Failure Analysis

There are several reasons why an O-ring can fail. An example of this is due to incorrect dimensions in combination with the groove dimensions. On this page, you can get an indication of why your O-ring has failed and what you can do to prevent in the future of the o-ring and what the suggested solutions are for it.

 

O-ring Size – Gland Design

O-ring Failure Description:

The O-ring does not do its job as expected without visible defects.

Reasons:

Incorrect groove or swivel design. Incorrect size of the O-ring. Hardware damage or misalignment.

Suggested Solutions:

Underperforming O-Ring seals can typically be improved by optimizing the O-Ring size or gland design for the specific application conditions.

 

Compression Set

O-ring Failure Description:

A compression set is the degree of permanent deformation after pressing the O-ring. If the imposed load disappears, the material returns to its original shape in a short time. There is always a certain form of permanent distortion. It is possible that the compression set of an O-ring is so high that it no longer returns to its original shape.

The O-ring has a flat cross-section, in which the flat sides correspond to the matching sealing surfaces.

Reasons:

Excessive compression. Temperature too high. Incomplete cured elastomer.

Suggested Solutions:

Choose a material with a better compression set or choose a material with higher temperature resistance.

 

Over Compression

O-ring Failure Description:

The seal exhibits parallel flat surfaces (corresponding to the contact areas) and may develop circumferential splits within the flattened surfaces.

Reasons:

Incorrect design, no account has been taken of thermal or chemical volume changes or excessive compression.

Suggested Solutions:

Gland design should take into account material responses to chemical and thermal environments.

 

Explosive Decompression

O-ring Failure Description:

Explosion after decompression is a phenomenon that can occur when high-pressure gases enter the rubber. This is a phenomenon that must be taken into account in the oil and gas industry, for example. As long as everything remains under pressure, nothing is wrong. When the pressure drops, the gas enclosed in the rubber will expand. With slow pressure reduction, the gas will exit the material through the normal route. If this happens very quickly, the gas cannot leave in the normal way and, due to the rapid expansion of the gas, the material can explode.

Reasons:

Quick pressure changes. Low-modulus/hardness elastomer.

Suggested Solutions:

You can use special AED compounds that can prevent this. Some have been tested according to the NORSOK M710 conform. The NORSOK M710 has been developed by the Norwegian petroleum industry and the requirements rubber compounds must meet the use in applications in the oil and gas industry.

 

Outgassing Extraction

O-ring Failure Description:

This failure in an O-ring is often difficult to detect when examining the seal. The O-ring can show a decrease in cross-section.

Reasons:

Improper or improperly cured elastomer. High vacuum levels. Low hardness/plasticized elastomer.

Suggested Solutions:

Avoid plasticized elastomers. Ensure all seals are properly post-cured to minimize outgassing.

 

Installation Damage

O-ring Failure Description:

When you don’t use the right tools to install an O-ring, he can cause some damage. For example, it may happen that you pull the O-ring over a sharp part, so that part of the O-ring is shaved off. This can result in leakage.

Reasons:

Sharp edges on components. Improper sizing of elastomer.

Suggested Solutions:

Avoid sharp parts that could damage the O-ring. Use an O-ring assembly kit when mounting or dismantling O-rings. This makes it easier to install and remove your O-rings without causing damage.

 

Abrasion – Friction

O-ring Failure Description:

The seal has a flat surface that is equal to the direction of movement.

Reasons:

Rough sealing surfaces. Too high temperature. Process environment containing abrasive particles.

Suggested Solutions:

Use recommended gland surface finishes. Consider internally lubed elastomers. Remove abrasive components.

 

Extrusion (Pressure of Oversized Gland Clearance Gap)

O-ring Failure Description:

Extrusion is a phenomenon that can mainly occur in high-pressure applications. The O-ring is pressed into the existing gap and the O-ring can be peeled off.

Reasons:

This can be caused by an incorrect gap space due to the excessive pressure of the application.

Suggested Solutions:

If the pressure in your application is high and the correct gap is used, use a material with a higher hardness.

 

Spiral Twisting Failure

O-ring Failure Description:

In a dynamic application, an applied O-ring may occur. This can cause the O-ring to twist and damage the O-ring.

Reasons:

This damage can be caused by a lack of lubrication, too high compression or an incorrect groove.

Suggested Solutions:

Use an X ring! These are specially designed for use in a dynamic application. X-rings require less compression and experience, so less friction. The stability and the sealing capacity with dynamic applications are greater than with an O-ring.

If you still want to use an O-ring, choose the right lubricant to optimize the lubrication of the O-ring.

 

Thermal Degradation

O-ring Failure Description:

The seals may exhibit radial cracks located on the highest temperature surfaces. In addition, certain elastomers may exhibit signs of softening a shiny surface as a result of excessive temperatures.

Reasons:

The temperature is too high for the O-ring. The O-ring becomes hard and can crack.

Suggested Solutions:

Choose a compound that is suitable to withstand the temperature of your application. There are special materials for high temperatures, up to 327 °C!

For example, use Silicones or FFKM.

 

Chemical Degradation

O-ring Failure Description:

The seal may exhibit many signs of degradation including blisters, cracks, voids or discoloration. In some cases, the degradation is observable only by the measurement of physical properties.

Reasons:

The O-ring cannot withstand the chemical and/or thermal environment.

Suggested Solutions:

Choose an O-ring that is more resistant to chemicals.

 

Plasma Degradation

O-ring Failure Description:

The seal often exhibits discoloration, as well as powdered residue on the surface and possible erosion or elastomer in the exposed areas.

Reasons:

The chemical reactivity of the plasma. Improper gland design. Incompatible seal material.

Suggested Solutions:

Plasma-compatible elastomer and compound. Minimize exposed area.

 

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