When choosing a gasket always consider the application’s TEMP – that’s the temperature, environment, media and pressure. This will lead you to the best material for the job, providing you can predict what those values will be. In reality, all but the media can vary. In response, engineers sometimes select gasket material to handle the worst possible combination of conditions. This is not a good idea, and here’s why.
Compromising Performance, at a Price
Consider an application where a simple nitrile rubber gasket will handle the normal operating conditions. Then throw in the remote possibility of exceptionally low ambient temperatures or hotter-than-normal media. This could lead you to look at silicone or PTFE gasket materials.
These will handle extremes better than nitrile rubber, but both are considerably more expensive. And there’s another point to consider: will they work as well as the nitrile over the normal working range? If nitrile best satisfies the typical needs of the application, that’s probably the material to go with.
Consider Risks and Probabilities
There are of course exceptions. If the likelihood of failure is related to the chance of extreme deviations from normal conditions, how much deviation do you design for? Four-sigma? Six? More? It depends on how much risk you’re willing to accept, and that is driven by the cost of failure.
If you’re sealing steam in an accessible location the consequences of a gasket failure are probably not too severe. But if the application is sealing-in sulfuric acid in a high volume processing plant, the costs of both downtime and failure could be very high.
Make an Engineering Decision
Here’s the bottom line: gasket failure always has a cost. You can probably reduce the risk of failure and extend the period between gasket replacement by specifying more sophisticated gasket material – Viton/FKM rather than neoprene for example. But, this increases the upfront costs. So estimate risks and costs – a Failure Mode Effect Analysis (FMEA) might help – and make an informed decision about the right gasket material for your application.