VISUAL INSPECTION
A crucial step in this failure analysis is to inspect the mechanical damage of the O-ring gasket. Obviously, all three O-rings have been damaged, which will inevitably lead to leakage. Surprisingly, all three O-ring fractures were directed towards the direction of the pressure source rather than away from it. However, ignoring other possible causes of failure may lead to overlooking more critical factors that can provide preventive measures.
In the example presented in this article, the O-ring did not cause any other mechanical damage. For example, there is no evidence of extrusion failure related to pressure in this type of O-ring. When the fluid pressure exceeds the strength that the material can withstand, the rubber will be squeezed into the gaps between the fittings, leaving an area of "damaged" rubber. This situation obviously does not exist on this O-ring. And there is no indication that this O-ring has produced any form of compression between the assembled parts.
In addition, the rubber material shows no signs of chemical or thermal degradation. Unlike other damage points, this O-ring does not exhibit significant expansion, hardening, softening, blistering, compression deformation, embrittlement, or loss of tensile strength. Very simple, there is no damage compared to other more obvious damages. Based on these reasons, it has been proven that the chemical and thermal incompatibility factors of these sealing materials are not potential causes of failure.
Analyze the fracture
The failure of O-ring often occurs during the assembly process where the O-ring is stretched to meet the application requirements. In this case, although the O-ring passed the initial leak test and was used for several weeks. This is impossible for a damaged O-ring. Therefore, during installation and initial pressure testing, the O-ring must be undamaged.
This means that the O-ring must have been damaged during use, that is, after it was installed in the groove, which is a very rare situation in static O-ring sealing devices. This type of damage in use can usually be traced back to one or two reasons.
The common cause of damage to O-rings in use is tearing, which spreads from the twisting point. In this case, a part of the O-ring seal is crushed in the metal parts that fit during installation, usually due to accidental protrusion of the groove during installation. O-ring seals damaged in this way will show obvious signs of mechanical damage, including severe crushing of some parts, missing parts of the O-ring seal, and semi-circular cuts in cross-section.
In some cases, a tightened O-ring seal may pass the initial leakage test and be damaged during use due to the propagation of initial tightening damage to the O-ring seal. However, there is no evidence of tightening damage in these failed O-ring seals.
