Troubleshooting O-Ring FailuresAugust 27th at 9:29am
Like any device subjected to errors in installation or exposure to high stresses, O-rings too are liable to failure. Different materials of O-rings have different shell life. Shell life for materials like natural rubber, polybutadiene and polyurethane (millable) usually have a shell life of five years whereas, materials like HNBR, Butyl and Nitrile have a shell life of fifteen years. Some materials such as Fluorocarbons, Fluorosilicate, silicone and Ethylene propylene are said to have an unlimited shell life. Despite have long shell life, the O-rings can fail to perform effectively in just matter of days. O-rings usually fail due to the combination of various effects acting on the ring. Below is the list of the categories that makes the O-rings to fail:
It is important to visually inspect the damaged O-Rings to find potential causes of it's failure. Below are some of the symptons. related causes, and ways to troubleshoot and correct such O-Ring failures.
Nibbing or extrusion is one of the main causes for the failure of the dynamic seals. Hydraulic rod and Piston seals are one of the most affected seals by extrusion or nibbing. Extrusion and nibbing is also sometimes found in static seals due to high pressurization.
The extrusion in the O-rings can be avoided using the following techniques;
One of the most common reasons for O-rings failure is compression setting of the rings. For an effective seal to be formed, it is crucial that there is a continuous seal line between the O-ring and the gland surface. The O-ring must maintain its integrity without excessive deformation in order for the seal to be effective. There are several factors that results in the compression set failure in the O-rings;
Spiral failure of the O-rings are usually found on the seals of long stroke hydraulic piston or rod seals. Spiral failure occurs when the O-ring hangs-up at one point across its diameter and slides and rolls simultaneously. Factors that may cause spiral failure of the O-rings are as follows;
With the rise of space travel in the recent years, O-rings failure due to explosive decompression is one the rise. Explosive decompression is also termed as O-ring embolism. Once the seals are operated under high pressure for a certain period and then reduced to low pressure too rapidly, the gas trapped internally in the O-rings expands causing ruptures on the O-rings and affecting the integrity of the seal adversely.
Abrasion is also one the most know causes for the failure of the O-ring seals. Abrasion can be found in seals that are dynamic either in oscillation, rotary or reciprocating motion. The possible causes of O-rings are as follows;
O-rings are precision devices that may fail to perform effectively if not installed with proper care and selection. Some of the causes for O-rings to fail attributed to improper installation are as follows;
Chemical degradation in O-rings can be seen in joint having toxic chemicals. The degradation of the O-ring is caused by the chemical reaction between the O-ring and the fluid the seal is holding. This can occur at room temperature or high temperatures. Changes in physical properties such as the size or shape of ring are visible.
Using the O-rings that are compatible with the chemical it is sealing
Selecting a high temperature resistant
Weathering or ozone cracking can be seen in seals that are exposed to UV light, ozone or air pollutants. Ozone cracking in the O-rings can be recognized by small surface cracks that are perpendicular to the direction of stress.
Periodic replacement of the O-rings
Protecting the seal inside a compartment
Thermal degradation in the O-rings can be seen visibly on seals having rapid changes in the ambient temperature of the seal. The thermal degradation on the O-ring can be categorized by the radial cracks visibly on the side exposed to higher temperature. O-rings also softens further degrading the performance.
Plasticizer extraction is the deformation of the O-ring due to the deterioration of its elastomer. Plasticizer extraction can be determined by the decrease in the cross-section of the O-ring.
At Phelps, we offer a wide range of Metric as well as American standard sized O-Rings in various materials. Please call our sealing experts @ 1-800-876-SEAL with you questions and fluid sealing requirements.