2nd expansion tank in 4 months

Hey guys looking for a little info here..I am the head of Maintenance for a big hotel chain in ohio..this is the problem we have 3 hot water heaters in one room all have expansion tanks...in april we noticed one of the expansion had a pin hole in it and was shooting water across the room...so we replaced it and just noticed today that the new expansion tank is leaking now. what would cause these to go bad so fast.The two other water heaters still have the original expansion tanks on them and both still look new. These water heaters are about 7 years old.....thanks in advance guys

Josh in ohio

Did you use the proper potable water expansion tanks? Whats the model number of the new one that failed?

If you used a boiler expansion tank designed for a closed system, the oxygen in a open system would eat through it quickly.

Potable expansion tanks for DHW systems have a liner inside the tank similar to a milk jug.

I just talked to the maintenance guy who replaced it he said the new tank is a Extrol 30 4.4 gal hot wat0001.....he said he got it from johnstone supply

Extrol is used for Hydronic heating so it is the wrong one.

Amtrol Therm X Trol is for domestic hot water applications...
http://www.amtrol.com/thermxtrol.htm

Yep as I expected, you have the wrong type

Expect to pay 2.5X more for the correct tank

Johstone # L86-193, L86-194, L87-200, and L87-201 are the potable water tanks.