How to Recognize the Common Causes of O-ring Failure?

Heat Hardening and Oxidation

Failure pattern: Seen in both static and dynamic seals, the surface of the O-ring appears pitted and/or cracked, often accompanied by the flatness of high compression set.

Problem sources:

• Excessive temperature causing elastomer hardening evaporation of plasticizers, and cracking from oxidation.

Damage During Installation

Failure pattern: Occurring in both static and dynamic seals, this failure mode is marked by short cuts (notches) or a skinned (peripherally peeled) surface.

Problem sources:

• Sharp edges on mating components of the O-ring groove;
• Sharp threads over which the seal must pass during assembly;
• Oversized O-ring ID on piston;
• Undersized O-ring ID on rod;
• Twisting or pinching the O-ring during installation;
• Not lubricating the seal during installation;
• Seal elastomer has low tear resistance (typical of silicone).

Excessive Swell

Failure pattern: Easily identified by a marked increase in seal dimensions this problem can occur in both static and dynamic applications. It results in reduction of physical properties and can result in improper sizing between seal and groove. Dynamic applications are especially prone to this problem because friction accelerates seal failure.

Problem sources:

• Like a sponge, the seal absorbs the surrounding fluids and swells to the point of malfunction because of incompatibility between seal compound and system environment (i.e. chemical incompatibility, high humidity, etc.).

Weather or Ozone Cracking

Failure pattern: Occurring in both static and dynamic seals exposed to atmospheres containing ozone and other air pollutants, this failure mode is marked by the appearance of many small surface cracks perpendicular to the direction of stress.

Problem sources:

• Ozone attacks of the polymer chains, causing O-ring material to crack.

Explosive Decompression

Failure pattern: Тhis failure mode is marked by random short splits or ruptures going deep into the O-ring’s cross section. When the seal is first removed, its surface may also be covered with small blisters.

Problem sources:

• Absorption of gas by O-ring while operating in high pressure conditions. Subsequent rapid decrease in system pressure traps gas within the O-ring’s micropores, causing surface blisters and ruptures as the gas escapes.

Recognizing the causes of O-ring failures will allow preventing future failures in the work of sealing applications. It also will inevitably increase the service life of seals and improve cost effectiveness related to them.