Orings Failure Analysis - Western Rubbers

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Orings failure analysis guide

Among the most common reasons for O-Ring failure is either incorrect groove design or improper selection of compound. By correctly identifying the reason for failure, necessary changes can be made to tend design or material and eventually lead to improved seal performance. Analyzing the cause of failure and going to the root of every problem is extremely crucial in assuring efficient seal functionality and safety. As you can see below, we have listed down some common O-Ring Failures; the observations and causes for the same. Understanding the causes behind the failures, serves as a precautionary set of measures that should be observed in the given conditions.

	Failure description	Reason for failure
Dimentional defect	Visible flattened cross section No visual defects	Inaccurate groove/gland design.. Incorrect o-ring dimensions Misalignment of mating surfaces
Compression set	Visible flattened cross section	Incomplete curing of elastomer before installation Excessive compression Chemical incompatibility Excessive temperature
Molding damage	Flattened surface, corresponding to the mating surfaces, with some cracks	Failure to account for thermal/chemical expansion during molding Excessive compression
Explosive decompression	Blisters and pits visible on the seal surface. Absorption of gas at high pressures, and then immeditae decrease in pressure The absorbed gas ruptures the seal surface when the pressure is rapidly reduced.	Rapid pressure chages during molding operation Low hardness of elastomer
Shrinkage defect	This failure cannot be detected on visul inspection of the o-ring. There is a shrinkage in the cross sectional size of the seal.	Improper curing of elastomer. Low hardness of elastomer High vaccuum pressure
Installation damage	Cuts and incisions visible on the o-ring body.	Sharp edges on the installation eqiupment Inaccuate sizing of the elastomer Low hardness of elastomer
Abrasion damage	Flattening of the o-ring on one side. Loose particles or scrapes may be found on the seal surface. This failue is usually found in dynamic seals	Improper/rough finish of the sealing surfaces. Excessive temperatures System contamination ny abrasive particles
Extrison and nibbling defects	Ruptured edges visible on the low pressure side of the o-ring.	Excessive clearnaces. Irregular clearance gaps O-ring material could be too soft High pressure between mating surfaces Degardation (swelling, cracking, shrinking, etc.) of o-ring material due to system fluid
Spiral cuts	Deep spiral cuts appear on the surface of the o-ring (around the circumference)	Tight installation of the o-ring Slow stroke speed Inadequate lubrication Low elastomer hardness Uneven surafce finish
Thermal degradation	The o-ring develops cracks. The elastomer might begin to soften and develop a shiny surface	Excessive temperatures Incompetent thermal properties of the elastomer