Fittings for higher strength pipe are actually made to a different specification, in this case astm a694. The F is a grade which probably stands for forging.
The Y will be to a different specification, probably some sort of plate
Pipe to 3183 is now referred to by the yield strength in MPa, so X52 should now be called L360. 3183 has a number of letter designations for pipe strength which means different things.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.