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.
In general, COMPRESSION SETis caused by one or more of the following conditions:
- Selection of O-ring material with inherently poor compression set properties.
- Improper gland design.
- 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)
- Volumetric increase of the O-ring due to swelling in system fluid.
- Excessive squeeze due to overtightening of adjustable glands.
- Incomplete curing (vulcanization) of O-ring material during production.
- Installation of fluid incompatible O-ring material during assembly or retrofit.
Suggested solutions to the causes of Compression Set are as follows:
IDENTIFICATION OF COMPRESSION SET FAILURE
- Use of "LOW-SET" O-ring material whenever possible.
- Selection of O-ring material compatible with intended service conditions.
- Reduce system operating temperature.
- Check frictional heat build-up at seal interface and reduce if excessive.
- Inspect incoming O-ring shipments for correct physical properties.
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.