Pex to sharkbite to galvanized?

Simple answer, no.
Main reason is brass in direct contact with steel will corrode.
One way around it if you you used a galvinzed coupling, dielectric nipple then a FPT to Pex fitting.
Should be getting rid of every inch of galvinized you can. It's all going to leak at some point and close up on the inside.

Mikeron said:

Can pex be fitted to galvanized pipe via a straight sharkbite coupling?

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Sharkbites are not sized for galvanized pipe. The diameters are different. You need threads.
Brass is generally accepted to connect to galvanized pipe as dialects unions cannot be concealed

did you get the answer you were looking for...

There will be a very small galvanic current which will very slowly cause the galvanized pipe to corrode. Shark bites do come in threaded applications so that pex can be joined to galvy. Knowing the risks, I would have very little concern about doing this and would expect it to last years.

Tally Wacher said:

There will be a very small galvanic current which will very slowly cause the galvanized pipe to corrode. Shark bites do come in threaded applications so that pex can be joined to galvy. Knowing the risks, I would have very little concern about doing this and would expect it to last years.

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You need a threaded end on the galvy for that application.

best to get rid of the galvanized pipe...

It is a given, you will need to rent a threader.