O-RING FAILURE ANALYSIS

 

Prevention of seal failures through proper design, material selection and maintenance certainly minimizes the risk of failure. Attention to the condition of replaced seals, as well as the equipment performance over time, will result in improved process reliability, reduced operating costs and a safer work environment.

O-ring seals often fail prematurely in applications because of improper design or compound selection. This section is designed to provide the user with examples of common failure modes. By correctly identifying the failure mode, changes in the design or seal material can lead to improved seal performance. 

From the end-user╠s point of view, a seal can fail in three (3) general ways: 

  • Leaking 
  • Contamination 
  • Change in Appearance 

These three effects are demonstrated as Ishikawa (fishbone) diagrams with special emphasis on the following three analysis areas.

 
 

ENVIRONMENT ANALYSIS

 
One major factor in possible seal failure is the extreme and harsh environment in which seals are expected to perform.  The sealing environment can consist of virtually anything from inert gases at room temperatures to aggressive chemicals at very high temperatures. The sealing environment may result in chemical degradation or swelling of the sealing components. Elevated temperatures may cause seal degradation, swelling or outgassing. And the pressure█or more often, the vacuum environments█can cause outgassing and weight loss.

Contributing factors to seal failure in the sealing environment include: 

  • Chemical█ the type of chemical(s) in service 
  • Thermal█ the operating ranges of the seal (also any thermal cycling) 
  • Pressure/Vacuum█ the range of pressures or vacuum levels in the process

 

SEAL DESIGN ANALYSIS

 
Analysis of the seal application is crucial to the understanding of possible failure. Most seal design is performed by component suppliers and equipment manufacturers. The designs are refined as experience is gained. As quickly as process technology changes, however, the experience gained with seal design may not be relevant to the latest process technology. Vacuum applications have historically relied on high levels of compression and gland fill to reduce permeation and trapped gases. These techniques, when applied to new materials, or at higher operating temperatures, can result in premature seal failure. 

The seal design and application can provide information about the cause of failure: 

  • Static Seals█ axial and radial, confined or unconfined 
  • Dynamic Seals█ axial (open-close) or radial (reciprocating or rotary) 
  • Sealing Gland Dimensions█ 

    • shape (square, trapezoidal, etc.) 

    • compression 

    • gland fill 

    • stretch 

  • Installation Procedures█ stretch


 

ELASTOMER ANALYSIS

 
Analytical techniques are used to identify the specific polymer type and compound. They can also be used to identify contam-ination sources on the surface, or surface properties which may have contributed to the failure. Traditional elastomer test methods can determine chemical compatibility, changes in dimension, hardness or physical properties. In vacuum systems, the analysis of outgassing components may lead to the identification of failure mode. ISC can test and coordinate outside laboratory testing to evaluate, identify and recommend solutions to seal failures. The ISC lab is an A2LA accredited test lab for traditional elastomer properties.
 
 

SEAL FAILURE - LEAKING

 
 
 

SEAL FAILURE - CONTAMINATION

 
 
 
 

SEAL FAILURE - APPEARANCE CHANGE

 
 

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