How To Prevent O-ring Damage

Leaks in a system can range from a minor inconvenience to severe problems with severe consequences. Choosing the correct o-ring and maintaining these will help prevent leaks and damage. There are many reasons why an o-ring could leak; This article looks at at the causes of these leaks and ways to prevent them.

Causes of leaks

There are three main reasons why o-rings might leak.

• Size: If the seal is too big, the excess material will cause it to bunch up in the groove, cause excessive compression, and give an uneven surface. If the ring is too small, it will be stretched excessively, which leads to the material not being sufficient to form a leak-free seal.
• Installation: o-rings allow for some stretching, and in fact, need some stretching to fit snugly. Incorrect installation will cause the internal and external dimensions to change. Stretch should be between 1%-5%, with 2% as the ideal in most applications to provide an effective seal. A stretch greater than 5% is not recommended. The resulting stress will cause accelerated aging and cross-section reduction, ultimately leading to leaks. An exception from this rule is a floating seal. A floating seal is an o-ring that sits freely in a groove. These are used where some leakage is permitted as well as when reduced friction is needed. Reas our article on the o-ring installation to learn more. 
• Material: Using the wrong material for the system temperature, chemical, or pressure will cause damage to the o-ring and cause the seal to fail. Look at the various material choices available in our seal material guide, which covers many of the components used in o-rings, to learn more about material choices. To find out if an o-ring is compatible chemically use our chemical resistance chart. 

Common reasons for damage to o-rings

Compression

When an o-ring is exposed to extreme pressure levels, it will develop circumferential splits on a compressed surface. Ultimately these splits will cause the seal to break. All o-rings will allow for some compression and will return to their original shape when this compression dissipates. There will always be a degree of deformation. This permanent deformation is also known as the compression set. When the compression set becomes too high, it will not return to its original shape, and leaks will occur.

Solution

Choose a material with a better compression set or a higher pressure resistance. Some materials have been developed specifically for use in applications requiring low compression sets (e.g., if the seal has been exposed to hot water for an extended period). Perform a check on the groove dimensions in your application, as the compression set can be affected by incorrect groove dimensions.

Rapid Pressure changes

Rapid pressure changes are a specific problem when gasses build up inside the gaskets under very high pressure. While this is not a problem when the system remains pressurized, it could become a problem when the system is suddenly de-pressurized. When pressure suddenly drops, it causes the pressurized gases inside the O-ring to suddenly expand. This causes blisters, pockmarks, and pits to appear on the surface of the seal, severely weakening the structure.

Solution

While a system with stable pressures will always be the preferred method to keep seals in optimal condition, this is not always feasible. However, if pressure leaves the system slowly, the gases inside the seals will be able to escape gradually without causing any damage. Some manufacturers do make special seals that combat this problem. These are available under the NORSOK M710 standard.

Installation damage

Installation damage takes on many different forms, from skiving of the seal with metal parts to cuts, nicks, twisting, and gashes resulting from the sloppy installation of dirtied, uneven, or incorrectly lubricated seals. Failure to precisely size the O-ring for the application can also lead to installation damage; not only that, as stated above, excessive compression or stretching of the O-ring can lead to the seal becoming unusable.

Solution

Never stretch the O-ring more than 5% and always use the correct tools like O-ring kits and O-ring pickers when removing and installing O-rings. Protecting sharp corners and threads utilizing tape or protective sheaths will avoid nicks to the surface. Make sure hardware has suitable lead-in chamfers aiding the make-up of the hardware, along with adequate lubrication. Read our O-ring installation guide to learn how to measure and install O-rings properly, or our silicone oil and grease guide for lubricating tips.

Excessive friction

When excessive friction occurs, the gasket has a grazed surface; with excessive wear, there may be deeper lacerations and breaking in places. In dynamic applications, abrasion is caused by repeated contact between the O-ring and the housing, resulting in excessive friction between the two. Insufficient lubrication and finish of metalwork can aggravate the risk, as can the introduction of abrasive substances into the sealing system.

Solution

Make sure the correct lubrication is used for the sealing system. The correct surface finish for metal also influences seal choice. You can decrease the ingress of pollutants through the use of wipers or scraper rings.

Chemical attack

Different chemicals will cause different kinds of damage; these may include blisters, cracking, a change in hardness, or discoloration. In some cases, certain chemicals react with some elastomers. This usually results in a greater crosslink density, which results in a more rigid, more brittle material. Also possible is chain scission, resulting in reduced strength. A loss of integrity is caused by a reduction in cross-link density, resulting in an adhesive material often softer than the original material.

Solution

It is crucial to select the suitable elastomer material to ensure the seal is compatible with the application media. Excessive heat and pressure stress on elastomer seals exacerbate chemical attacks. Tameson has an online guide for chemical compatibility of the main elastomer material types, which you can consult when choosing a using our online guide.

Chemical swell

Chemical swelling happens due to the chemical similarity between elastomer and media; subsequently, media infiltrates into the elastomer. As the volume of the seal increases, the sealing effect gets compromised, and the seal loses its integrity. As a result of chemical swelling, physical properties such as tensile strength can be lost and the seal is larger than the original size. It can happen across the seal or in localized places that have been exposed to the chemical media.

Solution

Choose an elastomer sealant with proven resistance to chemical environments.

Out-gassing

When out-gassing occurs within an O-ring, there are usually no visible changes. In extreme cases, shrinkage can be observed. Out-gassing happens when substances are discharged under vacuum conditions from an elastomer. These components can be either a part of the elastomer formulation, the decay products of the components, or other gasses captured in the polymer matrix during the molding process. For semiconductor applications, the out-gassed molecules can affect wafer processing by causing contamination. For industrial applications, it can hinder vacuum performance.

Solution

Pure polymers and materials with no volatile ingredients (e.g., plasticizers, waxes, etc.) provide reduced out-gassing. It is also beneficial to use materials rated for the right temperature needed to keep out-gassing to a minimum.

Thermal degradation

Thermal degradation shows as radial cracking on surfaces bearing the greatest temperatures. The surfaces may also become shinier in places if the seal material is susceptible to thermal softening. It is common for thermal degradation to be accompanied by a compression set if the upper-temperature limit of the chosen seal material has either been exceeded, or excessive temperature cycling has occurred. The cross-link density in elastomers can increase at high temperatures, causing them to become harder and less elastic.

Solution

Select a material with higher temperature resistance. Several reliable high-temperature seals that can manage temperatures up to +325°C (+617°F) are available from several suppliers made of perfluoroelastomeric compounds containing a high amount of fluorine(FFKM).

UV Degradation

Exposed surfaces on the O-ring will present with discoloration in the early stages, with excessive exposure leading to cracking and disintegration in severe cases. Whenever an elastomer material is exposed to UV light, it can have destructive effects. A UV light has a short wavelength; thus, it has a high energy level, making it able to interact with the molecular structure of an elastomer that is exposed. These conditions usually cause the polymer chains to break and crack, allowing water ingress and premature failure to occur.

Solution

Generally speaking, black materials tend to resist UV damage more than other colors; fluorinated materials also show some resistance. For UV processes used in sterilization procedures and semiconductor manufacturing, there are specialized solutions available.