Your permanent magnet should lose no more than 1% of its magnetic strength over a period of 100 years provided it is specified and cared for properly. There are a few things that may cause your magnet to lose its strength:
Heat above the maximum level rated for the magnet material in your separator will decrease the strength of the magnet. Standard rare earth material from MPCO has a maximum temperature of 176°F and standard ceramic material has a maximum temperature of 400°F. Higher temperature materials are available and may have been used in your system. Consult the factory if you have questions on what the maximum temperature is for your system.
Sharp impacts to the magnet from physical abuse or handling can result in the decreased magnet strength. The magnet material inside your separator is brittle and these impacts can lead to fractures in the material, weakening its strength.
Welding on or around the magnet can lead to decreased magnet performance. This can be a result of the heat or current generated from the welding process.
If your magnet housing is compromised, moisture can enter the housing of the magnets. This can lead to oxidation of the magnet material which will eventually lead to a weakened magnetic system. If the housing is compromised, the magnet should also be replaced for sanitary concerns.
It is always best to consult a magnet professional while specifying your magnet.