Seal failure-analysis wizard

Description

The ring is compressed incorrectly or fills the groove in the wrong proportion because its size or the gland geometry does not match the application. It shows up as leakage from the start or uneven wear around the circumference.

Probable causes

• The chosen ring size (ID × cross-section) does not match the groove.
• The groove depth or width is wrong (incorrect squeeze or fill ratio).
• Material volume change (swell) was ignored when the groove was designed.

Fix

• Recompute squeeze and fill ratio per standards (ISO 3601, groove charts).
• Verify the ring size against the groove — use the correct ID and cross-section.
• For a swelling medium, design the groove with allowance for the volume change.

Description

The ring loses its original round cross-section and stays permanently flattened, so it no longer exerts a sealing force. It develops under prolonged compression at elevated temperature when the material loses its elasticity.

Probable causes

• Operating temperature too high for the material.
• Excessive or long-term compression of the ring.
• A material with poor compression-set resistance for the conditions.

Fix

• Choose a material with better compression-set resistance (FKM, FFKM).
• Reduce squeeze to the value recommended by the standard.
• Verify the operating temperature is within the material’s continuous range.

Description

The ring is squeezed beyond its elastic reserve, overstressing it and damaging it before it reaches normal service life. It is often linked to ignored material volume changes in the medium or with temperature.

Probable causes

• The groove is too shallow for the chosen ring cross-section.
• Ignored material swell — after swelling the ring exceeds the groove capacity.
• Thermal expansion added on top of mechanical squeeze.

Fix

• Design the groove with allowance for volume changes (fill ratio < 90 %).
• Choose a low-swell material for the medium (check the compatibility matrix).
• Check total squeeze including thermal expansion.

Description

Gas absorbed into the material at high pressure expands violently when pressure drops rapidly, tearing the ring from the inside. The surface shows blisters, splits or fractures. Typical of gas and oil & gas applications.

Probable causes

• Rapid pressure changes in a gaseous environment (decompression cycles).
• A material without an AED-resistant compound structure.
• High gas-saturation pressure before decompression.

Fix

• Choose an AED / RGD-certified material (FKM or FFKM in an AED grade).
• Slow the decompression rate where the process allows.
• Use higher hardness and a tighter groove for better mechanical support.

Description

Under vacuum, volatile components (especially plasticisers) evaporate from the elastomer, so the ring loses mass, hardens and shrinks. It leads to loss of sealing force and contamination of the vacuum space. Critical for semiconductor and vacuum applications.

Probable causes

• A plasticised elastomer exposed to high vacuum.
• A material with a high content of volatile additives.
• Elevated temperature accelerating the evaporation.

Fix

• Choose a low-outgassing material (FFKM in a low-outgassing grade).
• Avoid compounds with a high plasticiser content.
• For critical applications, verify vacuum / semiconductor certification.

Description

The ring is cut, scratched or nicked while being pulled over sharp edges, threads or grooves during assembly. The damage is visible as cuts or missing chunks of material and causes immediate leakage.

Probable causes

• Sharp edges, threads or burrs along the installation path.
• A missing lead-in chamfer on the shaft or in the housing.
• Insufficient lubrication during assembly.

Fix

• Chamfer and deburr every edge on the installation path.
• Use an assembly mandrel / sleeve over threads and grooves.
• Lubricate the ring with a compatible lubricant before assembly.

Description

In a dynamic application the ring surface is gradually worn away by motion against the mating surface, especially if it is rough or carries abrasive particles. It shows as flattened, abraded areas and loss of material.

Probable causes

• A mating surface that is too rough (high Ra).
• Abrasive particles (slurry, sand) in the medium.
• Insufficient lubrication in a dynamic application.

Fix

• Choose an abrasion-resistant material (PU for dynamics, XNBR for abrasive media).
• Improve the mating-surface finish to the recommended Ra.
• Add a wiper ring or better filtration against abrasive particles.

Description

Under high pressure part of the ring is forced into the gap between components and progressively torn away, leaving the characteristic "nibbled" edge. It arises from a combination of high pressure, a large gap and a soft material.

Probable causes

• High pressure combined with too large a gap.
• Too soft a material (low Shore hardness).
• A missing back-up ring.

Fix

• Add a PTFE back-up ring against extrusion.
• Choose higher hardness or a more extrusion-resistant material (PU).
• Reduce the gap between components to the value from the standard.

Description

In slow reciprocating motion the ring twists about its axis instead of sliding, producing spiral 45° cracks around the circumference. Typical of long hydraulic and pneumatic cylinders with insufficient lubrication.

Probable causes

• Insufficient lubrication in slow reciprocating motion.
• Too high a friction resistance (rough surface, high squeeze).
• Uneven motion causing partial sliding and partial rolling.

Fix

• Improve lubrication and reduce surface friction.
• Consider an X-ring (quad ring), which is less prone to twisting.
• Verify the motion uniformity and the ring squeeze.

Description

Sustained exceedance of the material’s temperature limit causes it to harden, become brittle and develop radial cracks. The surface is often glossy or baked. The material loses elasticity and sealing ability.

