3 Reasons for oil seal Failure and Their Solutions Discussed
The oil and gas industry is one of the most challenging industries due to adverse conditions and demands involved. A few engineered components such as oil seals are required to perform in these adverse conditions, where they may be exposed to various extreme conditions. Although most of these seals are precision designed for a long-term performance, they may fail due to several reasons. This post gives a brief insight into the challenges that the seals are exposed to, and explores various reasons behind their failure.
An Overview on the Challenges Endured by Gas and Oil Seals
Mechanical seals are always designed in adherence to the conditions of a particular application where they may be used. Oil and gas seals are designed to resist the following:
- Aggressive Corrosive Chemicals
- Sour Gas (H2S)
- Decomposition
- Explosive Conditions
- Extreme Pressures and Temperatures
Analyzing the Top 3 Reasons for Failure of Oil Seals and Corrective Actions
Like any regular mechanical seal, oil seals fail due to several reasons or one of these reasons. Here, the failure reasons are also followed by their solutions.
- Chemical Attack: As said, the oil seals are exposed to several types of chemicals. The seal may exhibit a variety of signs ranging from cracking, blisters, and discoloration to a change in hardness levels. Why does this happen? The material of your seal is not compatible with the chemicals it is being exposed to. This chemical attack will affect its cross-link density, increasing or decreasing it. The seal material becomes hard and brittle when this cross-link density increases and becomes softer when the cross-link density decreases.
Solution: Selection of the right sealing material is important for ensuring the compatibility of the seal with chemicals. This chemical incompatibility leads to chemical attacks, which accelerate at high temperatures or pressures. So, check the compatibility of the elastomer seal material before choosing it for your application.
- Extrusion and Nibbling: At times, the oil seals may have a chipped or nibbled appearance. In extreme cases, the surface of these seals may peel on its own, thereby lending it a shaved appearance. What is the cause of extrusion and nibbling? Stress induced by high pressure is one of the main reasons for extrusion and nibbling. This stress widens the clearance gap between the mating edges, where the seal may get entrapped, and it leads to severe physical damage.
Solution: Many industry experts suggest using backup devices to avoid the formation of clearance gaps between the mating edges. The selection of a properly sized oil seal is also important to avoid extrusion and nibbling.
- Out-gassing: This is one of the common causes of oil seal failure, which happens due to the volatility of any of the constituents of the elastomer. These constituents may be the part of elastomer formulation, or gases may get trapped in the elastomer during the process of molding. Although the oil seals may not show any visual indications of out-gassing, at times they may shrink due to extreme out-gassing. The out-gassed molecules may cause contamination in wafer processing in several semiconductor applications, and also it can affect vacuum performance in industrial applications.
Solution: Use the materials that are rated to the temperature of application. Also, ensure that the elastomer used is free from volatile ingredients such as waxes, plasticizers, and so on. Both these will help you avoid the chances of outgassing.
The above mentioned are only the top three causes of oil seal failure; however, there can be several other reasons for the same. In addition to these solutions, it is important that you source these seals from some trusted manufacturer such as SSP Seals. The company provides customized oil seals in different specifications to its clients in the oil and gas industry.
Failure and Diagnosis
Often, when parts such as oil seals fail prematurely they are replaced and returned under warranty; however, in most cases the seal itself isn’t the reason the failure has occurred. In this guide, we will take you through the causes and how to avoid premature leaks and failures in the future.
Lip Leakage Diagnosis
If the lip has worn out then this is often caused by the seal not being sufficiently lubricated before installation causing abnormally high temperature, the presence of foreign matter, disproportionate internal pressure or an excessively rough shaft surface. Similarly if when removing a seal, if the lip has hardened and there are visible cracks, you can be sure that this has again been caused by abnormally high temperatures, excessive internal pressure or insufficient lubrication. The cause for the abnormally high wear has occurred due to friction as the amount of lubricant was below the specified level and therefore did not reach the seal lip. Alternatively, insufficient lubrication can come from dry-wear conditions because the vehicle’s oil levels are low. Another sign of this is if the lip wear band is smooth and glossy.
Alternatively, if the lip has softened, then the main cause of this is the lip having the incorrect material required for the application. In order to prevent this from reoccurring make sure the correct seal is sourced for the specific application before installation.
If you notice the lip of the seal has worn unevenly then this is due to cocked seal installation or an excessive shaft offset. As before, both should be checked during installation but crucially before the vehicle is out on the road.
Installation errors tend to be a big factor in automotive parts failing prematurely. This is apparent if you can see that the lip of the seal is scratched, caused by improper assembly, improper handling, an incorrect shaft chamber or the presence of foreign matter entering the seal. The scratches are often caused by being assembled over burrs or other defects in the shaft chamber, the lip coming into contact with sharp metal parts during transit or storage or if the seal was handled with gloves contaminated with metal particles.
As stated improper handling can be a factor in causing a seal to fail prematurely, the tell-tale sign is the seal lip being swollen or soft. The swelling is caused by the lip being soaked in solvents or petrol before installation. Alternatively, if when removing a seal you see the fit trace is disconnected locally then the seal could have been deformed because of an improperly designed assembly jig or a gap in the press-fit occurred due to rough handling.
However, although problems during fitting can contribute to the part failing, other issues may be the key factor. If the lip’s waist (flex area) is broken, then this can be because of improper assembly but can also triggered by excessive internal pressure. Similarly if the lip is turned-under, the lip edge is severely worn and the wear band is concave then this is connected to an incorrect shaft chamber, improper assembly and excessive internal pressure meaning the oil seal area exceeded the maximum pressure it was originally designed for. To prevent this reoccurring, identify the maximum pressure for the seal and check it is compatible with the vehicle. However, if the lip edge is severely worn but there are circumferential grooves on the wear band then the cause is that the shaft finish was rougher than the specified range again this can be prevented by sourcing the correct part for the specific application.
Similarly, if the lip edge is severely worn and there are grooves or indentations on the surface. Foreign matter can affect the seal in many ways whether the cause is due to a shaft or seal that has been contaminated with foreign particles being used or the contaminants were embedded in the seal lip. The cause can be triggered when the seal is assembled in the presence of dirt and/or dust causing the contaminants to become embedded in the sealing lip. In addition, if the seal or the housing was assembled with silicone, the sealant will have contaminated the shaft or seal.
If, when removing a seal the garter spring has become disconnected then this has likely been caused by an incorrect shaft chamber or improper assembly, checking the installation can ensure you and you customers are happy with the finished job.
However, if there isn’t an obvious fault with the oil seal, the cause is often difficult to diagnose, but before you prematurely condemn a good seal first check if the shaft is scratched or the diameter is incorrect, if the shaft rotational direction does not match the helix on the seal, there is excessive shaft offset or runout, the shaft is worn or the seal has been installed incorrectly.
Press-Fit area leakage diagnosis
Below we identify four common causes of premature leaks due to incorrect handling/installation.
If the oil seal is cocked then this can be caused by an improperly sized bore diameter, incorrect shaft chamber or improper assembly jig.
Like with the lip leakage diagnosis if the oil seal is problem free, check if there is a scratched or an improperly sized bore or excessive bore surface roughness. Similarly if the seal OD is damaged or chafed the bore is often the cause. Ensure you check if there is an improper sized bore diameter, incorrect shaft chamber or improper assembly jig before installation.
All the causes mentioned can be avoided if the correct steps are taken when assembling, ordering and fitting a part.
