"W" ??? ... isn't W a very reduced strength condition for forming puropses ? If i'm right, nobody would use W material (without heat-treating it to say T6 or T73).
also what sort of AN fitting ? ... an AN-4 is a bolt; we'll need to know which AN fitting you're considering.
You have to identify the fitting(s) You want to used based on configuration [elbows, tees, sizes, etc]... then trace it back to the procurement spec for operating limits. Or have a company document that specifices working pressure loads... and any other loads present [bending, shear, vibration, abuse, etc]
NOTE: W = 7075-T73 die forging, D = 2014-T6 die forging
In MANY instances, the D material parts are hard to find! The D material is not readily avaialble due to minimal use. The W material is slightly stronger/tougher and has better corrosion & SCC resistance; and is a very commonly forged material.