Lip Seals -- Failure rate Monitoring and Energy loss

Some manufacturers of lip seal did a research work on the life of lip seals and they found that on the average the Mean Time to Failure of lip seals was around 77 days of operation or around 1644 operating hours. And the maximum life is around 3000 hours or around 180 days of operation.

But there is another disturbing fact. The same group of researchers also found out that the energy loss per lip seal is around 147 Watts of power. So, it is not difficult to calculate the total loss of energy when we are using more than 500 lip seals all around the plant for 24 hours of operation. It is a substantial amount of money.

So, I feel that there are three important issues to the question of reliability of the seals.

The first issue is how do we improve the life or durability of the seal?

The next issue is how do we monitor the condition of the seal? There seems to be no proven method of monitoring the condition of the lip seal except for the fact that some engineers have tried out the use of Infra-red thermography heat pictures to monitor the condition of lip seals, which I think is neither too elegant not does not seem to always work.

The third important issue is how do we reduce or contain the energy loss due to use of lip seals?

Usually we understand the defect after the failure has taken place. And the consequences of the failure can be high, including safety like the contained fluid catching fire. Evidence of secondary failures like grooving in the shaft is also not very uncommon to find.

Hence this is a critical failure mode that needs to be addressed in a variety of ways, like proper selection of shaft material, hardness of the material, direction of grinding of the bearing and seal areas, surface roughness, lowering the coefficient of friction, minimizing the effect of unbalanced forces in the system and alternative use of non-contact seals. We have tried out these measures improve durability of the lip seals and it works.

Since a direct monitoring method is yet found the alternative is to use a probabilitic way of assessing the life and condition of the seals by measuring parametes that has a direct influence on seal life. This is possible and I found my method to work in all cases and conditions. The only problem is it is sometimes difficult to establish the 'probabilistic parameters', which may vary from case to case.

However, reducing energy consumption is again a tricky issue. This can also be dealt in a probabilitic manner and by keeping the influencing parameters within control or to an optimum limit of a probabilistic combination.

Dibyendu De
Design Innovator -- Plant Reliability