Why Do O-Rings Fail? Here Are the Most Common Reasons


O-rings are one of the most common seals used in equipment design because they are reliable and have simple mounting requirement. While these type of seals are often inexpensive, their failure can lead to significant amount of loss in production, downtime and maintenance costs.

Therefore, it is important to look out for early warning signs and understand the various types of common O-Ring failure to prevent any unwanted damage or cost during critical operation.

Here are 5 of the most common reasons why O-Ring fails, the type of typical damage and the recommended corrective actions:

 

1. Extrusion/Nibbling

O-Ring surface peeled off or nibbled off at the opposite
side of pressure, often only on part the circumference.
o-ring-nibbling-1503842699

Cause

- Material overflow on one side, also temporary

- High/pulsating pressure (Hardware expands or contracts)
- Sharp groove edges
- Radial clearance is too large


Examples of Extrusion

extrusion 1 editpaint (2)
Corrective Action

- Back-up rings
- Different seal profile
- Decrease clearance 
- High-modulus/hardness elastomer
- Proper gland design


O-Ring surface nibbled off


2. Twisting/Spiraling


Spiral marks or tears in the O-Ring surface.twisting spiraling 1

Cause

- Irregular rolling/sliding of the O-Ring because of 
   - High surface roughness due to missing or wrong lubricant
   - Out-of-round hardware
   - Mounting error


Examples of Twisting/Spiraling

twisting spiraling 2


Corrective Action

- Careful installation
- Other seal profile
- Change hardware or working conditions

 
Spiral marks on O-Ring surface


3. Permanent Distortion


Distorted O-Ring, usually flattened on one side or both sides. o-ring-compression-set-1503842658

Cause

- Inadequate material quality
- Insufficient state of curing
- Contact with incompatible media/thermal overload
- Wrong groove lay-out

 
Example of Permanent Distortion

permanent distortion flattened editpaint3permanent distortion with cracks edit
Corrective Action

- Correct material selection (medium, compression set)
- Right groove lay-out
- Reduction of working temperature

 

(Left) Obvious flattened O-Ring on both sides, axial, material thermal overcharged
(Right) O-Ring with cracks

 

 

4. Ozone Cracking

Cracks vertical to the direction of tension (stretched O-Rings)
ozone cracking
and shows signs of premature ageing.

Cause

- Stretching, time and temperature

- High ozone concentration

Examples of Ozone Cracking

   ozone cracking after editjpeg (2)

Corrective Action

- Select ozone resistant materials

- Change of storage conditions


 

Stretched O-Ring

 


5. Abrasion

Flattening on one side of the O-Ring cross section and the area
o-ring-abrasion-1503842627of abrasion is smooth and shiny with loose particles.

Cause

- Wrong surface roughness
- Abrasive media
- Insufficient lubrication
- High, pulsating pressure with static use
- Dynamic motion
- Poor elastomer surface finish

 Examples of Abrasion

abrasion 2 edit
Corrective Action


- Improve surface roughness

- Reduced squeeze or friction
- Avoid system contamination
- Consider internally lubed elastomers
- Eliminate abrasive components



Abrasion area appears to be smooth and shiny

 
**All images were derived from NOK Freudenberg
 

 

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by SLS on March 26, 2019

categories: Product- Non-Bearings

Written by SLS

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