Probable causes

• Operating temperature above the material’s continuous limit.
• Local overheating (friction heat, hot spots).
• A material under-rated for the temperature peaks.

Fix

• Choose a material with a higher temperature ceiling (FKM to 200 °C, FFKM above 230 °C).
• For static high-temperature applications consider VMQ (silicone) with its wide range.
• Remove the source of local overheating or improve cooling.

Description

The medium chemically attacks the elastomer, which swells, softens, hardens or breaks down depending on the type of incompatibility. It shows as a change in the ring’s volume, mass, hardness or colour. The most common cause of premature failure.

Probable causes

• Material incompatibility with the operating medium.
• A change of medium or additives without re-evaluating the material.
• Elevated temperature accelerating the chemical breakdown.

Fix

• Check compatibility in the chemical matrix and choose a resistant material (FKM for most acids/fuels, FFKM for solvents and the most aggressive media).
• Always re-evaluate the material choice when the medium changes.
• For an aggressive-medium-plus-temperature combination consider FFKM.

Description

In plasma processes (especially semiconductor manufacturing) reactive ions erode the ring surface, which powders, discolours and loses mass. It is often worsened by a wrong groove that exposes more surface to the plasma. It leads to particle contamination of the process.

Probable causes

• Exposure to reactive plasma in the process chamber.
• A wrong groove exposing excess ring surface.
• A material without a plasma-resistant compound.

Fix

• Choose a plasma-resistant material (FFKM in a specialised semiconductor grade).
• Design the groove to minimise the exposed ring surface.
• Verify material purity and certification for semiconductor processes.

Observation

Thinned lip, weakening seal, a gradually increasing leak.

Probable causes

• Normal end-of-life, an abrasive shaft, or insufficient lubrication.

Fix

• Replace the seal; for premature wear improve shaft finish and lubrication, or choose a more wear-resistant material.

Observation

A brittle lip with radial cracks, loss of elasticity.

Probable causes

• An overheated lip (high speed, poor lubrication or wrong material) → oxidation.

Fix

• Choose a more heat-resistant material (FKM, HNBR) and verify lip speed and lubrication.

Observation

A deformed, softened lip with loss of the sealing edge.

Probable causes

• Chemical incompatibility — the chosen material does not suit the medium.

Fix

• Check the chemical matrix and choose a resistant material (FKM for oils, fuels and most chemicals).

Observation

A burnt lip, black carbon deposit, a burned groove in the shaft.

Probable causes

• Running dry before lubrication is established at start-up.

Fix

• Ensure lip lubrication before start-up; where dry-run is a risk choose a dry-running-capable material (PTFE).

Observation

Rapid loss of lip contact force, a sudden leak.

Probable causes

• The spring fell out during installation or corroded (aggressive medium).

Fix

• Check spring seating during installation; for aggressive media use a seal with a stainless-steel (SS) spring.

Observation

An immediate leak from start-up, a visibly inverted lip.

Probable causes

• An installation error — the lip caught on a chamfer or thread and folded back.

Fix

• Use an assembly sleeve over chamfers and threads, lubricate the lip and press squarely; check lip orientation after fitting.

Observation

Cuts and nicks on the sealing edge of the lip.

Probable causes

• Keyways, splines, threads or burrs damaged the lip during installation.

Fix

• Deburr the shaft, cover keyways and threads with an assembly sleeve, and fit over a protective mandrel.

Observation

A visible step (groove) worn into the shaft by the lip.

Probable causes

• Long-term wear or too soft a shaft (< 45 HRC).

Fix

• Fit a repair sleeve (Speedi-Sleeve type) or an offset spacer for a fresh running surface; use a harder shaft (≥ 45 HRC).

Observation

Uneven lip wear, a periodic (pulsing) leak.

Probable causes

• A bent shaft or worn bearings — runout > 0.05 mm TIR.

Fix

• Correct shaft misalignment and replace worn bearings so runout drops below 0.05 mm TIR.

Observation

Oil seeps between the outer diameter (OD) and the bore.

Probable causes

• A metal OD in an imperfect (e.g. aluminium) or scratched bore.

Fix

• Use a seal with a rubber OD, which seals even an imperfect bore; check bore finish and condition.

Observation

The lip pushed back, the seal displaced or extruded.

Probable causes

• Pressure above 0.05 MPa without support for a standard low-pressure seal.

Fix

• Use a high-pressure seal type or reduce pressure below the limit; reduce pressure further at higher speeds.

Observation

Fine cracks on the lip rubber or the OD.

Probable causes

• Storage / UV / ozone on materials without a stabiliser (NBR, ACM).

Fix

• Store away from UV and ozone; for outdoor use choose an ozone-resistant material (FKM, or HNBR).

Observation

Rapid lip wear with visible abrasive scoring.

Probable causes

• Abrasive particles bypassed a weak or missing dust lip.

Fix

• Use a dual-lip seal (with a dust lip) or add an upstream V-ring; improve contaminant exclusion.