Service Life

Definition and Distinction

In sealing technology, service life describes the period during which a seal or a sealing system seals reliably in a specific application. What is meant is therefore how long the sealing function is maintained under real operating conditions before a replacement or repair becomes necessary. In practice, service life is frequently understood as the operating time up to the necessary change.

Service life is not a fixed material property that is “always the same”. It arises from the interaction of medium, pressure, temperature, motion, mating surfaces, lubrication, and installation. Therefore, two identical seals can reach very different service lives in two systems.

Typical service life specifications, depending on the application, are for example operating hours, cycles (stroke counts), switching cycles, or kilometers run. Decisive is that the metric matches the use case and that it is clear from which threshold the service life is considered ended.

Service Life vs. Storage Life

Storage life describes how long a seal is stored unused before it is installed. Even on the shelf, a material can age. With elastomers (rubber materials), ozone, UV/light, heat, and permanent deformation (e.g., through stacked goods or wrong packaging) influence the later usability.

Storage life and service life are indirectly related, because an aged component can fail more quickly in operation. Nevertheless, they are different parameters: service life evaluates operation, storage life the condition before installation. Customary storage principles are therefore cool, dry, light-protected, and stress-free.

When Does Service Life End? Metrics and Criteria

Service life ends when the seal no longer meets defined functional limits. This does not mean only “visible damage”, but often a measurable threshold. In sealing technology, depending on the system, criteria such as the following are frequently used:

Whether test bench data or field data are reliable depends on how similar the conditions are to the real application. Even small differences in temperature, particle load, or surfaces can shift service life noticeably.

Static and Dynamic Seals: Different End Criteria

With static seals, there is no relative motion between seal and mating surface. Here, aging and permanent deformation frequently determine service life. Leakage then often occurs gradually, particularly with temperature cycles or pressure fluctuations.

With dynamic seals, at least one sealing surface moves — for example with piston or rod seals. In addition to aging, friction and wear act as dominant drivers. When the lubricating film breaks down, frictional heat rises, and service life can drop sharply.

Influencing Factors on Service Life (System View)

Service life is in many cases determined by a chain of interactions. A typical pattern is: more friction → more heat → faster aging → poorer elasticity → even more friction. Therefore, the system view pays off — that is, the question of which operating factor actually limits the seal in the field.

Important influencing factors are:

• Medium and chemistry: a medium can cause swelling (volume increases), trigger extraction (constituents are leached out), or accelerate chemical aging. This changes hardness, strength, and sealing contact.

• Temperature: continuous and peak temperatures accelerate aging and frequently increase compression set (permanent setting). With dynamics, frictional heat is added.

• Pressure, pressure peaks, and gap: high pressure can lead to extrusion — that is, the pressing of the seal into a gap. Whether this happens depends strongly on groove geometry, gap dimension, and, if applicable, support.

• Motion and speed: more speed increases friction work and thereby heat input. At the same time, lubrication conditions change.

• Surfaces: mating surfaces that are too rough or damaged increase abrasion. Score marks or edges can also damage sealing lips.

• Lubrication: missing or unsuitable lubrication reduces service life, because friction, temperature, and wear rise.

• Contamination and particles: particles cause abrasive wear. Filtration and cleanliness in the system act directly to extend service life.

• Installation: wrong initial compression, twisted seals, or installation damage often lead to early failure, although material and design are fundamentally suitable.

Typical Failure Patterns as a Diagnostic Aid

Failure patterns help to narrow down the service-life-determining factors. Frequent patterns are:

This classification is not a complete diagnosis, yet it frequently provides the first starting point to solve service life problems systematically.

Permanent Deformation (Compression Set) Briefly Explained

Compression set is the permanent shape change of a seal after long compression. The seal then no longer recovers sufficiently and produces less contact force. As a result, leakage occurs particularly with static seals — for example when pressure drops or when the gap changes slightly through temperature variation, although the seal still looks visually intact.

Increasing Service Life: Practical Levers

Service life usually improves through measures that target the main causes directly. In many cases, it is not “the one better seal” that is decisive but the suitable design of the overall system.

When service life specifications are required in specifications, it should be clear under which conditions they apply and which end criteria are used. With critical applications, specialized consultation can be sensible to bring test bench, design, and field data together consistently.