edition adopted by the purchase order, piping code and owner specification. These references do not replace the gasket manufacturer’s service limits or a site-specific joint assembly procedure.

Häufig gestellte Fragen

Can a flange gasket be reused if it looks undamaged?

Normalerweise nein. Appearance does not confirm remaining thickness, recovery, chemical condition or the ability to recreate uniform seating stress. Use a new gasket unless an approved manufacturer and engineering procedure explicitly permits reuse.

Can an RTJ ring gasket be reused?

RTJ rings are normally treated as single-use sealing elements because seating plastically deforms the ring against matched grooves. Check the governing project procedure and ring manufacturer requirements.

Will higher bolt torque make a reused gasket seal?

Not reliably. More torque can overload the gasket, bolts or flange and still leave low-stress areas. The correct goal is controlled bolt load with a new specified gasket and acceptable flange condition.

Should bolts also be replaced whenever a gasket is replaced?

Nicht automatisch. Fastener reuse depends on the bolting material, Service, thread and corrosion condition, any yielding or damage, and the site procedure. Inspect and replace fasteners according to the governing requirements.

Specify a complete flange joint

Send the flange standard, Größe, Druckklasse, gegenüber, Material, Dichtungstyp, bolting specification, Servicebedingungen, Mengen- und Prüfanforderungen. SASA FLANGE can review the component description before quotation.

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