When you say "filters" do you mean the cartridges or the actual filter housing itself? The Purex IS a Pentair (Purex was bought by Pentair several years ago and the Clean and Clear plus, which is one of the 4 cartridge styles of filters has only been available under the Pentair name for several years now.)
The filter housing should last quite a while and this filter is NSF rated for commercial installations. The actual cartridges inside the filter have a lifespan of anywhere from one year to about 5 years, depending on how they have been cared for. If they are hosed off on a regular basis and soaked once or twice a year you should be able to get 3-5 years out of them.
how-to-clean-a-cartridge-filter-t4465.html
If there has been damage to the actual filter vessel, I doubt it was caused by too high a chlorine level (unless, of course, you have been running EXTREMELY high FC with low CYA for an extended period of time but in this case you would probably suffer damage to other components before the filter). Cracking of the fiberglass vessel is more likely caused by too much pressure which could be caused by having a pump too large for the filter, not cleaning the filter often enough , a clogged filter from the use of phosphate removers or from algae blooms (in other words, not watching your pressure gauge!), or maybe a broken pressure gauge. (These things can also cause damage to a cart.) It also could be caused by physical trauma to the vessel. UV from the sun and high heat can also take it's tole on equipment. It does here in Florida! If I remember correctly you live in Arizona (putting that info into your profile would be helpful) so I imagine it's much the same there.
If you ARE referring to the actual cartridges, you got six years use out of them!
That is excellent and replacing them is just one of the maintenance costs of owning a cartridge filter. Remember, 3-5 years is the average lifespan of a cart. Next time, instead of getting the OEM replacements get one of the replacements from either Unicel, Pleatco, or Worldpool (Aladdin). It will save you a LOT of money and the cart is just as good!
As far as damage to the carts, I have never seen chlorine damage them but I have seen very low pH damage carts. Pouring acid or putting trichlor tablets into your skimmer can cause damage to carts (because of the very low pH of trichlor). I have seen this on more than one occasion, which is why I would tell my customers NOT to pour acid or put trichlor tablets in a skimmer (there are a lot of other reasons why also.) I have seen this type of damage as cracking of the rubber endcaps on the cart and of the endcaps turning 'gooey' and starting to 'dissolve', possibly coating the inside of the filter vessel with the residue.