Troubleshooting O-Ring Failures and Best Practices for Preventing Failures
There are a number of parameters such as pressure, friction, and temperature, which determine a high performance O-ring design. These parameters also ensure reliability and extended lifetime of the O-ring seals.
Causes of O-ring Failures
Typically, O-rings are damaged easily when subjected to extreme temperature, vibration, abrasion, or chemical attacks. Unexpected failures can also be attributed towards the design, environment, mechanical factors, and improper installation.
Impacts of O-ring Failure
In most plant applications, the failure of an O-ring causes evacuation of the entire environment and equipment. This results in loss of production and downtime, as well as increased maintenance costs.
By troubleshooting O-ring problems at an early stage, we can identify and resolve them quickly, thus eliminating the possibility of a failure. This not only saves the time required to put the production equipment back on line, but also reduces the time taken to redesign the sealing system. Troubleshooting is also an effective way to reduce the overall risk.
Modes of O-Ring Failure
- Extrusion or Nibbling
- Plasticizer Extraction
- Chemical Degradation
- Thermal Degradation
- Plasma Degradation
- Installation Damage
- Explosive De-Compression
- Compression Set
Extrusion or Nibbling:
O-rings develop worn out edges due to excessive clearances, pressure, low harness elastomers, and excessive gland fill, a condition called nibbling. Such problems are resolved by reducing the clearance and using high harness elastomers with proper gland designs. Using polymer backup rings also prove beneficial in such cases.
This type of failure is particularly apparent in O-rings used in dynamic sealing applications. The motion of the O-ring against the moving surface causes friction, which in turn causes abrasion and reduces the sealing effect of the O-ring. By ensuring that the surface is finished to an appropriate surface finish and using O-rings with greater resistance to friction wear are some ways to prevent this type of failure.
Over compression is a case wherein marks and cuts develop around the circumference of the O-ring due to irregular finishes and insufficient lubrication. This condition can be minimized by following a proper installation process. Using internally lubed elastomers and maintaining a gland surface finish within 8-16 micro inches RMS helps to overcome the condition greatly.
This type of failure is typically hard to detect and can be prevented by avoiding the usage of plasticized elastomers, unless their use is necessary for the application. In addition, steps should be taken to ensure that the seals are post-cured regularly in order to reduce the outgassing effect.
Cracks, voids, and blisters over the surface of O-rings are typical signs of an incompatible chemical environment. The problem is prevented by ensuring that an appropriate, chemical-resistant elastomer is selected.
When exposed to excessive temperatures, O-rings develop radial cracks. It is very important to choose an elastomer with high thermal stability under such instances. Evaluating the possibility of cooling the seal surface helps too.
Discoloration, powdered residue over the surface, and elastomer erosion, are some common problems that occur when O-ring surfaces are exposed to iron and electron bombardment. Usage of plasma-compatible elastomers and compounds with minimized exposure region resolves such O-ring problems.
Due to irregular installation, O-rings develop small nicks, cuts, or gashes over their surfaces. These nicks and cuts can be further exacerbated during operation and lead to O-ring failure. Preventing this failure is possible by ensuring that the O-ring groove does not have sharp edges and properly sized seals are fitted in the sealing groove. Care is to be taken while installing the O-ring as well.
Due to drastic pressure changes, O-rings exhibit pits, blisters, or pocks over the surface. This problem can be prevented by using a high modulus elastomer with slower decompression.
This failure occurs when the O-rings are use for an extended period and are stuck in a permanently deformed position. The primary causes for this failure include excessive compression and swell volume due to absorption of chemicals. While the chemical absorption can be tackled by using an O-ring made from a compatible material, the excessive compression is prevented by ensuring that gland or mating surfaces are tightened to specified norms.
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