Failure Analysis in Sealing Technology

Definition and Aim of Failure Analysis

Failure analysis in sealing technology is the systematic investigation of a conspicuous or failed seal in order to determine the trigger mechanism and to derive effective corrective actions from it. The focus is on the chain condition → mechanism → damage pattern → action. This is particularly relevant because in hydraulics and pneumatics, many seals operate under varying pressures, temperatures, and motions, and otherwise faults appear as repeat damage.

Triggers for an analysis are usually symptoms such as leakage, pressure drop, increase in friction, noise, juddering (stick-slip), or contamination of the medium. Decisive early on is the classification of the sealing point: static (no relative motion, e.g., flange) or dynamic (relative motion, e.g., piston rod). This distinction influences which mechanisms are plausible — for example abrasion with motion or extrusion at high pressure.

Typical Practical Questions

In practice, one first clarifies when the symptom occurs (directly after installation or only after operating time), where the leakage becomes visible, and under which conditions (cold/warm, pressure peaks, high speed, standstill). Equally important is the medium: hydraulic fluid, compressed air with oil mist, water content, cleaning media, or additives can attack materials differently.

The damage pattern often provides early indications when one looks carefully. Cracks, notches, spiral marks, flattened areas, chunks missing, swelling, or discoloration can frequently be linked to typical cause categories. The informative value rises when the installation position is known and the seal is not cleaned or damaged in an uncontrolled way.

Approach: Step by Step to the Cause

A robust failure analysis follows a reproducible procedure. As a result, the risk decreases that one builds a plausible but wrong narrative from isolated observations. In many cases, clean documentation, dimensional measurement, and inspection of the mating surfaces are already sufficient before elaborate laboratory analytics become necessary.

A proven approach typically comprises seven steps:

1. Capture operating data: pressure profile, temperature, speed, service life, medium, filtration, events such as dry running or medium change.

2. Secure evidence: secure the seal in its installation position, mark the leakage point, take photos with a scale reference.

3. Visual and dimensional inspection: locate damage spots, check squeeze and gap dimension, assess wear.

4. Inspect mating surfaces: assess roughness, score marks, corrosion, edges, coatings, and dirt ingress.

5. Evaluate the material: hardness, elastic recovery, swelling, crack formation, thermal aging.

6. Form and reconcile hypotheses: bring findings together with operating data and geometry.

7. Define and track actions: document implementation, verify effectiveness through service life and renewed inspection.

Inspection of Installation Space, Tolerances, and Sealing Point

Geometry errors are frequent primary causes, because seals rely on a defined squeeze (compression) and a limited extrusion gap. The extrusion gap is the gap into which the elastomer material can be pressed under pressure. When it becomes too large or when pressure peaks occur, the risk of extrusion and subsequent material breakout increases.

For O-rings, orientation along standards such as ISO 3601 helps, because dimensions, tolerances, and designations are standardized there. This supports fault clarification when, for example, a similar but wrong cross-section diameter was installed or when the tolerance chain of groove, diameter, and component clearance becomes critical. In hydraulics and pneumatics, surface condition and lubricating film are additionally central, because they influence friction, wear, and stick-slip.

Suitable Analysis and Test Methods (From Simple to Advanced)

The choice of method depends on whether a geometry/installation problem, a surface problem, or a material/media question is more likely. A stepwise approach is often sensible, starting with simple checks and going deeper only when needed.

Typical Damage Patterns: Linking Pattern → Cause → Action

Damage patterns appear unambiguous at first glance, yet many mechanisms overlap. Therefore, the combination of pattern, operating conditions, and installation space inspection is decisive. In practice, categories prove useful because they couple thinking about causes and actions.

Extrusion and Nibbling

Extrusion means that the sealing material is pressed into a gap under pressure. Nibbling describes the “nibbling away” of material at the edge, often triggered by pressure pulsations and repeated pressing in and out of the gap. Typically visible are frayed edges, local chunks missing, or irregular edge defects.

Promoting factors are high pressure, pressure peaks, large component clearance, too low hardness, or missing support elements. Effective actions therefore target the mechanics of the sealing point: reduce gap, check tolerance chain, dampen pressure peaks, and if needed use back-up rings. In addition, a more extrusion-resistant material or an adjusted hardness can be sensible, as long as this remains compatible with friction and low-temperature behavior.

Abrasion, Compression Set, and Chemical Damage (Brief Overview)

Abrasion often shows as a dull, roughened surface or one-sided wear. One sometimes finds particles in the medium or fine score marks that match the direction of motion. Causes frequently lie in insufficient lubrication, mating surfaces that are too rough, or dirt ingress. Remedies are improved surface quality, suitable lubrication, more effective filtration, and a sealing geometry that supports a stable lubricating film.

Compression set describes a permanent deformation after prolonged compression. The seal then recovers too little and can leak more easily under pressure or temperature changes. Typical is a permanently flattened contour. Actions are a suitable material selection for temperature and service life, as well as control of the actual squeeze in the installation space.

Chemical damage arises when the medium, additives, or cleaning chemicals are not compatible with the material. One then frequently sees swelling, softening, discoloration, or crack formation. Here, it helps to clarify which medium is actually present, whether additives have changed, and how temperature and oxygen influence act. Consequences are often material changes, media release tests, and defined cleaning and maintenance processes.

Terms, Indicators, and Quick Classification (Mini Glossary)

With complex damage cases or safety-critical applications, specialized consultation and, if necessary, laboratory analytics are sensible, so that finding and action match reliably.