I am considering converting an old refrigerator to hold a keg of beer.
 How long can I expect a refrigerated keg pressurized with CO2 to
remain good?

Hi paz,

Good day and thanks for your question.

"Kegged beers are usually unpasteurizedand its shelf-life is 30 days."
(All Brew Newsletter)
http://www.whatalesyou.com/newsletter/8-99.pdf

"Common kegs have a shelf life of 27 days from date of process in the
brewery. (provided the keg has been properly stored at the right
temperature from day one)  If the keg reaches a temperature of 50
degrees Fahrenheit or warmer, then a process called "secondary
fermentation" will occur, thus limiting the lifespan of the keg to a
couple of days."
http://www.dsicontrols.ca/beer_questions1.htm

I hope this answers your question. If you have any clarifications,
please don't hesitate to ask. Thank you for using this service and
have a nice day

Warm regards,
aditya2k

Search strategy
"kegged beer" "shelf life"

A follow-up to the answer:

Q. How long is the shelf life of a properly stored keg of your beer in
a home kegerator?
A. Assuming you are using a co2 tap your keg should last from 90-120
days. On the other hand if you are using a self pump tap it will only
last about 24 hours. Cheers!
http://www.portlandbrew.com/ask.html

Cheers,
Aditya