Compression Set Failure

Probably the most common cause of O-ring failure is compression set. An effective O-ring seal requires a continuous "seal line" between the sealed surfaces. The establishment of this "seal line" is a function of gland design and seal cross-section which determines the correct amount of squeeze (compression) on the O-ring to maintain seal integrity without excessive deformation of the seal element. There are a number of factors which can contribute to compression set failure of an O-ring seal. These are listed below.

 

FAILURE ANALYSIS
In general, COMPRESSION SETis caused by one or more of the following conditions:
  1. Selection of O-ring material with inherently poor compression set properties.
  2. Improper gland design.
  3. Excessive temperature developed causing the O-ring to harden and lose its elastic properties. (high temperatures may be caused by system fluids, external environmental factors or frictional heat build-up)
  4. Volumetric increase of the O-ring due to swelling in system fluid.
  5. Excessive squeeze due to overtightening of adjustable glands.
  6. Incomplete curing (vulcanization) of O-ring material during production.
  7. Installation of fluid incompatible O-ring material during assembly or retrofit.
PREVENTION/CORRECTION
Suggested solutions to the causes of Compression Set are as follows:
  1. Use of "LOW-SET" O-ring material whenever possible.
  2. Selection of O-ring material compatible with intended service conditions.
  3. Reduce system operating temperature.
  4. Check frictional heat build-up at seal interface and reduce if excessive.
  5. Inspect incoming O-ring shipments for correct physical properties.
IDENTIFICATION OF COMPRESSION SET FAILURE
Below is a typical example of classic O-ring compression set. In simplistic terms, the O-ring ceases to be "O" shaped and is permanently deformed into a flat sided oval, the flat sides of which were the original seal interface and under compression before failure.

 

Compression Set
Compression Set Example
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