O-rings can fail for several reasons but there are more common reasons as to why this can occur. So, this article will help to identify the indications and causes of O-ring failure:

Extrusion and Nibbling

Indications of this problem appear as nibbles or nicks taken from the low-pressure side of the seal.

This is caused by high stresses as a result of high pressure, causing the ring to be pushed into the clearance gap.  As the O-ring becomes trapped, the sharp edges cause damage to the seal.

Abrasion

When abrasion occurs, the contact faces of the O-ring will have a grazed surface while lacerations might be visible.

The cause of this is down to repetitive contact between the O-ring and the housing whereby the friction is excessive between the two. If there is not enough lubrication then this can also cause failure due to abrasion.

Chemical Attack

The visible signs of chemical attack can be blisters, alteration in hardness, discolouration and cracking.

The cause of this is down to the way in which some chemicals interact with certain elastomers. This can often lead to cross-link density and that can cause the material to become brittle and hard.

Compression Set

A common sign of this problem is the way in which the o-ring changes its shape and becomes less circular while the surfaces appear flattened to the point where it has taken on the shape of the groove. This permanent appearance means that it is unable to return to its original shape.

The cause could be due to the elastomer being exposed to high temperatures causing the o-ring to set or poor-quality polymer formulation. As a result, the O-ring loses its elasticity, preventing it from returning to its shape.

Chemical Swell

The O-ring will look larger than its original design and this is likely to be consistent over the whole of the O-ring or in areas that have been exposed to chemical.

The cause is down to ingress of media within the elastomer which is down to a likeness between the compound and the media.

Rapid Gas Decompression (RGD)

The seal will show signs of blistering, cracking and could even have splits where it has ruptured.

High-pressure gas and elevated temperatures over long periods can cause this to happen. The external pressure reduces but the gas that is dissolved within the material is released and as it expands, it can cause the seal to fail if the rate of decompression and expansion is high.